Carrier Bearing Preload

01yellercobra · Jan 27, 2019

So I'm going to be rebuilding the center section in my Cobra tomorrow. I'm clear on everything but the preload for the carrier bearings. I'm looking through the manual and I swear I saw something that said add 0.008" of preload to both sides. But then tonight I found a chart that shows no preload on the left side and 0.020" on the right side. Anyone know which one it is?

Also, am I supposed to set up the backlash, then spread the case and add the preload? Yes, I have a case spreader to do it correctly.

01yellercobra · Jan 27, 2019

I did some more digging and found someone that exposed it a little more. He set backlash then spread the case and added 0.007" preload to both sides. Followed by checking backlash one last time.

OLD H2S · Jan 27, 2019

Thats more like it..The bearings are going to wear in .0005 each side and that is going to open up more back lash, a lot. Mine are up to .016 now and could use a re-shim but I was just in there last week and everything was nice and smooth adding more pressure is an easy way to upset the "groove" and have to start over with a new set because they are getting too noisy. Has anybody tried the heavy duty set up from FRPP?
This is the main reason I have gone to a solid crush sleeve on the pinion to have one less variable to screw with the set up, every thing changes when you start racing even at low HP. The rear end gets loose every week and needs adjusting till it will stay at a tight setting and the factory did not do a good job on the initial set up.

Silver95bird · Jan 27, 2019

I've always had good luck this way: take out the factory shims, measure them and add the totals together. When reassembling I always make sure the total combination adds up the same. I might have started with a .550 and a .500, and after the gear change ended at .530 and .520, you get the idea.

I was always a fan of a tight backlash. Standard axles are .008-.015" iirc, and the fn10/cobra axle was as close to .010" as you can get. Probably to do with the centers being aluminum. I always shot for the .008-.010 range. That and a factory trak-lok setup, but with the biggest shims in the package. I got a little scratching on a tight corner, like right turn at a stop sign, but to me that just tells me it's working. Some don't like it.

01yellercobra · Jan 28, 2019

I kinda cheated the system. Since I kept the original gears I used the shims that came out. Tooth pattern looked good and backlash was between .010" and .011". I checked multiple times with and without the caps torqued down. The solid spacer was a bit of a pain at first. But once we realized it needed a chamfer filed into the corner it worked a lot better. It'll be a few days before I get everything back together and can take it for a test drive.

OLD H2S · Jan 28, 2019

And check it again soon..the new pattern will wear off and in so lots of metal junk to drain. Use cheap fluid for the first week then drain and use the good stuff.

01yellercobra · Feb 21, 2019

So I figured I'd update with my screw up and my fix. After we got it back together I drove it a couple miles around the house and everything seemed good. Drove it to and from Palm Springs and everything seemed ok. But it seemed louder than before. When I got home I put the car back up to check the oil. Ended up finding the pinion was loose again. Ripped it all apart to see what I could find. The theory is that the front bearing surface had a burr so the bearing wasn't sitting correctly. I tried retorquing the pinion nut and it was still tight. When I pulled it apart I found some marks on the inner race that lead us to believe the bearing didn't sit correctly. The fact that a new bearing wouldn't slide all the way down also lead us in that direction. So I hit the pinion with some 320 grit and the bearing slid on and off smoothly.

I ended up changing both pinion bearings and starting over. Originally the spacer was .465". This time around it ended up at .435". Which makes more sense since the crush sleeve was .437". I also noticed that previously the end of the pinion nut was even with the end of the threads. This time around there was 2 or 3 threads showing. This time I ended up at 24in-lbs for rotation force. And backlash was around .011-.012" depending on where we measured. I put about 40 miles on it and when I got home I check the pinion and everything was still tight.

For those wondering about the noise I run aluminum diff bushings and the cradle bushings are that UHMW Delrin. So not a lot of material to soak up the NVH. I've been hearing it since I upgraded the bushings.