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Old 06-09-2010, 09:21 PM   #1
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Default loud diff in rc8b

I have a rc8b that seems to have loud differentials. it also does not have a good free role. i have replaced all the bearings and replaced the rear diff and pinion gear. i am running 5,000 in all diffs. nothing seems to help. if anyone could help me that would be great.
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Old 06-09-2010, 09:23 PM   #2
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You must not have it shimed correctly.
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Old 06-09-2010, 09:30 PM   #3
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sorry i am new to the sport. where are the shims located. i have it built per the manual says. should i add or remove any shims.
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Old 06-09-2010, 09:44 PM   #4
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ok. this is going to be hard to explain. First make sure your ring gear is on the diff case as square as possible. After i put all my diffs together i spin them on my center diff mouting bracket to make sure it's even all around. Next make sure your pinion gear is tight in the bulkhead and does not have back and forth play. I hold the cup joint with one finger and the pinion with another and sqeeze pretty hard. Then tighten the grub screw with the other hand. Once that is tight and you put the diff case inside the bulkhead, check and see how much it moves sideways or perpindicular to the center line of the chassis (long ways). If it has play you have to figure out witch side to shim it on. On one side it will give a tighter mesh (the ring gear side), and the other side will give you a looser mesh. Now you basically want to get it as tight as posible without any binding. Aparently, you have it to tight with binding, so you will have to play with it and see what works best. I usually end up with a very small tick of play all around. And it's important for it to be even all around. Small tick, that is all. Put a bead of mobile one around the ring gear and your set. It should be smooth. I want to be careful how i say this, but if it has just a tiny bit of resistance (no catching or binding), and it's about as close as you can get, it will break in and be butter smooth. But you don't have to get it that close, and frankly you would be better off just having a tick of play for right now.

be grateful. Every step in the process i just outlined was learned the HARD way.
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Old 06-10-2010, 06:05 AM   #5
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i forgot to add that you might not need any shims at all, if there is no play you don't need it. But, you might still need to shim to obtain a proper mesh.

another thing. The mesh between your bell/spur is extremely important as well. That could also be causing your problem. You need a tick of play there too. Not to mention some end play on your clutchbell (bout 1mm at the most. I go for a little less.).
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Old 06-10-2010, 06:12 AM   #6
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Here is a little video on shimming an RC18T differential. 1/8th scale is about the same...just larger ;-)

http://www.youtube.com/watch?v=Tm1V5cdMq5A
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Old 06-10-2010, 07:02 AM   #7
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thanks guys i will be tearing it down tonight.
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Old 06-10-2010, 07:02 AM   #8
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I've encountered a diff that needed to be shimed away from the pinion - just take your time and you'll see which direction to shim your diff's.

Also - make sure your center diff and Clutch Bell are not too tight - that can cause the drive train to bind up as well.


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Old 06-10-2010, 07:41 AM   #9
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i currently have the engine out of it and i still have the problem
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Old 06-10-2010, 07:43 AM   #10
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would there need to be any changes of the shims inside of the diff on the sun gear. it currently has two washers under it.
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Old 06-10-2010, 07:51 AM   #11
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Typically you shim the diff under the bearing on the outside of the diff....but it does require some diff teardown to put the shim in there. So it's usually wise to dry fit the diff with the new shims to see if they are OK.
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