Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing back axle dif lubrication

i have a 1994 morgan 4/4 with a ford 1800 zetec engine. i do most of my car maintenance myself . I would be grateful for any advice as to how often; if ever, the oil in the back axle dif needs to be topped up or changed if , topped up do i need to drain existing, also any advice on which oil to use.and how much to put in . regards sarnia

I think the closest to the original Manufacturer's recommendation is Castrol Syntrax. They do a formulation for limited slip diffs.

I can't imagine that it's particularly critical, though. I have a Quaife Automatic Torque-Biasing LSD in my car, and when I contacted Quaife to find out the correct oil, they told me that as long as I changed it every couple of years it didn't really matter so long as it's a hypoid oil.

It's not an LS diff in a 4/4, so just a decent Hypoid is okay

Depends if it's got an LSD. If not and it's not been changed since new then I'd get it nice and warm and drain it, re-filling with a good quality synthetic gear oil such as Motul 300 75-90. If, however, it has an LSD it needs changing more frequently, at least
every 20k miles because of the wear particles which can adulterate the oil. In this case it needs a different oil compatible with mechanical LSD's such as Motul 75-140 Competition. If you dont know whether the car is fitted with an LSD just jack up the rear axle and turn one wheel by hand. If the other wheel turns in the same direction you have an LSD. If it revolves in the opposite direction you dont. Hope this helps.

If you look at used oil analysis of diff and gearbox oils, the diff oil gets up to 300 ppm of iron in 30,000 miles.

Gearboxes less, say 150 ppm of iron in 30,000 miles.

Yes it is a good idea to change both diff and gearbox oils around 30,000 miles or after 5 years or so as that is the assumed working life oif the oil.

The specification you require is a 75W/90 GL5 oil.

This is thiner at low temperatures 75W and reverts to a 90 grade as the diff temperature increases and the GL5 advises of the Extrem Pressure property of the oil.

Do not use a limited slip diff oil or put in an additive unless you know 100% that you have an LSD diff as the additive tends to a small extent make the oil useful life shorter.

There is no need for a 140 grade LSD oil unless the vehicle is used for racing where the working temperature increases outwith normal.operating temperatures of a normal road vehicle.

I was amazed how dirty my diff oil had become at 9000 miles from new ( 3.5 years) when I changed it. In hindsight I'd have done it after the first year - I expect it'll stay cleaner after the initial change so its going to be a 2 year thing, like the brake fluid, for me.

The mazda gearbox by contrast had very clean oil at the same time/miles, so I think I'll be doing that every 5 years.

If it is an BTR axle, go go the site of BTR and you can read. You also can find it in Gomog.BMW used the BTR axle and they have the correct oil. ( Also in Gomog )

Stefan
ARP4
+4
+8

Here it is


http://www.gomog.com/allmorgan/axlefilling.html

Here is a used oil analysis after 22,000 miles on the Mazda 6 speed box of the same vintage that Morgan use the 5 speed is a bit different to this.

http://www.billswebspace.com/11%20MIATA-TR-041412.jpg

The oil has dropped below the viscosity rating but not by a large amount.

Not that much of an issue at 22,000 miles as long as your mileage says similar to what you are doing at present as you will then hit around 22,000 miles.

If you have the facilites at home to change it. I would maybe do it sooner and use either Redline MT90 or Castrol Syntrans as that tends to give a slicker change in the Mazda boxes from changing the oil in a good number of them.

I’ve been thinking of changing my diff oil as it is just approaching 30,000 miles since the ratio was changed. 2011 4/4 so assume BTR. I see Rimmer are selling Castrol SAF-XO Final Drive Lubricant which GoMog say is correct. Can anyone confirm as garage just say sae90. Also anyone got a picture of the rear of the diff showing drain & fill points as on mine they are not immediately apparent.