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1969 GTO Clone (Custom S), just bought and headed out of the driveway last night. 500' away, a loud pop/sound from the back end and both tires instantly locked up.
No movement in any gear or neutral. With my son, we placed the rear tires on casters and slowly towed it home. That was a bitch.....
In low gear, the car would move several inches. Tranny seems good and it feels like the back drum brakes are 100 percent on.
I'll pull the drums first, but has this occurred to anyone? I'm hoping it's not the rear end and the car would move slightly.
Any thoughts?
Thanks!
 

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Chances are the pinion nut backed off and the pinion was slightly gliding fore and aft, not staying precisely in place. I've see it many times on higher mile, never touched 8.2's. The locking up often occurs on a coast. I'm very careful to properly clean, use blue LockTite, and stake a new pinion nut upon final assembly of a rearend build so the pinion nut never comes loose.

The first lockup I ever ran across it was in the 80's with a friends 4.33 HD STT in his '69. The pinion in the 3.90's and 4.33's are extremely small in mass compared to a 13 tooth pinion out of a 3.08 or a 16 tooth pinion out of a 2.56. When these small 9 tooth 10 toith pinions get loose, the entire rear needs to be sent to a very experience builder.

Regret reading of your differential trouble. Your only solution is to drop the rear cover and drain the grease and the debris. Chances are the ring and pinion will be damaged, if a single track rear, the spider gear shaft in the carrier may have slid forward under the pinion, locking it up... If it is 3.36, 3.55, 3.90, or even a 4.33 Pontiac 8.2 ratio, quality new gears are avail to be professionally set up. if the Pontiac 8.2 is a 2.93, 3.08 or 3.23, going to have source nice used gears. From experience, nice used gears are harder to set-up properly. If the pinion was getting loose in the donor rear, the wear pattern can be all over the place.
 
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