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1979 Grand Lemans (Bertha)

  • Thread starter Thread starter pontiaclemans79
  • Start date Start date
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pontiaclemans79

Hello, I am Chris. I am having a problem with my old Pontiac. I believe it may be the transmission. Sometimes, when I go from park to drive, (it never happens in reverse) my transmission slips. It sounds like the engine is racing, and I hit the gas but she doesnt move. I then have to slip it back into park, then wait a few seconds, then back to drive again and it is okay, most of the time. This has happened a few times in the past when I drive locally. I am afraid to take her out of my small town and on any major highway. Someone please help diagnose a problem!

Thanks!!

I really do appeciate it.

P.S. I have enclosed a picture of my car.
 
wow that thing is in great shape!!!

What trans is in it? TH 350 TH 400???

I am assuming one of these... either way, how does the trans fluid level look? Is is low or to full? also, does it look or smell burnt?

Next thing I would say is to check your vacuum lines. There should be a vacuum modulator near the bottom of the transmission, check that out also. Make sure all the lines are good and not dry rotted. Then it might not hurt to go and pick up an adjustable modulator for about $15 from your local parts store. I put one on my '93 Bonneville, and it shifts into the gears very crisply now, almost like a whole new trans. The adjustable modulator can be adjusted so your shifts are somewhat firmer or softer. It will also help the initial clutch engagement.

Another thing to check is the fluid filter inside the pan.

Last thing is that it might need a rebuild if none of this helps. I have rebuilt some transmissions myself and can tell you that they are not really the monsters many people think they would be. In most cases like this, the clutches are just bad and a good cleaning and basic rebuild will take care of it. You can rebuild a TH 350 yourself complete with a new torque converter for about $200 - $300. Expect AT LEAST double that to have a shop do the work for you.

I would start with the stuff mentioned on top here and see if that helps.
 
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