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My new 4.6L stroker engine is done and the PSC steering upgrade is good.  I replaced the front CJ springs with new YJ springs and they are getting broken in. like them a lot, much better.  The irritating part is the rear suspension.  Getting massive axle wrap. All new springs and related hardware.  Put in a new custom CV drive shaft and it was destroyed in under 40 miles.  Rear pinion sitting at 6 degrees.  Let out the clutch and rear pinion nearly points to the sky and binds the yokes.   Had a bigger, better one built, and while the Jeep is streetable, with gentle throttle, it is not trail worthy.  I am exploring a number of options, but each option comes with draw backs.  If affordable, I would ditch the leaf springs and go to a 4 link set up w/ coils.

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Rare CJ8...I know your chassis is modified with 3/4-ton truck axles (Sterling at the rear.)  If you mean that the rear U-joint angle measures 6-degrees, that could be the problem.  When you run a CV at the transfer case end, each of the double Cardan joints cancel each other, i.e. the “angle” of that joint becomes irrelevant.  When you do a CV at the transfer case end, the rear axle pinion shaft-to-driveline angle should be 1.5 to 2.0 degrees with the vehicle resting on the ground, axles fully weighted.  This is the upward canted pinion so common with CV drivelines. 

Essentially, you could run 0-degrees at the pinion shaft/yoke end, but this would not enable the rear U-joint’s needles to rotate, resulting in rapid wear of the single-Cardan rear U-joint.  The 1.5-2.0 degree angle is simply to keep the U-joint’s bearing cap needles rotating.  Again, the CV is always self-cancelling anglesthe rear axle shaft pinion is then set close to a straight line with the sloping driveshaft (1.5 to 2.0 degrees rear U-joint angle maximum). 

This could account for both the axle wrap and the tearing up of the rear driveline.  Also, if you're running Jeep springs at the back, the main leafs could be too weak to resist spring wrap, a contributing factor.  Modifying the rear springs with a stiff main leaf and lighter secondary leafs could resist spring wrap.  The stiff main leaf would act like a traction bar. 

If the rear driveline joints are at correct angles, if the driveshaft is the proper length with the axle pinion angle set, and if you have a properly centered slip coupler on this rear CV driveline, the spring wrap and shaft binding should go away.  If the spring wrap persists, Summit Racing and others have a variety of traction bar solutions. 

Link and coil suspension is an option, but as you share, expensive.  I would start by correcting the rear pinion joint angle and the driveshaft length.

Moses

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Additional details:  Originally, the output from the T case and the yoke on the rear axle were exactly parallel with each other.  Suspension 'experts' said with a CV style shaft, the rear axle yoke should be indexed up a bit to point toward the T case yoke.   In that configuration it was nearly binding on the yoke to shaft.  and at full droop testing it bound up for sure.  (Will add a center limit strap after this wrap issue is resolved.)  So I added a 4 degree steel shim between axle spring perch and the leaf pack.  Testing showed needed more, so went with a 6 degree shim.  No better.  Some suggest cut off the spring perches to rotate the rear pinion up then re-weld.  (That's a lot of work!)  Even so, on acceleration rear pinion points up in an ugly way causing yoke binding too.    it literally moves up 4+ inches. not fully convinced doing that will stop the wrap.   sitting on its own weight and as full tank of gas plus tool boxes, etc., measured the driveline angle at 23 degrees.  

So this is where I'm at.  its so-so ok to street drive but on a hill in low range, watch out.  It destroyed the first CV shaft in short order.  Maybe add more leafs but that equals stiff springs and might not address a cure.  Also the rear end squats 2" lower than front that is not aesthetically pleasing.  Add camp gear and more squat. Then we're into the bump stops.  I have a set of 2" lift blocks that I can have machined to a specified degree (replacing a shim), but that only adds more fulcrum leverage to leaf wrap.  (How do full size trucks OEM avoid this?)  Might consider some sort of center traction bar, but exhaust and air tank in way and that seems a bandaid fix, not a remedy.  So I'm basically grounded after a two year new engine/PSC steering and fuel delivery  system upgrades and countless unplanned costs.  plus a 1000 other little things.  

 

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So back to my points, RareCJ8.  The rear CV driveline has the CV at the transfer case end.  Those double-Cardan joints self-cancel each other’s angles.  Regardless of driveshaft slope angle, you need 1.5-2.0 degrees of pinion shaft-to-driveshaft angle. 

When you rotate the axle upward to set the pinion joint angle, you also shorten the space between the transfer case and rear axle pinion yoke.  The driveshaft is then too long for the space between the transfer case output yoke and the rear pinion yoke.  This creates bind.  If you have a slip coupler in the rear driveshaft, the shaft could be bottoming in the slip joint.  Either way, if the shaft is too long, you will have severe binding as the shaft rotates.  Given the amount of angle change you applied, the shaft shortened considerably.  If the rear driveshaft needs to be shortened be sure to have a slip joint  built into the assembly.  End goal is a rear pinion angle of 1.5-2.0 degrees. 

When you measure for shaft length and the pinion angle, the rear pinion angle should be 1.5-2.0 degrees with the Jeep setting on level ground and full weight on the springs and axles.  This is “curb height”, which is the baseline for driveshaft fitting.  Do not measure with the vehicle lifted by the frame.  If springs and axles are hanging, the measurement will be too long.  From what you describe, it sounds like the rear driveshaft is too long for the pinion angle you are trying to achieve. 

As for how to rotate the axle for the 1.5-2.0 degree pinion angle, you can use steel shims or relocate the spring perches.  If the steel shims will not rotate the axle far enough, you would need to relocate the spring perches. 

Regarding spacer blocks with a slope to replace the shims, that’s an option.  My Ram 3500 has angled spacer blocks as part of the 4” lift kit.  Longer U-bolts, accordingly.  I never get spring wrap or any other issues.  When the driveline is the correct length for curb height, and pinion joint angle is correct, there should be no wrap-up with stiff springs.  If your springs are not up to stiffness, you can have spring stacks built to reduce risk of wrap-up.  I’m not clear what springs you run, they should be ¾-ton truck capacity at least.

Modifying the rear springs with a stiffer main leaf and lighter secondary leafs could resist spring wrap and still provide reasonable ride quality.  Here, a spring shop takes rear vehicle weight (loaded and unloaded) into consideration.   The spring sag with the load could indicate too light a spring rate, although I know you carry a substantial trail gear load.

Stiffer rear springs or main leafs would level the Jeep and also provide some anti-wrap capability.  (Spring arch can be configured for your front/rear ride height correction in the process.)  The stiff main leaf at each side would act like a rear traction bar.  If the driveline/rear pinion is at the correct angle, driveshaft sized to proper length, a slip coupler on the rear driveline, etc., and the rear spring wrap persists, you could consider anti-wrap bars or the fulcrum solutions. 

In looking over the offerings at Summit Racing, there are many traction solutions to counter spring wrap.  As you suggest, this is a last resort.  Correct all other issues before considering traction bars, fulcrums, etc.

Moses

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  • Moses Ludel changed the title to Rear Driveline Bind and Severe Spring Wrap
As for springs, brand new dorman 63” 4 leaf packs -application is OEM 88-98 chevy 1500 truck.  After this install Jeep taken to Driveline Service in sparks to “build it right.”  They had it two days.  Paid for extra long slip spline and testing verifies no bottom out.   Trust them to build it right.   It lasted about 30 miles before the double cardan component failed.   There is a pin inside that assembly that sheared off.  Took it back, they alleged I was jumping and abusing Jeep and waited too long to come back.  I reminded them you installed this just last week, uh…ok, we will rebuild it.  No damage to yoke assembly at rear pinion.
They did rebuild and field testing continues to show extreme rear pinion climb when clutch released to move forward.  Brand new axle u bolts torqued to spec.   I’ve come a long way, spending far too much $ and now at an impasse.  All new parts to no avail. 
 
Upgrading rear springs has proven to be a folly so far, however the ride quality is vastly superior.  Thanks again.
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RareCJ8...So the wild card might be the new, longer truck springs?  A few cell phone pics of the springs, their frame mounts and hangers, and the angle of the stacks would be helpful.  I'd like to see how the springs align with the frame at curb/static height and the arch of the installed springs.  Leaf springs, as you know, double as a "torsion" member to keep a hypoid/beam axle from rotating.  Let's see if the spring installation or alignment is failing to do so and why.  You never had this problem before the spring install.  A CV driveline is an improvement, not a detriment.  The rear U-joint and pinion yoke/driveline angle is off, but it sounds like there's more going on here.

Moses

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RareCJ8...Your photos are excellent and helpful.  The driveline looks well built, joints are massive and more than adequate for this application.  The pinion angle at the rear axle is too many degrees for a CV driveline.  Again, I'd want to see a 1.5-2.0 degree U-joint angle at the rear pinion joint.  The CV double-Cardan joints are self-cancelling, so no should be no issue there. 

The CV joints and center yoke do not appear to bind or rub, though that is an obvious concern with 23-degrees of static driveline slope.  As the suspension/axle move downward, the slope is even greater.

This is a "spring over" axle and rear spring configuration.  The GM 1500 rear leaf springs are designed for a spring over arrangement, so nothing's unusual.  The leafs look stout and level.  Regardless, the axle wants to rotate and twist/wrap these rear springs under torque application.  The springs aren't offsetting the axle housing's rotational force

These springs look relatively flat, very little arch as if fully loaded.  I'd want to know the vehicle's rear axle weight/load and the weight capacity of these springs.  The local truck scales can provide an accurate read on the front and rear axle's weight with the Jeep normally loaded.  A spring shop has listings for the spring rate of these OEM replacement 1/2-ton GM truck rear springs. 

Let's start here.  These rear springs may be incapable of resisting the heavy axle assembly's rotation force.  Your axle ratio(s) and tire size/unsprung weight also come into play here...If the vehicle's rear weight on the axle and the spring capacity don't align, the main leafs may not be stiff enough to resist spring wrap.

Moses   

 

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local spring shop can add some arch to them to address rear squat.  Pix show rig sitting as ready for a trail ride and 1/2 tank fuel.  scales are in the works eventually. Spring guy can also add a stiffer leaf to the pack which makes sense but not too much to defeat flex and trail manners.  fine balance.  I've yanked the pax in and out so many times i have it down-- especially after cutting off, weld in and cut off , weld in the spring hangers.  The old springs were located according to jeep OEM location and fitted to the Ford Sterling 10.25 axle.  turns out the spring perches on the ford axle are a bit wider than the spring hanger locations.  Careful loos shows how had to outboard the hangers to match the axle perch.   No m1029869819_IMG_1711(1).thumb.JPG.49021950f1a74391bc6933ba1ad8785b.JPGore leaf spring binding, which was an earlier problem.  this is what i got before the hanger mounts were out boarded.  fast way to destroy spring bushings.

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once the new YJ springs were set up in front took rig to a local creek for flex testing to help locate placement of the bump stops.  Using OEM GM style bumps.  passenger door open is a boo boo for good photos...  with the bumps installed we tested it again and its perfect.  suspension cycles nicely and makes no contact with sheet metal.  Nice and clean.  lots of thought went into this build  and the rear axle wrap is the last major barrier to getting this out on the dirt.  

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Well, you certainly have maximum articulation for leaf springs front and rear!  Are the hangers at the rear springs now aligned properly, or are they still offset?  These hanger photos are the current alignment or from the past?

If you pursue a rear spring stack upgrade, the main and second leafs are crucial to anti-wrap.  Think of these two leafs in the stack as the "torsion bars".  A custom spring build can make the stack a "progressive" spring rate, increasing load capacity as the springs compress.  There is also room to build ride quality and articulation into the equation.  You're on it with regard to the "balance" here.  The spring shop needs to understand your expectations.  A scale/weight ticket would be helpful.

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yes, the spring/shackle hangers depicted above and in the ditch are out boarded and now the spring is free to move unhindered.  observe the hanging tires are off the ground.  so bumps in right place and noting fancy-- OEM GM bump stops from the wrecking yard and easy on/off with threaded studs.  No need for fancy $$$ gas filled bumpstops.   Will go see the spring shop guys next week.  hopefully able to add to the set i have-- and from whom i bought them.  

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  • 2 weeks later...

am hesitant to add more leafs to rear packs since this will limit droop and compression.  More of each is why went to the chevy springs over the OEM packs.  Been reading a lot about fighting wrap.  the leading contenders are similar to these as below.  different designs and each with pro and con.    Attaching to the axle tube can bring on unwanted movement of the tubes in the center section.  A bar will add to the direct torque.  beefing up the tube to center is a possible plan.  The other idea is to base a bar off the u bolt plate, mounted in double asheer  and the fwd mount can twist/rotate to accont for articulation.  With this idea need one each side.  Some suggest a telescoping design to allow the bar to follow the spring arc.  

 

Still researching.     Just upgraded to Yukon front hubs.  pulled the trigger on this but it is 6 months back ordered.  These default to lock if broken compared  to open with the Warn hubs.  

 

 

 

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RareCJ8...The illustration system would be great for a drag car with limited travel and no axle articulation.  The second design (photo) looks better suited for use with leaf springs as shown.  It appears to target spring wrap and would clearly prevent leaf flexing/twisting.  The arc of the bar must follow the normal spring/axle arc over the range of travel.  The axle must remain square with the frame over the suspension's range of travel.  The bar's attachment point at the front must create matching bar and spring arcs.  If the bar is not positioned properly, spring movement will be inhibited.

As you share, the Heim at the rear does allow for axle articulation.  The point of attachment (U-bolt plates at each rear leaf spring) is where the axle wants to rotate;  the Heim is above the centerline of the axle housing, which creates a leverage effect...Do you have access to the owner of this vehicle?  You could ask some pointed questions about axle articulation and spring movement.

Telescoping bars sound useful for articulation;  however, that telescoping movement would defeat the idea of stabilizing the springs.  The telescoping bar would not offer an opposing force. 

Moses 

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