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Right diff oil .
axle - 25/11/21 at 09:09 AM

Hi All
I have been in search of the right oil for my diff. I can not get the recommend oil for the Sierra from a Ford dealer. The diff on my car is also slightly noisy ( Not whining) . After searching high & low I came across this oil can anyone tell me if you have used it or what are your advise on this matter. I am hoping it will be the right oil and also will help the noise.

https://www.ebay.co.uk/itm/154651613514

[Edited on 25/11/21 by axle]

adithorp - 25/11/21 at 11:17 AM

You probably need to tell us what diff you have.

Standard Sierra, Sierra LSD, some other LSD

[Edited on 25/11/21 by adithorp]

axle - 25/11/21 at 11:27 AM

It is 7.5" standard no LSD

big_wasa - 25/11/21 at 12:26 PM

Just a standard mineral gear oil.
I did mine in the summer Sae ep 90 gl4 in mine.

Gl5 has more additives in it.

pigeondave - 25/11/21 at 01:21 PM

Maybe give someone like road and race transmissions a call.

They could probably advise.

sales@rrtransmissions.com

+44 (0)1959 525 105
09:00 - 17:00,
Monday - Friday

you might need to use them if it gets too much

Mike Wood - 25/11/21 at 01:58 PM

Some potentially useful info: https://www.caterhamlotus7.club/forum/techtalk/sierra-diff-oil

Cheers
Mike

axle - 25/11/21 at 02:21 PM

quote:
Originally posted by pigeondave
Maybe give someone like road and race transmissions a call.

They could probably advise.

sales@rrtransmissions.com

+44 (0)1959 525 105
09:00 - 17:00,
Monday - Friday

you might need to use them if it gets too much


Thanks for all the replies, road & race transmissions had the good answers . The noisy diff was more with the prop shaft and related to my own set up, nothing major.
They do have a oil suited to this diff , but the above choice of Liqui Moly - Hypoid Gear Oil - GL5 as above was fine with them.

[Edited on 25/11/21 by axle]

[Edited on 25/11/21 by axle]

mcerd1 - 26/11/21 at 11:18 AM

quote:
Originally posted by axle
but the above choice of Liqui Moly - Hypoid Gear Oil - GL5 as above was fine with them.

I don't think the Sierra / Granada diff's are that fussy - any decent quality 75W-90 GL5 should do it
(unless you've got an aftermarket LSD - Ford LSD's just use the same as the open diff's as the viscous bit is a sealed unit)

any of these would do:
Comma EP80W-90 GL-5
Castrol Transmax Universal 75W-90
Castrol Transmax Axle Long Life 75W-90
and loads of others too...


All the Ford workshop manual call for is SAE-90 hypoid oil [old Ford spec: SQM2C-9002-AA if anyone cares]

The Hypoid oil (GL5 aka: Extreme Pressure) bit is important though, you shouldn't really use GL4 if you want it to last...
Its the offset in the pinion below the centre of the crown wheel (making it a Hypoid) that causes the extreme pressure and needs the extra additives:



on the other side if you've got a type 9 ford gearbox, don't ever use GL5 hypoid oil in it - the same additives that protect the diff eat the yellow metals in older gearboxes (you need GL4 for a type 9, BGH recommend Comma in there boxes)
A lot of people on here have this combination of a type 9 and sierra diff (me included) so you need 2 different oils - don't be tempted to use one in both

[Edited on 26/11/2021 by mcerd1]

axle - 26/11/21 at 12:35 PM

Thanks for your reply I agree and Thanks again for making the point about GL4 ,