Transmission gear problem

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Sep 4, 2022 | 06:28 PM

69vette$

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Transmission gear problem

Hi guys

So today I replaced my 69 Corvette TH400 automatic transmission pan(stock) with an aftermarket 1/2 inch thick aluminum (deep) one, the problem I am having is while the car on jacks I went through the gears and they all seem to shift fine from P to 1, except that now in P and N the tires spin forward, but R is fine (spins in reverse) and all the other gears are also fine (spinning forward). I checked the linkage adjustment from underneath and it also shifts fine. This problem did not exist before I replaced the pan, but I can't see how they can be related?. Any help would be greatly appreciated.

David

Sep 4, 2022 | 09:21 PM

Motorvation

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From: Sandusky, OH

Don’t do that. You can “f” up the trans really quick spinning the tires on stands. Put it back on the ground and then feel the gears. Check the shifter adjustment,too. The thick pan rail may have changed the geometry.

Steve O.

Last edited by Motorvation; Sep 4, 2022 at 09:23 PM. Reason: No info

Sep 4, 2022 | 09:22 PM

kansas123

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From: Wichita Kansas

So you replaced the original pan with one that is deeper. How are you ensuring you have the correct amount of fluid? If you are going by what the original dipstick indicates, you may have too much fluid in the pan/transmission?

Sep 4, 2022 | 09:58 PM

Tampa Jerry

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From: Temple Terrace Florida

If you are putting power to the wheels while the suspension is hanging, you stand a good chance of doing serious damage to the rear and suspension components. The half shafts must be horizontal. Jerry

Sep 4, 2022 | 10:39 PM

Mooser

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From: North of Toronto - Ontario

In park, the park pin should lock the transmission up solid. Might need to adjust the linkage since your new pan flange thickness might be affecting your positions a little, (not sure why park wouldn't be reverse but...) Disocnnect the cable and shift the transmission into each gear by hand on the linkage and check the cable position.
The AIM has a section on proper shifter setting with a little spacer that makes sure the transmission is fully into park
The fluid level in the trans is based on the level of the bottom of the casting and is irrelevant to the depth of the pan, add until it reads correct on the dipstick.
M

OH, and yes don't run the car in gear with the rear suspension hanging

Sep 5, 2022 | 10:25 PM

69vette$

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Of course, you have to go by the original dipstick otherwise using a longer dipstick defeats the purpose of having a deep pan/more fluid.

Sep 5, 2022 | 10:36 PM

69vette$

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Thanks for the advice, tomorrow I'll check the linkage again. I noticed from inside the car it shifts solid into park but from underneath the linkage travels very short distance into park even when I shift it by hand with the cable disconnected. I can't believe someone suggested that I should use a longer dipstick than the original which would of course defeat the purpose of having a deep pan.