The main weakness of the Seven S2 lay with the Standard 10 axle. The unit is prone to leakage resulting in seized differentials. The problem arise because of the differential housing being prised open under acceleration forces. The location of the axle is constructed in a very simple and light manner. But unfortunately it puts a lot of stress on the axle casing. An A-frame locates the central lower point and 2 radius arms is placed on top near the wheels, causing the axle casing to twist on every acceleration.
Credit to: www.locost.info for the drawing.
My differential was probably broken due to lack of oil. I discovered several cracks in the casing and some of the bolts holding the differential were loose. The crown wheel and pinion was completely ruined, but I was able get a similar differential from a Triumph Spitfire, although the gearing is 4.11:1 compared to the original 4.55:1. Be aware of the Spitfire is produced with 2 axle dimensions - only the early (smaller) will fit with axles in Standard 10 assembly.
Despite the independent rear suspension on the Triumph Spitfire, the car is a good source for Standard 10 rear axle parts. As mentioned the differential can be exchanged as a whole assembly, provided the gear wheels is splined for the early axles. The hubs, bearings and seals at the wheel end is similar, and can easily be obtained from companies specialized in Triumph Parts.
I brought the outer seals (Part No. GHS111) and a set of wheel studs (Part No. 21H5774) from Moss Europe
To renew the outer seals you need to remove the hubs from the axles. This can be very, very difficult - now you are warned. Even with right special tool I managed to bend one of the hubs - so it has to be exchanged.
It is essential to use a classic EP (extreme pressure) oil to GL4 (Hypoid/Hopoy) specification only for the differtial; example Castrol EP 90 (GL4)
DO NOT USE GL5. Virtually all oils now sold are to GL5 spec and will "melt" the copper washers in the diff.
Quantity needed 1.5 pint = 0.7 liter.
Here is a guide to fit new bushes in the A-frame: Bush Replacement
The picture shows the correct way of mounting the radius arms, the small damage near the rubber bush (upper arm) shows what happen if the arm is mounted the other way around.
For some reason the radius arms on my car have been rose jointed at the front mount. This allow adjustment and gives a better location of the rear axle, but problably puts more load on the frame.
The bush was stubborn and very difficult to exchange, so I ordered a new set of radius arms at Redline with the correct bushes fitted.
Ital - 44.18 Kg
English 49.57 Kg - with standard diff casing, saves 4.725 kg with alloy differential housing.