A little tranny help, please?

[81 Redhead]

Just bought an '81 C10. It runs decent. Only trouble I have now is that the automatic ain't automatic.
It'll cycle through the gears if you start out in L1, then shift to L2, then to D.
Starting from a dead stop in D, the engine winds up but the tranny won't shift.
PO sez the tranny was rebuilt just before he bought it. He put about 300 miles on it (it's a farm truck), then parked it. It sat for nearly 3 years before I got hold of it a couple weeks ago.
I'd really appreciate any input or ideas about what's ailing this thing. Thanx in advance!

[clinebarger]

Im guessing you have a TH350? check for vacuum at the modulator valve on the pass. side rear of the transmission.

[81 Redhead]

Originally Posted by clinebarger

Im guessing you have a TH350?

Probably so, if that's what came factory with that truck.
(81 2 wheel drive, long bed, 350 4bbl)

Thanks

[81 Redhead]

There is vacuum at the modulator valve. Is it common for the mod to get hung up or something if the truck sat for a couple years? All the fluid ran out the speedo cable. Got fresh fluid in it. Planning on a fluid and filter change soon.
Thanks for your help.

It's a TH350. I found the thread with a pic of pan shapes. Square with a corner angled off, and 13 bolts.

[PRattenbury]

Is passing gear hooked up right?

[81 Redhead]

Originally Posted by PRattenbury

Is passing gear hooked up right?

I'm not sure. My Big Bro usually does this stuff for me, but I moved to TX and he's in SC. I'm having to take pics and email him, then wait for him to reply. Lol.
I think the passing gear's hooked up. If that's the detent cable people talk about. It's on the same bracket as the throttle cable, hooked to the driver's side of the carb. Bro sez he doesn't think it's a problem with the tranny itself, because it does shift if you go through the gears manually. It just doesn't shift by itself. Him and I are both thinking modulator valve, but I'm not much of a mechanic. lol.

[gchemist]

Remove and clean the govenor. Check for stripped gears.

[81 Redhead]

Ok, so I broke down and bought a new modulator for 9 bux...
Fixed a slight kink in the vacuum line, headed down the road and what do ya know...
IT SHIFTS! Lol.

Thanks for the input, Guys. Very much appreciated!