non-redline GL-4 fluid options for LSD transaxle?

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wolfestone

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I'm shopping for fluids which are in the 75w90 range, for a porsche transaxle (AOR transmission, limited slip diff).

As I understand it, this transmission uses brass components in the synchros, so it's hit or miss whether certain GL-5 fluids will cause corrosion or not.

The only GL-4 fluid I've found so far is redline, and I would prefer to have some other options if they exist.

Other fluids people seem to favor in this transmission are swepco 201/203 (GL-5 but has LSD additives), Mobil delvac (also gl5, no LSD additives), and mobil 1 (gl5, seems to be some conflicting information on whether or not this harms the synchros).

Am I correct on the GL-5/bronze corrosion stuff, or is that internet rumor?

price/value is less of a concern, compatibility and protection are most important.

Thank you for any suggestions.
 
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what does the car spec. many porches spec gl-5(mostly awd)

I'd get motul gear 300 75w90, or redline 75w90NS
 
Originally Posted By: Rand
I'd get motul gear 300 75w90, or redline 75w90NS


The Motul Gear 300 NS is great, high VI stuff, but is almost twice the price of the Red Line fluids.
frown.gif
 
Motul or Redline, based on my experience. I have never liked AMSOIL, and I will never recommend them, but I will also be the first to say that you should never rule something out because of your own, or someone else's, bias.

Still, RL is the only thing that has never failed me on the track, and that's many years and many thousands of miles....
 
Thanks all.

Does anyone know if the motul 300 75w90 ls is safe for yellow metals used in the porsche synchros? I have emailed motul but not optimistic I'll get a reply.
 
"Does anyone know if the motul 300 75w90 ls is safe for yellow metals used in the Porsche synchros?"

Yes. It is rated GL4 so you won't have an issue with it attacking the syncros.

http://www.motul.com/us/en-us/products/106

There are lots of GL4 rated 90 weight gear oils around. The Motul is likely a top product. Some VW guys swear by Chevron Delo 80W-90. I'd also suggest Amsoil MTG. I use (and love) their MTF in my Honda front drivers.

I wouldn't bother with the factory fluid ... whatever it is.
 
Hmm. My car has a limited slip, so I'd probably need the LS version of that oil: http://www.motul.com/us/en-US/products/107

Which doesn't look like it's GL-4 rated even though the non-LS version is.

I'd be happy using a Motul product (I'd prefer to stick with a major brand name if possible) but would need to make sure this one in particular would be a safe choice.

The car sees such a low amount of use, and the price of a transmission rebuild is sufficiently scary that I have no problem springing for a top quality oil on this one.
 
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This article is for you!
http://www.widman.biz/Corvair/English/Links/Transaxle.html

There are only a few cars with hypoid manual-transaxles. Porsche, Subaru, Audi and the Corvair are among the few.

But the Porsche community is well stocked with info and history so it shouldn't be much of a challenge to find the 'best' fluid.

Many Subaru owners have settled on Subaru Extra-S or Motul Gear 300. Is your LSD a clutch-pack or a Torsen-type?

Originally Posted By: wolfestone
Am I correct on the GL-5/bronze corrosion stuff, or is that internet rumor?

Yes you are. A GL-5 rating does not mean it will be corrosive to brass/copper but most are. Look for a specific reference to compatibility AND performance with brass synchros. Some may not harm the brass but they lack the performance enhancing additives you desire.
 
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The Porsche AOR transmission (944 Turbo) I believe was from Audi.

Personally, I would run Red Line 75w90ns:
http://www.redlineoil.com/product.aspx?pid=47&pcid=7

... or Amsoil MTG:
http://www.amsoil.com/shop/by-product/tr.../?code=MTGQT-EA

... or the Motul Gear 300 that you've mentioned.


Anyway, here's what LN Engineering have to say:
http://www.lnengineering.com/oil.html#Z37

What gear oil is best for my Porsche transaxle (manual gearbox)?

There are many excellent choices for gear lubes, both synthetic and non-synthetic that are appropriate for use in our transaxles. I have had excellent success with the tried and true Swepco 201 80W-90 gear oil everyone has been using for years, but many do seek the benefits of a synthetic hypoid or gear lube.

For transaxles that call for a GL-4 spec gear oil, I have had excellent results with Amsoil's fully synthetic GL-4 gear lube, not to be mistaken with a GL-5, which is "backwards compatible." Another excellent GL-4 is manufactured by Redline, MT-90, which is a true GL-4 75w90 gear oil.

For transaxles that are compatible with GL-5 spec gear lube, you have many choices. Swepco for starters, being the most popular choice for gear lube among most Porsche owners. Another favorite of mine is Delvac 1 75w90 (previously known as Mobilube SHC), not to be mistaken with the Mobil 1 gear lube found at your local flaps. This stuff is the factory GL-5 fill from Porsche and is an industry standard in semi / mixed fleets, where a limited slip differential is not employed. For transmissions with limited slip differentials, there are numerous choices available like Motul.
 
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Originally Posted By: bror jace
"Does anyone know if the motul 300 75w90 ls is safe for yellow metals used in the Porsche synchros?"

Yes. It is rated GL4 so you won't have an issue with it attacking the syncros.


I would dare say that it is "THE BEST" in that weight GL-4 fluid catagory, especially their non-limited slip stuff with it's 230 (??) VI.
BUT, you DO pay big $$$ for it!
frown.gif
 
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FYI Motul 300 is a GL-4 / GL-5 spec fluid so it is NOT really a
dedicated fluid.

Folks often times don't realize that it isn't just about whether or not the fluid could cause corrosion with the GL-5 spec, many of these now use nonactive sulfur additives which do not react with yellow metals like brass, and copper.

THE BIGGER ISSUE TODAY IS THAT MOST GL-5
FLUIDS DO NOT have the correct friction modifiers to offer the best performance in synchronized transaxles and COULD cause faster wear to components.

Bottom line....if an application calls for GL-4 use ONLY
a product that states it is a pure GL-4 spec.

Products that call themselves "GL-4/GL-5" or "GL-4+" are one size fits all that usually is not a good solution.
 
This is interesting. I didn't realize that there were other drawbacks to GL-5 in a GL-4 application other than the yellow metals issue.

Now I have another question then: Are the friction modifiers that make GL-4 behave differently from GL-5 the same kind of friction modifiers that make a fluid LSD or non-LSD specific?

i.e. if I go for a GL-4 fluid that's got LSD additives, is that likely to give me the same synchro issues (wear not corrosion) as a GL-5 would?

Or, does GL-4 by it's nature mean it's generally ok for limited slip differentials?
 
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With all these questions, what is the reason that is compelling you to use a non-OEM fluid here? Is there something you think that is inferior about the Porsche fluid that you think an aftermarket fluid addresses?
confused.gif
 
The OEM fluid specs are somewhat contradictory. There were several transmission variants, some with and some without LSD. I have not seen any mention yet of LSD specific fluid (is it unheard of for an LSD transaxle not to call for LSD additives?)

My owner's manual (from 1989) says: Hypoid oil SAE 80 labeled "For Service API/GL 4 or MiL-2105"

The factory workshop manual supplement for the turbo cars (printed 1991) says: "Hypoid transmission oil SAE 75W 90 to API Class GL 5 or MIL-L-2105 B or SAE 80 to API Class GL 4 or MIL-L-2105"

The transmission section of the factory workshop manual (general, not turbo specific) (printed 1991) says "Hypoid transmission oil SAE 75W 90 to API Class GL or MIL-L 2105 B, or SAE 80 to API Class GL 4 or MIL-L 2015" (note that they omitted the number after the GL rating, either by mistake or for some other reason).

The service manuals do not actually seem to mention any specific brand of fluid.

I have not been able to find any hard facts which explain why the owner's manual says one thing and the workshop manual says another. Regardless, it doesn't specify whether or not it needs LS additives.
 
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I think that omission in the factory workshop manual was a simple mistake, it was the same paragraph you indicated from the factory supplement (75w-90 GL-5)

I would follow the recommendations from the owner's manual because it was the original fill in your Porsche. 80w GL-4

Castrol, Shell, Febi, and Pentosin offer the fluid you need and you can use 75w without a problem. I would DEFINITELY go with a
GL-4 ONLY spec fluid.
 
Understood.

Is the lack of limited slip additives a concern? I am not sure if additives are more necessary with different types of LSD. I do fully recognize that none of the manuals I have make any mention of needing LSD fluid.

I'm also not 100% sure what type of LSD this car has (due to my own lack of knowledge) , I have this exploded diagram of it. I know it's 40% lockup.

psYwcA6.gif


I have some Pentosin MTF-2 on hand for another vehicle, looking at the bottle that seems to be a 75w90 GL-4.


Is the following correct regarding GL-5 vs. GL-4?

-A key difference is that GL-5 has more 'extreme pressure' additive (usually sulfur based).

- Most recent GL-5 fluids use a deactivated sulfur which is safer on yellow metals. Active sulfur in older fluids was a factor in corroding bronze synchros/yellow metals.

- The EP additives work by bonding to the teeth surfaces of the gears under heat/pressure, and creating a solid protective layer. This layer then wears/peels off sacrificially, and protects the gear surface from wear.

- This EP additive/process also happens to the bronze synchro rings. Because there is more of the additive in GL-5 fluids, and because the synchros are made of a softer metal, when the additive wears/peels off the synchros, it takes with it a few microns of synchro material each time.

- Supposedly this higher concentration of additive contributes to faster synchro wear.
 
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