How to shim your Arrma diff

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Hey... so I've read literally this entire thread. And sadly I'm only slightly less confused. I get that you have to shim your diffs sometimes, and I understand why. I still don't understand how you know when you need to shim, and what parts of the diff need to be shimmed.

I have a Fireteam and an Outcast 4S V2... I also have a new Traxxas Sledge that I haven't even run yet (please don't judge me; I might just sell it).

The first two have had some use just around where I live. No major air... by that I mean they may have gotten as high as five feet in the air. Landings have been about 50% okay and 50% sketchy or just plain bad. Nothing broken yet. But I'm new to this and just the other day read that I need to be letting off the throttle when they land to avoid driveline damage. Upside is that the ground here is dirt that is pretty soft. These things do a great job of making visible tracks and throwing dirt and gravel everywhere. So that might be a saving grace at this point.

Anyway... at what point should I be pulling these diffs and checking them? I had the front diff out in my Fireteam recently when I thought I had blown it, but it turned out to be user error with regard to the little cups that screw into the knuckle that cover the pillow balls (is that what they're called?) that the knuckles pivot on... one was out too far and causing the wheel to rub a little bit and not turn.

I had opened the diff and everything in it was fine, and had a decent amount of fluid. But at the time I wasn't even aware of this whole "shimming" thing so I didn't think anything else about it and reassembled it.

So... what do I do? Leave it for now? Pull it and check?
 
Just assembled using NEW parts & pieces a center diff for the 6S Typhon buggy.
Using a GPM housing and output cups. Internal gears OEM.

Being a machinist and long time mechanic on small mechanical devises, rather that screwing around with OEM shims under the sun gears & output end at bearings .... Made my own shims from PEEK ... That material is a VERY tough aerospace plastic with high self lubricity.

Made a few sets of differing thickness starting with a set at @ .010" ( .25 mm ) and one set at OEM spec of .008" ( .2 mm ) *Pic below

The .25 mm shims the gears felt notchy when turned, the .2 mm was smooth, so went with them at each end.
As too the axial movement of the output cups within housing as well ring gear you could just feel a very minimal amount.

My last trick that I've been doing for YEARS now is to stretch on over the output cups 3 o-rings. The first one is a 1.6 x 7.1 that rests against the bearing inner race not touching the dust shield / seal. The next 2 are 2.4 x 5.6 having it 3 per side. ( THIS WORKS ON FRONT / REAR DIFF TOO )
* What this does is SEAL up the output shafts and keeps what lubricant placed in this area ( Moly grease for mine ) intact and keeps the dirt and debris out !!
Assembled it looks like this .. Pic below

e.jpg


d.jpg


g.jpg
 
Just assembled using NEW parts & pieces a center diff for the 6S Typhon buggy.
Using a GPM housing and output cups. Internal gears OEM.

Being a machinist and long time mechanic on small mechanical devises, rather that screwing around with OEM shims under the sun gears & output end at bearings .... Made my own shims from PEEK ... That material is a VERY tough aerospace plastic with high self lubricity.

Made a few sets of differing thickness starting with a set at @ .010" ( .25 mm ) and one set at OEM spec of .008" ( .2 mm ) *Pic below

The .25 mm shims the gears felt notchy when turned, the .2 mm was smooth, so went with them at each end.
As too the axial movement of the output cups within housing as well ring gear you could just feel a very minimal amount.

My last trick that I've been doing for YEARS now is to stretch on over the output cups 3 o-rings. The first one is a 1.6 x 7.1 that rests against the bearing inner race not touching the dust shield / seal. The next 2 are 2.4 x 5.6 having it 3 per side. ( THIS WORKS ON FRONT / REAR DIFF TOO )
* What this does is SEAL up the output shafts and keeps what lubricant placed in this area ( Moly grease for mine ) intact and keeps the dirt and debris out !!
Assembled it looks like this .. Pic below

View attachment 266876

View attachment 266877

View attachment 266878

Just a heads up those GPM diff cups wear down fast at the output because they lack a steel insert. https://www.arrmaforum.com/threads/my-daily-rant.10352/page-52#post-866073
 
New to Arrma RC, this is my second RC car coming from a WLToys RC, and curious why the diffs need shims?

Basically to take out any excess play in the gears, excess play will cause the gears to wear down faster and if the play is too much they will strip.

The WL Toys cars do not have near as much power going through them and the diffs suck anyway so no point in shimming them.
 
Basically to take out any excess play in the gears, excess play will cause the gears to wear down faster and if the play is too much they will strip.

The WL Toys cars do not have near as much power going through them and the diffs suck anyway so no point in shimming them.
Ah! I see. Thank you for explaining that. I will add that to my list of things to do.
 
I'm in the UK, does anyone from the UK know where to buy these?

So far this is the closest thing I can find to the outer shim kits in the UK they are .2mm thick instead of .1mm thick like the Tekno ones though. https://www.ebay.co.uk/itm/25455855...RcWmopC8v/Tl9T0XFQ0RmqZSyY|tkp:Bk9SR6L1_t6GYg

There are also the Arrma ones these are also .2mm thick https://www.ebay.co.uk/itm/18551226...GPo7wWwa3VHsjxitpPAcrCHg==|tkp:Bk9SR7iZmd-GYg

I am not sure of other shims that would work for the internals other than the ones that Arrma sells. I will get some measurements of the shims in the Mugen kit and see what I can find.
Large Mugen shims are 5x18x.2mm and the small ones are 3.5x12x.2mm.
 
This is something we get asked a lot on the forums and nearly every single time the answer to those threads are to watch this video. So as suggested, I created a sticky thread for this very question.

We can also use this thread to have a "one place to go" for this information.

Also check out the thread: Shims that work for Arrma diffs


Enjoy!
Thank you woodie
 
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