Background/history: 2000 TransAm Orig tranny made it to 110k before loosing 3rd/4th. At 20 min of hwy driving at 70mph Would act like went to third and out of lock up at constant throttle. I could manually shift to 3rd then back to 4th and it would go back into 4th and lock up. After a few of those issues I Lost 3rd/4th gear.
Took it to a builder for a rebuild, he installed upgrade parts - shift kit, vette servo, bands etc (I installed a new external trans cooler flushed lines and new aluminum radiator).
4K miles on the rebuilt trans (just out of warranty) I Took it on a road trip and burned out 3/4 again. Same symptom - around 70 mph and with constant throttle - exact same thing when trans went out the first time.
1/2 gear pulls perfect, same exact issue as in First failure. Any Ideas? Thanks in advance.

 

What was the cause of the first failure?

What clutches were burnt....forwards?

 

You most likely have a hydraulic leak in the 3rd clutch apply circuit that the builder did not address. There is more to building a trans than just throwing seals, clutches and a few upgrade parts in them.

 

I expected as much. Thank you for the reply.

 

Yup, these trans are notorious for having potential leaks in the 3/4 clutch apply circuit; hence many rebuilds fail in short order.
What are your plans? Take it to another rebuilder, buy a rebuilt from a sponsor or try it yourself?
The sponsor PerformaBuilt should be at the top of your list. There are also several good shop (and ex-sponsors) located near Dallas TX which might be within your driving range.

 

Yes, now I plan to do some research on a few companies. I’ll look into performa, iv used a b+m 4l80 unit before (ease of no core requirement and no clue of quality of builders in my area) it’s still in my track car after a few seasons. Dallas is definitely in my range.
I tried a local guy and this is what happened. Live and learn, “research” is what I should’ve done more of. Thank you guys