Transmission shifting

Flex

Registered User
Hey guys,

The car is not an SC but the transmission is from one:). In January of last year, I picked up a rebuilt SC transmission from another member. It runs great but has one peculiarity. Between 60-70 km/h if you take your foot off the gas it feels as though you are riding the brakes. The car jerks hard as though you had hit the brakes.

If you tap and release the gas while the car is between those speeds, it jerks hard as though you were quickly alternating between the gas and brake.

Any ideas?
 
This is an automatic, correct? If so, AOD or 4R70W? From your description, it sounds like the torque converter is locked at those speeds, and isn't unlocking when you release the throttle. What gear are you in when this occurs?

-Rod
 
Hey guys,

The car is not an SC but the transmission is from one:). In January of last year, I picked up a rebuilt SC transmission from another member. It runs great but has one peculiarity. Between 60-70 km/h if you take your foot off the gas it feels as though you are riding the brakes. The car jerks hard as though you had hit the brakes.

If you tap and release the gas while the car is between those speeds, it jerks hard as though you were quickly alternating between the gas and brake.

Any ideas?


Valve body

This happens when there is a tear between the passeges in the valve body gasket thus making it seam like shifiting in a lower grear sorta like puting on the brakes. Its not a converter issue its a valve body issue
 
This is an automatic, correct? If so, AOD or 4R70W? From your description, it sounds like the torque converter is locked at those speeds, and isn't unlocking when you release the throttle. What gear are you in when this occurs?

-Rod


Rod,

I should have posted that. The car is a 90 LX with an AOD. The donor transmission was from a wrecked AOD backed SC. The transmission was recently rebuilt by a shop.

It occurs in OD and D. Just not as pronounced in D. Oddly it will only do it between 60 and 70 km/h. I eliminated the converter as a suspect. If it were defective, it should do it all the time. From my understanding, the converter shouldn't be able to stay locked at just that narrow point or am I missing something?
 
Valve body

This happens when there is a tear between the passeges in the valve body gasket thus making it seam like shifiting in a lower grear sorta like puting on the brakes. Its not a converter issue its a valve body issue

Jim,

Have you had this same thing happen? I thought about having the transmission serviced thinking that it had to be something done incorrectly when it was rebuilt or a quirk of a shift kit.
 
Jim,

Have you had this same thing happen? I thought about having the transmission serviced thinking that it had to be something done incorrectly when it was rebuilt or a quirk of a shift kit.


Flex

Yes the same thing happened with the 90 XR7 we rebuilt the engine for with AOD the guy had a Trans Go shift kit put in. We found out after going through the Valve body that the gasket had a tear in it. The owner installed the valve body pinching the gasket when installing it
 
We found out after going through the Valve body that the gasket had a tear in it. The owner installed the valve body pinching the gasket when installing it
Easy to do when in a hurry. Gotta be careful... :)

The converter shell itself, on an AOD, is always connected to the direct clutch. The direct clutch is engaged in, you guessed it, 3,4 (D/OD) The direct clutch should release when you let off the gas allowing the car to coast. The throttle valve (TV) is what responds to the gas pedal. So, yeah.. I'd take a look at the valve body first.

TV cable is connected, right?
 
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Easy to do when in a hurry. Gotta be careful... :)

The converter shell itself, on an AOD, is always connected to the direct clutch. The direct clutch is engaged in, you guessed it, 3,4 (D/OD) The direct clutch should release when you let off the gas allowing the car to coast. The throttle valve (TV) is what responds to the gas pedal. So, yeah.. I'd take a look at the valve body first.

TV cable is connected, right?


Yes it is. Ok, so it seems that it is the valve body. Could this cause any harm to the transmission?
 
Could this cause any damage to the transmission if I don't redo the gasket immediately?
 
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