I have these same 2 problems. Is it a big deal to fix? I can get the parts from GMPD for $45.00.

Thanks

Q: What's that buzzing/grinding noise at low RPMs?

A: It could be related to this technical service bulletin:

Bulletin #: 277142
Publish Date: 10/92
Models: 1984-1993 Firebirds w/ Hydra-matric 4L60/700R4 Trannys
Condition: buzzing noise from tranny at idle (more so when in reverse)
Cause: pressure regulator valve oscillating due to oil pressure instability at lower idle RPM
Correction: a new pressure reg. valve has been made to improve oil pressure stability at lower RPM (part #8684048)


Q: Why won't my automatic tranny shift into overdrive at wide open throttle?

A: It's designed not to shift into overdrive if your foot is all the way to the floor. You must be at 2/3 throttle or less before the tranny shifts into OD. So when you hit the top of 3rd gear, you'll have to let off the gas to allow for the shift. But putting your foot back into it will probably cause a downshift resulting in the same problem.

B and M makes a kit modified kickdown valve (part # 70237) which fixes this problem. It costs about $30 and can be ordered through the Summit or Jegs. GM also makes a modified upshift valve which it included in police packages and that part # is 8673948 and sells for around $15. This will allow the tranny to shift into OD at full throttle.

 

It's messy but not hard unless you install the pressure regulator valve wrong. The valve you speak of will allow you to stay in 4th gear longer 3/4 throttle, I used that one wasent impressed. GM makes a valve that is supposed to allow the transmission shift into 4th at more throttle but I havent messed with one.