Transmission will not shift into gear after the truck has warmed up?

PATRICKGRAPES

MEMBER
1995 GMC SONOMA
4.3L
6 CYL
2WD
AUTOMATIC
134,000 MILES

I'm having trouble getting my truck back on the road! When I start the truck up it will go into drive and move, but once up to temperatures it won't anymore. There's no reverse at all even at startup. It's the year with the obd2 port but OBD1 brains. I have a 1995 GMC Sonoma with a 4.3 vortex. 2wd it has roughly 130,000. I bought it from a friend who got it with some problems. They changed the transmission fluids and filter and it worked for a while. He started to have problems with it going over 30 and the ABS light came on a couple times now it won't really do anything. I just recently ran the codes for 67, 81, 82. I changed out the TCC solenoid, and both 1-2 and 3-4 solenoids. Still having same issue. Truck doesn't make any crazy noises or smells I just can't figure it out.

5 Replies

STEVE W.

MECHANIC
13,443 POSTS

The description sounds like it's rebuild or replace the transmission time because the seals are worn and bypassing fluid so that the clutches are slipping, and the low pressures are preventing the truck from moving. That would also keep it from having reverse. What you might try to see if you can limp it along a bit more would be to dump some Lucas transmission additive in it, then see if anything improves. If it does great, you just proved that it's wear and pressure bypass, if it doesn't it's too far gone or there is a mechanical failure like a cracked seal or piston or one of the solenoid shuttles has a very worn bore.
The earlier problems and the fluid change helping it all point toward wear more than a broken part though.

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Saturday, March 11th, 2023 AT 4:31 PM

PATRICKGRAPES

MEMBER
3 POSTS

Thanks for the quick response, I was hoping to not have to rebuild it or replace it right now lol. I’ll try tomorrow with the Lucas and see what it does! Thank you

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Saturday, March 11th, 2023 AT 4:41 PM

STEVE W.

MECHANIC
13,443 POSTS

Good luck and let us know what happens.

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Saturday, March 11th, 2023 AT 7:00 PM

PATRICKGRAPES

MEMBER
3 POSTS

Put a whole bottle, nothing ended up happening. Sadly, looking towards the rebuild or replace.

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Sunday, March 12th, 2023 AT 11:00 AM

STEVE W.

MECHANIC
13,443 POSTS

I was afraid that would happen, but it is worth a try. Sounds like it has at least one internal pressure leak through a failed seal. At least it's a 2wd so a lot easier to drop that trans out.

https://www.2carpros.com/articles/how-to-remove-an-automatic-transmission-rwd