ok, from time to time when cruising in town I will come to a stop light and come to a complete stop, and several seconds later the truck will produce a "slam" feeling, almost like it is pushing back down in to first gear, but it is doing it HARD and long after I stop the truck completely. It almost feels like someone tapped the back bumper lightly when it happens, anyone have any idea whats up? Maybe the converter unlocking?

 

driveshaft clunk

 

Start by removing the rear driveline & greasing the slip-yoke splines. If you have upgraded to the 4L80E, you may have something else going on....

 

all stock... drive shaft clunk? it is definatly a "CLUNK" but please explain...

 

#09-04-17-002: Bump Feel/Clunk Noise at Stop or From Launch (Clean/Lubricate Propeller Shaft Slip Yoke Splines) - (Sep 21, 2009)


Subject: Bump Feel/Clunk Noise at Stop or from Launch (Clean/Lubricate Propeller Shaft Slip Yoke Splines)


Models: 2007-2009 Chevrolet Avalanche, Silverado

2009 Chevrolet Suburban, Tahoe

2007-2009 GMC Sierra

2009 GMC Yukon, Yukon XL

All Equipped with 4L60 Automatic Transmission (RPO M30) and 2WD



Attention: This bulletin contains a procedure to clean/lubricate the slip yoke splines and replace the slip yoke, if necessary. Check the history on this vehicle. If the lubricate procedure has been performed previously, then continue on and replace the slip yoke.



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Condition
Some customers may comment that the vehicle has a bump feel or a clunk noise at a stop or on launch. Customers may also comment that the bump feel or clunk is noticed after the vehicle has come to a complete stop and that it feels as if the vehicle was bumped from behind.

Cause
This condition may be caused by a slip/stick condition in the interface between the rear propshaft slip yoke and the transmission output shaft splines. Braking to a complete stop can force the propshaft slip yoke forward into the transmission while the vehicle rebounds slightly backward after stopping its momentum and create this condition.

Correction
Note: A bump feel or noise may also be due to fuel movement in the fuel tank when not completely full. If the condition is eliminated after filling the fuel tank the noise is isolated to the fuel movement in the tank. Please make no repair attempts, as this noise is considered an operating characteristic.

Verify the customer's concern.

Clean/Lubricate Slip Yoke Splines


Remove the rear drive shaft. Refer to One-Piece Propeller Shaft Replacement in SI.
Inspect the rear slip yoke splines on the drive shaft.
Clean the slip yoke splines with brake cleaner or equivalent and a shop towel.
Assure the yoke is free of rust or other foreign material.
Lubricate the slip yoke spline with grease, P/N 12345879 (in Canada, 10953511), using a brush or swab to completely cover the entire spline with a light coating of grease.
Reinstall the rear drive shaft. Refer to One-Piece Propeller Shaft Replacement in SI.
Road test the vehicle and verify that the noise is gone.
Note: Do Not replace the slip yoke unless the cleaning and lubrication procedure is ineffective.

If the vehicle has a repeat concern after lubricating the slip yoke splines, it may be necessary to replace the propeller shaft slip yoke with a new nickel-plated slip yoke, P/N 20877209.
Replace the Propeller Shaft Slip Yoke


Remove the rear drive shaft. Refer to One-Piece Propeller Shaft Replacement in SI.
Replace the propeller shaft slip yoke with a new nickel-plated slip yoke, P/N 20877209. Refer to Propeller Shaft Slip Yoke Replacement in SI.
Install the rear drive shaft. Refer to One-Piece Propeller Shaft Replacement in SI.
Parts Information
Part Number
12345879 LUBRICANT
20877209 Slip Yoke

 

The rear suspension is unloading. Pinion shifting downward which pushes the drive shaft forward. Either the DS or the leaf springs making the clunk.

 

looks like just another reason to take this piece of junk to the dealership...

 

Got to suck when you have a relatively new truck doing this ****....

Sorry Noah....

 

my old truck did it too, I just never thought much of it, when I got this truck and it was doing it within 6 months... that was a problem.

 

You can lube the splines yourself with any grease. The stickier the better(as in will last longer til you have to grease the splines again). It's easy to do, and doesn't take much time.