correct diff oil capacity for my Caterham 1700 Supersprint (de Dion, Sierra diff.)

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tomp164's picture
Last seen: 1 day 19 hours ago
Joined: 20/09/2022
correct diff oil capacity for my Caterham 1700 Supersprint (de Dion, Sierra diff.)

The web says 0.9 litres is the correct amount to put in, as does the build manual, (though it doesn't specify which diff this applies to). However, I've put a full litre in and the oil isn't yet up to the filler plug level.  About 1.2 litres came out!  Was it previously overfilled?


Geoff Brown
Geoff Brown's picture
Last seen: 19 hours 19 min ago
Joined: 17/04/2014

Ford Diff Fill to overflowing approximately 1.2 L. 

Filling to overflow with a Sierra Diff is no problem having owned several Sevens with the Ford unit. The problem is with the BMW Diff where the recommended fill level is approximately 0.9L. The original instruction for the BMW fill was also to overflow - approximately 1.1-1.2L but subsequent problems with output seals leaking caused CC to 'create' an easy fix by reducing the fill amount.

Fortunately Sierra Diff output seals are far more robust.

BUT raising a car on axle stands for the Winter does impart strain on the output seals whichever diff though it would be the BMW that would ultimately fail.

aerobod's picture
Last seen: 2 hours 44 sec ago
Joined: 17/04/2014

With the BMW diff, it the seals are pushed in all the way against the bearing retaining circlips instead of being flush with the diff face or the diff isn't centred such that the driveshafts can move out when they are fully articulated instead of remaining in full contact with the side bearing, you can get leaks. If the shafts are properly located in the seals, there shouldn't be any leaks - not a single drop from mine in 35,000km, including storing on axle stands in the winter.

This BMW diff with the BMW seals that Caterham fit is fitted to millions of cars, without any leak issue that seems to be documented as a problem.