TH350C Servicing / Lockup Solenoid

[brrian]

81 GP. Before I pulled my V6 I was testing the TCC lockup circuit & it wasn't working as I thought it should. I assumed it was how I was testing (wrong) but now that the trans is out & I can bench test it, I know it's the solenoid I must have never actually had working lockup. So, I'll replace it.

I'll drop the pan & drain the fluid. I know I can flip it over for servicing & just want to know... how messy is it? The easiest place to do this is in my basement but if it's going to be ATF everywhere, I'll take it somewhere else.

 

[Bonnewagon]

I usually hang a trans in my garage, by the front, and let all the oil drain out the tail into a pan for a few days. That way I can lay it upside down and pull the cover off and not make a mess. The solenoid is towards the front of the valve body. Just follow the wires right to it. It is a simple on/off solenoid that needs 12 volts pos and neg. It may be stuck with crud so if it does not clean up just replace it. It is good for about 3 or 4 hundred rpm in high gear.

 

[stew86MCSS396]

Yeah follow the wires when you have the pan off. It's a relatively simple circuit but some years they may have a high gear pressure switch in the system so of course if you were chasing wires or applying voltage here and there w engine off/on idle in park...well no high gear then no complete circuit. ymmv

 

[brrian]

I usually hang a trans in my garage, by the front, and let all the oil drain out the tail into a pan for a few days.

I love this idea! This is what I'll do. Thanks!

 

[Ribbedroof]

30 gallon oil drum works great for draining/holding for disassembly

 

[78Delta88]

For a trans coming out, I usually remove the the cooler line coming from to trans going to the radiator. Usually it will be the top line of the two, but every type is different. Once line is removed I attach relevant size rubber line and purge everything into 5 gallon bucket.

Removing the trans pan while in the vehicle is about one of the messiest jobs you can come across. To protect the floor I use 4x8 sheet of luan plywood cut in half, so 4 x 4 foot piece of luan, or old panelling. The best pan I found is the large black mortar mixing pan from hardware store. Good quality ones are the thicker plastic and fairly robust. The cheaper chinesium ones are thin plastic, and rip... leak.

 

[brrian]

I got it drained & the pan off. I didn't do any of the above because I was impatient, but I managed to keep things fairly clean.

Anyway - yes, there's a pressure switch in there, normally open & I had to bypass it to test the circuit. With 12V applied to the solenoid, there's slight movement of the bottom plastic thing on the solenoid (it pushes forward slightly). But there's no distinct click. And there's a crack in it, noted in the first picture. It seems weak.

What is it supposed to do - is it pressurizing something, or is there a moving part that should be pushing on something? Should energizing it make an obvious, audible click (in YouTube videos it can be heard from outside of the closed transmission)?

 

[78Delta88]

Most solenoids are about $40, and with its age and being suspect bad or marginal... Just replace it.

 

[Bonnewagon]

All it does is block an oil gallery. So it is either ON or OFF and that lets ATF flow or not. Don't confuse it with the high gear sensor. That is part of the circuit too. The one in my 1983 Pontiac Bonnewagon always worked so I never took it apart. But my Mom's Oldsmobile had a sticking solenoid and when you came to a stop it remained engaged and stalled the car. When I fixed it I found an upgraded version that was supposedly superior to the stock unit. Some research may be valuable here.

 

[brrian]

All it does is block an oil gallery. So it is either ON or OFF and that lets ATF flow or not.

It looks like there's a pin in the center... should it pop out when energized? That's essentially what a solenoid does I guess. I'll test the new one before putting it in & want to know that it's working properly.

& ATF is non- (or very low) conductive, right? I have to cut & splice wiring for the new solenoid & ill use watertight butt splices but the whole circuit is in ATF.