drive shafts?

[Horse_gal_jen]

we have 2001 chev 6.6 crew cab short box. I expect the vibration I feel is from a U-joint. I have checked both the main and 4x4 drive shafts. The front one has a U-joint gone, would this cause the vibration when in 2x4 and if so are the U-joints the same in both drive shafts?

[Duramaster]

When is your vibration? Is it at launch? Does your truck have a two piece steel driveline or a one piece aluminum driveline?

[Horse_gal_jen]

no it doesnt seem to be at launch, when I am moving but more when pulling a trailer. it has the two piece steel, but I do know that there is a U-joint gone in the front drive shaft that goes from the transfer case to the front, not sure if there is one gone in the main driveline

[NutNbutGMC]

no it doesnt seem to be at launch, when I am moving but more when pulling a trailer. it has the two piece steel, but I do know that there is a U-joint gone in the front drive shaft that goes from the transfer case to the front, not sure if there is one gone in the main driveline
The two-piece shaft is a known culprit for low-end shudder. There is / was a TSB for the replacement of said shaft. I had mine (2-piece) replaced on a 2001 model and it makes a difference and resolves the issue. One thing to be aware is that there is a certain way to remove / replace the shaft. When the bulletin first came out in 2001 there apparently were no specific removal/reinstallation instructions and some shop techs were cutting the cross-piece on the frame. Do not allow this. There are specific instructions against this. Just a reminder and a checkpoint before the fact and not after.

The problem is the center carrier joint. Apparently there is too much of an angle in the drive component, thus the one-piece (and much larger) shaft.

[JohnC]

Jen:

No, the front shaft should not be moving in 2WD, so that is not the problem. If you have the 2 piece drive shaft, and I suspect you do, that that is likely the culpret.

[Duramaster]

As I recall, there was/ is a trade off. Updating to the one piece driveline got rid of the launch shudder BUT you ended up with a high speed vibration. It has been a while since we have had any dealings with this complaint.

[NutNbutGMC]

As I recall, there was/ is a trade off. Updating to the one piece driveline got rid of the launch shudder BUT you ended up with a high speed vibration. It has been a while since we have had any dealings with this complaint.That may have been the case, as I am certain that you have seen these issues in all facets. When I made the upgrade, there was not an issue of a high speed vibration as such. Just saying this for the record of conversation. Thanks for the info DM. I always enjoy hearing from the front-line experts.

I have that TSB somewhere or I think it should be here on the forum. I know it was posted and referenced quite a few times back in those days.

[Duramaster]

Here is the bulletin.







Launch Shudder/Vibration On Acceleration (Install New One-Piece Propeller Shaft)


Models: 1999-2002 Chevrolet and GMC K2500/3500 Extended Cab Long Box and Crew Cab Short Box Pickup Models

With Automatic Transmission




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This bulletin is being revised to add model information, remove procedure steps and change parts information. Please discard Corporate Bulletin Number 01-04-17-001A (Section 04 -- Driveline Axle).


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Condition
Some customers may comment on a vibration during acceleration from 0-40 km/h (0-25 mph). This may also be referred to as launch shudder. This condition may be more noticeable when the vehicle is carrying cargo or is used for towing.

Correction
A new propeller shaft is available for service to correct this condition. This new propeller shaft is a one-piece design and will replace the current two-piece design.

Install a new one-piece propeller shaft on affected vehicles. Refer to the service procedure and the parts information listed below. Match the affected vehicle with the appropriate propeller shaft. Refer to the usage information below. This fix does not apply to the Chassis/Crew Cab Models (K35943).

•Remove the propeller shaft assembly and the center bearing. Refer to the Propeller Shaft - Two Piece procedure in the Propeller Shaft sub-section of SI2000. For this bulletin, it is not necessary to mark the components for re-assembly.
Center Bearing Support Bracket




Important: The center bearing support bracket (1) must be removed in order to provide enough clearance for installation of the one-piece propeller shaft. Avoid damaging the crossmember during removal of the center bracket. For proper clearance, no more than 13 mm (½ in) of the bracket may remain on the crossmember after removal.

•Remove the center bearing support bracket from the kick-up crossmember using a cut-off wheel.
•After removal of the center bearing support bracket, grind the rough metal edges smooth that remain on the crossmember.
•Coat the exposed metal surfaces with frame coating using the information found in the applicable Service Manual and GM Refinish Material Booklet #4901M-D-2002 (English) or #4901M-D-F2002 (French).
•Install the new propeller shaft. Refer to the Propeller Shaft Replacement - One Piece in the Propeller Shaft sub-section of SI2000 for installation guidelines and yoke retainer tightening specifications.
Parts Information
P/N
Description
Usage

15077431
Shaft Asm.- Prop
K25953 w/ LQ4, MT1, C6P

(99-00 8600# GVW)

15077434
Shaft Asm.- Prop
K25953/35953 w/ M74 (Allison Trans)

15077435
Shaft Asm.- Prop
K25953 w/ LQ4, MT1

(HD Model 9200# GVW)

15077436
Shaft Asm.- Prop
K35953 w/ LQ4, MT1

(11,400# GVW)

15093466
Shaft Asm.- Prop
K25743 w/LQ4, MT1

(HD Model 9200# GVW)

15093467
Shaft Asm.- Prop
K25743 w/M74 (Allison Trans)