I recently did my first rear end rebuild. It was a 742 cased aftermarket geared 3.55 clutch type sure grip. I put in new bearings, clutch pack, gears and seals. I bought books and read all about it for months. I put it in and had no issues for about 100 miles. I drove it to the track planning to take the car down the 1/4 mile, but started hearing some noise from the rear end. Mainly when i was turning at slow speed and sometimes some clunking. I thought at first that it was just the new tight clutches slipping, but after a while it had me concerned. The car also was acting a little weird going through sweeping corners on the highway like a little vibration in the steering wheel. I pulled the driveshaft and checked the u-joints (both are new) and they seem to be ok. Then i pulled the axles, but couldn't really look at them as i don't have a press to pull them off. I figured i was that far so i went ahead and pulled the pumpkin as well. I'd like to find someone in the OKC area who is familiar with these 8 3/4 rear ends to verify the specs of my build while dismantling (backlash and pinion depth) and make sure there is no damage, and then reassemble.

I'll pay extra if they let me hang around and see if/where i screwed up.
To this point i don't know what the problem was. I don't see any catastrophic failure and the wear on the gears look good (to my untrained eye)

Know of anybody that can help?

Did you put some posi additive in it? Sometimes clutch type sure-grip units make a considerable clunking when turning without the additive
Gus

My dakota has been doing that for a long time when first coming off a highway run. Clunk and chatter for the first couple turns then Quiets down. I have sure grip additive in it but going to try the good Factory GM/ford or mopar stuff this time.

Ya, i put a bottle of the sure grip additive in there. I started pulling the unit apart. 0.008" of backlash. I think the pinion nut started backing itself off. It was only reading 7.5 inch pounds. Since they were new bearings, i think i had it set up at 25 inch pounds. I'm gonna pull it all the way apart and check the cross shafts and spider gears. If all is good i think i might chalk it up to not tightening the pinion nut enough and reassemble.

That was the bearing preload on the pinon bearings. I torqued the nut to 200-300 ft-lbs + with red lock tite. Now when i'm measuring it its only measuring 5 - 7.5 inch pounds of preload indicating the nut loosened up a bit.

Any chance one or both of your pinion bearing cups weren't fully seated? Hard to imagine the nut loosening with that kind of torque and loctite.

I talked on the phone with cass a number of times while building it. When i was setting the bearing preload i used the entire stack of shims he sent me and it was still to high (i think like 40-50 in lbs)
I called and he sent me another shim pack, but said he has never had to use more than 1 shim pack. I double checked that the races were fully seated and measured numerous times with a snap on dial torque wrench. I was convinced the bearing preload was too much and added 1 more shim to pull it into range. Yes i think i set it at right around 30 in-lbs as the book i had said 25-35 in-lbs for new bearings.
Is there a chance my yolk is too loose on my new pinon splines and that is causing it to loosen up? I have a hard time believing the bearing "wore in" that much.

I do think i put the nut on and off like 3 times trying to get the shim stack right. That might have been my problem. When i set it up this time i'm definetly going to use the old one, and then when i do my final torque i'll put a brand new one on.
Anyone know the part number for a pinion nut that i can get locally?

Are the heat marks on my carrier housing normal? There are blue spots indicating high heat on 4 spots around the housing where the wedge of the cross shafts sit. Is this normal?

NO sir, My initial guess is that the clutches are set WAY too tight, they are improperly installed, or they're not getting lubricant.

The heat marks are caused by the induction hardening process during production.

Thanks again Cass.
After further diagnosis. My pinion nut was most definitely NOT backed off. It took an elephant sitting on a 4 foot cheater bar to break it. I guess i was measuring bearing preload improperly before.
I pulled a shim out and torque the nut again. It seemed REALLY tight. I then rotated the pinion about 50 revolutions in each direction and it seems to loosen up a bit. Final reading after that was about 23 in-lbs.

I'm gonna install tonight and see if that helps.

Would a bearing preload of 5 - 7.5 in-lbs cause a clunk in the rear end, and possibly a little steering wheel vibration on sweeping corners?

any thing to do with turning is going to be suregrip unit.