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Transmission shudder

A

Alfonso Gomez

Guest
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

Technical Advisor
Joined
May 29, 2001
Messages
3,682
Location
New Haven, Ct. USA
Corvette
Nope, but someday.
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, :hb
 
A

Alfonso Gomez

Guest
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, :hb

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

Well-known member
Joined
Feb 1, 2003
Messages
694
Location
Maryland
Corvette
1995 White Coupe LT-1 Auto
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.
 
H

HD2HVETTE

Guest
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.
 
R

rcrqtrmile

Guest
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

Well-known member
Joined
Nov 23, 2001
Messages
280
Location
Savannah, GA, USA
Corvette
87 Silver Coupe Way over 200k miles
Lubegard ATF additive is a GM fix for some transmission problems. Plus, it increases the temp stability of the fluid.

JS
 

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