Big Rock Important Big Rock Diff Post.

Stapleton219

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While disassembling the Big Rock front/rear diffs, I found a washer/shim that is not depicted on the parts list or the exploded view parts diagram. If you think of the diff assembly as a ring and pinion, this shim is on the back side (no teeth side) of the ring, before the bearing. This shim is only in this location and only on the front and rear diff. I contacted support, they were puzzled when they found the same shim and reached out to Arrma. Apparently this shim was added last min as a running change to tighten the gear mesh of the diff. FYI.
 

Kauaiguy

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While disassembling the Big Rock front/rear diffs, I found a washer/shim that is not depicted on the parts list or the exploded view parts diagram. If you think of the diff assembly as a ring and pinion, this shim is on the back side (no teeth side) of the ring, before the bearing. This shim is only in this location and only on the front and rear diff. I contacted support, they were puzzled when they found the same shim and reached out to Arrma. Apparently this shim was added last min as a running change to tighten the gear mesh of the diff. FYI.
The Kraton has the same shim on the f/r diff.In this picture the shim is on the bearing,without it the gearmesh is to loose.
 

PPS-RC

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Thanks for the heads up! I'm about to tear into mine next week. I was curious about shimming when looking at the exploded view.
 

Stapleton219

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I don't know why they couldn't make a note in the manual or on the parts diagram. The first time I disassembled and reassembled the diffs, I took them out thinking they were added by mistake, especially after I found several stripped screw heads and a cross threaded rear hub from the factory, but then I reached out to support and they said they were supposed to be there so I put them back in. They are very thin and do make a small difference in gear mesh. My diff feels gritty with the shims in and smooth with them out but they are in...
 

PPS-RC

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Well, I got into my Big Rock front diff, and there were no shims at all.

Does anyone know how thick these shims are?
 

Stapleton219

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Well, I got into my Big Rock front diff, and there were no shims at all.

Does anyone know how thick these shims are?
The shims are very very thin and there's only 1 on the front diff and 1 on the rear diff. The first time I took the riffs apart I didn't even see them because they stuck to the back of the bearing-look there. As a reminder, the shim is outside the diff and only on 1 side before the bearing.
 

mrfurious40k

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I found that shim lying on the workbench after reassembly of my first diff. And also realized that it appeared nowhere in the manual or exploded parts diagram. Luckily I had not taken the second one apart yet so I had one for reference. Good rule to follow when working on anything that comes in pairs is to leave one together so you have a parachute in case you go down in flames during reassembly.
 

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