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The TH (turbo-hydramatic) 700R4 was developed for use after 1982 in GMC and Chevrolet cars and trucks.

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High pitch screeching after 20mins running

Hi all, my 200R4 starts a terrible high pitch screeching after 20mins running. Sounds like “fingernails on a blackboard” but in a circular motion. And happens in or out of gear. From an ‘85 Olds. Highish milage but newish oil/filter. Video is on Youtube “700R4 transmission screeching”

Thanks in advance

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The first thing that comes to mind is the 700R4s front pump. I did some addition research on a few forums and a few people also said mentioned a possible torque converter but those usually went along with a problem in reverse, which you didn't mention. So I'm more inclined to learn towards that front pump I mentioned.

Unfortunately there no way, that I know of at least, to diagnose that without physically pulling the trans and inspecting the pump.

If that is some thing you have the ability to do there are lots of very good videos online that you may want to follow along with. If not I would recommend taking it to a mechanic that you trust.

I hope this helps!

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Thanks so much. Yes, most evidence is pointing to the pump. Yes the screeching didn't change/stop when in reverse either.

The screeching happens in and out of gear therefore pointing to pump.

I assume the pump with have to be replaced/rebuilt?

I'm gong to change the filter as a final attempt to fix cheaply because a a partially blocked one can affect the pump. This is a 'hail mary' but I have to try because there is no-one here I can trust


Yes, replacing or rebuilding would be my best recomendation at this time. Good luck!


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Gerry Moriarty will be eternally grateful.
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