Kraton Rear Diff Crown Gear Mesh

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Primarrma

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Arrma RC's
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Hi,

I've just finished fitting a whole new rear diff setup in my Kraton. I've kept the old diff housing, but I've put a brand new set of bearings, a new diff cup and out drives. I've even replaced the spiral gear to the center prop shaft out drive and added new bearings.

My issue is that the mesh on the crown gear feels really poor, it has some play in it, but it is really noisy spinning one way and not too bad the other. I've added two shims on the crown gear side to help push the crown gear towards the spiral gear. I've tried it with 0 shims and it feels a little worse and I can't get 3 to fit in, so I'm stuck at 2.

Does anyone have any suggestions, the old rear diff was ok, but the spiral and crown gear were worn away a fair bit so I don't want to see this happen again, but that seemed to be caused by a bearing failure at the spiral gear on the center drive shaft out drive. The diff housing looks ok also?

I should also note that the rear diff is not yet been fitted back into the car, it is rough and noisy just turning it by hand. I have tried leaving some play in the center drive shaft out drive and also tried it right up tight against the bearings, without much change. I've greased the gears, but I just feel it doesn't seem smooth enough. I hope I'm not being paranoid, but I don't want to strip these gears, as I've just bought them and are brand new.

Thank you.
 
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I actually just ran into this on the Typhon. I was going to pull a complete housing/diff/output shaft set out of my parts bin that I got as a complete new set off of ebay and it felt the same way, very notchey. Kinda like the teeth are tight in a spot. I too used a single .02 shim to tighten up the fitment, but with our without the shim it felt the same. Im going to run it and see, its been in the car since new like that.
 
I use 3 shims on the outside of the diffs. Yeah its a a little loud in the beginning but that's okay because things will loosen up I have a hot racing diff cup and all my differentials and I even use shims on the outside bearing for the center differential as well I want to make sure the teeth are well-connected and that was 5 months ago and the car still rolls like butter through the grass. When I read did my differentials in the past I noticed the diff cup was making contact with the crown gear so that's why I tightened it up to try to eliminate that. I'm sure hot racing differential housings would probably really improve that considering their aluminum.
 
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I think I may have figured out what is going on in the rear of the car. I managed to fit 3 shims on the outdrive on crown side of the diff and it still didn't help. Then i realised the crown gear wasn't turning true, and what I think it was, is the gasket in the diff cup got some diff oil under it when I put the diff cup together and it didn't seat properly. When I tightened down the screws, the cup was sitting slightly off square. This caused the crown and spiral gears not to mesh correctly and create a noise and feel like the gears were binding.

After re-seating the gasket it fit better and the binding was completely gone, the mesh is noisy one way, but I think that is the nature of the gears being used. The car is almost completely back together and ready for a treat run. Can't wait as I've fitted a tbone rear wheelie bar now(The whole reason I found the issues). Thanks for all your help and advice.
 
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