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Discussion Starter · #1 ·
My high mileage TH700R4 suddenly has an occasional problem when shifting or operating in 3rd gear. My engine will suddenly start revving as if the transmission has gone into neutral. I had been using a 1-1/4" deeper pan and extended filter for the last 6 to 7 years so I suspected a leaking filter seal allowing it to suck in air. I replaced the seal and it did the same thing. Then I installed the original pan and a stock filter and that didn't help either. And no, it's NOT low on oil.

When I had the pan off I noticed there wasn't any debris in the pan and after I cut the filter open I just found some shiny aluminum chips that likely came from the input drum but no sign of clutch material.

As it has well over 100,000 miles of gentle use I'm wondering if the 3/4 clutch pack piston seal has become hardened with age and occasionally isn't sealing. I ordered a 12 ounce bottle of G.M. seal conditioner that is supposed to soften seals. I asked Dana Wilkes (a High Perf TH700R4 rebuilder) what he thought and he recommended overfilling it a bit to see if that helps.

Any other suggestions?
 

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Discussion Starter · #2 · (Edited)
My high mileage TH700R4 suddenly has an occasional problem when shifting into or operating in 3rd gear. My engine will suddenly start revving as if the transmission has gone into neutral. I had been using a 1-1/4" deeper pan and extended filter for the last 6 to 7 years so I suspected a leaking filter seal allowing it to suck in air. I replaced the seal and it did the same thing. Then I installed the original pan and a stock filter and that didn't help either. And no, it's NOT low on oil.

When I had the pan off I noticed there wasn't any debris in the pan and after I cut the filter open I just found some shiny aluminum chips that likely came from the input drum but no sign of clutch material.

As it has well over 100,000 miles of gentle use I'm wondering if the 3/4 clutch pack piston seal has become hardened with age and occasionally isn't sealing. I ordered a 12 ounce bottle of G.M. seal conditioner that is supposed to soften seals. I asked Dana Wilkes (a High Perf TH700R4 rebuilder) what he thought and he recommended overfilling it a bit to see if that helps.

Any other suggestions?
Update: Since it is still using the same synthetic Valvoline ATF I installed when I overhauled it 10 years ago I decided to change it as well as installing a deeper 4L-65E pan and filter. I bought a DORMAN pan that appears to be identical to an AC Delco pan as it is made from 16 gauge steel and has a drain plug. The 4L-65E pan holds about 1-1/2 more quarts than the original TH700R4 pan and the 4L-65E filter is about 4 times as thick as a TH700R4 filter. I doubt the new ATF, pan, and filter will solve my problem but it's a chance to further upgrade my TH700R4 to 4L-65E specs (it already has the 13-vane pump, 9-disc 3/4 clutch pack, wide band, 500" boost valve, 5-pinion planetaries, and Torrington thrust bearings).

The nice thing about the '87 and later TH700R4's (later renamed 4L-60's) is they can be upgraded to later specs to handle 450 to 500 ft/lbs of torque and with greater reliability while retaining their non-computer controlled shifting.
 
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