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

[wolfestone]

I talked to the dealership service department today and they couldn't really tell me what fluid to use, seeing as it's an older car and they don't really deal with many of them any more.

Whether or not I need limited slip additives is the part which has me most confused at this point.

 

[MolaKule]

It looks like you could use Motul Gear 300 LS 75W90.

You shouldn't need any non-slip additives with this lube.

Modern MTL chemistries have a buffering agent to guard against copper alloy attack.

 

[wolfestone]

I just read over your whitepaper on the GL4 vs. GL5 and found it very insightful, thank you.

With the Motul fluids the only things that concern me is the Gear 300 75w90 LS is a GL5 fluid, and the Gear 300 75w90 'regular' is a GL4/GL5 fluid.

I think I'm suitably convinced on the corrosion front, but what about the GL5 / LS friction modifiers vs. the synchros? Is that likely to be a concern over a GL4 fluid?

Thank you all again for the help. I may not be much closer to making a decision but I am gaining a much better understanding.

 

[Lubener]

I used a GL-4 80/90 gear oil in my old truck's manual gearbox.Lots of yellow parts inside. Got it from NAPA and was made by CRC. A gallon was around twenty bucks.

 

[MolaKule]

Quote:
I think I'm suitably convinced on the corrosion front, but what about the GL5 / LS friction modifiers vs. the synchros? Is that likely to be a concern over a GL4 fluid?



No. As I stated before:

"Modern MTL chemistries have a buffering agent to guard against copper alloy attack."

This also applies to GL-5 rated lubes.

In the case of the Motul Gear 300 LS 75W90, it simply has a higher AW treatment rate.

 

[wolfestone]

I'm sorry, I may have misunderstood something from the whitepaper. Thanks for your patience.

In the whitepaper, where it says "Manual Transmission fluids use a different friction modifier specifically designed for synchro engagement, a modifier that does NOT contain the same chemical compounds as do differential lubes."

Are you saying that many GL-5 manual transmission fluids will contain the correct friction modifiers for synchros? i.e. it's the transmission/diff designation of the fluid that would control this, rather than the GL-4 vs. GL-5 rating?

 

[antiqueshell]

@Molakule:

I recall in that white paper that it said the extra/different amount of adds in the GL-5 fluid could actually not corrode the metals but actually WEAR the yellow metal away.

I hope I stated my comment correctly.

 

[wolfestone]

Originally Posted By: antiqueshell
@Molakule:

I recall in that white paper that it said the extra/different amount of adds in the GL-5 fluid could actually not corrode the metals but actually WEAR the yellow metal away.

I hope I stated my comment correctly.


I believe that's consistent with the paper by Richard Widman - iirc it stated that EP additives attach to the gear surfaces then 'peel' or wear off sacrificially. In the case of softer metals (bronze synchros) he suggests that the increased amount of additive found in a GL-5 fluid takes a few microns of synchro material with it as it peels off, wearing the synchros down.

 

[antiqueshell]

@wolfestone:

That's why I would definitely stick with a GL-4 fluid. It was the fluid spec'd when the car was made, and Porsche, and for that matter Audi and VW are VERY particular when it comes to things like this. Actually years ago VW allowed GL-5 fluids to be used when they first came on line, but after problems with what I have mentioned they reverted back to the GL-4 spec.

Don't forget that GL-5 does NOT supersede GL-4. They each address two very distinct applications.

 

[martinq]

Originally Posted By: antiqueshell
FYI Motul 300 is a GL-4 / GL-5 spec fluid so it is NOT really a dedicated fluid.

Gear 300 is a fantastic performing fluid in both GL-4 and GL-5 applications. It can meet both ratings because it uses a different add-pack than is typically found which is why it is listed as:


"
All mechanical transmission, synchronized or not synchronized gearboxes, gearbox/differential, transfer
gearboxes and hypoid differentials without limited slip system operating under shocks, heavy loads and
low revolution speed or moderate loads and high revolution speed.
...
Suitable for any type of seal and yellow material used in gearboxes design.
"


But, it does not seem to have the performance-enhancing additives you usually find in a modern MTF like Synchomesh, Red Line MTL/85/90, Amsoil MTF/MTG and Pentosin MTF2.

In an non-clutch LSD transaxle (with hypoid) I would certainly recommend Motul Gear 300 or Subaru Extra S.