This is another tranny. I work on a lot of cars.
I just bought an 81 C10 with a TH350. I was told
the tranny was bad before i bought it. But I dont think it is.

It shifts very well. The vacuum modulator was unhooked.

It doesn't like going into reverse. If you send a minute or so going back and forth from drive, 1st and reverse it will finally engage. It doenst slip. It simply doesn't even try to go into reverse.

Before I change the tranny, I want to know if I should check anything on the valve body and or vacuum modulator.

 

First thing to stop working when the fluid is low is reverse. Check the fluid level hot, in neutral, and running.

 

Is the linkage adjusted proper?

 

its in the tranny. Fluid is good and the linkage is good.
Reverse works great once it goes into reverse.
It just doesn't want to go into reverse. In a few hours I will go place the shifter in the reverse position and see it the pump is weak.

 

I'll tell ya right now from experiance with the th350... once reverse starts to act up, the rest of it will fail. Plain and simple. Get another.

 

I have another one, it just seems strange.

I double checked the fluid, it was a little low.
Still slow to go into reverse. If you jut put the shifter into reverse and wait a minute, or so it will engage.

 

If you had also lost a forward gear, I would more suspect serious internal damage. But only reverse not working sounds more like a valve body issue (stuck valve, dropped linkage arm). Drop the pan and see if there's anything down there that doesn't belong. There is an S shaped linkage rod that attaches the detent cam to a control valve, and it sometimes has a tendency of falling off.

 

That was the answer I was hoping for. Will get the pan off in the next day or so.
I have another valve body. For some reason I am having a lot of issues with tranny's this week.
3 different TH350, 3 different issues.

I may just swap valve bodies. I need to drive it a little more but the brakes are scary. Will fix them when it stops raining.

 

Before you drop the pan be sure the dipstick is correct for your tranny! If it's too long it could be reading full, but still be low. It could be the valve body, but sure sounds like low fluid.
If you rev it a little does it move in reverse sooner? That also would mean low fluid level.

 

guess I can compare the dipstick to one of the other ones I have.

No reeving it up doesn't help.

I think the pump is going out, it engages in forward gears fine but soft. If I let the truck warm up it shifts a little harder in the forward gears.

I will pull the pan and look around, but I think I will just change the tranny. Not sure if I want to mess with swapping valve bodies.