M Danger

so I go to the local race shop today and they carry 3 diff redline gear oils. I did some research here on the list but still didnt come up with a firm answer.

so I read the bottles and ended up getting 1- 75-90, 1 75-90-NS, and one MT-90, for my non-LSD 951

anything wrong with this?

H2

I thought that Redline 75-90 NS was the recommended GL5 gear oil? Am I wrong. The MT-90 I thought was for older cars. It's GL-4 rated. Not a lot of difference but, in some cars, it can improve or worsen shifting.

Harvey

Zero10

You're going to mix all 3 in your transmission?.... Yikes!
I used Redline 75-90 the first time I filled mine, and it was pretty notchy. It's one of their thicker fluids.
The second time I filled with Redline MTL, and it shifts VERY well, although some claim that it is not thick enough to provide adequate protection for the ring and pinion. It carries a GL-4 rating though, so it should be fine.

Zero10

Okay, from the data sheets.....
75-90:
vis@100*C: 16.4
vis@40*C: 115
gear rating: GL5+
Type: gear oil
75-90NS:
vis@100*C:15.6
vis@40*C:95
gear rating: GL5+
type: gear oil / transmission lubricant
MT-90:
vis@100*C:15.6
vis@40*C:90
gear rating: GL4
type: transmission lubricant

And one I added to the list....
MTL:
vis@100*C: 10.6
vis@40*C: 56.2
gear rating: GL4
type: transmission lubricant

After reading this I can't recall whether we require GL4 or GL5..... I thought it was GL4, but most GL5 lubricants are fine for GL4 applications? The older GL5 used to corrode brass synchronizers IIRC.

You have no LSD, so the additives will only make shifting worse. LSD additives make the gear oil slightly more slippery. This will cause reduced drag with the synchros and harder/notchier shifting. You want drag there.

You want to run a transmission fluid, not a gear oil or else you will also have trouble shifting. So, this narrows it down to MT-90 or 75W90NS. MT-90 is a 'stickier' oil for synchro's, but only bears a GL4 rating as to the 75W90NS having a GL5+ rating.

Enough education yet?....
IMO run MT-90 or MTL, but again, MTL is a 70W80 not a 75W90... (hence the much lower viscosities)

sharky47

I just called up Jason at Paragon and he sent me what I needed. Easy job and makes me feel better knowing there's fresh fluid in there.......

M Danger

well so a combo of the 3 doesnt sound too bad. Ive seem to have read that most people run mostly 75-90, NOT NS

yoyoguy2

I use MT90, i heard there were problems with the gl5 being to slippery for the synchros, so gl4 was recommended. gl5 is a better gear oil, no t necessarily a better transmission oil.

thor455400

aaahhhh!!!you guys are confusing.what in the h.ll is gl4,gl5,????? what are we supossed to uuuussseee????i posted this topic last week and got every thing from mobil to swepco.im still lost on what to use!!!and how do i know if i have an lsd.why would that make a diffrence on the fluid?does porsche use clutches in the rear?

The DareDevil

Here's page 109 from the owner's manual: "Filling Capacities"

Zero10

Straight 75-90 is a gear oil not a transmission fluid. It will do an excellent job protecting the gears, but it will make shifting more difficult.
MT-90 isn't a bad fluid, 75-90NS is mentioned as a transmission fluid, but it is designed to be a gear oil.

Interesting that the owners manual says 80W. I recall reading somewhere that it was 75W90, being that porsche specs 80W I feel better about running 70W80.

GlenL

These threads are always so frustrating...

Thanks to Mr. Devil for posting the manual page. It shows everything you need to know: use 2 quarts of 80w GL4 oil.

Two additional bits of info: "hypoid oil" is "gear oil" and GL5 is more slippery than GL4.

So, what's a guy to put in his car?

First off, it's hard to find 80w oil. Using 75w90 will be fine.

Secondly, using GL5 will lube the synchos more than GL4.

Conclusion: using 75w90 GL4 is a correct choice.

How this translates into the available oils is another issue.

I'm using Redline 75w90NS in both of my P-cars and it's working well in the 120K mi. 944. (928s require GL5 and I want to use the same in both.) The synchros are working just fine. The NS is for "non limited slip" differentials.

Using the Valvoline or Royal Purple 75w90 synthetic oils, or the mixture from the first post, will be fine as well.

The DareDevil

Call me Derek

Pauerman

I use Redline Shockproof gear oil in my LSD boxes. The oil comes in SuperLight, LightWeight and Heavy configurations.

The bottle reads:

The Shockproof chemistry significantly reduces the thinning effect of high timperatures, and can be rated as a 75W250 Gear Oil, which provides three-times the viscosity in the thin layers between the gear teeth, but has the lower internal fluid friction of an SAE 75W90, which means very little power loss for the protection achieved. Shockproof Gear Oil has a 40% lower coefficient of friction and 250% the load-carrying capacity compared to conventional gear oils, which means that metal-to-metal friction is greatly reduced.

Improved durability in high-performance use is the primary benefit of the Heavy Shockproof and along with the improved durability is an improvement in efficiency, but if further improvements are desired, and durability is not a major concern, LightWeight and SuperLight Shockproof can be used. The cushioning effect of the Shockproof chemistry allows the use of one of the lighter viscosities in many performance applications with little sacrifice in durability.

Redline Shockproof can be used in conventional, limited-slip, or locker differentials.

I find the cold shifting with the Heavy Shockproof to be mildly notchy, so I just shift a little slower. Once warm, shifts are extremely smooth. I really like this oil and the additional protection it provides.

Charlie944

I have used MT-90 for over 100K in my 84' NA trans (changed a few times of course) with great success and smooth shifting. Also used it in my turbo trans non-LSD with the same results.
I will have to check out the Shockproof oil, I recall many of the turbo users on this board using it here a couple years ago.

GlenL

I used the shockproof for one Winter. Pulled it after a bit more research and other's feedback. They've changed their information on the product but it used to spell out that it's not for high temp uses. That is, not for use running road courses.

Here's a thread:

https://rennlist.com/forums/924-931-944-951-968-forum/171903-redline-lightweight-shockproof-cherry-or-butterscotch.html