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Discussion Starter #1
Just got a 2004 GTO...I got into it today and shifted it hard and heard a clunking coming from the rear, wondered if anyone has any ideas as to what is making the noise...possible U joint? any suggestions would be much appreciated!
 

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Clunk under high torque

There is a TSB (technical service bulletin) that says the crossmember / X member bushings that support the rear differential are insufficient & need to be replaced. They have a lot of play & allow excess travel. The parts are fairly inexpensive & the repair manual says it should take about 45 minutes to replace them with the proper equipment. I would double that time for the driveway. I have the same issue. I haven't done the replacement yet. I'm planing on doing it when I do the cross drilled & slotted rotors because I'll be half way there plus I'll have that weight off of the rear axle. I have to go to work but if I can locate the detailed TSB I'll post it when I get home. It has the part #, equipment & procedure. The bushings are readily available in the aftermarket. I actually plan on replacing all the bushings with more solid ones cuz the OEM ones are pathetic. Those who have done this claim that it makes all the difference in the world. I believe the entire kit is about $150 + some knuckle busting / wrench turning.:cool
 

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There is also a tech bull that says some clunking is normal for the Cadillac and GTO.

Your Pontiac dealer should be able to pull up the bulletins, test drive the car with you in it, and help you decide the next course.
 

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Here's the TSB

You've gotta love the thoroughness of this:

Knocking Noise from Rear of Vehicle on Aggressive Launch or Acceleration (Install Rear Suspension Crossmember Front Mount Insulators) #04-03-09-003A - (Apr 20, 2004)
Knocking Noise from Rear of Vehicle on Aggressive Launch or Acceleration (Install Rear Suspension Crossmember Front Mount Insulators)
2004 Pontiac GTO

Built Prior to VIN Breakpoint 4L246712

This bulletin is being revised to change a torque specification within the correction procedure. Please discard Corporate Bulletin Number 04-03-09-003 (Section 03 -- Suspension).

Condition
Some customers may comment on a knocking noise coming from the rear of the vehicle. This noise occurs during an aggressive launch or acceleration and will be more common on vehicles with a manual transmission.

Cause
The cause of this condition may be contact between the body and the rear suspension crossmember.

Correction
Install insulators, P/N 90447991, and new bolts, P/N 92038482, between the body and the rear suspension crossmember using the procedure listed below.

Important
Only remove the bolts from one side of the suspension crossmember at a time, and DO NOT loosen the opposite side, until the insulator is installed on the first side and all fasteners have been tightened to the specified torque setting.

Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in the General Information sub-section of the Service Manual. Position rear hoist.
Support the rear suspension crossmember just under the brace using an adjustable jack stand.
Remove the 3 brace to underbody bolts.
Remove the front mount bolt attaching the rear suspension crossmember to the underbody.
Lower the jack stand slightly to allow clearance between the crossmember and the underbody.

Important
When installing the insulator onto the crossmember front mount bushing, face the corrugated side upwards, so it bears against the underbody.

Install the insulator between the underbody and the upper part of the crossmember, ensuring to seat the insulator firmly onto the center of the crossmember front mount bushing.
Raise the crossmember using the jack stand until it is pressing firmly against the underbody.
With the jack stand still in position to support the crossmember, install the new front mount bolt and the 3 brace to underbody bolts. Tighten
Tighten the crossmember front mount bolt to 125N·m(92 lb ft). Use J 45059 Torque Angle Meter in order to tighten the bolt an additional 40 degrees.

Tighten
Tighten the brace bolts to 65N·m(48 lb ft).

Remove the jack stand.
Repeat steps 2 to 9 for the opposite side.
Parts Information
Part Number
Description
Qty

90447991
Insulator, Rear Suspension Crossmember Front Mount (2 Per Package)
1

92038482
Bolt, Rear Suspension Crossmember Front Mount
2

Parts are currently available from GMSPO.

Warranty Information
For vehicles repaired under warranty, use:

Labor Operation
E9407*
Rear Suspension Crossmember Front Mount Insulators -- Install
0.5 hr

There you have it. Get down & party!:party::cheers:party:
 

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Discussion Starter #7
That may be one of the most thorough things i've ever read. its sweet though! thanks a lot man, im actually installing new rotors all the way around sometime in the next week so that will be the time!
 
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