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  1. #1
    RC Racer
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    Differential Shims

    Ok,

    So i've researched the forums looking for a definitive answer on shims in the differentials. From what i've found, people add shims to reduce the "clicking" noises or eliminate the occasional "rough" hang-up or catch between the ring gear and differential pinion gear; which, is what my basic issue is. I also read that 6mm shims are the recommended size and usually 1 or 2 are needed.

    I just rebuilt my diffs, and still have the profound clicking noise, as well as a slight snag at one point between the gears, which occurrs in only that one spot. Further inspection of each tooth on both gears reveals nothing which would warrant replacement - Everything is a brand new piece...!

    Lastly, I also noticed that when rebuilding the differential housing with the bulkhead and shock towers, if i tightened the screws down, the outdrives from the diff would be almost impossible to turn. I had to back the screws out a couple turns to allow the outdrives/diff, etc. to spin. Why is this the case? I would imagine that not having tightened down screws could lead to a possibly weaker structure; or, could back out through repeated use

    I will try to add a shim or two to hopefuly solve my issues.
    "Incoming rounds always have the right of way!"

  2. #2
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    Quote Originally Posted by BASH N SLASH View Post
    Ok,

    So i've researched the forums looking for a definitive answer on shims in the differentials. From what i've found, people add shims to reduce the "clicking" noises or eliminate the occasional "rough" hang-up or catch between the ring gear and differential pinion gear; which, is what my basic issue is. I also read that 6mm shims are the recommended size and usually 1 or 2 are needed.

    I just rebuilt my diffs, and still have the profound clicking noise, as well as a slight snag at one point between the gears, which occurrs in only that one spot. Further inspection of each tooth on both gears reveals nothing which would warrant replacement - Everything is a brand new piece...!

    Lastly, I also noticed that when rebuilding the differential housing with the bulkhead and shock towers, if i tightened the screws down, the outdrives from the diff would be almost impossible to turn. I had to back the screws out a couple turns to allow the outdrives/diff, etc. to spin. Why is this the case? I would imagine that not having tightened down screws could lead to a possibly weaker structure; or, could back out through repeated use

    I will try to add a shim or two to hopefuly solve my issues.
    I have put shims on both front and rear just to do it since I had them torn down anyways but when I had them on without the shim I never heard a clicking noise.

  3. #3
    RC Competitor
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    I have the same issue with the rear diff on my p4de where either the gears inside the housing or the diff itself snags in one spot. I've taken it apart multiple times and even after cleaning/rebuilding the diff the problem persists. If you find a remedy for this please let me (us) know... I haven't seen any mention of diff shims in this forum so I wasn't sure it was necessary for our trucks, but maybe in our case it is.
    p4de mmp2400 - stock p4de - wraith

  4. #4
    Marshal Dadx2mj's Avatar
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    I've never heard of anyone shimming the diffs in a Pede 4x4 or Slash 4x4. IMO there must be something wrong if the diffs wont spin properly when the housing and shock tower are tightened down. Leaving it loose is just not right. Also adding shims is not going to fix a high/low spot issue on a diff. Shimming is only used to tighten up the mesh over all it will not fix a high/low spot issue.

    I think there has to be something wrong with the diff housing, or a bad bearing, or the diff itself. The housing and tower screws should be able to be tightened down and the diff spin freely if it doesn't there is something else wrong.
    BlindMan Racing
    Rusty - MERV - Pede 4x4-Alias
    SPC Lipo Power

  5. #5
    RC Turnbuckle Jr. spenniepoos's Avatar
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    I have never had to shim my diffs no matter how much I abuse them and trust me I like chaos when out and about with my pede........peace
    Famous last words...watch this!!!!

  6. #6
    RC Qualifier
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    Shimming diffs on a Pede

  7. #7
    RC Racer
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    X2MJ,

    I completely agree with you. Something has to be wrong with the diff housing or the other supporting components. However, i find it difficult to beleive a brand new diff housing, gears, etc. would display the same issues as a used one. Heck, my pede is practically new. When I broke it all down, I was hesitant to replace the parts because they were still practically new and didnt show signs of deterioration. I just replaced it all for the heck of it. So, I've basically still got a good back up set which could go in the rally or pede.

    Traxxas normally has excellent quality control, Thus i also find it hard to beleive that my original set and new set are suffering from the same fate. If shims are necessary, why wouldn't Traxxas include a pack of 8 or so to assist with a possible common issue that occurs in a lot of their rc's... Diffs. This is not to say the problem is Traxxas; I honestly think its 80% of driver problem. Everyone loves the ridiculous power of their brushless rc line ups and its certain that the average user is popping wheelies, goosing the throttle and braking hard to avoid curbs, trees, etc. not mention, how many people stay on the throttle upon landings.

    Is the XO-1 planetary gear set that much better than the pede/slash/rally gear set? If so, why wouldn't Traxxas just use it from now on in the rtr's? Or maybe they do in the slash ultimate edition? Anyways... I've rambled for far too long. Good points X2MJ... I just don't know what my issue is and Ive followed every bit of valuable instruction on rebuilding the diffs, it's not my first rodeo with diffs, but I'm still learning something new everyday and have a lot left to still learn. Thanks for the reply
    Last edited by BASH N SLASH; 07-26-2013 at 09:10 PM.
    "Incoming rounds always have the right of way!"

  8. #8
    RC Racer
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    Not to drag this on... Ok, yeah I guess I/we are; but I was researching diff issues in these forums and came across a coue different threads which mentioned shimming the diffs. I know for certain one was under the 1/10 rally, another was under the slash and I think... (Memory failing) but I think there was mention of it under the pede 4x4 mixed into comments under a separate type of thread. I will try to find them and link to them. I'm just doing this on the tiny iPhone screen, so zipping from thread to thread can be challenging with my large digits
    "Incoming rounds always have the right of way!"

  9. #9
    RC Qualifier
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    Quote Originally Posted by BASH N SLASH View Post
    Not to drag this on... Ok, yeah I guess I/we are; but I was researching diff issues in these forums and came across a coue different threads which mentioned shimming the diffs. I know for certain one was under the 1/10 rally, another was under the slash and I think... (Memory failing) but I think there was mention of it under the pede 4x4 mixed into comments under a separate type of thread. I will try to find them and link to them. I'm just doing this on the tiny iPhone screen, so zipping from thread to thread can be challenging with my large digits
    I guess I should remove my shims since I never heard it click at all but it's such a pain and a mess to remove those shims specially if nothing went wrong because of it LOL. I shimmed my 1/16 MERV before and it was all over the MERV Main Thread.

  10. #10
    Marshal Dadx2mj's Avatar
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    If you cant tighten up the diff housing something is not right. Might not be the diff itself it could be a bearing or a crack in the housing or any number of things.

    Shimming the diffs in thsse trucks is not common at all and I doubt your issue, that does not mean someone or even a couple people might not have done it. It is not your issue though. If tightening all the screws locks the diff output up shimming it will make it worse not better.
    BlindMan Racing
    Rusty - MERV - Pede 4x4-Alias
    SPC Lipo Power

  11. #11
    RC Turnbuckle Jr. rag6's Avatar
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    ^^^ I have a high spot somewhere in my brand new rear diff, I can feel it catch as you are describing, and that is not right. My brand new front diff has way too much drag, and something is up. I am subbed to this thread.

    My slash platinum spun nice and free from the get go.

    I have never heard of shimming a pede or slash 4x4 diff, but if you shim 1 side, I would assume it would push the ring gear away, then shim the other side, and bring the ring gear closer. Effectively loosening or tightening the gear mesh. Adding shims can add drag, but if there is room for a shim, by all means make the mesh as sweet as you can. My front diff already has a ton of drag, so must look somewhere other than shimming. Waiting for all driveline parts to be acquired before working on the issue though.

    All parts on my build are brand new. I have been concerned about my unfree diffs, and this thread could really help...
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