I plan to replace the differential fluid in a couple of weeks. I have read several posts that recommend doing 8-10 figure 8's after replacing. I am thinking...is this done at the factory every time a new Corvette comes off the assembly line? My guess is "no". I could be wrong, but if they don't, then the factory must not see any need or benefit to doing so if it was important. I would think also that with the differential gears spinning around, that the fluid would reach all internal diff parts that need lubricating. It might sound like a good idea, but if the factory doesn't do it, there must not be much benefit to doing it.

 

The factory generally has a different method of putting fluids in cars. The differential is no exception. You probably don't have to, but spending the extra 5 minutes to do so probably wont hurt.

 

Here's the TSB:

Document ID# 2048181
2005 - 2008 Chevrolet Corvette

--------------------------------------------------------------------------------

Subject: Rear Axle Clunk and/or Chatter Type Noise on Turns (Drain/Refill Rear Differential Fluid) #07-04-20-002A - (01/09/2008)

Models: 2004-2008 Cadillac XLR (Including V-Series and Export)

2005-2008 Chevrolet Corvette (Including Z06 and Export)

--------------------------------------------------------------------------------

This bulletin is being revised to change the fluid recommendation and to remove the requirement of adding friction modifier. Please discard Corporate Bulletin Number 07-04-20-002 (Section 04 -- Driveline/Axle).

--------------------------------------------------------------------------------

Condition
Some customers may comment on a clunk and/or chatter type noise from the rear of the vehicle while making turns.

Cause
This condition may be caused by slip/stick of the posi-traction clutch plates due to insufficient limited-slip axle additive. As plates slip and stick, a jumping or jerking feel occurs accompanied by a clunk noise.

Correction
Important: DO NOT remove the differential cover from the rear or the two sides. It is not necessary to flush the old fluid from the differential.

Drain and refill the rear differential fluid using the procedure listed below.

Draining Procedure:

Raise and support the vehicle.
Clean any dirt from around the differential drain plug.
If not equipped with a differential cooler, remove the drain plug (1) and washer (2) from the differential.

If equipped with a differential cooler:
4.1. Using a bent tip screwdriver, remove the quick connect fitting retaining ring (3) from the quick connect fitting (4) and discard the retaining ring.

4.2. Remove the differential cooler inlet pipe from the differential nut.

Drain the fluid.

Filling Procedure:

If not equipped with a differential cooler, install the drain plug (1) and washer (2) to the differential.
Tighten
Tighten the differential drain plug to 35 N•m (26 lb ft).

If equipped with a differential cooler:
2.1. Install a new retaining ring.

2.2. Connect the differential cooler pump inlet pipe (2) to the differential. A distinct snap should be heard or felt when assembling the cooler pipe to the fitting.

2.3. To ensure the cooler line is properly installed, give the cooler pipe a gentle pull.

Clean any dirt from around the differential fill plug.
Remove the fill plug and washer from the differential.
Important: DO NOT add any limited-slip additive (friction modifier). With this new fluid (Dexron LS Gear Oil 75W-90) it is no longer required to add friction modifier. If friction modifier is added, it will cause the fluid to lose some of it's friction reducing properties as well as reducing seal life.

Fill the differential with the new DEXRON® LS gear oil, P/N 88862624 (Canadian P/N 88862625). Refer to the table listed below for lubrication specifications.
Check the fluid level to ensure it is even with the bottom of the fill plug hole to no lower than 6 mm (0.25 in) below the opening.
Install the fill plug and washer to the differential.
Tighten
Tighten the differential fill plug to 35 N•m (26 lb ft).

Important: Steps 8-13 are for vehicles equipped with the differential cooling system. For vehicles not equipped with the cooling system, proceed to step 14.

Raise the vehicle so the wheels are about a foot off the floor. Make sure the wheels can spin freely without obstruction from the hoist or any nearby items.
Start the vehicle and put the transmission in second gear. Slowly accelerate to 10 mph and hold this speed for one minute.
Turn the vehicle off .
Raise the vehicle.
Check the fluid level in the differential. Add fluid until the recommended level is reached.
Lower the vehicle.
Once the differential fluid has been changed, the vehicle must be driven in 8-10 tight figure eight maneuvers to heat the fluid and allow the fluid to be worked into the clutch plates.
Lubrication Specifications Application
Quantity

Metric
English

2004-2005 XLR (Including Export) and 2005 Corvette (Non Export)
1.72 liters
1.85 quarts

2006-2008 XLR (Including V-Series and Export) and 2006-2008 Corvette (Non Z06)(Non Export)
2.0 liters
2.11 quarts

2005 Corvette Export
1.88 liters
1.99 quarts

2006-2008 Corvette Export (Non Z06)
2.16 liters
2.28 quarts

2006-2008 Corvette Z06
2.75 liters
2.91 quarts


Parts Information
Part Number
Description

88862624 (US-1 Quart)

88862625 (Canada-1 Liter)
DEXRON® LS Gear Oil

Warranty Information
For vehicles repaired under warranty, use:

Labor Operation
Description
Labor Time

F9709*
Drain & Refill Rear Axle Fluid
0.6 hr

* This is a unique labor operation number for bulletin use only. It will not be published in the Labor Time Guide.


GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION


© Copyright General Motors Corporation. All Rights Reserved.

 

S L O W figure "8's" are the recommended way to work the new fluid into the clutches. It isn't nonsense, it just works.

 

Iathrash - thanks for the information. Actually, that was what I was looking for, something that confirmed whether or not it should be done. Mine is not making any sort of noise, clunk or chatter, I am just going to change the fluid out as a precaution and peace of mind. Plus, I enjoy working on the car. I replaced all 4 sway bar end links last weekend, but it needed to done. Anyway, it looks like I will do some (slow) figure 8's. Thanks again for the info.

 

I think the figure 8's at the dealer/mechanic is so that the clunk won't be there when you pick up your car. A short drive with sharp left and right turns would probably do the same.
But, hey, figure 8's only take a few minutes, so ----

 

I would think the diffs were installed full of fluid already and perhaps some machine synthetically did figure 8s with it out of the car beforehand. This is just coming out of my head though no evidence to support my claim.

 

Ford 9" gurus are also adamant about the figure eights...
Forward and Reverse.
It gets real fun and adds new craziness to the neighborhood's culdesac.

 

The TSB was issued in Jan 2008 and the factory had already been using the newer pre-mixed fluid for a while, so not all '08's had the new fluid. Those that did have the new fluid from the factory don't need to do the figure 8's when changing fluid. I have a late Oct '07 build, which never had the chatter problem, so when I changed fluid just prior to 100K miles, I bypassed the figure 8 procedure.

Doing that procedure certainly won't hurt the car, even if you have the newer fluid. But if you don't or never did have the chatter issue it's not necessary. The procedure is just the quick method to cure an existing chatter problem.

 

If you are doing a fluid change to solve a chattering issue, best to do the figure 8s.

 

Makes sense to me. And also I would think a longer drive would get everything up to temp and work the fluid into the clutch packs probably better than cold figure eights.

 

only if you think the factory service manual procedures are all nonsense like a lot on here seem to think.I just go with what GM engineers request as they seem to know a bit about these cars

 

The TBS only applies to cars that came from the factory filled with the previous fluid and that have a chatter issue. They don't have a habit of issuing TSB's to resolve issues on cars that have not yet been built, because they have already identified those issues and resolved them. You can do the figure 8's with cars produced after the TSB date, but it won't fix a problem that doesn't exist.

 

I follow the guidance in the 09 Owner's Manual and get my fluid changed after 24 hours of track use. Have never done any figure 8s after having it changed. Have never had the chattering issue.

Bill

 

I think that the purpose of the figure eights is to get the new fluid into the clutch packs and stop the noises right away. When the car is driven, the new fluid will eventually work its' way into every part of the diff, but no service advisor wants the car coming back after a few minutes because the noise is still there. He then has to tell the customer that everything will be fine after driving some mileage, but right now it will still make the bad noise. Doing the figure eights makes it so that the noise is cured when the car is picked up. Also, this allows the dealership to verify that the fluid change worked as it was supposed to. They don't have to wait for the results.

 

That's exactly right and it's only for cars that had the chatter problem.

 

Question - I know that the fluid level is full when it is even with the bottom edge of the fill plug hole and begins to run out, and the purpose of doing figure 8's is to get fluid into the clutch packs. So my question is, once the old fluid is totally drained, and I add new fluid to the bottom edge of the fill hole, and before I do any figure 8's, I assume that the new fluid hasn't reached the clutch packs yet. So after doing the figure 8's to work fluid into the clutch packs, will I need to re-check the fluid level?

 

No, it's full at that point...the new fluid has just not yet replaced the old fluid that is squeezed in between the clutch plates and the level will not be affected when it does.