Differential Oil?

[greymrj]

Sure the answer must be on PH somewhere but I can not find it. Diff lost all its oil last week (I am going to do a post on that disaster as soon as I have photos) but what do I put back in? The 'bible' quotes GL5 LS90 but that is an oil for limited slip diffs which are on V8's and a very few V6's. Mine is not an LS diff.

The oil that came out appeared to be an non synthetic hypoid, I would guess at 80 grade. (Certainly smelt like it as it spread out!)

I have found some evidence that the correct 'modern' oil for this Ford diff would be GL5 FS 75w/90, which is a fully synthetic.

I know that few people change their diff oil but does anybody know for sure what is right for my S1?

[phillpot]

Have a look around Opie Oils website for some advice, might be worth looking under Sierra as well as TVR.


My old Haynes Sierra manual says SAE 90EP to API GL5.


New (second hand) diff or were you able to repair it?

[greymrj]

Yes, I am inclined to use the 'old' oil choice in what is essentially an old diff, one which was designed to specifications essentially 30 years ago. I very much doubt that TVR modified the diff internals in any way so if it was good enough for a V6 Sierra it should still be fine. I will ask my motor factor friend if the are any advantages in the new oil, if not then hypoid 90 is going in.
Fortunately for me the diff casing damage was relatively minor and I have just been waiting for an aluminium casting 'putty' to cure before refilling it and going on a test drive. Disaster indeed but it is now clear it could have been a whole lot worse. I will post with more details and pics as soon as I get a chance.