Transmissions and Drivetrain Need help with your trans? Problems with your axle?

High rpm shifts

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Old 04-24-2024, 10:51 AM
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High rpm shifts

I have a 82 trans am with a 350 swap and a turbo 350. A) when I put it in gear it wants to die but the idle in park is rather high. And B) when it shifts from 1st to second it climbs all the way to redline and shifts hard squaking the rear tires. The same happened from 2nd to 3rd. What could cause this?

p.s if I’m in a parking lot for say going like 15 it’ll rev high until it seems to catch and accelerate again
Old 04-24-2024, 11:11 AM
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Car: 1983 Camaro Z28
Engine: Originally LU5, but now Carb'd
Transmission: TH350
Axle/Gears: 323
Re: High rpm shifts

And B) when it shifts from 1st to second it climbs all the way to redline and shifts hard squaking the rear tires. The same happened from 2nd to 3rd. What could cause this?

The governor controls the shift points. It's a matter of replacing the springs to fine tune the shift points.

Old 04-24-2024, 11:47 AM
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Re: High rpm shifts

Try replacing the vacuum modulator. Get a RED STRIPE one - not a green stripe, not a purple stripe, and above all, NOT the big black can - then adjust it in quarter-turn increments and see if you can get it to make sense. There's no real good way to know which one you're getting other than to open the box and LOOK. Trying to look it up by application is a fool's errand, although if you look ones up for more "sporty" cars such as Corvette or Z28 you're more likely to get the small gold can with a RED STRIPE one.

Of course, make sure the vacuum is actually hooked up properly to it, and is leak-free. The transmission has only 2 "eyes" on the world around it: the governor, as described above, which tells it how fast it's going; and the vacuum modulator, which tells it how much drive the driver is demanding out of it. If the transmission thinks 100% of the time that your foot is 100% on the floor 100% of the time, which is what a poor vacuum connection makes it "see", then logically, it's going to do EXACTLY what you describe.

As far as the high idle and "die" and all that, a vacuum leak (including the vacuum modulator's connection) can also cause both of those things. Neither is a transmission problem, in any possible scenario.

Last edited by sofakingdom; 04-24-2024 at 01:39 PM.
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Old 04-24-2024, 12:31 PM
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Re: High rpm shifts

Originally Posted by sofakingdom
Try replacing the vacuum modulator. Get a RED STRIPE one - not a green stripe, not a purple stripe, and above all, NOT the big black can - then adjust it in quarter-turn increments and see if you can get it to make sense. There's no real good way to know which one you're getting other than to open the box and LOOK. Trying to look it up by application is a fool's errand, although if you look ones up for more "sporty" cars such as Corvette or Z28 you're more likely to get the small gold can with a RED STRIPE one.

Of course, make sure the vacuum is actually hooked up properly to it, and is leak-free. The transmission has only 2 "eyes" on the world around it: the governor, as described above, which tells it how fast it's going; and the vacuum modulator, which tells it how much drive the driver is demanding out of it. If the transmission thinks 100% of the time that your foot is on the floor 100% of the time, which is what a poor vacuum connection makes it "see", then logically, it's going to do EXACTLY what you describe.

As far as the high idle and "die" and all that, a vacuum leak (including the vacuum modulator's connection) can also cause both of those things. Neither is a transmission problem, in any possible scenario.
that actually make a lot of sense. I’m only 17 and got this car out of a field from sitting since 2010 for free (and there no rust on it besides the driver floor board). Eventually it’s getting a 5.3 swap and a tranny out of a c5 vette and a ford 9 inch
Old 04-24-2024, 01:47 PM
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Re: High rpm shifts

a tranny out of a c5 vette
Probably not. Look at how the C5 is put together and you'll see why.

Get one out of about a 04 - 06 Cadillac Escalade. It'll be a 4L65E instead of 4L60E, i.e. has 5-gear planets. Look for codes xKZD, where x is the year (4 for 04, etc.) You'll also want a converter with considerably higher stall speed than stock.

​​​​​​​a ford 9 inch
I'd recommend against that. There's no need whatsoever for that unless you put 3 bar worth of boost on it. A 7½" 10-bolt is plenty otherwise. Not the one you have now, necessarily; but, one out of a 98-02 F body. The 9" eats SIGNIFICANT power just to spin it, and weighs ALOT more. And then there are all the fitment imperfections.
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