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Old 08-11-2019, 05:28 PM
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Default th350 question.

I have seen info stating that Pontiac put the TH350-C in some 81 birds. Maybe in the V-6 cars? Anyone verify one and what is engine its connected to. Thanks!
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Old 08-12-2019, 09:52 AM
78w72 78w72 is offline
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cant say on the v6 cars for sure, but all 81 birds had the th350c as far as i know, it was part of the computer controll that came out in 81. th350c had the lock up converter. my 1981 turbo t/a has the th350c & other non turbo 81's ive owned have had it too.
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Old 08-12-2019, 11:32 AM
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Yes my 81 T301 had a lock up TH350. Previous owner had taken out the computer so not sure how they drive. I had Continental make a 13" for me that loosened it up a little, but never wired a lockup.
My brother in law back in the early 80s had a 81 Z28 that had one he was always cussing it was so sloppy locking and unlocking.
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Old 08-12-2019, 11:40 AM
78w72 78w72 is offline
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they shift & drive very good if the computer & internal lock up solenoid are in working condition. shifts just like a normal th350. the lock up is a very basic speed sensor.

i had the stock lock up converter opened up & a little more stall speed added on my 81 turbo.
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Old 08-12-2019, 04:28 PM
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Thanks for the replies! I noticed on a pick up truck that the vacuum seemed to be involved in the lock up. Wondering if this was the case on the 81 birds.
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Old 08-12-2019, 04:39 PM
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not sure on trucks, they usually have some differences or a delay in technology vs cars.

on 81 birds it is mph based from a sensor in the speedo that activates an electric solenoid inside the trans that engages & releases the lock up. theres a section on testing & trouble shooting in the GM manual. are you working on an 81?
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Old 08-12-2019, 04:53 PM
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I bought an '80 a few years ago, had a th350-C with it. I am trying to see how much the "C" helped the fuel economy. I assume the tall gears were the same "C" or no "c"
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Old 08-12-2019, 05:08 PM
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i havent really tested the fuel economy on mine, when i feel it engage the lock up the rpm drop is barely noticeable, probably because its a tight converter anyways. but GM felt it was worthwhile so id guess there was some improvement in mpg.

pretty sure trans gearing was the same c or no c. rear ratios could differ based on the car, all turbo t/a's got a 3.08 posi, other models & engines were 3.42-2.xx ratios. if thats what you meant by tall gears.
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Old 08-12-2019, 07:03 PM
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My brother in law had his Z28 at the dealer several times to no help it may have been more and issue of lick unlock while hunting for gears.
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1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever!
1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand
1965 GTO 4 barrel 3 speed project
2004 GTO Pulse Red stock motor computer tune 13.43@103.4
1964 Impala SS 409/470ci 600 HP stroker project
1979 Camaro IAII Edelbrock head 500" 695 HP waiting for track time
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Old 08-12-2019, 10:32 PM
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I bought a 81 turbo parts car, got the TH350 lockup trans, but no engine (thankfully).
I had a TH350C in my old 67 Bel Air, my first car. Bolted right I place of the original glide. This all sounds silly. I had the 283 properly built by a local engine builder. It got all good parts.
I wanted to put a 700R4 trans in it. He talked me out of it. This was likely the early 90's...
He had been pulling TH350C's out of oil field pickups and install I got TH 400's.

He built me a nice lockup TH350. I had to install the brake switch used on cruise controls, so the converter would unlock with brake applied. There was a vacuum switch that I installed in line with the brakes switch, I unlocked the converter at full throttle.
My TH350C allowed me to cruise at 350 RPM's less....I liked it! Of course my engine builder did a great job on the trans! Wish he had not moved and changed his business focus.

I no longer have the old Chevy, but still have the engine and trans. Still have the Pontiac trans too....
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Old 08-12-2019, 11:20 PM
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Quote:
Originally Posted by 77 TRASHCAN View Post
I bought a 81 turbo parts car, got the TH350 lockup trans, but no engine (thankfully).
I had a TH350C in my old 67 Bel Air, my first car. Bolted right I place of the original glide. This all sounds silly. I had the 283 properly built by a local engine builder. It got all good parts.
I wanted to put a 700R4 trans in it. He talked me out of it. This was likely the early 90's...
He had been pulling TH350C's out of oil field pickups and install I got TH 400's.

He built me a nice lockup TH350. I had to install the brake switch used on cruise controls, so the converter would unlock with brake applied. There was a vacuum switch that I installed in line with the brakes switch, I unlocked the converter at full throttle.
My TH350C allowed me to cruise at 350 RPM's less....I liked it! Of course my engine builder did a great job on the trans! Wish he had not moved and changed his business focus.

I no longer have the old Chevy, but still have the engine and trans. Still have the Pontiac trans too....
Very cool story! Thanks for the RPM info too !
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