1997 Grand Prix GTP transmission issue

[Ken Ben]

First let me begin by saying I am new to the forum and if I ask a question that is already been discussed, I apologize.
I searched around in this thread and did not find any posts that relate to the issue I am seeing so again I am sorry if this topic has already been covered... I simply have not found it if it has been covered.

Anyway, I am working on a 1997 Pontiac Grand Prix GTP for a female friend of mine and have made a number of repairs to the car trying to get it road worthy for her.
Wheel bearing on the front left, Strut bushings both rear struts, Tie rod ends, Alternator, battery, supercharger coupling...just to name a few.

The problem I now find is that if you drive the car with a "easy foot" all is well.
However, if you accelerate from a dead stop with any great deal of throttle the transmission seems to "chatter" or hammer really hard.
This only happens while it in automatic first gear acellerating.
It's almost as if the clutch pack is slipping and then grabbing and slipping and grabbing.... only very harshly.
I have found that if I put the transmission in 1st gear manually I can accelerate with full throttle and this chattering event does not occur.
The chattering, or hammering as I prefer to call it, only occurs when taking off from a stop and the car is in drive.



Due to the fact that it only happens in drive and not in manual first gear I wonder if there is an issue with lower than required fluid pressure and if there is a way to adjust the line pressure.

Any help would be greatly appreciated.

If someone does reply and they would like to email me directly, you can email me at kbenoit204@comcast.net

Thanks,



Ken

[BillBoost37]

Ken,

I know the feeling/issue you are having from experience. It's common with higher mileage etc. It's either clutch slippage, FWD band slippage, or FWD band beginning to break. The reason it doesn't happen when you select manual 1 or manual 2 is because those engage a secondary band in addition to the FWD band, therefore adding more hold power.

I would suggest not full throttling from a stop and you'll find the trans will likely last quite some time. In my Regal the trans had this issue when I got it at 160K, I drove it to 186K before I pulled it out for a different issue.

[Ken Ben]

Thank you Billiboost37 for the reply.
What you described makes clear sense to me.
Not knowing much about Pontiac's, I was not aware of the transmission design having two bands. ( This reminds me of a mopar 904 trans.... Overrunnning clutch for breakaway gear with the addition of a low/reverse band for manual low and reverse)

I have been road testing the car quite a bit and if driven moderately to an average style of driving there is no issue.
It's only under heavy acceleration that this chattering occurs so I will remind the girl who owns the car to be easy on the gas during takeoff to avoid this.
Once the car shifts into second there is no issue with chatter under heavy acceleration so she can gas it then...... : )


Thanks again for the input.

Kind regards,

Ken