Is 90 (GL5) replaced by 75W-90 (GL4)?

[1975DCS]

Is 90 (GL5) replaced by 75W-90 (GL4)?
Some oilmanufactures rate 75W-90 as both GL4 and 5.
And a straight 90 seems to much more hard to get...
Or if they have a straight 90, they talk about suitable for heavy machinery...

So is it safe to put 75W-90 (if it is an GL5) in the rear diff as well?

[4WheelDrifter]

AFAIK GL5 can be used in the rear diff, but the gearbox oil must be GL4.

[1975DCS]

What is AFAIK?
Can this product for example: http://www.lubadmin.com/upload/produ...lang_1/198.pdf be used for both?

[4WheelDrifter]

AFAIK = As Far As I Know.
I'm sure there are some oil recommendations around here somewhere.

[4WheelDrifter]

Ah, yes. Try here and here.
Good old Porkkis.

[PeteRR]

GL4 and GL5 are seperate specifications rather than a supercession of specs.
You use GL4 in the gearbox because GL5 oils meant for final drives were originally too 'slippery' for proper operation of gearbox synchronisers, also GL5 would attack some soft yellow metals often found in gearboxes.

Oils that state both GL4/GL5 specs are supposed to be suitable to use in either.
When I changed the oils in my quattro I used Red-Line lubricants. They have seperate oils for each application. I used 'MT90' which is a 75W-90 GL4 synthetic oil in the gearbox/front diff. And '75W-90 Gear Oil' which is a GL5 synthetic oil in the rear diff.

[4WheelDrifter]

BTW, don't spill any gearbox oil on yourself. No one will want to come near you for weeks. BTDT It stinks!

[1975DCS]

Unfortunately Redline is very bad available and if you can find it (through a biker shop) it will cost a small fortune. That it strange because in America they are relative cheap given the Dollar Euro exhange rate, you would expect it to be even cheaper here. 10 US Dollars equals about 20 Euro when it comes to Redline it seems...

I did read some of those Gearbox threads and it seems in this threads that you can only use GL4 (75W-90) in the gearbox and both 75W-90 or 90 in the diff as long as it GL5 right?

I was affraid that the oilmanufactures were saying "our oil is this good it can cover 2 GL rates"... And although 90 seems the same as 75W-90 when hot I had my doubts...

So I can use the 75W-90 from Elf (see previous link) without any problems allround or should I also order this heavy machinery 90 oil: http://www.lubadmin.com/upload/produ...lang_1/504.pdf

[PeteRR]

If I had to use one of those two Elf oils, I'd go for the 75W-90.
Although they both state truck or agricultural use primarily which would have me possibly looking at other, more road car orientated options.

[1975DCS]

On the 75W-90 Technical Data Sheet at least VW and Audi are mentioned...
But the 90 is a different one. Funny enough I have found similar on other 90 oils...