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Thread: Shim diff

  1. #1
    RC Enthusiast
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    Mar 2014
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    38

    Shim diff

    Hi,

    I am pretty new, and have just got a mini e-revo for my 8 year old son. First day he rode it full speed into a wall, broke the chassis, steering arm and bulked. I have just ordered the new parts and installed everything on the new chassis. I then also put in a center diff (had no oil so added 50k). I have now noticed that the servo gears also stripped, so new ones are on order.

    I also added thicker shock oil and stiffer springs.
    front:
    Traxxas GTR Shock Spring, Blue (2.92 Rate) (2) - 1/16 Summit
    Core RC Silicone Oil - 1000 cSt - 60ml Click to select

    back:
    Traxxas GTR Shock Spring, Purple (3.2 Rate) (2) - 1/16 Summit
    Core RC Silicone Oil - 1300 cSt - 60ml Click to select

    I read the following post,

    http://traxxas.com/forums/showthread...-your-bulkhead

    I am just wondering, why do you need to shim your diffs? Is it to enable the teeth to fit together tighter? How do you know if it needs to be done?

    Also, when attaching the motor to the slipper clutch gear, how tight must the fit be? I read somewhere that I should put a piece of paper between the teeth, but when I do so, the teeth don't catch, they just slip (i.e. too far apart).

    Thanks
    Last edited by richardmarais; 03-26-2014 at 10:00 AM.

  2. #2
    RC Enthusiast
    Join Date
    Sep 2011
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    48
    Let me answer the easy one first.

    Gear mesh. With the motor mount a little loose - slide a small piece of paper between the spur and pinion. Push the motor into the spur so the paper pushes into the spur. Push fairly hard. HOLD THE MOTOR IN THIS POSITION WHILE YOU TIGHTEN DOWN THE MOTOR MOUNT. when you pull the paper out it should be evenly crinkled.

    Shims. There are lots of threads on this. First off - you do not know if you actually need to shim you diffs UNLESS they are ALREADY CLICKING (from the mesh being too loose). BUT you can also do a little preventative maintenance by shimming early. On my brand new Merv I put one shim in front and one in back. I tried two in each and that was too many - they bound up the diff. You will know if you have too many installed. It is a PIA process cause you have to shim - put back together - test and perhaps tear it down and remove shims if you installed too many. THE SHIMS YOU REQUIRE MAY BE DIFFERENT THAN MINE. It is a bit if trial and error process.

    Hope this helps. 'As you can see - I only have 16 posts on this forum - but have been running RCs for 20 years. My MERV is my first Traxxas.
    Last edited by bbking9; 03-26-2014 at 10:10 AM.

  3. #3
    RC Qualifier
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    Lehi, Ut
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    Yep shimming your diff just keeps that ring gear pressed nice and tight on the pinion. That way under serious acceleration or braking the gears don't have enough lateral play to slip a tooth.

    If your diff is clicking definitely do it, but other than clicking you really can't tell unless you open it up and try putting a shim in there.

    If you are just running 1 nimh you probably won't have any problems with that for a while, but if you ever need to open up your bulkhead I would highly recommend shimming it. Even if it's not clicking it's nice to know that everything is nice and snug.

    As far as gear mesh goes I've heard of the paper method, but I've never tried it. I just press the motor against the spur and spin the wheels if it feels like too much binding I slightly press the motor away until it feels good. I've never had a problem with my it. But that might not be the best way to do it.
    1/16 Summit beadlocks with 2.2 rock lizards

  4. #4
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    Thanks for the advise SB

    I am looking to get Shims for my 1/16 E-Revo and 1/16 Summit front and rear diffs for spares for the next time I open the bulkheads.

    Does anyone know what the part number for the compatible shims are?
    Last edited by cooleocool; 03-27-2014 at 09:29 AM. Reason: merge

  5. #5
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    Lehi, Ut
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    These are the ones I used.

    http://www.rcplanet.com/Associated_D...p/asc21141.htm

    I know there are others that work, but I don't remember what they are.
    1/16 Summit beadlocks with 2.2 rock lizards

  6. #6
    RC Competitor
    Join Date
    Feb 2014
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    91
    heres another option

    http://www.hobbytown.com/Shop/Caland...Shim-Set-20pc/

    i know you may only need a couple so the associated set is a good choice, but i have two MERVs so i got this set from my LHS.

  7. #7
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    Yeah my front only took 2 shims and my rear took one. But my brothers merv needed 4 in the back (and that was with a new diff and bulkhead) and 3 in the front. The numbers seem to be all over the place.
    1/16 Summit beadlocks with 2.2 rock lizards

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