Th350 help

[bschevyk10]

I have a 1980 Chevrolet k10 with a th350 and np205. Couple years ago I put a new engine in. When I did I pulled the transmission and engine together. Then put the new engine and trans together and put it back in. And had to have it go to the shop for tuning/timing. I drove the truck back home. Then realized the trans pan was leaking. So I put a new gasket on it and filled up the trans. But then after that it wont go into any gears at all. Any ideas?

[SilverMiner]

I'm a 1980 K10 owner with a 205 as well. Mine is at the transmission shop right now being rebuilt because it crapped out on me out of the blue.

Are you aware that your TH350 is actually a TH305C, which means it has a lockup converter? Perhaps you knew because you had already removed yours, but I had no idea until I crawled under mine to remove it after it blew up on me while out of town. No gears, forward or reverse. I was very surprised to have remove the wiring connector on the drivers side to drop the tranny. I've owned many, many 73-79 rigs but this was my first 80. Never heard of a TH350C before this, but thanks to this forum and others I was quickly educated.

After replacing the engine, how long did the transmission work?

[andrewmp6]

Did the trans shift on the drive to the place?I'd crawl under it and make sure the vacuum line is on the trans.

[bschevyk10]

It was hauled into the shop on flatbed but it drove back from the shop. And I checked the vacuum line and it was connected at both ends. At the trans and intake manifold. And it is a brand new hose the shop put it on. Is it possible the engine isn't making vacuum or not enough? And if so how would I check that. I don't have a vacuum gauge on the truck.

[Liberty]

It is possible you have a big enough vacuum leak to cause this.

My truck has vac leaks all over that makes my TH350 a bit hesitant to shift into any gear on a cold start until the engine warms up or I give it some gas.
Capping some of my vac lines on my canister helped this a little

[bschevyk10]

I suppose it is possible there could be a vacuum leak somewhere. But on Sunday I checked to make sure the vacuum line was connected and it was. Brand new line too. Shop put it on. The shop also put new lines to the heater and brake booster and new grommet on the brake booster cuz it was old and loose. So everything is new and shouldn't be leaking. And I don't recall my truck having a canister. I have a 5 way adapter on the back of the intake manifold 3 lines go to what I mentioned earlier and the other to are capped off.

[cadillac_al]

Are you sure you got it full of fluid?

[andrewmp6]

You need a vacuum gauge to test it.But when you drove the truck did you put it in drive or did you try manually shifting the trans after it wouldn't shift?

[cadillac_al]

Even with no vacuum the truck would move and shift very late. After i fill a trans, I run it through all the gears and check the fluid again. Many times it will need a little more.

[GRADYS Performance]

Vacuum modulator and vacuum to it only affects shifting. It will not cause the transmission not to go into gear either forward or reverse when vehicle is sitting still.

[Liberty]

Well now that just raises questions on my own TH350...

[bschevyk10]

So maybe the clutch plates or something inside went wrong and the transmission needs rebuilt?

[andrewmp6]

If the trans sat around a few years before you used it i would think hard about pulling it out and having it rebuilt.

[bschevyk10]

Y should I not have it rebuilt

[Liberty]

I think andrew was saying you should have it rebuilt.