Proper rear differential fluid and additives?

[Kuhlsnu]

Hello all,

I just purchased a 2003 cts. I've driven it about 2 weeks now and just started noticed a whine between 40mph and 50mph only if I am slightly accelerating. If I am off the gas or pressing down further no noise. So I am going to start by changing the differential fluid (no idea when it was changed last).

I seen the faq on the cadillacfaq page but it is for a cts-v and has slightly different gear oil specs.

In my manual it says 80w-90 GL-5 axle lubricant (gm part no. US 12345977).
I want to know if it needs the same GM additive like the CTS-V (1052358) and if I can use a pennzoil or mobil 1 gl-5 axle lubricant at 80w-90 with the proper additive ie 4 oz?

Also is there any major chains were I can pick a bottle of the additive up do I need to order online?
Any other comments are helpful!

[RobertCTS]

It's a somewhat common problem for the early differentials to go sour Very pricey!! Use the recommended Mr Goodwrench products.

[Kuhlsnu]

btw how much is very pricey? and right now I dont have any indication that it will turn sour. It really sounds like it needs some additive.

I was reading a corvette board and it had nearly the same differential and they had a TSB that told them to put 8 oz of the additive in the car instead of the 4oz and a synthetic gear oil with a different GM part number:
http://forums.corvetteforum.com/show....php?t=1497063

Also I was reading about several people who put the pennzoil gear in their car and had no problems but they doubled up on the additive because the gm part has the additive in the fluid already whereas the other is clean.


Did I post this in the wrong area? I assumed more people would know this off the top of their head. Its a pretty common maintenance procedure.

[z06bigbird]

Parts MGR at Caddy dealership will know exactly what you need. It is engrained in his brain.

[Kuhlsnu]

Has anyone ever heard of changing the fluid eliminating the whine?

[ByByBMW]

I don't know about the whine but I use Amsoil Severe gear in my C6 with the GM additive and it corrected the clunk associated with the LSD gear packs. It has enjoyed very good success among the C6 crowd.

[C66 Racing]

Kuhlsnu,
AMSOIL recommends the AMSOIL Severe Gear Extreme Pressure Synthetic 75w90 for your 2003 CTS. This is the same fluid I use in my 2002 Corvette Z06 on the track (and have been since the start of the 2004 season - no failures other than a failed left axle seal which is a common C5 Z06 issue), and the same fluid I run in my 2006 CTS-V.

This fluid comes with friction modifier already in it and I don't use any extra additive in my Z06 or CTS-V. For the Corvette C6, I do recommend adding one bottle of the AMSOIL Slip-Lock Differential Additive which seems to quiet down the chattering of the C6 diff well.

If you do decide to try this fluid or additive, it can easily be ordered online or by phone through AMSOIL. Info is in my signature. PM if you have any questions.

[Kuhlsnu]

Thanks for the advice everyone!

When I replace the fluid it says to do it on a level surface but I noticed in the faq is just said drive it up some rhino ramps. Will this effect it? Sounds like I probably need to jack the front up once its rear is up on the ramps?

Has anyone ever heard of this quieting down the whine? Or should I just go and get a 1 year extended warranty for $1k... wait a month and then take it in for the $1.5 or $2k job?

[Z71]

If you do it on ramps you cannot get the right amount in and you will be low when its level.

As for quieting down the whine, don't count on it. That is from the ring and pinion gears meshing.

Lube won't solve mechanical problems.

I have the Amsoil SVG 75W-90 in my CTS for about 20,000 miles now. Mixing the additive is critical. If you decide to use the additive for the LSD here is what I did. Add about 1/2 qt of gear lube to the axle cavity, then take the bottle of additive and mix it with the remaining gear lube it the qt and then add it to the axle, top of with another bottle (takes between 1 & 2 qts). This insures the additive gets thoroughly mixed with the lube, top of the axle, install the fill plug. Take the vehicle out for a drive, find a open area (big parking lot) and drive in the figure 8 about 10 times to get the lube to work its way in the clutches. Driving the the figure 8 forces the clutch pac to engage/disengage when the car changes direction. Drive the car normally.

Mike
2005 CTS
2008 GMC

[C66 Racing]

I agree with Mike - your car must be level when you fill the diff.

In my CTS-V, when I changed the diff and tranny fluids about a month ago, I drove the front tires up on Rhino Ramps, then jacked up the rears with my aluminum racing floor jack and put the Rhino Ramps under the rear tires.

[Kuhlsnu]

Someone should really edit that faq then... there is probably tons of people missing about 100ml of fluid in their differential. A matter of fact I do remember some posts on the cts-v board about the differential not holding the correct amount as specified. I bet thats their culprit.

[mikes2nd]

Im going with redline and they also have their own additive

http://www.redlineoil.com/products_g...5&categoryID=6