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Shimming Rear Axle End Play

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  • Rear Axle: Shimming Rear Axle End Play

    I have read here some say they, "split the difference" and install equal shims on each side of the car, though the Shop Manual says to shim the passenger side. Some speculated the Shop Manual guidance may be because of how the assembly line was set up. I have, occasionally, split the difference too, especially if several shims were required. Well today, while greasing axle bearings and replacing a pumpkin gasket, I learned why the Shop Manual says what it does, at least on conventional rear ends: With the pumpkin cover off, I saw the thrust block, located between the two axle ends, floating at .002" to .006" clearance (determined by wheel bearing end play). That filler block has an oblong hole in the middle, to accommodate the spider gear pin which passes through it, with about .075" clearance on each side of the pin. With the passenger side axle removed, and the driver's side axle axle installed, resting against the filler block, it rests dead center in the oblong hole; any shimming on the driver's side moves the block off center in the oblong hole. Not sure it's a big deal if it were off center by as much as .050", but it seems like good science to keep it centered.

    In light of the above, it seems best to first install the driver's side axle, with no shims, since it is what centers the filler block. Then install the passenger side, and shim as needed. That procedure will insure the filler block remains centered in the oblong hole. I am due to swap in a TT rear end in another Hawk soon, and will remove the pumpkin cover too, just to see how it fits together, but pretty sure it's gonna be similar to today's conventional rear end.

  • #2
    Thanks for posting this topic. I'm just an old backyard shade tree mechanic. My experience began as a child in the barefoot south where any car or farm implement we had was usually someone else's discard and everything we had usually needed work to get it going and keep it going. By the time I joined the Air Force, I managed to pass enough skill tests to get some formal training. However, 'cept for that stint...I really never had a paying job as an auto mechanic.

    I've spent years in the hobby and have done extensive mechanical work. However, when it comes to transmissions, and rear axle gearing...I still consider myself a novice. The main reason is that I've been fortunate enough to not have much issues with either transmissions or rear-ends. I have removed axles and replaced bearings from time to time. Even replaced bolts in a ring gear, and a pinion seal. However, every time I have been into these things, you would find a manual, and a chair to sit in while reading up on what step to take when. Even then, when removing a bearing, I always made very sure to do my best to press the new bearing to the exact spot the old one was on the shaft. Regarding shims...I have always kept them laid out in the order removed and replaced them exactly back in the same order. The problem with my method is that I'm assuming the last person who worked on it did it properly. We know, as these vehicles get older, fewer and fewer of the moving parts remain untouched, and the ones that have survived untouched are probably worn.

    Your posts serves to remind me that just because I have the ability to take something apart and put it back together in the proper order...does not make me a good mechanic. It reminds me that details like numbers & clearances are there for a reason and not to be taken lightly. I believe I could count all the times I have ever had to dive into a rear axle or remove the differential cover (except for routine lubrication)...the number would be in single digits. So...I must be more lucky... than good. If I have to open one up, I'll still have my manuals and a chair. Heck, now I'll probably even carry this laptop with me. Because, now I can look up stuff here on the forum and probably find a YouTube video to watch someone else do the job. Something I didn't have available the last time I had to work on a smelly opened up differential housing.

    Thanks again, we need reminders that such details can be the difference in a job done and a job WELL done.
    John Clary
    Greer, SC

    SDC member since 1975


    • #3
      Yes, thanks for the heads up. I also shimmed both sides. Maybe at some point I will pull the cover and see how far off center the block is.