Royal Purple Gear Oil

I've used the Royal Purple Max Gear 75W90 in the past with OK results although I eventually went to Ravenol VSG (gold) full-synthetic 75W-90. If you've already got the Royal Purple, it seems reasonable to try IMO. All transaxles have slightly different behavior so one size doesn't fit all, and it isn't too difficult to change again. (I had a bad result with the Redline 75W90 NS having terrible LSD clutch chatter on slow turns that didn't get any better after adding Redline's friction modifier).

 

Steve: We have had the same problem with the Redline products. We went to another oil and the problems IMMEDIATELY disappeared.

 

I wasn't surprised when I had the LSD chatter with the straight Redline 75W90 NS installed, but it did surprise me that adding their recommended amount of their friction modifier seemed to make no difference at all (it just stayed equally bad). Did you also find that the Redline friction modifier had no effect?

 

Steve: We had the EXACT same problem. At first, we immediately encountered the chatter, then we followed Redlines instructions about quantities of friction modifier, but with no improvement, then we added additional friction modifier and it still chattered. Mobil 1 plus a tube of generic LSD additive worked perfectly, great shifting and totally quiet LSD.

 

I would say "no, nothing significant", but it's just so darn annoying/distracting/unacceptable.

 

Jarrod: Clutch-type limited-slip differentials have a series of clutch plates lined with friction material the lock together when one wheel spins more that the other one. These "clutches" have to allow some slippage when the car turns a corner and the rear wheels turn at different speeds. LSD gear oils have additives (used to be sperm whale oil) the provides lubrication to allow this slippage, but still enough "grip" to lock up the clutch under wheelspin. If the plates cannot slide past each other (slip) at low speeds, they grab and release in a "chattering" sequence. The driver feels this as it causes the rear tires to not turn smoothly through the corner. This is not desirable, but generally is not a major reliability issue. However, it does not help LSD life.

 

42mm, but a 1.625" 12-point socket worked for me (but it was "tight").

 

Redline 75W90 NS for my '86 Testarossa, but with the use of GM "Limited Slip Axle Lubricant Additive" worked fine to eliminate the chatter. I use a 1-5/8 inch 12-point socket as well. EDoug

 

There is no magic bullet oil for them. Different cars respond differently so I'd say ty it.

I will say I used RP at a clients request once and it was the only time in my experience that a client came back in a week and asked me to drian it out.
He said it destroyed his shift quality.

 

That's fine, or you can do it in the other order -- put the first quart into the transfer gear fill plug and then fill the main reservoir up to the bottom of the main fill plug hole (by the time you get the main reservoir filled, any excess that was put into the transfer gears will have had time to overflow into the main reservoir. With your method, when you start to get some running out of the main fill plug hole, it will drip for a long time and you'll waste some oil.

 

What oil is recommended for these boxes. I used redlline(shifted great) and got chatter, will replace this week.

 

In my personal experience limited slip additive can take 200 or more miles to get rid of chatter. Put enough in for 18 pints and be patient.

In my case a little chatter does not bother me. I had a Buick Grand National that chattered so bad it would spill the drink in the cup holder and people stopped and stared. A little LSD additive fixed it.
Just dont expect it to be gone when you are backing back out of the shop.

 

I had a 430 Ediff in the shop that the client and I both thought had a failure. The chatter was really bad but inconsistent. I pulled the diff and found the clutch plates were totally dry. As I pulled the first floater plate, I could see oil starting to ooze across the friction material. I hand lubed the plates and discs and put it back together. No more issues. I suspect the car had been sitting for a very long time. I use Mobil 1 75/90 with the LS modifier already in it. Haven't had any issues.