which diff oil Austin A40 axle?

[geeeman]

unsure which diff oil to use in my Ginetta which has austin a40 open diff

millers classic?

[skeggysteve]

Fairly sure that cars of the A40s age would use straight sae90 gear oil in the diff and gearbox.

[BritishRacinGrin]

My guess is GL-4 EP90.

[john2443]

Yes, checked in the Sprite manual, EP90.

[caziques]

Sulphur and phosphorous additives used in modern EP oils attack copper based products.

Invariably older differentials had copper thrust washers, hence using GL5 can result in aforesaid washers disintegrating.

Many years ago Unipart used to do a semi-synthetic GL4 EP90.

[Incorrigible]

I've got a feeling the thrust washers in these were fibre, but I can't remember

Yes yes, I'm really helpful, I know

Anyway your requirement for GL4 depends on this as explained above. It's just a lot easier to get hold of GL5 these days

[opieoilman]

I think the original spec would have been a SAE90 GL4, but things have changed a bit. I can't think of a SAE90 GL4 that is available any more, but if you go for a GL5 oil from a reputable company, the additives should not attack the metals. The other option is a 80w-90 GL4 oil, the only difference between that and a SAE90 is that the 80w-90 will flow a little better when cold.

Cheers

Tim

[nta16]

I wasn't going to bother to post this but as opieoilman has posted I'll back up his post with my experience of running classics as dailies for about 200,000 miles in 20+ years and the oils I've used, so fully road tested rather than just ideology or bar, internet 'wisdom'

for years now with Spridgets if you asked for diff oil you got given 80w-90 GL-5 spec

GL-5 is fine for the diff

the modern alternative is longer lasting oil with reduced cold weather drag such as Castrol Syntrax Longlife 75W-90 (GL-5 spec) or Mobilube 1 SHC 75W-90 (GL-5 spec)

I've used fully synthetic 75w-90 GL-5 in my present Midget diff for the last 3 years and it's yet to wear out but I expect to be told it will expire, same when I used fully synthetic Mobil 1 in my classics's engines I was told by old fart classic owners, that hardly ever drove their classics, that my engines would be spoilt yet I done many 10,000s of miles and the engines were fine

if modern things frighten you then you can still get Castrol EP90

ETA: note opieoilman it's on your site!

Edited by nta16 on Tuesday 25th February 10:56

[geeeman]

hi thanks guys

i went with the castrol ep90 gL4 as a safe bet

want to use the car on the road a bit this year if the weather holds up

[nta16]

be nice to see that on the road

you're probably not going to be using the car in the cool weather so the thick stuff will be fine (apart from adding a very little to the transmission losses) and it might keep the noise down from the diff

have this to give you an idea of the 'thickness' of different oils

[nta16]

drain and refill every 6,000 miles that's well over the top even for me, that company must have stock to shift

most classic owners would change it every sixth decade !