My diff (MN6 car) makes scuffing/clunking noises in slow parking lot manueuvers (where limited slip would disengage). I think its fairly common from what I've seen. I have the OEM fluid altough it was replaced when my leaking diff was fixed I assume with OEM fluid, Will changing the diff fluid to Redline or Amsoil help? I've read about everything in the forum archieves and there are conflicting reports. Many say it help, but then there is this post by C5tech:

"Some C-5's have reaccuring differential noise...If this is the case,you should remove the synthetic and install GM mineral base GL5 (dont have part # at my fingertips) plus the additive as per GM...I have done this many times and it works,with out a repeat occurance I have also had customers that installed Redline and the noise came back after 2-3,000 miles...What happens is that the additive does not stay mixed with the synthetic causing it to settle...Again,this only happens to some vehicles and it is due to varnish buildup in the posi clutch plates.Because of the design of the differential,you cant clean out the clutch plates as compared to a conventional rear end.Simply draining and refiling doesnt eliminate the varnish buildup.The GL5 seems to compensate for this...I will post the part # tommorrow..."

 

1. Don't automatically trust that the proper OEM Synthetic fluid was used

2. The proper OEM fluid is not enough; the GM "additive" must be mixed with the OEM fluid.

I bet all you need do is add a bottle of the lim-slip additive.

 

Limited Slip Axle Lube Additive
The GM part # is 1052358. You should add this before putting the new fluid in the diff.
The local stealer here charges $9 for it. GMpartdirect.com shows a list of $5 but you have to buy 12 of them.

Amsoil and Redline claim that there fluids already have an additive in them. Amsoil says it both ways on there website:

AMSOIL gear oils are formulated with friction modifiers for limited slip differential applications. There is no need to add limited slip or additional additives.

AMSOIL Series 2000 Synthetic Gear Lube provides limited slip performance. Although generally not necessary, original equipment manufacturers' limited slip additives may be used in conjunction with AMSOIL Series 2000 Synthetic Gear Lube.

Redline says:

LIMITED-SLIP COMPATIBILITY Red Line Gear Oils, with the exception of the 75W90NS, already contain friction modifier required for operation in limited-slip differentials. Additional additive is not required.

I have emailed Redline and asked them if it would not hurt to add the GM additive to Redline.

Here is the reply from redline

The 75W90 would be suitable for the limited slip in your Z06 it contains 5% friction modifier, typically what is needed to reduce the chatter from the limited slip when making a slow tight turn. Adding more friction modifier if it isn't needed reduces the lock up of the limited slip and reduces it's effectiveness, so I wouldn't add it unless it is needed due to chatter and then only just what is needed. The friction modifier isn't a lubricant but just an additive to make the fluid slipperier for chatter control. The 75W90 should be suitable right out of the bottle without the need for the additive. Thank you for your interest in Red Line Oil.

It states in the GM manual that no WOT for 300 miles after the diff fluid is changed.

I used the series 2000 amsoil 75w-90 and added the bottle of the GM additive and have had no problems for 2-3,000 miles

 

Maybe... but it looks like others have had the same scuffing/clunking from the factory. Will probably let my dealer do a replacment of fluid first if its under warranty.

 

The additive is a necessity.

 

I had a similar situation. I developed leaks in an already changed differential oil and GM friction modifier change. The dealer shot tracing dye in the real differential after diagnosis of loose differential plate covers. They were retorqued, the car test driven and checked with a black light the next day.... NO leaks. Then I developed the metal rubbing sound and could not figure out what it was for I had not a hint of it for 23k. I brought it back to the dealer and we decided that the dye might have diluted the solution enough to let the differential rub, ie be noisy. So they R/R the synthetic 75w-90 and GM friction modifier and it went back to the way it was. ie no rubbing no noise. The differential oil change and GM friction modifier were covered under warranty.

Incidently the 2001 comes with factory fill synthetic 75w-90 differential oil .

Best of luck!!


[Modified by ruking1, 10:42 AM 6/26/2002]

 

hmmm, interesting... because I don't remember any posts where the fluid installed at the factory (very specificially worded sentence) ever caused any problems.

But, hey... I don't read them all :)

 

I agree with Black......................experienced the differential chatter on my 99 FRC. The dealer R&R'd the fluid due to a seal replacement under warranty. Three weeks later the chatter was back. I drained and replaced with AMSOIL Series 2000 and GM limited slip additive. Its been over 2000 and no chatter return. :yesnod: Convinced me.

 

The 75W90 would be suitable for the limited slip in your Z06 it contains 5% friction modifier, typically what is needed to reduce the chatter from the limited slip when making a slow tight turn. Adding more friction modifier if it isn't needed reduces the lock up of the limited slip and reduces it's effectiveness, so I wouldn't add it unless it is needed due to chatter and then only just what is needed. The friction modifier isn't a lubricant but just an additive to make the fluid slipperier for chatter control. The 75W90 should be suitable right out of the bottle without the need for the additive. Thank you for your interest in Red Line Oil.

The bottle says different. :confused:

 

Slap ya some AMSOIL Series 2000 Gear lube in it.
NO friction modifier needed. :nonod:
Then it will shut up. :yesnod:

 

I had the rear differential noise when making sharp turns or turning in circles this noise was really bad and worried me. So i brought the car to west coast corvette( chevy dealer gave me the run around wanted car for two days) had them change a4 filter and fluid and also rear end fluid john the mechanic said noise might take a day to quiet down they did a very through job took about an hour or so to do. when i left the noise was gone instantly :D Its been about 3K miles since, silence is golden

robert