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MG Midget and Sprite Technical - Diffs, axles and carriers

The 3.9 diff I’ve fitted to my 1963 midget axle whines - despite being sold as ‘a good un’ by a nice chap on the classified section. I’ve got another 3.9 that probably also needs a rebuild so I thought I’d send it away to Hardy engineering and get it done while still being able to occasionally drive the car with the current one fitted.

The problem is that the carrier (casing) on the spare is badly corroded where the brake line union bolts to it. I have a very nice condition bare carrier but it is the early type with a filler plug. Can I have the 3.9 internals rebuilt into the early type carrier? According to Daniel’s book that might not work but it is rather confusing.

Also will either type of carrier/diff fit in any Spridget axle? Mine is a HAN7 26*** axle so has the filler plug in the axle casing.

Thanks for any info/thoughts.

John Payne

John
Speak to Bill McDonagh at Hardy's. Bill has years of experience with Sprite gearboxes and Diffs and will be able to tell you what he can or cannot do to privide you with a good diff to suit your needs.
Alan
Alan Anstead

Cheers Alan, that's good to know.
John Payne

AFAIK there are a number of differences between early and late carriers, so I don’t think you can swap bits between them.

Any complete diff can be fitted to any Spridget axle.
Dave O'Neill 2

From the BMC Special Tuning Manuals, you can fit the complete differential cage (ATA 7036) into either carrier assembly, but cannot swap parts within the differential cages, i.e. crownwheel and pinion, diff etc.

The complete carrier assembly can also be fitted to either axle case, but the combinations can mean that you end up with either 2 fillers or no fillers!

We have the later cage assembly fitted to the earlier axle case, and have had to add the threaded filler hole to the case.

I tried to upload the ST Manual pdf file, but it shows the BBS instead - bizarre!

Richard
Richard Wale

Thanks Dave and Richard,

Good to know that I can fit any diff to my case, just got to see what can be done with my diff. I’ll give Hardys a ring and see what they recommend. Worst case scenario I’ll just have to remove the one I’ve already fitted, send it away and wait till it’s done.

Cheers all
John Payne

This thread was discussed between 11/05/2020 and 12/05/2020

MG Midget and Sprite Technical index

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