TH350 rebuild?
 

I was cruising around in my 81 TA on Saturday and I made a left turn, got on it a bit, and something let loose kind of loudly and all of a sudden I have no forward gears or reverse. Something broke internally, so I pulled out the trans today. The trans is one of those dual pattern transmissions. Luckily I have a spare true Pontiac TH350 so I'm gonna take it to a local shop that I've used before and have them rebuild that one. Is there any latest and greatest parts that I should ask about? This car is bone stock but I may hop it up a little in the future. Would a stock rebuild OK or? Any suggestions are appreciated.

Sounds like you broke the forward drum or input shaft. I broke my forward drum in a th350 at the track last year. Made a hell of a bang. https://uploads.tapatalk-cdn.com/202...dad0ef6b73.jpg


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a TH350 or a TH350c?
either way a simple rebuild with raybestos linings and a trans-go shift kit install should be plenty to firm up the tranny. No real work needed on one till you start getting in the 350-400 hp range. Even then you are only looking at a few hard parts. Be sure to check the speedo DRIVE gear while its apart...hate to have to go back into one just for the speedo.

what is a dual pattern 81 th350? 81's use the th350c which is same as a th350 but has a lock up converter. should be able to have a basic rebuild done for a decent price, i just had one rebuilt for a 81 t/a for about $350 including name brand rebuild kit from a good family owned shop, bigger trans shops wanted around $500-750.

what power level caused this?

I read on JakeShoe's website he recommends the input and drum upgrade at 400-800hp. i'm rebuilding a th350c and was planning to put a basic 455 in front of it. I don't plan on going to the track, so i'm hoping it'll be ok.

I would guess just under 500 HP. Maybe 480? The engine dyno had it at 460hp and 560tq. But we added ported heads after that.


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Thanks guys, so I guess it is a Turbo 350c. I'm gonna to give a regular turbo 350 then. This car will never see 400HP.

I rebuilt one this summer,a light duty from a 6 cylinder car and added extra clutch plates and the hardened sprag and a Trans Go shift kit,not to hard to rebuild them

from my research there is nothing wrong with keeping the 350c, it's pretty much the same as a th350, but with lock up.

one thing I did run into with mine. Mine was originally a v6 application. it has a few less clutches then a normal v8 th350. changing the pistons to v8 pistons did require additional expense, but it has been fun building and learning.

the only big difference from a performance stand point i have found. the mod to dual feed the direct drum will disable lock up. I don't plan to do that, but will be running 5 clutches. I'm also installing a transgo shift kit and the Sonnax 35723HD-02 sprag.

Hughes recommend I run the GM20L for my application.

I bought Cliff's book, it has been very helpful as well as watching a few video's from Precision Transmission.

BONE STOCK car......not sure what the ecm is going to think with NO lock-up signal? Are you still running factory ecm with feedback q-jet?

the 81 ecm doesnt know or care if the converter is locked up or if you dont have the th350c trans, all it does is sends a one time signal to the solenoid for lockup at a certain speed, it doesnt get a feedback signal to say it locked up or not. on my 81 t/a it originally came with a th350 when i bought it & i used that trans for many years, just a few years ago i found a correct 81 th350c & had it rebuilt with the stock converter to be more correct for the car.

for the converter, you can have a good converter shop open it up & add some stall speed for usually a very decent price, i had a local converter shop do that to mine & they added about 500-800rpm over stock & it was about $150. i didnt add a real shift kit but the guy that rebuilt it did a slight mod with one or some of the fluid control balls/holes that firmed it up quite a bit.

Sorry the car has a stock 77 400 in it. All the ECM stuff is gone. There was a plug harness on the trans on the driver side that was cut. Is that what makes it lock up? It was already cut. I've been de-hacking this car since I got it. Shoot the starter bolts were 3/8 all thread with two nuts...LOL.

yes that connector on the side of the trans is the lockup.