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  1. #1
    RC Racer
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    Apr 2017
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    Shims on each side of the diff?

    Hello all,

    Today I shimmed my rear diff for the second time. I put two shims on the same shaft, as was said on a video I watched. I was wondering if that is the correct way to shim, or if I should put the other shim on the opposite side of the diff. That way, the pressure would be equally distributed throughout the bulkhead and not just on one side.

    Thank you!

  2. #2
    RC Champion grizzly03's Avatar
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    Quote Originally Posted by MiniSummit50Mph View Post
    ...I was wondering if that is the correct way to shim...
    The correct way to shim a diff is (by trying and checking) to remove excess play and not by a predetermined amount of shims. To make it easy put one shim on the ring gear side and see how much play between ring gear and pinion. If there is still play add another shim (same side) and check again. Trying to push the gears together is what takes out the play and is what shimming does. If after adding a shim the gears are too tight take that shim off and your done. That's a basic diff shimming.

  3. #3
    RC Turnbuckle Jr. Squeegie's Avatar
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    ^What he said!

    I used this video for reference when I did mine years ago:



    Good luck!
    Creativity is intelligence having fun. -Einstein

  4. #4
    RC Racer
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    Quote Originally Posted by grizzly03 View Post
    The correct way to shim a diff is (by trying and checking) to remove excess play and not by a predetermined amount of shims. To make it easy put one shim on the ring gear side and see how much play between ring gear and pinion. If there is still play add another shim (same side) and check again. Trying to push the gears together is what takes out the play and is what shimming does. If after adding a shim the gears are too tight take that shim off and your done. That's a basic diff shimming.


    Thanks for the reply. I put two shims on, but it was binding when I was rolling it on the ground. I took one out, and now it doesn't bind. I wanted to have two because I already stripped out my rear diff with one before, but I guess that doesn't work. However, I did just recently notice a crack in my bulkhead and have since ordered a new one. Another note is that my slipper clutch was so worn out that it wasn't even acting as a slipper. A new assembly is also ordered for that as well. I was wondering if these two things could be the culprit for my first diff to strip even with the shim. I'm still really confused as I have heard of people putting 2 to even 4 shims in their bulkheads. I have no clue how that doesn't bind the gears together.

  5. #5
    RC Champion grizzly03's Avatar
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    A cracked bulkhead can cause stripped diff gears. A crack allows the parts (bearings,gears) to flex/move because the rigidness that holds them is compromised. I don't use a set number of shims. Each diff will be different amount of room. I use 3Racing shims to do shimming on all my vehicles. Their shim sets come in multiple thicknesses, not one set thickness like many of these people you "heard of" using. That's why they say "use this many." The 3Racing shims sets come in 0.1/0.2/0.3mm thickness.

    Shimming my mini I install 1 4mm x .2mm thickness shim on the pinion where the arrow is. Then I use 8mm shims where the other arrow is and start with a .3mm shim. Test gear tightness/binding. If it needs more add another. Test & Repeat. When it's too tight take that last .3mm shim and swap it for a .2mm shim. If still too tight try the .1mm shim. Using these smaller shim thicknesses you can be more accurate.

    No need to install the bulkheads back in to test. I just hold the two half's of the bulkhead together and turn the pinion gear to check how tight they are.

    Here is a quick link of the different sizes they offer:
    ebay.com/3RACING-Stainless-Steel-3-4-5-6-7-8-10-12MM-Shim-Spacers


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