Transmission
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Instructor
Joined: Apr 2021
Posts: 133
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Transmission
I’m pretty sure I have a th 350 I have questions, first if I put it in 1 shouldn’t it red line and not shift until I put it into 2nd because if I’m in first it will shift at 3,500 but there’s a lot of resistance as in the resistance you feel when your in to low of a gear. The second thing is let’s say I put it into 3 wich is just drive so that it shifts through automatically if I’m not on the gas hard when it goes to shift it’s a insanely hard shift and a bad noise and you can feel it and it’s not good. But if I’m on the gas fairly hard when it goes to shift around 3,500 it shifts smoothly. Last thing i don’t have any transmission lockdown hooked up because jt doesn’t seem to be working when it is hooked up and when I’m driving if I’m going like 40 and I let completely off the gas my rpm will drop to what it does at idle and then if I want to go on the gas again the car won’t move until the rpm comes back up to what it was when I let off so I can pretty much rev the car without going anywhere I’m very confused and happy any to know if I should just screw this trans and manual swap😂 or is it a easy fix I’m just dumb?
Race Director
Joined: Mar 2017
Posts: 11,923
Likes: 4,495
From: Virginia
I’m pretty sure I have a th 350 I have questions, first if I put it in 1 shouldn’t it red line and not shift until I put it into 2nd because if I’m in first it will shift at 3,500 but there’s a lot of resistance as in the resistance you feel when your in to low of a gear. The second thing is let’s say I put it into 3 wich is just drive so that it shifts through automatically if I’m not on the gas hard when it goes to shift it’s a insanely hard shift and a bad noise and you can feel it and it’s not good. But if I’m on the gas fairly hard when it goes to shift around 3,500 it shifts smoothly. Last thing i don’t have any transmission lockdown hooked up because jt doesn’t seem to be working when it is hooked up and when I’m driving if I’m going like 40 and I let completely off the gas my rpm will drop to what it does at idle and then if I want to go on the gas again the car won’t move until the rpm comes back up to what it was when I let off so I can pretty much rev the car without going anywhere I’m very confused and happy any to know if I should just screw this trans and manual swap😂 or is it a easy fix I’m just dumb?
But a manual swap is unlikely to be easier than fixing some of the possible issues.
One possible cause of hard shifts is a failed differential snubber bushing. High-idle will make it worse. As for the unexpected shift points, more Forum searching may be in order. You may be able to change the shift points with a different, or adjustable vacuum modulator (I have not done this on my 79 auto, so this suggestion is just an avenue of further research).
https://m.roadkillcustoms.com/how-to...uum-modulator/
Burning Brakes
Joined: Jun 2019
Posts: 1,211
Likes: 938
From: Georgetown, Tx
I'm no automatic transmission specialist… But, you describe, perhaps three problems, 1) the transmission shifting from first gear to second while in the first gear position, 2) hard shifting with bad noise under average driving condition, 3) rpm falls to idle when letting off the gas at 40mph and not reengaging until the speed is matched.
My experience with automatic transmissions is this… torque converter and internal automatic transmission parts slowly wear out over time. Often, the failure begins in the torque converter and debris is pushed into the transmission, thus causing it to fail. My opinion, what you describe is a failing transmission. You can only confirm this from a reputable transmission shop.
Converting from automatic to a manual transmission is all about your personal preference. It is not an easy task. You cannot, just remove the automatic and put in a manual transmission. You'll need a new flywheel, pilot bearing, clutch disk and pressure plate, and on and on… It is a lot of work but can be done.
Please let us know what you find.
My experience with automatic transmissions is this… torque converter and internal automatic transmission parts slowly wear out over time. Often, the failure begins in the torque converter and debris is pushed into the transmission, thus causing it to fail. My opinion, what you describe is a failing transmission. You can only confirm this from a reputable transmission shop.
Converting from automatic to a manual transmission is all about your personal preference. It is not an easy task. You cannot, just remove the automatic and put in a manual transmission. You'll need a new flywheel, pilot bearing, clutch disk and pressure plate, and on and on… It is a lot of work but can be done.
Please let us know what you find.
Safety Car
Joined: Mar 2006
Posts: 4,526
Likes: 5,108
From: Chester VA
Blue,
You very well may have a TH350. But if you do, it's because someone swapped it in place of the original TH400 that all automatic 1973 models came with.
Larry
You very well may have a TH350. But if you do, it's because someone swapped it in place of the original TH400 that all automatic 1973 models came with.
Larry
Last edited by Catfish4818; Aug 31, 2021 at 09:09 AM. Reason: oopsie!
Race Director
Joined: Jul 2015
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From: SW Florida.
take a pic of your pan and google gm trans pans. then you will know what you have. if th350, it needs a throttle cable. and trans was put in by somebody else. also needs mounts reworked and different drive shaft. so most likely is the original or type turbo 400. easy repairs on a 400. replace vacuum modulator and check for engine vacuum AT the modulator. pull pan and replace filter and check kickdown solenoid for check ball working correctly. then check kickdown switch at carb for voltage and function. new fluid. those are the only easy fixes. if it needs a trans, now is a good time to consider a 200-700 type overdrive setup. very little more money than a rebuilt 400.
Last edited by derekderek; Aug 31, 2021 at 11:22 AM.
Thread Starter
Instructor
Joined: Apr 2021
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look at your pan and google gm trans pans. if th350, it needs a throttle cable. and trans was put in by somebody else. needs mounts reworked and different drive shaft. so most likely is the original or type turbo 400. easy repairs on a 400. replace vacuum modulator and check for engine vacuum AT the modulator. pull pan and replace filter and check kickdown solenoid for check ball working correctly. then check kickdown switch at carb for voltage and function. new fluid. those are the only easy fixes. if it needs a trans, now is a good time to consider a 200-700 type overdrive setup. very little more money than a rebuilt 400.
Last edited by 1973bluevettee; Aug 31, 2021 at 11:22 AM.
Race Director
Joined: Jul 2015
Posts: 13,082
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From: SW Florida.
350 has throttle cable. no switch, no vacuum. is this your pan shape? https://www.summitracing.com/parts/m...IaAj8FEALw_wcB or this... https://www.summitracing.com/parts/m...oaAvAAEALw_wcB
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Burning Brakes
Joined: Aug 2013
Posts: 1,071
Likes: 322
From: palm springs ca
The turbo 350 shifts 2 ways without changing the shift lever. One is called a govenor shift that has weights that will swing out with RPM and shift to the next gear. And as we all know the vacuum modulator does the regular shifts. The govenor can be made to shift at different RPM's and is there to protect from over revving.
Dom
Dom
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Instructor
Joined: Apr 2021
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350 has throttle cable. no switch, no vacuum. is this your pan shape? https://www.summitracing.com/parts/m...IaAj8FEALw_wcB or this... https://www.summitracing.com/parts/m...oaAvAAEALw_wcB
it is the 400 pan so I have a 400