Transmission shudder

[Alfonso Gomez]

Recently, I have noticed a shudder in my 87 Coupe. It has a stock 400r7 tranny. It shifts smoothly from 1st to 2nd and to 3rd. But when it shifts into 4th, it shudders slightly. Now, when in 4th, if I accelerate, the car it begins to shudder badly. Some friend told me it was probably the converter lock-up is not working properly, but I don't know the first thing about auto trannys.
The engine is basically stock with a few bolt-ons: Hypertech thermomaster chip, air foil, Dynomax high performance mufflers with Y-pipe and crossover.
Is the tranny giving up or is it a minor problem easily fixed?

 

[c4c5specialist]

Hi there,
One way to make sure its the converter.
Simply touch your brake pedal while you are steady cruising or when the shudder occurs, while keeping your foot on the gas.
This will disable the TC clutch and tell you if that is what is causing the problem.
Allthebest,

 

[Alfonso Gomez]

Hi there,
One way to make sure its the converter.
Simply touch your brake pedal while you are steady cruising or when the shudder occurs, while keeping your foot on the gas.
This will disable the TC clutch and tell you if that is what is causing the problem.
Allthebest,

I just checked it. When shuddering started I kept my foot on the gas pedal & touched the brakes and the shuddering stopped.
Thank you very much.

 

[jmccloud]

Shudder in transmission

I've had 3 GM cars that shuddered when under load at just high enough speed to have the TC locked up (40mph on some, 47mph on others).
When slightly accelerating or beginning up a slight hill, there would be a lot of shuddering until the TC unlocked.
All 3 cars were 'repaired' by changing the plug wires. The first one cost me $100 diagnostic at the dealer.
So there was nothing wrong with the TC's. The engine was misfiring due to plug wire arcing.
Look under the hood at night with all lights off and check for arcing. If you see sparks, try replacing the wires before tearing the transmission out.
Good luck.

 

[HD2HVETTE]

A tranny service with conditioner added to the new fluid could resolve the issue. Has worked in our shop on a nmuber of GM trannys with the same problem.

 

[rcrqtrmile]

Converter Lockup Shudder

I have a 92 that would shudder going in and out of OD. I put a bottle of GUNK Synthetic Transmedic Transmission Shift Improver & Protectant in and it worked immediately. I suspect it only delays the inveitable but since it is winter and the garage is about 30 degrees anything that get me to spring is good.

 

[jsinga]

Lubegard ATF additive is a GM fix for some transmission problems. Plus, it increases the temp stability of the fluid.

JS