Torque converter staying locked

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May 16, 2022 | 10:06 PM

groran

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Joined: Feb 2007

Posts: 66

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From: California City, Ca.

Torque converter staying locked

This is 95 3500 auto/diesel. I have been working on the truck on and off and sitting in dry desert conditions. Anyway, the last time I drove it, all the transmission functions were normal. It has a torque converter lock-up switch that was on it when I bought it. I never used it. When driving normal with the switch off, it would shift OK, and then at about 45-50mph, the TC would lock up like normal and at about 35mph, let off the throttle, and the engine would go to idle when the TC would unlock. Took a ride today and when slowing down to about 20mph, the TC didn't unlock, and the engine didn't go to idle, the engine starts bogging down. So I turned the lock-up switch off and it stopped lugging down. With the lockup switch off, at 60mph, the truck is at 2000rpm, and when I turn on the lock-up switch, it acts normal, locks up and rpm goes to about 1600rpm until I slow down to 30mph or so. What's going on? One trans shop I called and explained the situation to says the previous owner must have put a lockup switch to keep TC locked up going down a hill to act as a brake of some sort. The trans shop also said if the trans is not going into lockup, it's the truck computer.