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Adjusting AMC 20 Axle Shaft End Play


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Hi everybody,

my first post here, found this Forum on my search on informations about the AMC 20.

As i am from Germany, i must pre- apologize for all the misspelling that will come up.

But now we come to my Problem with my 79 CJ7, i have rebuild the rear axle with new bearings and seal just some weeks ago.

Yesterday there was oil under the rear tyre, it came out of the brake drum and as i disassembled i saw it comes out of the axle.

I realized that there is a lot end Play even without any shims.

Does this mean that the axle Housing is worn and needs to get replaced?

Thank you for the support

Greets from Germany

Thierry

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Hi, Thierry, and welcome to the forums!...The axle shaft end play is adjustable with shims.  The steps are in the factory service manual and also in my Jeep CJ Rebuilder's Manual: 1972-86 (Bentley Publishers, available through Bentley and parts retailers)

 

If the end play is not correct, the axle shaft will wobble and leak oil.  This is due to the tapered axle bearing cones having too much clearance.  The seals could be damaged at this point.  Check them closely, and follow the factory steps for setting the axle shaft end play.

 

Another overlooked issue is the axle shaft-to-wheel hub torque on the axle shaft nut.  This is quite high to bring the hub into proper fit with the axle shaft serrations.  (The wheel hub is supposed to be replaced if removed from the axle shaft.)  Whether you install a new wheel hub or not, the goal is to tighten the axle shaft's end nut to bring the hub into proper spacing.  The spacing is a factory measurement to assure a tight hub on the axle shaft taper.  This is measured from the hub's outer face to the end of the axle shaft. 

 

The stick out length of the axle shaft threaded end determines how tightly the hub fits on the axle shaft.  High tension between the hub's inner taper and the axle shaft is critical.  This requires considerable torque on the axle shaft nut.  If the spacing or stick out length is correct with very high torque applied to the axle shaft nut, the serrations will likely seat properly.

 

You will find this exchange at the AMC/Jeep CJ forum very useful, please read through it:  http://forums.4wdmechanix.com/topic/375-positioning-the-seal-amcjeep-cj-with-the-model-20-rear-axle/?hl=%2Bmodel+%2B20+%2Baxle

 

Moses

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Hi Moses,

 

thank you for your response and the link to the other Thread.

 

I am not sure on how to adjst the end play as it seems to be the other way around, there is play without any shim.

So it should get more with shims or am i wrong?

 

Will try this later.

 

The Hub and shaft on driver side is a new 2 piece version in the same length.

It was mounted the way that the Manual told with the correct spacing.

 

Thierry

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It seems that i need some adjustment washer that help to get less Play.

Just mounted without any shims or washers, there is about 4mm play.

So i will use some washer with the size of the outer bearing cup to get to the proper end play.

Looks like the only possibility to me.

Greets

Thierry

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Hi, Thierry...Make sure the correct axle shaft is at each side of the rear axle, they are different lengths.  There are also different length axle shafts in '80s CJs: different axle widths for narrow versus wide track axles.  1979 is a "narrow track" axle by that standard.  Make sure the axle shafts are the correct length for your 1979 Jeep CJ-7 rear axle.

 

Shims go at the left side of the axle only and fit behind the brake backing plate.  The plates with the built-in seals and the tin dust shields each fit on the outside of the brake backing plate.  The play that you have (4mm) sounds like the sequence of parts assembly may be wrong.  Check the parts sequence and compare with the illustration in the parts diagram I have included below:

 

AMC Model 20 Rear Axle Shaft Seals.pdf

 

Looking at this diagram, parts #6 and #7 go outside the brake backing plates.  Only the shims fit inside the brake backing plate in the sequence shown.  Check your parts sequencing at both sides of the axle.  Shims fit at the left side of the axle and inside the brake backing plate.

 

The #9 seal goes into the end bore in the axle housing before any other parts get installed.

 

Moses   

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Hi Moses,

 

well checked everything twice and it still looked the same.

 

What i did now was that i inserted some adjustment washers between teh bearing cup and the brake backing plate.

Now at least i have got the correct end play.

 

It could be that the axle housing is just not good anymore, i already had some really bad broke bearings that were blocked.

And i had to drive another 20 miles with them, so that will be the Problem.

 

Well at the moment it looks good, at least it works and no more Oil is coming out of the Brake drum :)

 

Thank you for your help

 

Thierry

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Thierry, 4mm is a considerable space if that's from damage.  Be safe...I trust that the information above plus the PDF were helpful.  You know the parts sequencing and have worked through this.

 

Keep us posted, we look forward to your participation at the forums!  Always interested in Jeep enthusiasm at Europe...Let us know how you use your 1979 CJ-7 Jeep 4x4!

 

Moses

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  • 3 weeks later...

New to the site, recently got a 85 cj7 getting ready to do the bearings and seals in the rear amc 20 previous owner installed one piece axles, will they use stock bearings? Also has anyone tried to omit the inner seal to allow gear lube to lubricate the bearings?

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Hi, zar, welcome to the forums...Bearing type depends upon the axle shaft supplier (Moser, Superior, etc.).  Identify the make of these axle shafts for parts referencing in general.

 

If the bearings are the originals for the aftermarket axle shafts, there's a straightforward parts sourcing solution:  Get the numbers from the bearings, if they are cups and cones, you'll need both part numbers.  These numbers should interchange with all popular bearing manufacturers, and matching up bearings should not be an issue if you have the original bearings that came with the retrofit axle shafts...A bearing cross-referencing chart or catalog will narrow down the picks.   

 

When matching any bearing set, be sure to match the ball or roller counts.  Often, a heavy-duty bearing may have a lighter duty counterpart of the same dimensions.  In the case of an axle shaft bearing and its severe load demands, you want the proper load capacity bearings.

 

For quality bearing sources, I use Timken, NSK, SKF and Federal brands...

 

Moses

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  • 5 years later...

Hi Moses, 

I have your book and I am working on a AMC 20 axle that was leaking at the driver axle seal.  I installed axle seal, axle and drove the cup in flush with the axle flange.  At this point I checked axle endplay and have 0.006". I then installed the shim that was on the vehicle, backing plate, etc and torqued the backing plate to 38 ft lbs.  I rechecked endplay and had 0.006". moved on to install hub and after torqueing to a minimum of 250ft lbs and getting my 1 and 5/16" both axle have 0.090" of endplay.  Do I need to replace the outside shim or is there a shim kit that goes between the bearing cup and backing plate. Both axle seals where previously replaced two times by two different people and I am beginning to believe end play has been the cause all along.  

Thanks,

Brian

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Bkapp79...You have the 0.006" right as the optimal endplay.  Add shims to increase end play, remove to decrease.

The problem sounds like parts orientation.  There should be no shims at the right/passenger side of the axle.  Simply put all parts in correct order at the right side and secure the flange bolts to position the right side brake backing plate and other right side parts.  I apply a light, even film of sealant or paste between the axle housing flange and the brake support plate as shown in the book.  Torque bolts and nuts to specification.

Note:  The seal/retainer plate goes at the outside of the brake backing plate with the dust shield outside of the seal/retainer plate.  Bolts face inward.  Nuts are at the inside of the axle housing flange.  Use a thin film of sealant at the brake backing plate-to-axle housing flange to keep moisture away from the bearing cup.  Torque hardware to specification before sealant or paste sets up.

There is a spacer block in the differential.  I am guessing you have a non-locker axle?  When you tap on the left side axle shaft, you are moving both axle shafts and the floating block in the differential to the right side.  The right side bearing cup seats against the right side brake backing/support plate.

At the left side, the shims go between the axle housing flange and backside of the brake backing plate.  Use a thin film of sealant, paste or Gasgacinch between clean shims and these parts.  In the illustration below, the brake support plate would fit between parts #5 (shims) and #6 (seal/retainer plate).  This allows the left side bearing cup to pass through the shims and stop against the brake backing/support plate.  When you tighten the flange/backing plate bolts and nuts, the left side axle shaft end play should reduce to the 0.006".  Again, the seal/retainer plate goes at the outside of the brake backing plate with the dust shield outside of that seal/retainer plate.  Bolts face inward.  Nuts are at the inside of the axle housing flange. 

With the axle shafts tapped from the left side toward the right to seat the right side cup against the right brake backing plate, you tighten the left side flange bolts and check your left side end play.  You want 0.006" endplay at the left side with both axle shafts shifted to the right side of the axle.  There should be zero end play at the right side now.

When weight is on the rear tires, the two axle shafts will center up at approximately 0.003" endplay each.  Tapered roller bearings enable shafts to center. 

This is a generic illustration for '81-'86 AMC 20 CJs.  Despite this being a drawing, you can see the shims (#5) that go at the left side of the axle (driver's side on a U.S. model);  these shims can fit around the bearing cup to allow the cup to butt against the backside of the brake support plate (not shown).  The brake support plate sandwiches between #5 (shims) and #6 (seal/retainer plate) shown:

image.png

See whether this solves the problem...Be sure to pack the tapered roller bearings carefully with quality grease so you don't have to pack them again for a long while. 

Moses

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Moses thanks for the reply 

I was working on some other projects the last few days and just had time to pull this thing apart and get back with you.   When I posted the other day I had only taken apart and reassemble the drivers side.  I replaced the axle seal installed the axle and bearing cup and set 0.006" of endplay and installed all parts in the order that are shown in the above diagram.  Today I disassembled both sides and found that the drivers side cup in backing out and that is how I am loosing endplay.  I could remove the shim but that would only make my endplay go from 0.090 to 0.085" after the bearing cup walk to the end of the axle flange.  when i had 0.006" end play my driver side bearing cup was seated into the axle flange about 0.090" deep.  so this is why i asked if they make shims that go behind the bearing cup and #6 on your diagram.  i also after tearing all the way down today wanted to verify someone didn't swap axles on me my drivers side axle is 28.5" and passenger side is 31.5" 

WIN_20210325_20_33_32_Pro.jpg

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Bkapp79...You have explained the issue.  Here is what I would check first: 1) the axle shaft lengths as you suggest, 2) any axle shaft(s) inner end wear, 3) the center block wear in the differential (inspect with a bright light from the left and right end(s) of the axle housing), 4) the bearing cup or cone stack height (wrong cup and/or cone, which is doubtful from your photo unless wrong at the passenger side); this would position the cup incorrectly or 5) the brake backing plate has too much wear where the cup rests.  Since the cup is recessed in the left housing bore, the first four possibilities are more likely unless the right side brake backing/support plate is worn or bent outward where the cup rests. 

The left axle shaft, as you note, is setting too far into the housing and creating the 0.090" endplay issue that you describe.  Bearing cup position is dictated by the axle shaft lengths, any wear at the inner ends of the axle shafts, the differential centering block condition and wear, the seated bearings on the axle shafts and the axle shaft stickout lengths from the centering block.  The shims position the left side brake backing/support plate to locate the left side bearing cup and achieve final/correct axle shaft endplay for both sides.

Shimming the bearing cup recess with a spacer ring or whatever would be a bandaid remedy and likely place the wheel hub(s) and brake drum(s) in the wrong positionThat would not be a safe solution.  If the bearings fit properly on the axle shafts (full press fit to align the axle shafts) and the shaft lengths are okay, look closely at the inner axle shaft ends, the axle differential and the differential/axle shaft centering block.

There are two distinct sets of axle shaft lengths, narrow and wide track.  Confirm your axle housing width (flange to flange) and the axle housing style.  Then determine whether the right or left side axle shaft is too short.  I doubt this is the case, as the difference in shaft length would be way more than the 0.090" you're seeking...If the axle shafts are the correct type for your axle housing, go through my list of possibilities.

Let us know what you find...  

Moses

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