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I recently rebuilt an AX 15 to swap into my CJ with a Dana 300.  I swapped it from internal to external slave and replaced all synchros, bearings, etc.  Since reinstalling, it is very difficult to shift into 1st and 2nd gear when running.  I can shift back into 1st when I come to complete stop and return the transmission to neutral first.  I can shift from 1st to second and 3rd to second if I do a combination of double clutching and rev matching.  All other gears shift well, and the transmission will shift through all gears when parked.  I'm trying to decide if it's a clutch issue or if I need to pull out the transmission and take a look at the 1st/2nd gear synchros.  The only reason I think it may be a clutch not engaging/disengaging fully is that the white strap that retains the pushrod on the slave has not broken loose after using it, leading me to believe that maybe the clutch isn't fully engaging.   

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bobdavis...Sounds like the clutch is not disengaging completely.  You may not have enough movement of the release arm with the pedal depressed.  Did you reuse the CJ hydraulic master cylinder with a YJ/TJ external slave cylinder?  Did you bleed the air out of the master cylinder, slave cylinder and line?

If the clutch release is still an issue after bleeding, there are a couple of remedies:  1) use a master cylinder with more fluid displacement, 2)  raise the clutch pedal height while making sure there is normal (slight) clearance between the pedal pushrod and master cylinder piston or 3) use an aftermarket master cylinder with a larger piston bore.  When the pedal releases, the master cylinder's piston should be fully retracted.

Start by noting the travel of the pedal and release arm.  See whether the release arm moves the clutch cover fingers enough to disengage the clutch disk completely.  The clutch disk should rotate freely when the pedal is depressed in neutral or any gear.  In neutral with the clutch pedal depressed, you should be able to rotate/move the disk back and forth freely.  Use wheel chocks and set the parking brake;  have someone depress and hold the clutch pedal.

Stack height of the release bearing is important.  Again, when the pedal is released, the release bearing should be slightly away from the clutch cover fingers.  When the pedal is depressed, the disc should rotate freely without the release bearing pressing the clutch cover fingers against the disk hub.

Make sure that the clutch disk is installed with the disk hub's shoulder facing rearward.  Otherwise, the clutch will not disengage.  (You likely have ruled this out already.)  Often overlooked is the possibility of the crankshaft pilot bushing/bearing dragging on the transmission input shaft nose.  This will cause the input gear to rotate with the crankshaft even with the clutch fully disengaged.  If the bushing/bearing is too tight, wrong size or misshaped from driving it into place, it can seize on the input gear nose.  Sometimes this resolves, sometimes there's a need to replace the pilot bearing.

Moses

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  • Moses Ludel changed the title to CJ Jeep AX15 Swap Clutch Will Not Disengage

Moses - Thanks for the quick and thoughtful reply.  The master and slave cylinders are new Luk units spec’d for a 1995 wrangler with a braided stainless line and adapters from Novak conversions to make the connections.  I used a brake pedal from a YJ to mount the master cylinder shaft, so I think the pedal travel should be correct.  I have bled the unit several times, both by pedal pressure and by reverse bleeding with the slave off the transmission.  There is a bit of a “whooshing” sound coming from the slave cylinder when pressing the clutch pedal in.  I’m not sure if this is normal or indicative of possible air in the line.  As a last ditch effort to rule out the slave/master as the source, I have ordered an all in one pre-bled system that should arrive this week.  I guess once I mount that, if there is still an issue, I will pull the transmission to check the throw out bearing, clutch mounting, and arm functioning again.  Thanks again for the help, it is much appreciated.   

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bobdavis...Let us know how this resolves.  You did a lot of homework and are on the right track...The release arm travel is the key here.  I would look to the clutch release before condemning brass blocking rings at the synchros.  You do thorough work, and the transmission build is likely okay...Your symptoms sound like classic disk or pilot bearing drag.

As for pilot drag, are you running a crankshaft bushing or a bearing?  Bushings are more likely to be an issue, fit or peening during installation can cause bind/seizure at the input gear's nose.  Also, the stack height is critical.  If the input gear is pressing against the face of the bushing, that is another source of drag.  You are running a 4.2L with a 4.0L bellhousing and shim/spacer?  Shim/spacer thickness is also part of the stack height and input gear's depth in the pilot bushing or bearing.

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Note Part #19 in the 1995 4.0L six transmission/bellhousing.  Shim/spacer is part of the stack height and depth of input gear into the pilot.

Start with the release arm travel, consider the possibility of 1) either air still in the slave or 2) a slave that is defective and not sealing.  A leaky slave seal can allow fluid to bypass the slave piston, which shortens the release arm travel.

Moses

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Moses - That is correct, I am using a 4.2 block with a bellhousing and spacer plate from a 4.0.  To tell the truth, I did not think about stack height for the throw out bearing, so I never took any measurements for this.  I did have an issue with the original pilot bushing (It was a larger diameter one that engaged the larger outside hole on the crank).  The splines of the input shaft were impacting the pilot bushing when I fully installed the transmission.  There were imprints on the bushing from the splines.   I removed that bushing and found a smaller one that would engage the deeper, smaller bore in the crank.  I confirmed this bushing fit the input shaft prior to installation, it fit passively but snugly.  It is definitely possible that the bushing was damaged during install or is somehow binding now.   I’m going to swap out the master/slave this week and hope it’s as simple as a bad or incompletely bled slave cylinder.  If no joy, I will start uninstalling the transmission to have a look at the throwout, shift arm, and pilot bushing.  I’ll let you know what I find.  Thanks a bunch for all the help.  I followed your video on rebuilding the AX 15 and found it very helpful, so I doubt there is an internal issue with the trans.    

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I'm thinking insufficient release arm travel or pilot bind...Release arm travel would be #1 in the ranking, the slave cylinder not moving the rod far enough.  Either the slave is not sealing/capturing pressure or there is insufficient fluid volume to the slave (same result). 

Let's see...

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Well, I got the new profiled master/slave combo installed tonight.  Unfortunately,  it did not seem to help.  I’m thinking it might be the pilot bushing dragging.  When I downshift, there is a brief, high pitched squeal coming from the front of the transmission.   I’m wondering if that could be the bushing binding on the input shaft instead of spinning freely.  If it is the bushing, is there a chance it will get better over time as the bronze wears, or is this a recipe for disaster.  I know that the bushing fit the input shaft well prior to installation, so I’m wondering if I need to replace the bushing or just remove and check it for burs or damaged areas from installation.  Finally, if I pull the transmission, I want to make sure the bearing throw is sufficient to disengage the clutch, are there any references on this subject that you know of?  I think I saw an adjustable throwout bearing at either Novak or AA, is something like that necessary to increase the stack height or is there some type of shim that can be put in place?  Any help is greatly appreciated.  

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bobdavis...Very likely the pilot.  It's a bushing?  There are Oilite bushings impregnated with oil available from Advance Adapters, McCleod and others.  These are self lubricating over time...Some aftermarket clutch pilot bushings are not Oilite type.  Applying lube/grease through the bore during assembly will lubricate a non-Oilite bushing over time.  Do not apply too much grease, just enough to draw to the bore and input nose under heat.  What is the pilot type, a bushing or bearing?  Where did you source it?  Is it Oilite type?  Were there instructions regarding the need for grease?

If grease is necessary, make sure the grease does not prevent the input gear's nose from fully entering the bore, that would be too much grease!...If already greased and slightly tight, the bushing might still burnish and function okay.  As you suggest, that's a gamble without first assuring that the bushing bore has no burrs, no peened bore edges from installation and no out-of-round.

Here's a technique that I would use to quickly see whether there is enough clutch slave and release arm travel...With the vehicle stopped and the parking brake set, engine idling, depress the clutch pedal to the floor and place the transmission in a higher gear like third.  The vehicle should not creep.  Now release the clutch pedal slowly and see at what point the clutch begins to engage, creating a load on the engine.  If the pedal is reasonably off the floor (I'd want at least two inches) before you feel clutch engagement and a load on the engine, you have enough clutch, slave and release arm travel.  The shifting problem is likely pilot bearing drag.  To rule out any problem with the transmission's synchronizers, which is doubtful, what lube did you use for the transmission?

The release arm and release bearing are "self-adjusting".  When you release the pedal, the cover finger return force and spinning T/O bearing move very slightly away from the cover fingers.  This becomes the set point for the slave travel.  The master cylinder displaces enough fluid to move the pushrod far enough to disengage the clutch.  If all the parts are "factory" stack height, as they should be with the 1995 parts prototype, the stack height should be correct. 

A stack height wild card would be a flywheel re-machined too much or a clutch disk that is too thick (most unusual with the correct replacement clutch assembly);  an overly thick disk could cause the cover fingers to set too far inward at the starting point for the slave/pushrod travel.  The slave would not have enough remaining travel to disengage the clutch.

Moses

 

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Moses - The pilot has a bronze oilite bushing.  I soaked it overnight it oil prior to install.  I will do the test in third gear as you described to make sure the stack height is correct.  I agree with you though, all the clutch parts were new and specd for the 1995.  It does have a new flywheel for the 4.2, but my understanding was the only difference between the 4.0 and 4.2 flywheel  is the reluctor wheel.  Assuming all is good with the engagement of the throwout and arm assembly, I’m going to pull the transmission and check the pilot for burs or damage from installation.   I have spent too much time on the rebuild of the transmission and transfer case to leave anything to chance at this point.  Thanks for your help, I’ll let you know how it turns out when I get the transmission out to inspect things.  

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Sounds smart...The 3rd gear/clutch engagement test should provide a quick answer about stack height and function of the master and slave...Glad the bushing is Oilite.  If it does "correct itself" regarding squeal and binding, you will have reasonable confidence that the bushing can self-lubricate from here.  Obviously, if it doesn't stop binding or squealing, you will be replacing the bushing.

I drive these bushings into position with a sleeve that has an O.D. matching the outer diameter of the bushing to stay away from the bushing bore.  This drives the bushing near the crankshaft bore.  Some attempt to drive the bushing into place with an old input shaft, using the bushing bore as the driving point.  This will distort the bore by bending the bronze edges inward.

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Moses - I pulled the transmission out today.  Unfortunately, everything looked good with the pilot bushing.  The input shaft slid out of the bushing freely, there was no evidence of nicks, gouges, or other distortion on the ID or outside flange of the pilot bushing.  I tried installing the clutch installation tool in the bushing and it slid in and out freely as well.  I don't think  the bushing is the  problem.  However, I'm running out of options.  Also, the clutch disk was installed facing the correct direction.   I'm thinking maybe installing a new pilot bushing just in case.  I am also wondering if I should try a slightly thicker throwout bearing.  I did try the clutch engagement test with the transmission in third gear.  I could feel the clutch engaging after letting up the pedal about 2-3 inches.  I'd like to avoid having to pull the transmission out again, but hate to just throw different parts at this  without a clear diagnosis.  Any thoughts?  Sorry to take up so much of your time, but I appreciate your efforts.   

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bobdavis...Before commenting on your latest findings, referring to the last sentence that I highlighted in red on my Wednesday reply, what kind of lubricant are you running in the AX15?  Did you experience any gear clash noise when trying to down shift?  If there is gear clash when shifting, you may have a lube with too much viscosity and lubricity.  The AX15 requires a lube that permits the brass blocking rings to act like "brakes" during the shifts.  Too much lubricity will not permit that friction to apply, and the transmission shifts feel like there are no synchronizers in place.  Given your latest findings, this needs to be ruled out.

The transmission removal accomplished two things.  The clutch engaging at 2-3 inches from the floor seems very normal.  So does the pilot bushing.  The clutch engagement point suggests that the stack height of parts is correct, and the master/slave assembly is working.  There would be no point changing the relationship of your 1995 prototype parts, including the release bearing length—unless this is the wrong release bearing or bearing collar.  

Walk through the 1995 parts once more just to confirm that they are correct.  This includes the throwout bearing and its length (stack height) or "thickness" as you describe.  Make sure the release arm (#21), pivot stud (#26) and return spring (#20) are correct for 1995.  Here is a diagram of 1995 parts.  The release bearing and collar (#22) can be seen;  try to gauge its proportionate length from the diagram:

image.png

You are in a good position to carefully confirm the stack height from the flywheel face to the innermost machined point on the transmission's front bearing retainer collar.  The transmission front bearing retainer and collar are 1994-up AX15 style, right?  You have plenty of support for the release bearing on that collar?  Here's a 1994-up AX15 front bearing retainer view (#12).  Note the long release bearing snout.  The earlier hydraulic release/throwout bearing front retainer design has a short snout:

image.png

I would also carefully check the stickout of the crankshaft flange from the block.  Check the runout of the flywheel face, using a magnetic dial indicator stand on the block flange and the dial indicator facing the flywheel face.  Rotate the flywheel slowly and see whether the flywheel is warped or not mounting squarely.  Place a straight edge across the flywheel face to check whether the face is dished, warped or uneven.

Lastly, I would carefully check to see whether the clutch disk is warped or has a dragging cover pressure plate.  You may have drag on the disk, either against the flywheel face or against the clutch cover's pressure plate.  Drag may be just enough to frustrate the transmission shifts but not enough to cause the Jeep to creep while in gear with the clutch pedal depressed.

What I am pointing to is partial clutch disk engagement at all times and never a full release or separation of the disk from the flywheel side or the pressure plate.  This slight drag could be from a friction material high point, a disk rivet issue or disk hub and blade warpage.  Make sure the disk hub is the correct type for a 1995 YJ application.

You haven't mentioned clutch "chatter" or shake on engagement.  Look for a reason why the clutch disk drags even when you depress the clutch pedal fully.  When driving, you likely tried shifting with the clutch pedal at the floor, and that was apparently not enough to get full separation of parts.

The pilot bushing sounds fine.  Check the clutch disk hub, clutch cover and pressure plate, flywheel and bellhousing alignment.  Look for anything that can cause a bind, even the bellhousing position (dowels and bellhousing holes) or the fit of the flywheel to the crankshaft.  Make sure the clutch disk hub did not become damaged during the transmission and transfer case installation.  If not supported, the weight of the transmission/transfer case can warp, twist or damage the clutch disk.

Make sure the stickout position of a 4.2L flywheel is actually the same as a 1995 YJ 4.0L flywheel.  Here, you need to make sure the 4.2L flywheel's face lines up with the bellhousing at the same point a 4.0L flywheel face does.  Stack height includes the location of the flywheel face.  This takes into account the crankshaft flange stickout from the block, thickness of the flywheel and flywheel flange plus how far the flywheel sets into the bellhousing.  Flywheel face position determines the position of the clutch assembly within the bellhousing.

Go through this reply carefully, and check off each item...You have an opportunity to find the source of your problem with the transmission and transfer case out of the way.  Make sure you find a clear problem before installing the transmission and transfer case.

Let us know what you find...

Moses  

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Moses - Thank you again for the thoughtful reply.  I used Redline Mt-90 as a lubricant after the rebuild.  It seemed a popular choice on several jeep forums.  I will go through your checklist and see if I can see any possible issues.  The only thing I can think of at this time is the release arm mounting.  It appears that it is symmetrical, but I'm not sure if there's one end that should mount on the pivot side and one on the  slave side?  The throwout bearing  is the one that  came with the LUk clutch kit that also included the clutch disk , alignment tool, and clutch housing.  All of these were for a 1995 wrangler.   The other thing I noticed on removal of the transmission is that the engine block only had one of the transmission mounting dowels.  I looked at the old transmission I removed and the dowel stayed in that bellhousing when I removed it.  I though that the mounting bolts would align the bellhousing to the  engine when tightened, but maybe not having both dowels allowed the transmission to be slightly off, causing either binding in the  pilot or clutch/flywheel?   Thanks again and have a great day.

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bobdavis...The LuK kit sounds complete.  I brought up the dowels for the concern you cite.  Shift of the bellhousing can bind the pilot.  Everything else flat and true, a shift here could put the input nose out of center with the pilot.  Yes, the release arm design is odd with the cross pivot stud.  Make sure the arm engages the release bearing properly.

Verify the LuK clutch parts number.  Is this a stock 1995 type bellhousing or aftermarket?  

2-3 inches off the floor for engagement is a minimum.  More space from the floor assures quicker pedal release;  however, the clutch must engage completely before the top of the pedal travel.  You do need freeplay at both the pedal and release bearing...If the bearing runs constantly against the cover fingers, you will wear out the bearing and damage the fingers.  Use the 1995 freeplay specification for pedal movement. 

Also, make certain there is a slight amount of play between the pedal pushrod and the piston in the clutch master cylinder.  If the pushrod has the piston partially forward in the cylinder with the pedal retracted, you will not get full travel of the piston.  The fluid displacement will be less than the amount needed to fully release the clutch.  When the pedal releases completely, the piston must retract and seat in the master cylinder.  I like a slight yet perceptible pedal pushrod clearance, measured at the pushrod, not the pedal.  Some FSMs give a specific clearance here.

If there is a silver lining to the work involved with pulling the transmission, it would be the need for a dowel.  The bellhousing bolts are not an interference fit.  They cannot align the housing precisely.  This measurement was once considered critical.  We always checked the transmission/bellhousing mounting index hole with a dial indicator, measuring from the centerline of the clutch/pilot and around the circumference of the bellhousing index hole to assure that the transmission fit well and centered with the crankshaft centerline and pilot bushing/bearing.

Moses

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  • 2 weeks later...

Moses - After a couple of weeks away on other projects, I pulled the transmission out of the Jeep.  I checked the pilot bushing for signs of uneven wear or misalignment, removed and reinstalled the flywheel, clutch plate, and clutch housing.  I rechecked all of these for trueness with  run out gauge, rechecked clutch alignment, and all torque specs double checked.  The throwout bearing and arm were removed and inspected and look good.  I installed the missing locating dowel in the block and reinstalled the transmission, making sure the input engaged the pilot passively and without binding.  All went in smoothly, but I’m still having the same issue shifting into 1st and 2nd.   I’m going to spend some more time looking at the clutch master and slave to make sure they are extending their full travel.  The clutch pedal is stopping about 1 inch from the floor, I assume that this is because the piston in the master if bottoming out, but I am going to disengage the arm from the pedal and check the travel of the pushrod again.   I’m also wondering if the pivot ball on the throwout arm can be threaded out or a washer placed under it to extend the pivot, which would push out the throwout bearing slightly further.  Any other suggestions on where to look are appreciated.   Thanks for your help as always.

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bobdavis...You did a thorough, labor intensive job here, lots of work, at least the dowel is in place now...

Some thoughts...First off, good idea to verify why the pedal stops 1" off the floor.  That could be the slave piston fully extended and bottomed in the slave cylinder.   If the release arm is retracting too far, as you hint, the overall release arm throw would come up short.

My first concerns would be the throwout bearing collar length or the height of the release arm ball stud—which you suggested when asking about shimming the ball stud.  Do you have the correct ball stud and release bearing/collar?  If the release bearing sets too far back at the start of the clutch slave piston movement, the piston would run out of travel (pedal off the floor) before the clutch cover fingers are depressed enough to release the disk.

Before shimming the ball stud at the release arm or creating a longer pushrod for the slave cylinder (another option), see how much free play or clearance exists at the release arm when the slave piston and rod are fully retracted.  You can do this without removing anything other than the slave cylinder from the bellhousing.  Remove the slave and push the rod into the slave cylinder to provide full piston travel.  Catch the release arm and pull it toward the bellhousing slave cylinder opening.  Carefully set the slave and rod into place just to position the release arm.  Now, pull the slave out of the way.  Carefully push the release arm inward and note the amount of travel before the arm stops with the release bearing just touching the clutch cover fingers:  This is the amount of slave piston travel that gets eaten up before the release arm and bearing begin to push the cover fingers inward.  If that play is excessive, you have too little slave piston travel left to fully release the clutch—which is what you suspect.

Clutch release bearing collars come in different lengths.  You may have the wrong bearing/collar assembly.  Or the release arm ball stud height is too short as you hint...In any case, there could be an issue that prevents the slave cylinder rod from moving the release arm far enough to release the clutch disk.  These could be possibilities:  1) release bearing collar too short, 2) release arm ball stud wrong and not enough height, 3) clutch disk too thick and causing the release fingers to fold too far inward with the clutch released, which would eat up slave travel before the release bearing reaches the cover fingers, 3) transmission/bellhousing setting too far rearward, again making the slave piston travel too far before the release bearing reaches the cover fingers, 4) flywheel too thin and moving the clutch cover too far forward, 5) the slave cylinder rod is too short, unlikely since you tried two slaves. 

Other than the clutch disk thickness and release arm ball stud height, these other prospects relate to stack height from the engine block to the transmission forward face.  You hint about the release arm being too far back, which is among the possibilities.  Make sure the part number for the ball stud is the 1995 prototype.  Check the other part numbers like the LuK clutch.  Again, I'm curious who manufactured the bellhousing, as this would be part of that stack height.  If there is too much release arm free play at the arm, you need to account for why.

If this were my project, I would build a fixture to see if the clutch will release properly.  Without doing anything more than removing the slave cylinder and rod, I would make a simple 1/4" steel plate with holes drilled to match the bellhousing's slave cylinder mount holes.  I would drill a hole in the middle of the plate and weld a 5/16" Grade 5 nut to the plate.  (Without a welder, the use of a nut on each side of the plate would work but involves more setup time.)  I would take a long Grade 5 bolt with full threads (well up the bolt shank) and grind the bolt's end to match the curvature of the slave rod end.

Bolting the plate at the slave location, square with the release arm, I would turn the bolt inward to move the release arm and just take the play out of the release bearing-to-clutch cover fingers.  This would be a reference and measurement for how far inward the slave rod sets to remove play from the release arm and bearing.  Comparing this with the stickout length of the slave cylinder rod would determine how much slave travel gets eaten up before the release arm play is gone.  The slave cylinder does have extra piston range to allow for normal clutch bearing retraction play and clutch disk wear over time. The cover fingers move outward as the disk wears, and this allowance is built into the slave piston travel.  The slave is "self-adjusting" to maintain the necessary and normal slight free play between the release bearing and the clutch cover fingers.

Turning the bolt in further would actually release the clutch disk.  With the cover fingers inward a reasonable distance (enough to release the disk) and the vehicle's four wheels chocked for safety, I'd remove the coil high tension wire, place the transmission in gear, and bump the starter.  If the vehicle does not lurch or show signs of the clutch grabbing, I would insert the coil wire, and with transmission in neutral, start the engine. Foot on the brake, I would carefully try to shift into 1st and 2nd gear to see whether these shifts are now easy and smooth.

If shifts are easy and smooth up and down through all gears (vehicle stationary), the clutch can release and the transmission is okay.  If the shifts still are not easy and the clutch disk is clearly disengaging from the flywheel and pressure plate (not dragging), the issue is transmission synchronizer action at the first and second synchro.  The aim is to separate issues:  clutch versus transmission.  For simplicity sake, you want this to be a clutch release issue rather than the 1st/2nd synchros.

Moses

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Moses - Thank you for the detailed reply.  I will answer a couple of the questions you posed.   I used a bell housing from a 1995 wrangler that I bought from an online jeep wrecking yard.  That bell housing came with the pivot ball and release bearing arm, so I think all of these are a matched set.   I will make up the fixture you described, but I already took a measurement of free play in the clutch fork with the slave removed, it measured at 1/4 inch.  I’m not sure what this should be though.  I will do as you described and see how the transmission shifts with the fixture in place disengaging the clutch.   It does make sense that the slave rod is not extending far enough to fully disengage the clutch, as none of the 3 slave cylinders I have installed have broken the plastic straps that retain the pushrod in the slave have broken when applying the clutch.  I checked the master cylinder piston travel and the pedal appears to be fully extending and retracting the piston on pushing the pedal, so I don’t think the issue is there.   Thanks for your continued suggestions, I will keep you posted on my results.  

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bobdavis...Do you mean that the release arm moves a total of 1/4-inch inward and outward with the slave removed?  That would not be excessive if this is the total release arm travel to move the release bearing from fully retracted to just where it touches the clutch cover fingers.  If this is all the further the release arm moves, it would rule out a throwout bearing collar length issue.

Regarding the issue with the slave rod straps, the slave rod straps should break with the first application(s) of the clutch pedal.  If you've removed three slaves with the straps still in place, the master cylinder is not moving the piston far enough, and this is likely your entire problem.  I asked earlier whether the clutch pedal rod had clearance between its tip and the master cylinder piston.  If the rod doesn't have play or clearance, the master cylinder piston is already pushing into the bore with the pedal retracted, and the piston cannot create a long enough stroke to displace the volume of fluid necessary to move the release arm far enough.  You have a short pedal stroke.  If there is a slight amount of rod to piston clearance and the straps are still not breaking, the fluid displacement from the master cylinder is not enough volume.  The slave piston is not moving far enough.  This could be the result of a clutch pedal height that is too low.

To get the master cylinder pushrod to retract far enough for the master cylinder piston to fully retract, you need to raise the pedal height.  Pedal height is adjustable on a CJ-7 by raising the pedal bump stop adjustment.  Once the pedal and master cylinder pushrod can allow the piston to fully retract, with just a slight amount of play between the pedal pushrod and the piston, you will get a full master cylinder stroke and more fluid volume to enter the slave cylinder.  Assuming there is no air in the system, the slave piston and rod should have the stroke length needed to break the plastic tabs on the slave pushrod. 

After a few full strokes of the clutch pedal, assuming there is no air in the system, the slave cylinder piston and rod will assume their correct adjustment point.  The clutch should operate properly with normal travel and free play.  Check the pedal free-play at this point.  This is the light pressure portion of the pedal stroke before the release arm begins to move the clutch cover fingers.  I check this with my finger tips on the clutch pedal.  The light movement is the clearance between the release bearing and cover fingers.  As you start to move the clutch cover fingers, pressure will increase noticeably.

The goal is to make sure the clutch slave travel allows the clutch pedal to reach the floor slightly before the piston bottoms in the slave cylinder.  As it stands now, the piston is not reaching the end of the slave cylinder.  If it were, the straps would have broken. 

Moses 

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Moses - Yes, the total movement of the clutch fork is 1/4 inch without the slave in place, from the throwout just touching the clutch fingers to the arm fully retracted in the slave cylinder access port.  I’m not sure if I can get any more travel out of the master cylinder.  I tried disconnecting the master cylinder rod from the pedal to see if the rod will either extend or contract any further and it didn’t seem to.  The clutch pedal is out of a YJ wrangler and doesn’t seem to have a bump stop.  When the pedal is disconnected from the master cylinder, the pedal can swing all the way to the bottom of the dash without resistance, so I don’t think there is a physical limitation holding the pedal from retracting the pushrod fully from the master cylinder.  I wonder if there are any adjustable pushrods for the master cylinder and/or slave cylinder so that I can play with slightly longer pushrods?  

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bobdavis...Sounds like your stack height is okay with that limited amount of arm movement.  When you remove the pedal rod, is the piston in the clutch master cylinder retracting completely?  The slave end should have enough stroke, since every piece is a 1995 prototype match.  The clutch will self-adjust as I mentioned.  You simply need enough clutch master cylinder piston travel to move the clutch slave cylinder piston and rod the necessary amount of travel.

So, the correct pedal and pedal pushrod travel will allow the clutch master cylinder piston to retract fully with the pedal released.  When the pedal reaches the floor, the clutch master cylinder piston needs to be near the end of the clutch master cylinder bore.  You want a slight amount of unused piston travel to prevent the piston from slamming into the front end of the clutch master cylinder bore and damaging the piston.  That would be all the fluid displacement the master cylinder can produce, which should be enough since the entire clutch and hydraulic linkage is a 1995 combination.  Right?

You could do the same test I described for the slave cylinder end, making a plate that matches the clutch master cylinder's firewall mounting plate.  In this case, the aim would be moving the clutch master cylinder piston with a rounded tip bolt.  With the clutch master cylinder detached from the firewall and the clutch slave cylinder installed at the bellhousing, you could attach the fixture to the clutch master cylinder and move the piston until the slave rod releases the clutch.  Safely prove that the clutch is fully released, that the transmission shifts smoothly, etc.  If you can determine that the clutch works and the transmission is okay, your goal would be getting the pedal to move the clutch master cylinder pushrod far enough to release the clutch.

There are pushrods available for brake master cylinders, brake boosters and hydraulic clutches.  If you need a longer rod, it should be available.  Try the Dorman Master Catalog online.  The catalog may provide dimensions for various pushrods. 

The use of a Wrangler clutch pedal could be a core issue.  Be aware:  The pedal pushrod attachment point on the pedal determines the ratio of pedal movement to pushrod movement.  The pedal pushrod needs to attach at the correct point on the pedal to achieve the right ratio of pedal movement to pushrod movement.  Also, the pushrod needs to push straight in and out at the clutch master cylinder.  

Why did the YJ Wrangler clutch pedal come into the project?  Is this a recommended part for an AX15/1995 YJ prototype changeover?  What does the YJ Wrangler pedal accomplish?

Moses

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Moses - I used the YJ clutch pedal in order to gain the stud that the eye on the master cylinder pushrod installs onto.   The CJ clutch pedal had a hole for the clutch linkage rod to attach to.  Rather than fabricate a mounting stud on the CJ pedal, I purchased the YJ pedal assembly, removed the pedal from the pedal box, and installed it onto my existing pedal mount.  It fit up well, and after removing the MC pushrod from the pedal and moving the master cylinder through its full range of motion, I don’t think the pedal is limiting either compression or rebound.  But I will recheck all of this prior to making the fixture for the slave cylinder to see if I can get the clutch to disengage.  I will report back after I check these issues.  Thank you. 

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bobdavis...Give the pedal/pushrod more consideration.  Think of the pedal as a pendulum with the clutch master cylinder pushrod moving X-amount for a given range of pedal movement.

You have only so much pedal movement.  There is only so much clutch master cylinder piston travel.  The pedal travel and clutch master cylinder piston movement or "ratio" is determined by the attachment point of the clutch master cylinder pushrod.  The higher the retracted pedal, the more movement.  The tabs not breaking on the slave cylinder pushrod indicates that the slave piston is not moving far enough. 

There are two additional possibilities:  1) air in the hydraulic system that does not let the slave piston move as it should or 2) a clutch master cylinder with too small a piston diameter, which would not displace enough fluid to move the slave cylinder piston and pushrod far enough.  Check the hydraulic clutch master cylinder's bore diameter and make sure it is the correct clutch master cylinder for this application.  You can quickly determine bore by measuring the piston/bore at the dust boot end of the hydraulic clutch master cylinder.  See whether that diameter is consistent with your '95 YJ prototype parts.  

Have you confirmed that the clutch master cylinder piston retracts all the way when the pedal is released?  If not, this would also restrict/limit the fluid volume displaced.  When the pedal is depressed, you need to displace enough fluid volume at the clutch master cylinder to move the slave cylinder's piston/pushrod far enough to disengage the clutch.

Moses

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Moses - I wanted to give you an update.  After reinstalling the transmission and watching the master/slave cylinder function during depressing and releasing the pedal, I am relatively convinced that the slave is functioning correctly and engaging/disengaging the clutch correctly.  I have been driving the Jeep the past week, and it has been getting better each time.   The 1st/2nd gear shifts are still a little harder/clunkier than the other gears, but it will shift up and down into them consistently.   Previously, I couldn’t get into 1st or 2nd gear on a regular basis.  So, I’m thinking it was either the input shaft binding on the pilot bushing or the synchros needing to wear in a little.  It seems to improve more every time I drive it, I’m hoping this trend continues.  If it does not improve or gets worse, I think I’ll have to open the transmission up again and look at the 1/2 synchro.  Thanks for all your help with this, I greatly appreciate it.  
 

Bob

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bobdavis...Sounds more promising.  It is possible for synchronizers to need break-in, and there has been a good deal of controversy about AX15 brass blocking rings supplied in aftermarket kits.  We have covered this extensively at the forums.  You may have such an issue, and yes, the problem could resolve as the synchro rings seat.  Pilot bind, possibly from the dowel missing, may have played a role.  If this is steadily improving, the brass rings could be seating.  You may also be experiencing clutch disk seating and an improved clutch release when the pedal is depressed.  The disk friction material may have been dragging slightly and is gradually seating in.

Worth mentioning is lubricant, which I asked about earlier.  In the eighties, while I was fielding the OFF-ROAD Magazine Q&A tech column, I got on the bandwagon over the use of synthetic gear lubricant.  HTP and Mobil each made quality products, and their virtues were obvious.  I encouraged the use of synthetics until a Toyota truck owner wrote me a polite letter, explaining that he changed the lube in his relatively new Toyota pickup's manual gearbox to synthetic Mobil.  The synchronizers would not function normally, and he experienced gear clash.  We concluded that the viscosity and lubricity of the lube was too good, meaning that the brass rings could not grip the synchronizer hubs.  Instead, the transmission had balky shifts.  When he changed back to the Toyota recommended conventional lube, the problem went away.  Synthetic lube is great, sometimes too great.

Synchronizer brass blocking rings act like brakes.  The ridges on the tapered inside contact surface squeeze the lube away and allow the ring to grip the hub and bring the hub up to speed during the shift.  That's the synchronizer action and how a synchronizer works.  If lubricant lubricity is too great, the brass ring slips and cannot clutch/grip the hub;  the shift balks or there can be gear clash.  If that sounds familiar, the type of gear lubricant could be playing a role.  This may resolve as the brass blocking rings seat.

At this point, drive with prudence and do not overload the synchros.  Update us on whether the brass blocking rings seat, the clutch release improves and shifts normalize.  We covered a lot of ground and provided others with insight into the hydraulic clutch linkage system and other relevant issues that impact shifting and clutch engagement/disengagement.

If/when you're confident that everything is working well, I would correct the pedal bottoming an inch off the floorboard.  You described the pedal stopping an inch off the floor board.  This means that the piston in the clutch master cylinder is bottoming in its bore.  The pedal should meet the floorboard slightly before the piston bottoms to protect the clutch master cylinder bore and the piston's end from damage.   This may resolve with a pedal height adjustment and/or the pedal pushrod may need shortening.  The goal is to maintain a full range of piston travel in the clutch master cylinder while the clutch pedal travel ends at the floorboard.

Shortening the pushrod can be carefully done on a grinder if you reshape the end to match the original rounded end.  Do not overheat the heat treated rod during the grinding process, go slowly to control the heat.  The goal is to have full piston travel:  the clutch master cylinder piston should retract fully when the pedal releases; the clutch master cylinder piston should nearly reach its full range of travel as the clutch pedal reaches the floorboard.  Pedal height and pushrod length determine this range of travel. 

Make sure you have adequate clutch pedal free play to assure that the clutch release bearing can move away from the clutch cover fingers when the pedal retracts fully.  Again, this is the first movement of the clutch master cylinder piston, which should have little pedal resistance, followed by more resistance as the piston moves the slave piston and release arm far enough for the release bearing to contact the clutch cover fingers. 

Moses

 

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