- cloud 9 wrote:
- So, the story goes....when I did the disc brake conversion I replaced the 80w-90 gear oil with ac delco synthetic lube.... Now during launch only the passenger tire will light up. I have been doing some research online and popular verdict is that you should NOT use synthetic lube in a limited slip posi rear. So I am pulling the cover to drain it out. I was curious , can I use brake clean or carb clean to degrease the gears and the posi? Will it hurt anything? And I have found some of the real ac delco 80w-90 and 2 jars of limited slip additive to replace it with. I just want my launch back
It's unlikely that the synthetic lube alone would, or even could ruin your LSD (Limited Slip Diff.) clutch pack.
I would first look at the surface condition and stacked thickness of your LSD clutches, their pre-load and the presence of a proper type and mixture ratio of friction modifier additive.
Synth gear lube offers your diff. several superior performance pluses, but certain (to my knowledge) un-scientifically analyzed problems have crept into the equation.
We observed several mechanical roller cam lobe scuffing issues switching to full synth in "race only" engines, and those surface galling issues went away after going back to conv. motor oil.
Crane cams had acknowledged this several years ago.
These cams were 8620 steel billet sticks, heat treated for proper surface and depth of hardness, bumping 9310 (hi-impact, nickel-alloy steel) mechanical roller lifter wheels.
This hardened 8620 alloy steel is basically the same material as used in your ring and pinion.
Perhaps the LSD makers found similar/related problems and forbade synth gear lubes to "cover their a$$" in the event of a warrantee claim, or law suit. (IDK)
Modern FMs (friction modifiers) [post-1972 endangered species act, banning sperm*whale oil] affect clutch pack's "slip-grip" behavior predictably while turning corners, whenever the outside wheel rotates a small amount faster.
Rule of thumb: More FM
= less chatter with more slip, <-and-> Less FM
= more chatter, higher grip. - (3%-8% are commonly suggested ranges for FM/Gear Oil mixture ratios).
Run-away single tire "wheel-spin" antics are very
destructive to clutch pack health.
Its a good bet your clutch preload is low, or gone, and in no small part from all this single wheel-spin "testing".
Remember, equal rear drive tire "hook" is a moving target.
Consider the following as a starting point to help you to begin understanding how complex this issue can easily get, and also, very importantly, in addition to your current differential issues, all
these factors, as well as others are in effect at all times.
Road surface tractive differences (L to R), rear tire pressure balance, tire tread type & condition, age of rubber, vehicle weight distribution, wedge-(suspension "cross pre-load" to ground), torque reaction in chassis, rear control arm kinematics, etc, , ,
- - -
I do not love clutch pack style LSDs, they are too much when you don't need them, and rarely enough when you do need them.
On a budget, I prefer Detroit Tru-Trak, (or No-Spin for rugged simplicity), and (IMHO) both use/tolerate synth gear lube without a problem, nor do they require, or mind the presence of friction modifiers.
As far as washing out the synth, don't bother. Synth is fully compatible with conventional gear lube.
The small percentage of remaining synth would not be enough to cause further harm, even if is actually was
the cause of a LSD going south, which I doubt.
If its drained out, just add the correct GL-5, correct FM (between 1 & 4 oz.) but first check the clutch pack plate condition and pre-load.
As for what brand FM, you can use GM #1052358 or Lube-Gard with the LXE (man-made sperm whale oil replacement),
ZDDP Zinc-Dialkyldithiophosphate, (EP) sulphur phosphorus, Amsoil SLIP-LOCK, RedLine limited slip friction modifier/ break-in lube,
Ford C8AZ-19B546-A. Some people have claimed reduced performance from LO versions, (Low Odor),
Royal Purple Max-Gear, and I know there are many more, incl Mopar, Honda, etc., etc.
* Please refrain from "sperm" whale oil jokes, this oil is contained up front in the head of the whale, but when the earliest whalers harpooned the whale in the head, they erroneously miss-named the ejected waxy substance.