GL4 or GL5

[ham204]

I was topping up the rear diff on my Sprint with GL4 which I use for all my other classics. I was surprised a few days later to read in the owner's handbook that the recommended oil for both the diff and the gearbox is GL5. So......any harm in leaving the GL4 in the diff?

It's an early (April) 1980 model, by the way.

[tamtrucks]

when i did my diff swap from 4.1 to 3.63 i stuck with gl4,been using it for 8yrs now,4yrs with t2000 when if first got in to triumph`s and 4yrs with dolly,no problems at all

[SprintMWU773V]

Weirdly I was looking into just the same thing for my Mazda only this afternoon. I discovered that a GL5 is actually very similar to a GL4 but that the concentration of EP additives is about 3 times higher, it's not usually used in gearboxes as it doesn't shift as well and can damage brass. Therefore in the gearbox of an MX5 you use a GL4, whereas in the axle of the MX5 you use a GL5.

This doesn't really relate to Dolomite's but as I say, timing is interesting.

In Dolly terms I'd probably stick to GL4 to be sure, it's not like it's hard to find though you'll probably have to go multigrade 80W90 rather than straight 90.

[tony g]

Yes 4 or 5 for axle, but gl4 only for gearbox. As stated gl5 contains stuff that harms brass gearbox parts.

Tony

[ham204]

But its Triumph themselves who suggest GL5 for both diff and gbox

[tony g]

Not according to my copy of the workshop manual. Where does it say GL5 ?

Tony

[SprintMWU773V]

I seem to recall in my handbook it mentions GL5 for both. Still wouldn't use GL5 in the box.

[ham204]

Not according to my copy of the workshop manual. Where does it say GL5 ?

Tony

In the Owner's Handbook - Lubrication section

[tony g]

Ok Ive never looked there. Still would use gl4 in the box though

Tony

[MIG Wielder]

If you look on Page 09-2 of the 1977 Sprint manual for Overseas cars it states GL4 for both diff; and gearbox. For temperatures both above and below 0 Deg C. Did this change for later cars perhaps ?
Tony.

[Galileo]

If you wandered into a branch of Unipart and asked for EP90 in the 70s you would have got GL4. Oh, and GL5 contains phosphorus and sulphur compounds that will turn your gearbox into an attractive garden ornament.

[soe8m]

The modern GL5 does destroy the bronze cupped washers in the diff centre.

There are GL5 oils that don't have that much phosphorus and sulphur compounds and are actually an ep version of a GL4. And there will be some GL4's with a higher phosphorus and sulphur compounds than others. The reason GL5 is not suitable for old type gearboxes is that the oil is too good. The synchro's cannot cut away the oilfilm of the cone and thus cannot brake their gear.

Jeroen