AMC axle end play and rear diff.

[valkster]

Hi, all. I was replacing the rear brakes last week on my 'Bessie' restoration and the end play at the rear axle was huge, at least a 1/16". The book says something like .006" is desired and is adjusted with shims at the left axle only. I have never had to do this and have some questions.
I have the AMC 20 stock rear setup. When I push/pull on the wheel hub I get the 1/16" play I mentioned but the wheel on the opposite side moves too. This caused a major concern as I figured it meant the entire differential gearset was moving. After removing the differential cover and watching the movement this is not what going on. The gearset is not moving and the gears show no major wear (no metal bits in the case either). Does this make sense to you'all that have worked on the rear axles? Since I've never torn one down I have only the books to go by and if I am seeing the exploded drawings correctly, then both axle ends are touching the "thrust block" inside the case (between the spider gears) because it is the only thing moving inside the case when I check the axle end play. Insight would be appreciated. Oh, am I the only one that will toss the torx bolts holding the differential cover on after this? It was a major pain removing them and grade 5 or 8 hex bolts seems like it would be easier to use in the future. Thoughts?

Sincerely,
Mark

 

[JEEPTHRILLS]

sounds like the axle bearings are a little worn. were the nuts still tight and cotter keyed?
anytime I have had play I swapped to 1 piece axles...cheap insurance...how many miles on this rig?


As far as the torx screws...I only remove them once.

 

[valkster]

Thanks. Yes the nuts and cotter keys were still there...mileage is about 120K. I've had her for about 16 years and put about 35K of that on her, the rest was from previous owners and not sure what all they had done to it. The axles have been "worked" on before though, there were hammer marks on the end of the axle shafts and the castle nut. The outer bearings are pressed on the axles, right? If so, when changing to a single type axle how do you remove it? Currently the boltss for bearing/seal cover is obstructed by the brake system...do you have to remove the brake shoe assembly to get to the cover when removing a single axle setup? Thanks again,

-Mark

 

[spankrjs]

Yes, the centering block in the diff is used with the factory two piece axles to set end play. That is why only one side is shimmed; both axles are "connected by centering block, the shims on one side allow for the slight play in the bearings that is necessary. But, when replacing bearings, you should still recheck the end play on the side with the shims. Add or subtract shims as necessary.

Another interesting note, the centering block can wear and throw out the end play. I tried to reuse the factory axles on my green Scrambler and ran into this issue. My axles would not "pull out" like they were loose, but they would "plunge in". The centering block showed wear on both sides. Not surprising, it has 125,000 miles on it. I ended up removing the centering block and installing Moser 1 piece axles

Some people do and some people don't, but make sure the centering block does not interfere with aftermarket axles. On my green Scrambler, the Moser axles were hitting the centering block and would not go quite in all the way. So I had to remove the block. Now, every time I install 1 piece axle I remove the centering block

 

[valkster]

Ok, thanks...If you remove the centering block then you have to shim both axles, correct? Again, when you swap to a single piece axle, do you need to remove the shoe assembly and remove the bearing cover first or do the single piece axles slip out of the outer bearings without removing the cover? I ask because from what I have read I have to seperate the two-piece axles with a hub puller so I can access the bearing cover. After removing the cover, the axle comes out with the bearing, which has to be pressed off. Is this right?

Thanks much,
Mark

 

[spankrjs]

You only remove the centering block if you are installing aftermarket axles. You must use the centering block with the factory axles.

Most aftermarket axles do not require shims on either side. They use a 1 piece unit bearing that has the necessary play built into the bearing.

The brake backing plate should come out with the entire axle shaft assembly, after removing the 4 bolts that hold it to the axle housing. If the entire axle/bearing assembly slides out of the axle housing, and the brake backing plate is still attached to the axle, the brake backing plate must have been modified, and needs to be replaced. The brake backing plate is what keeps the axle bearing/axle assembly from sliding out of the axle housing.

You don't necessarily have to remove the hub from the stock axle shaft to remove the backing plate. I usually cut the bearing off the shaft with a dremel, and then slide the plate off the back of the axle shaft.

The new bearings have to be pressed on to the new shafts, after the seals and brake backing plates are slid on first.

 

[valkster]

Thanks, spankrjs, for the info. I asked just in case my axles were shot and needed new ones. I got them out and they look good but the bearings feel "sloppy" compared to new ones. I got a KenTool T-500 hub puller this week off ebay for $40 and it made short work of the hub seperation on my stock setup. Nice old tool. I am glad I was NOT seated straddling the end of the hub when I gave it the final peck with a hammer, though...the hub and puller shot off the axle and landed about 2 feet away. Ouch!

 

[valkster]

Ok, I got the new bearings and seals installed. The axles both showed no marring on the inside ends and the differential block seemed fine on the ends. However, even without any shims on the left side I am still out of the factory spec for end play (about .020" end play). Is this OK with most everyones experience? If not, where could the extra play be coming from in most cases? The new bearings were not the cheaper type. The hubs and axles looked really good for their age and I am considering getting some circular shims from an industiral supply catalog to place on the end of the outer bearing race to reduce the play and increase the preload...thoughts anyone?

Thanks,
Mark