Leon Speed

Not a very exiting topic, but I need to know anyhow.

I have the choice between mineral hypoidoil SAE 85W90 (GL5) and synthetic oil SAE 75W90 (GL5). Should I go with the (I assume old school) mineral oil or go for the synthetic oil?

I have an open diff.

z driver 88t

Just replaced mine with Redline 75W 90 NS GL5. I did a bunch of forum searches beforehand. Some people like Royal Purple, some like Mobil, but concensus seems to be Redline 75W90 NS. No LSD makes it easy. Some LSDs complain that they get chatter unless they add a little friction modifier. But too much friction modifier is not good for smooth shifting synchros. Although mine seems fine without it.

kmascotto

I just did mine...and used synthetic oil SAE 75W90. Which I hope was a good choice.

Bill Ball

What's wrong with Mobil 1 LS? How is Redline said to be superior?

oups59

Mobil1 LS with LSD.

Bill Ball

Luc:

That's Mobil 1 LS. I've had no problems with it in my transplanted LSD.

http://www.mobil.com/USA-English/Lub...LS_75W-90.aspx

Glen McCartney

Royal Purple, I like the color

GregBBRD

I'm a fan of Mobil 1 75/90LS. Does everything that I think it should do, for "normal" everyday usage. Works well with the limited slip. It is syncro "friendly". It does a great job of protecting the gears and the bearings. And, it doesn't leak past the seals.

I'm not a person in a constant search for something better. Once I find something that works, I stick with it, unless I have some sort of a problem with that product. Therefore, I have not tried every single one of the transmission oils out there.

However, I do rebuild and have rebuilt a lot of transmissions, over the years. Redline leaks past the seals on a fresh transmission, to the point where I insist that if people want me to warranty the transmission from leaking, they can't use that gear oil.

Avar928

Mobil 1 "LS"

I don't have LSD and couldn't find any NS anywhere local. So far no problems. Internet research and a bunch of other car forums say that it won't hurt the diff.

Leon Speed

Thanks for sharing your experiences. Since the mentioned Mobil 1 and Redline oils synthetics I will go with the synthetic equivalent the more readily available LiquiMoly. I use LiquiMoly TopTech 1100 ATF for the gearbox and am happy with it.

NoVector

Greg - What's your thoughts on Dexron VI--do you use it?

(Sorry Aryan for posting an ATF question in a differential thread; but I see you''ll soon be flushing that too.)

GregBBRD

I do not.

By some sort of "RPN" logic, I figure that if regular Dexron II won't work in a vehicle that was made for Dexron VI, the reverse might not be the very best of ideas, either.

I use a special high performance fluid that survives in my 2 speed Powerglide (with transmission brake and 3,500 rpm stall) and 570 cubic inches of BBC (in my 63 Nova.)

I figure that if it survives there, one of my stroker 928 engines isn't going to stress it.

GregBBRD

Yes, definitely not an issue. It has a friction modifier for the limited slips, which is not a negative thing for open differentials.

Ed Scherer

Hmmm... I just looked back and see that I used Castrol Syntec 75W-90 (GL-5) on my last change (quite a while back) on my '90 S4 (PSD). I can't remember exactly why I picked that one. Looks like maybe that's been replaced by "Syntrax™ Limited Slip 75W-90" (same thing, different name, maybe?).

Any comments on that choice?


(Edit: Based on a post on another forum, "Syntec 75W-90" was renamed to "Syntrax Limited Slip 75W-90" in November, 2011.)

928 at last

That's what I used a while back too after checking here.....
Flavour of the day.

Doing the flush again this spring, so I'm reading this thread with some interest.....