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Discussion Starter #1
I'm referring to, the TH350c 3-speed with electronic converter lock-up (81 Vette)

Because I have 'trust issues' with local shops I'm considering rebuilding my TH350c transmission...how scary is it in this transmission?

BTW, the trans is operating just fine however it's leaking from what research tells me is the pump seal.

So, I figure being it's 31 years old and has 127,000 miles on it I would go thorough it.

Thanks for any suggestions, Ray
 

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Th350 is one of the easiest transmissions out there to build. The lockup doesn't add much to it.
Get an ATSG manual and you shouldn't have any problem.
Buy a lip seal tool.
 

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Th350 is one of the easiest transmissions out there to build. The lockup doesn't add much to it.
Get an ATSG manual and you shouldn't have any problem.
Buy a lip seal tool.
And a clutch compressor to get the low/reverse piston apart in the case, and a pair of slide hammers to get the pump out..
 

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Discussion Starter #4
Thanks for the feedback,

I ordered what 'should be' a comprehensive instructional step-by-step DVD on tear down, inspection and rebuild on the TH350 & TH350c transmission.

To fully tear my TH350c apart I wasn't sure on what 'specialty' tools were required.
^ I did see on YouTube, someone got the pump out with a large screwdriver behind the throttle-body, but didn't show details...any one know how???

Researching so many different 'rebuild kits'...prices varying from $80 all the way up to $495 and that's without a reman torque-converter!

Hopefully no hard parts are needed or, my local transmission shop will sell me "good used" or new parts.

Thanks again, Ray
 

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I've improvised on most all the tools before... a couple bolts a short chain and a hammer will get the pump out.
Usually any of the kits with all the frictions seals and bushings should get you fixed up for around $150.

If I were you I would still get an ATSG manual. It's money well spent.
 

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Discussion Starter #6
I've improvised on most all the tools before... a couple bolts a short chain and a hammer will get the pump out.
Usually any of the kits with all the frictions seals and bushings should get you fixed up for around $150.

If I were you I would still get an ATSG manual. It's money well spent.
Thanks for the feedback...

The DVD is good, really good and even shows how to get the front pump out, with a large screwdriver.

However, the DVD isn't about my TH350c but the TH350.

Not sure how much I'm missing out on or what needs to be tested/checked on the 3-speed electronic lock-up TH350c ???

I may still get the ATSG manual too.

To remove the in-case Low/Reverse Piston it appears I will need the GM REAR CLUTCH SPRING COMPRESSOR -Trans Tool T-0151 $27.00 on eBay
 

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Valve body is different, some changes in the front pump and obviously the torque converter. Highly recommend a mild shift kit. If high horsepower engine their are a few other upgrades you could do also. Almost all the gear train is the same between the two. Make sure you replace the thru case connector o ring, and if it was me I would replace the lock up solonoid with a quality replacement.
 

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Discussion Starter #8
Valve body is different, some changes in the front pump and obviously the torque converter. Highly recommend a mild shift kit. If high horsepower engine their are a few other upgrades you could do also. Almost all the gear train is the same between the two. Make sure you replace the thru case connector o ring, and if it was me I would replace the lock up solonoid with a quality replacement.
Thanks for the feedback,
The 81 is only rated at 190 hp (pathetic I know) but to make the engine a little happier I just removed the catalytic converter, smog pump, heat risers...and will be removing the egr. Basically all emissions/smog crap will be gone.

With only 190 hp, what would a mild shift kit do for the car?
I'm definitely not interested in any neck snapping or banging shifts...what kit would you recommend?
BTW...my dana-44 is a very weak aluminum differential, that I just rebuilt, so hard shifts are a no-no.

Thanks
 

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if it was me ,for a vette . i would find a 350 ,not a 350c. use a transgo stage 2 .lose the 1-2 accumulator spring,heavy duty intermedate sprag race , get the direct clutch piston cut down so you can put in an extra clutch plate(5) and steel . and a bit more stal in the convertor (not to much) .It'll work great
 

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A mild shift kit will make the trans life longer and will firm up the shifts but will not be neck snapping. In my opinion Rogerroost's recommendation is going a little far for what you want to achieve. Transgo does make a nice kit.
 

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Discussion Starter #11
Thanks for the feedback fellas,
A different transmission will not be happening, maybe if I was still in the earlier years of owning this car but realistically, at my age and owning it since 1981 I just want to go through the TH350c, stop the leak, freshen it up and put it back in the car.
I could see a mild shift kit, but first order of business is to find out what normal wear items need to be replaced and what hard parts may need replacing > hopefully I won't see anything ugly.
 

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Ray, I cant manage to locate my reverse piston tool. I did find my drum press which you will need one of. Lemme know if you need it. I don't do transmissions anymore.
 

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Your leak is most likely due to hard rubber. That being the case make sure you get the low-rev piston tool so you can replace those seals. Get a book and tear into it. That's the trans I cut my teeth on many many moons ago. 5-6 of them a day on the bench. About 30 yrs ago. With it being a lock up make sure you replace the converter because there is a clutch inside of it and I'm sure with that age the material has flaked off. Otherwise you'll get a shudder when it locks up. Good luck have fun it's just a bunch of parts.


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Yes compress the spring remove snap ring and apply air pressure to the hole at rear of case a pop the piston out. Make sure you remove the park paw actuator first. Stand trans case on floor bell housing down a gently apply air to circuit and pop the piston out. Be Careful!!


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Discussion Starter #16
Who made a lower drum spring compressor...this guy that's who! :partyguy:
The trans is fully apart...all rubber o-rings/seals were hard like plastic. The large pump o-ring was also like plastic and cracked as soon as I tried to remove it. That's where me leak was coming from.

The front clutches and steels look new... All steels look great without any burns or discoloring etc. The 1'st gear clutched 'may' be wore, not sure as they don't have the ridges like the other clutches.

Problem...the front planetary gear is missing a thrust washer and the gear has visibly eaten into its case. So far that looks like the only 'hard' part I may need. This is where I was seeing some silver dust when changing fluid.
2014-02-27 17.33.36.jpg
20140227_170934.jpg
 

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Pretty common for that to happen, obviously replace it. Replace the clutches and do a paper and seal kit. Should be good to go for a long time to come.:))THumbsUp
 

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Pretty common for that to happen, obviously replace it. Replace the clutches and do a paper and seal kit. Should be good to go for a long time to come.:))THumbsUp
Thanks for the feedback.

Question, would it be in my best interest to also replace 'all' the bushings, or any in particular?

What about the five plastic rings and one steel ring on the pump shaft, and can they be all plastic/teflon or, must they be the same as what comes off?

I have one plastic thrust washer and the other bronze...replace them too?

Lastly, I found a very local shop that rebuilds torque converters...he felt with 127,000 miles the clutch in my lock-up TC has been shot many miles ago, $125.00 to rebuild my oe TC.

Thanks for any further advice, Ray
 

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Replace all the bushings and thrust washers, replace all the seal rings on the pump shaft. Just order the seal rings for your trans and use what they give you. Yes either have the torque converter rebuilt or replace with new. Make sure you flush your cooler lines and cooler or you will pump all the old fluid with metal shavings into your new trans.
 

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you should look at the psi # on your convertor clutch pressure switch and replace it with a switch around 52-54psi . that will make l.u later ,nicer driving . The sprag race is one of the weakest links in this trans . I never build any performance 350's without it. bout $30. the spring in the accumulator commonly breaks & causes a leak. omitting the spring is common ,then it won't break & leak . adding a clutch to the direct drum is free and really helps the clutch pak . 350c limits you as to what shift kit you can get . non l.u 350 is just better unit. just my opinion as professional rebuilder
 
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