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GM limited slip differential additive #510512 11/03/04 06:14 PM
Joined: Mar 2004
Posts: 135
454MAG Offline OP
OP Offline
Joined: Mar 2004
Posts: 135
Anyone know what this stuff is ? The dealer told me it was whale oil.?.? I have found that it is absolutely necessary in a GM 10 bolt with an Auburn LSD.
Car is a 94 pontiac formula LT1 at 60k miles the rear end started making a terrible noise like a rusty bolt being worked during slow speed turns,driveway maneuvers etc. Changed the fluid with M1 75w90 and gm lsd add and it was fine for another 150k miles. At 200k miles I just changed the fluid with M1 75w90 and left out the add. Rear end made the same awful noise at low speed turns when the clutch plates were working. added the lsd add and noise went away. BTW the posi still works perfectly at 203k miles. Still leaves two nice 75 foot black stripes. It appears the M1 lasts at least 3x as long as the factory fill.

Re: GM limited slip differential additive #510513 11/04/04 09:46 AM
Joined: Nov 2002
Posts: 3,022
Mike_dup1 Offline
Joined: Nov 2002
Posts: 3,022
It used to be made from Whale oil. But that is banned in most countries, for many years in fact. Whaling is a no-no unless you want a run-in with Green Peace.

These are called Friction Modifiers and there several out there to chose from.

[ November 04, 2004, 12:57 PM: Message edited by: Mike ]

Re: GM limited slip differential additive #510514 11/03/04 10:12 PM
Joined: Oct 2004
Posts: 701
Mud Offline
Joined: Oct 2004
Posts: 701
Now made from some synthetic something or another, but yes, used to be whale oil derivative.

Lifespan of the additive in a posi seems to be in the 50K range, so your situation was pretty normal. Gives just enough slip to the clutch facings in slow speed applications to avoid grab/sudden release on the packs - that's the noise you were hearing.

I have cars with both GM and Ford LSD's and use the mfg recommended additive for them both. I also change rear gear fluid every 30-40K miles or so and always add the 4oz additive. IMO that waiting to 150K miles is too long on any gear oil, dino or synthetic.

For anyone with the Ford 9 rear axle, to avoid having to pull the axles and center to drain, or have to use a siphon, I weld in a bung at the bottom of the housing for an allen plug. Easy drain. This is easiest on a new installation, but can be done on an existing housing in the car - but you gotta pull that center to drain the fluid and get the plug welding done.

Re: GM limited slip differential additive #510515 11/05/04 09:46 AM
Joined: Jun 2002
Posts: 21,036
MolaKule Offline
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The Auburn LSD is a great piece of machinery in GM 10-bolts. Had one on my old '86 Suburban.

The LSD Friction Modifiers are a combination of esters, mostly phosphoric esters.

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