Gearbox oil

[S2_avant 19930325]

Trying to get some info on what oil to use for the gearbox. For exaple ,, im thinking of motul gear 300 ,, but its says GL4/GL5 ,, and in a thread i found that you should not use GL5 .. Hmmmm what to do ? and how to think ?

There is Motul gear 300 LS (limited slip) also ......

Best Regards

[Chris5044]

This is what i used from the research on this forum and works well in front and rear diffs and gearbox.

[steve briance]

GL5 can damage syncromesh.

There are no syncro rings in rear diff hence why GL5 is specced.

GL4 for gearbox. Pick your favorite from whatever brand you favour.

[S2_avant 19930325]

I found this ...

Does that mean that the oil is a GL5 oil ??

• Standards : API GL4 and GL5 / MIL-L-2105

[steve briance]

I saw that as well and to be honest, ive no idea what they mean by that!

Additives in GL5 can eat away at the syncro rings. Do those additives make it GL5, i dont know.

There are other GL4 oils which will work.

[S2_avant 19930325]

Castrol Transmax Manual Transaxle 75W-90 1L

Castrol Transmax Manual Multivehicle 75W-90 1L

Does one of these work ?
On the gearbox there is the "middle" diff , it uses the same oil , right ?

[Chris5044]

This is what i used from the research on this forum and works well in front and rear diffs and gearbox.

Hey guys, is this oil gl 5? its what I have in mine??

Gear 300 motul SAE 75w 90 Fully Synthetic

EDIT:
It states it is both GL4 and GL5... is this bad??

[Chris5044]

Castrol Transmax Manual Transaxle 75W-90 1L

Castrol Transmax Manual Multivehicle 75W-90 1L

Does one of these work ?
On the gearbox there is the "middle" diff , it uses the same oil , right ?

i think both diffs use the same oil yes

[Chris5044]

Ok on further research, its best to use GL5 in the rear diff and specifically GL4 in the front transmission (GL4 doesnt contain harsh additives that GL5 contain, which can damage brass parts in the transmission.. )

Then its discussed that GL4 and GL5 with motul 300 is still fine for both diffs, saying that the new oil isnt corrosive and works well.

So its a stalemate here, Would need more information, but its saying its ok to use.

Heres: the post and thread on another Audi forum.... ....

https://www.audizine.com/forum/showt...300-75w90-good

link to oil:
States safe for ALL transmissions
https://www.opieoils.co.uk/p-899-mot...ntial-oil.aspx

EDIT: I have now emailed motul to get an answer

[steve briance]

Hopefully motul will reply and with some sort of explanation as to what makes their oil acheive 2 different standards one which suits gearbox and one which doesnt.

As there are a huge number of alternatives from quality producers, why use something that leaves question marks?

[Nobbly]

I think the GL5 and GL4 differ in their copper strip corrosion test result limits, if the oil states that it is both GL4 and GL5 compatible then I wouldn’t worry as it must pass on both standards. GL5 I believe has other advantages such as wear reduction on gear teeth due to better EP additives.
Do your homework, buy a reputable brand and change it more often than the manual says!

[S2_avant 19930325]

How do you mean ? "Do your homework" , your advice is change it more often the the manual says. That is not fact based info , that is just a opinion.
Change how often ?? Why change it often from first place ? Isnt it better to buy correct oil instead of change it often ?
And that is not proof that is going to work.

The way to go is to ask , like Stever did ,he mailed MOTUL.
Thats doin homework.

[Nobbly]

If you use your car every day the factory intervals are fine, for most of us that isn’t so hence my remark. If you want to leave the lower half of your synchro rings in potentially corrosive oil whilst the car is parked up crack on.
I mainly meant do your homework on the oil, i.e. what is the result of oil ‘A’ on copper strip corrosion versus oil ‘B’, what EP additives are used, what is the lifespan before the additives degrade or drop out. Yeah you can ask the oil manufacturer but remember to take with a pinch of salt as they are in the business of selling oil, not saving old cars.
I work on wind turbine gearboxes which contain several hundred litres each so oil selection is very important… and some of the oil manufacturers claims versus our experience differ slightly to say the least!
So as ever it’s your car your choice, but make sure it’s an informed one.

[S2_avant 19930325]

Hi Nobbly ,, Chris5044 wrote "GL4 doesnt contain harsh additives that GL5 contain, which can damage brass parts in the transmission"

You wrote... think the GL5 and GL4 differ in their copper strip corrosion test result limits, if the oil states that it is both GL4 and GL5 compatible then I wouldn’t worry as it must pass on both standards. GL5 I believe has other advantages such as wear reduction on gear teeth due to better EP additives.

Just so i understand .... if a oil can pass GL4 AND GL5 ,, ,and GL5 is not recommended. How can GL4 and GL5 be ok ?

[Nobbly]

Hi S2,
The GL standards are most likely wider than corrosion only, tbh I’m not familiar with all the details but they’ll include viscosity index, pour point , shear strength etc…
It will be possible for a single lubricant to pass both standards, but how close they are to the lower limits will take a bit of digging to discover.