TH350 leak! Manual transmission swap?

[The Swed]

My TH350 transmission (See attached pictures) is leaking a lot after sitting for three days in the garage My friend said it’s most likely the front pump in the transmission? I have a 1967 K20 (4x4) with manual transmission with out a motor. Will this fit in a 1970 C20? I really wanted manual transmission but couldn’t turn down these two trucks for a $1000 dollars . FYI I know these trucks sat in a field for 14 years so the transmission seal may have dried out? I really appreciate all the help.

Thanks The Swed.

[cdowns]

Double posting is against the board rules

[mechanicalman]

Originally Posted by The Swed

My TH350 transmission (See attached pictures) is leaking a lot after sitting for three days in the garage My friend said it’s most likely the front pump in the transmission? I have a 1967 K20 (4x4) with manual transmission with out a motor. Will this fit in a 1970 C20? I really wanted manual transmission but couldn’t turn down these two trucks for a $1000 dollars . FYI I know these trucks sat in a field for 14 years so the transmission seal may have dried out? I really appreciate all the help.

Thanks The Swed.

Is the truck "up and running"?
If you drive it around, does it not start leaking for a couple or three days? (after wiping off with a rag after parking).

The hydra-matics have a tendency to leak back from the torque converter and create an "overfill" condition after sitting too long and then if the filler tube seal is not just right it will leak only after sitting.

Drive it then level off the fluid level. Let it sit a day and then start checking it every day, engine still off to see it creeping up on the stick.

It's really hard to get that to stop if the dipstick tube is not just right. I like to use a star washer between the dipstick and the bell housing and then a flat washer on the bell housing bolt to prevent the tube bracket from twisting when you tighten the bell housing bolt. You still may need to tweak the dipstick tube/bracket to put an even load on the seal.

[The Swed]

Yes the C20 is running very well! The leak happen after it sat for three days not on start up. Wait a minute I get what you're saying now my 51 Chevy PG would blow trans fluid out the filler tube after sitting for a time too. So I'll check it over time like you said. Thanks!

As far as Double posting goes I had 45 views without one reply and I realized I may have ask to many questions at one time so I just boiled it down to one question. I did put the I'm the I guess you missed that, maybe not

[mechanicalman]

Originally Posted by The Swed

Yes the C20 is running very well! The leak happen after it sat for three days not on start up. My 51 Chevy PG would blow out trans fluid after sitting for a long time.

As far as Double posting goes I had 45 views without one reply and I realized I may have asked to many questions at one time so I just boiled it down to one question. I did put the I'm the I guess you missed that, maybe not

I assume it's a T400, but if it's a T350 the detent cable can also leak under those circumstances.

[The Swed]

I appears to be a TH350. The pan doesn't have the TH400 shape. I would think a 3/4 ton would have a 400 but I don't know the history of the truck and the ID plate in the door doesn't brake it down to that detail. The engine has headers not sure what else may have been changed. What is a detent cable?

Thanks again!

[SS Tim]

70 Up C20 with a smallblock or L6 came with a TH350 from the factory if ordered with a three speed automatic (M49).
If the trans sat as long as you say it may very well need a reseal, both internal and external. Did you change the fluid and filter before you started driving the truck? Might you have created a leak? Have you verified the correct fluid level, hot with the truck idling in neutral? Do you have the factory service manuals?

* VIN/Model Decoders
* Power Team Charts (engine/transmission/gear ratio)
* Post Your Pickup SPID Blazer SPID Suburban/Panel SPID
* RTFM ... Read The Factory Manuals... download 'em here

[cooltx]

The detent cable is your kickdown cable. It has an o ring down there where it bolts on. Could be a possible leak there. Hope this helps. What the heck is double posting anyway?

[The Swed]

SS Tim it is an M49 so it is TH350. Thanks for all the links!

[The Swed]

Thanks cooltx.

[The Swed]

Just got home SS Tim, no I don't have the factory service manuals but I did put a new filter, pan gasket and fluid in. I used my flash light to look at the filler tube and traced the lines back to the radiator and found a rust 9/16 open end wrench sitting in the radiator saddle. It wasn't easy to get out but gee whiz not cool.