Diff question
 

I've got a O'Donnell Z01t. When I got to the track Sunday for a race I noticed that the rear wheels weren't pulling. To make a long story short I've replaced all the bearings, made sure everything is shimmed right, checked all gears and they all look ok, I even replaced the rear axle carrier, and bearings. It pulls when you first start it up, but after just about 30 secs the rear quits pulling. I put my foot in front of it and gased it and the front tires spin but the back doesn't. I noticed that when I do that the rear driveshaft is turning, but not the wheels. I'm at a loss to know what to do. I built the diff off the truck and everything was smooth, but as soon as I fired the truck up and ran it for a little bit it did it again. Anybody got any ideas?

Check that the grub screw is locked down on the rear pinion, If it backed out or came out you will lose rear wheel spin but the rear center cvd will rotate.

like trey stated check the grub screw.. also check the center diff for proper operation...

Yeah I meant to mention that the grub screw is tight. The diff is smooth as butter out of the truck.

Also
 

Check the grub screw on the rear axle cvd area and center rear cvd area not just the big one that holds the pinion gear, but the cvd....

if that ain't it, then check the diff gear shafts inside the diffs, the ones the round gears capture that go through the outdrives.....the small ones...

if that ain't it, check the rear wheels, sometimes they spin on the hubs, I would put kyosho hubs on it in the rear....long story....

Hope this helps....

I just tore it all back down again and put another shim on the pinion. Double checked everything again and can't find anything. I only know of one grub screw on this truggy and that is the one that hold the drive cup on the pinion. It is tight. I put the whole rear end together off the chassis and turned it before I mounted it back to the chassis and everything was fine. I mounted it on the chassis and test drove it and it did it again. After it started slipping I turned one rear wheel and the other one turns in the same direction, so it's got to be internal in the diff itself, but I couldn't see anything wrong in there as far as gear teeth. I've never shimmed the spider gears, so I'm not sure how to make sure they are shimmed properly.