General Category > Quadrajet Carb Talk and Tips

th350 question

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stevef:
Hi. I tried my hand at rebuilding my th350, but failed. First and reverse works, but it doesn't shift out of first. I tried the easy things that can be done with the trans in the car, but no success. So, I pulled the transmission back out of the car, and it's on the fixture. I noticed in Cliff's th350 book, page 103, that there's an air pressure test for the clutch packs shown, where you put air to 3 holes in bottom of the case. I have removed the valve body to expose the bottom of the case and the 3 holes shown in Cliff's photo on page 103. I'd like to air check those, but the holes are in an awkward location to get a  good seal with the air nozzle to get good pressure. I have an air gun similar to the one shown in the book, with a fairly small diameter angled tube and a tapered nozzle on the end if it. Any tips on how to get good air pressure in those holes, and how much air pressure should I use? The shift lever position doesn't matter does it?
I will be taking it apart and can air check the drums when they're out of the case, but I thought it'd be interesting to see what they're doing now, still being inside the case, if I can do that air check.
Thanks for any advice!

77cruiser:
Can the intermediate sprag be put in the wrong way? I've only done 1 350 but it worked fine.

Cliff Ruggles:
If it has no up shifts that is typically caused by no vacuum to the modulator or a problem with the governor.  A stuck modulator valve would be something to look at, but that is not a common problem with those unless it got bent somehow.

It's not easy to pressure test a TH350 thru the case but can be done with a little patience. I use small shop rag to help seal off the air in the passages around the end of the air nozzle being used. 

The selector position will have no effect.

Did you have the valve body apart for any reason?

I'd also verify check ball locations and separator plate gaskets in the right place and didn't get swapped out or shifted, etc........Cliff

stevef:
Hi Cliff. Thanks for the tip on using a shop rag to help seal around the holes. What air pressure is good to use?

I did take the valve body apart to clean it. I was careful to lay the parts out in order and put them back in order. But, I'll double-check it.
 
I have good vacuum, and the modulator valve and governor work good. I was very careful with installing the balls and gaskets, so I don't think that's it.

I'm thinking I have a leaking piston seal. That's why I'm interested in the air pressure test. So I'm going to re-do those, and double-check everything else too.

Thanks for the quick reply!

Mudsport96:
Was it just no upshift at all or was it acting like it shifted into neutral?
I would think if it was a piston seal, the trans would try to shift and leave 1st and not apply second.
If the governor was sticking it would never leave 1st or have to rev very high to build enough pressure to force a shift

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