Loud metal clunk in front end

Loud metal clunk in front end

Postby maximumoverdrive123 [OP] » September 12th 2009, 10:36pm

2000 AWD Astro

Developed a very loud clunk, rather violent in that the both front wheels snap when the clunk occurs. Almost seems like something is preventing the rotation of an axle then it finally lets go, hence the snap and loud clunk. CV are in excellent shape no tears in the boots. This happens at walking speed, afraid to take it for a spin.
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Re: Loud metal clunk in front end

Postby ghostrider1061 » September 12th 2009, 11:18pm

how many miles do you have on the cv's? do you have rack and pinion or gear box sterring?
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Re: Loud metal clunk in front end

Postby maximumoverdrive123 [OP] » September 12th 2009, 11:55pm

Found this technical service bulletin that seems to speak to the problem. The bulletin sounds if this condition is only for the rear end though?


Bulletin No.: 99-04-21-005B

Date: September, 2002

TECHNICAL

Subject:
Transfer Case Shudder
(Flush and Replace Transfer Case Fluid)

Models:
1999-2003 Chevrolet Astro (AWD)
1999-2003 GMC Safari (AWD)
1999-2001 Oldsmobile Bravada
with All-Wheel Drive (NV136) Transfer Case (RPO NP4)

This bulletin is being revised to add model years. Please discard Corporate Bulletin Number 99-04-21-005A (Section 04 - Driveline Axle).

Condition

Some customers may comment about a vibration (shudder) during tight turning maneuvers on dry pavement at vehicle speeds less than 8 km/h (5 mph).

Cause

This condition may be caused by a slip-stick of the clutch plates in the transfer case clutch pack. On 1999 and newer models, the preload that is designed into the clutch pack may contribute to the condition. In addition, contamination of the fluid may interfere with the friction modifiers.

Correction

Flush and replace the transfer case fluid on affected vehicles using the following procedure and the part number listed below.

Perform the following diagnosis prior to flushing and replacing the transfer case fluid in order to properly identify the shudder.

Diagnosis

1. Verify the shudder in the vehicle. The vehicle needs to be at operating temperature (driven at least 5 miles) for proper diagnosis. After the vehicle is at operating temperature, drive in a tight circle just short of steering wheel lock, at a speed less than 8 km/h (5 mph) in order to identify the shudder.

2. Identify what rear axle type the vehicle has.

^ If the vehicle has a standard rear axle, then proceed to step 3.

^ If the vehicle has a locking rear axle, remove the front propeller shaft. Refer to the Propeller Shaft subsection in the Service Manual. Drive the vehicle as outlined in step 1.

^ If the shudder goes away, install the front propeller shaft and proceed to step 3. Refer to the Propeller Shaft subsection in the Service Manual.

^ If the shudder does not go away, the locking rear axle may be the cause. Review the owner's records and determine if the rear axle was serviced at the first scheduled oil change. If records indicate that the axle service was done, then revaluate the condition using diagnostic information in the appropriate Service Manual. If the rear axle was not serviced, service the rear axle.
INFORM THE CUSTOMER THAT THE AXLE SERVICE IS AN OWNER'S MAINTENANCE ITEM NOT COVERED UNDER THE VEHICLE'S WARRANTY.

^ Install the front propeller shaft. Refer to the Propeller Shaft subsection in the Service Manual.


3. Flush the transfer case with the blue colored fluid (AUTO-TRAK II) using the procedure and part number listed below. Perform the flush procedure even if the transfer case contains the blue colored AUTO-TRAK II fluid in order to remove any possible contaminants. The AUTO-TRAK II fluid contains an improved friction modifier that should correct the slip-stick condition. Refer to the Transfer Case subsection in the Service Manual for information on draining and filling the transfer case.


Flush Procedure

Important :Refer to Corporate Bulletin Number 99-04-21-001, dated April 1999, for important information on removing the transfer case drain and fill plugs.

1. Drain the transfer case fluid.

2. Refill the transfer case with 2 L (2 qts) of new fluid, P/N 12378508 (Canadian P/N 10953626).

3. After refilling the transfer case, drive the vehicle a minimum of 8 km (5 mi).

4. With the transfer case at operating temperature, drain the transfer case fluid again.

5. Refill the transfer case with new fluid.

Important :The vehicle may require approximately 160 km (100 miles) of driving before the condition is completely corrected.
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Re: Loud metal clunk in front end

Postby astro355 » September 13th 2009, 2:05pm

RWD vans don't have a transfer case, that TSB is for AWD vans. When was the last time you changed the fluid in your transfer case?
Diagnose 1st, never be a parts changer!

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Re: Loud metal clunk in front end

Postby maximumoverdrive123 [OP] » September 13th 2009, 5:38pm

astro355 wrote:RWD vans don't have a transfer case, that TSB is for AWD vans. When was the last time you changed the fluid in your transfer case?



I've never had the fluid changed.
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Re: Loud metal clunk in front end

Postby astro355 » September 14th 2009, 8:52am

Ok then, I would follow the first recommended step of the TSB:

Correction

Flush and replace the transfer case fluid on affected vehicles using the following procedure and the part number listed below.

Perform the following diagnosis prior to flushing and replacing the transfer case fluid in order to properly identify the shudder.
Diagnose 1st, never be a parts changer!

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Re: Loud metal clunk in front end

Postby maximumoverdrive123 [OP] » September 14th 2009, 11:27pm

Pulled the front left wheel and had a look at the CV joint. Seems the CV going into the transfer case has a vertical and horizontal movement. The catching and snapping sound appears to be comming from this area. Maybe the CV joint is shot? Very difficult to figure out where the noise is comming from. All U-Joints in good shape. Any one hear of problems inside the transfer case on these models or problems with the CV going into the transfer case?
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Re: Loud metal clunk in front end

Postby guyonearth » December 4th 2009, 11:19pm

Is the looseness in the joint itself, or in the transfer case bearing? There is normally a little play where the cv joints go into the housing, but it shouldn't be alot.
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Re: Loud metal clunk in front end

Postby astro355 » December 5th 2009, 12:17am

I'd settle for an update sometime. :whistle:
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Re: Loud metal clunk in front end

Postby timelessbeing » December 5th 2009, 2:38am

I had the transfer case problem, and I'm pretty sure that only bumps in tight turns, not moving straight ahead. However I have a snapping too and it's from the control arms. Have someone listen to them or even feel the mounts while you turn the wheels all the way left and right.
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