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MG Midget and Sprite Technical - Differential.

Ive a standard 72 1275 midget. Dont know what diffs fitted but i'm wanting to get the revs down on motorways and fast roads. Has anyone changed the diff to a "rev friendly" one and from what vehicle did it originate ? If possible, looking for a straight swop, not changing halfshafts and the like.

G Bewick

'72 should have a 3.9 as supplied from new. Post August '77 Midget 1500s have a 3.7 which is better for M-way cruising. Riley 1.5s also had the 3.7.
David Smith

Don't expect to find a cheap one!


3.9 to a 3.7 is a straight swap, but it wont make a huge difference. Its around 200 rpm drop in 4th. A nice little improvement, but it wont turn your Midget into a motorway cruiser.

There is a company in Germany named "Bastuck" and they make 3.55 ratio crownwheel and pinion sets (and many other ratios). I can not remember the price but I think it was reasonable. I cannot comment on quality or service because I have not dealt with them. Of course a big expense is setting it up in your housing unless you can do it yourself or have a tame mechanic friend.

Bob Schapel
R L Schapel

I've been running the 3.5 from Bastuck for a few years now. It currently works out at 220 and I think I payed another 15 delivery. As you say you need a transmissions guy to properly set it up but I was lucky - he did it on the spot and charged me 40. I then sold the old gears on eBay so it worked out quite well.
f pollock

I am fine cruising at 50mph on A-road, but still being curious...
=> Did you feel a big difference on 1st,2nd and 3rd in term of acceleration ? I am wondering if the "win on motorway cruise" worth the "lost on B-road fun".

Maybe with a good head, good camshaft and good manifolds, you can have both :)
CH Hamon

It does take a little off the acceleration and I find myself reaching for 5th gear occasionally, but that's more down to habit as I run other cars with 6 speed gearboxes. Overall it's a slightly less frenetic drive and more relaxed at higher speeds, but I think you would need to have 80 BHP+ to make the best of it.
f pollock

15 for delivery? The last time I bought a standard 4.2 it was 15 for the diff itself! That was only 15 years ago. Mind you I had to rebuild it. It's still in the car and running perfectly. No I am not offering a rebuild service :)

Memories, memories. When I bought the Frogeye in 1978 I was very pleased with its performance on tarmac autotests and sprints. But I did wonder why everyone on the motorway seemed to be speeding. Yes it had a Morris Minor diff.

L B Rose

get some earplugs, crack on. A decent 1275 will hum along at 3-4000rpm for ages, no worries.
Rob Armstrong

I have a rebuilt 3.5 diff fitted to my 1970 Midget, which I purchased from Heathrow Transmissions in Hounslow 16 years ago! Never regretted it. 3500 rpm at 70 mph. Engine is tuned so still better performance than standard.It is a straight swap.
Geoff Mears

This thread was discussed between 30/06/2019 and 07/07/2019

MG Midget and Sprite Technical index

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