diffs

Post by **CornishWoody** » Mon Dec 08, 2008 4:49 pm

Hi everyone , Sorry to ask what may be the obvious , but where do the 3.9 & 3.7 diffs come from ? MG Midgets ?? & if so does that mean the same PCD as a Marina ?
Thanks
John

Post by **rayofleamington** » Mon Dec 08, 2008 5:03 pm

Midget is the likely source of a 3.9 and Wolseley 1500 (and maybe Riley) are likely source of the 3.7.
That's far from an exclusive list though!

Post by **mike.perry** » Mon Dec 08, 2008 5:16 pm

According to the Haynes Midget / Sprite manual, the 1275 Midget used a 3.9 diff and the 1500 Midget used the 3.9 and then the 3.7 diff. If the car was fitted with wire wheels then it would have had knock off hub nuts. As the diffs are removeable from the axle the PCD does not matter.
Diff ratios are stamped on the crownwheel.

Post by **IslipMinor** » Mon Dec 08, 2008 5:31 pm

John,

3.9 diffs are fitted to the 1275 and early 1500 engined Midgets, and the 3.7 to the later 1500 Midgets and all Wolesley 1500 and Riley 1.5.

Not sure what you mean by PCD? The diffs are all the same fitting pattern, and can be fitted to any axle with a slight caution. None of the 3.9 or 3.7 diffs had the oil filler on the side (I think?), so will need to have the oil filler on the back of the axle, which the Minor did on later models, but not earlier. Fitting an earlier diff into a later axle gives you 2 fillers, but a later diff into an earlier axle gives no fillers!!

The wheel PCD's are all the same at 4" on all the axles, but the Midget axle is narrower, so is not suitable for a Minor.

Does that answer the question though?

Post by **plastic_orange** » Mon Dec 08, 2008 5:46 pm

You just fill them up through the breather tube with the correct quantity of oil if fitted to an early axle.

Pete

Post by **CornishWoody** » Mon Dec 08, 2008 8:51 pm

Thanks guys ... i know what to look for now ..

Post by **bmcecosse** » Tue Dec 09, 2008 11:27 am

Yes - 3.7 diff from Wolseley or Riley - or later 1500 Midget. Just to add to the thread - ideally with a 3.7 diff fitted (and standard size 14 wheels/tyres) you need a speedometer with a 'tpm' of ~ 1236. There is a reasonably common Mini speedo with tpm of 1248 - I just bought one on ebay for £3 and so with this fitted the speedo will be possibly 3 % slow - but most read slightly high anyway - so I expect it be virtually correct.
tpm = turns per mile, and is noted on the speedo dial in small letters usually near the mileometer readout. For example - before I fitted my 3.7 diff, my car had a 4.55 diff - and a 1508 tpm speedo - and was ~ 1% fast on mileage.
The Mini speedo looks very similar to the Minor speedo - but does have one extra (green) warning light position at the top of the dial - may be useful for anyone fitting reversing light or rear fog warning light.
Edit -And this one on ebay appearsto be 1248 tpm - even better !
http://cgi.ebay.co.uk/austin-mini-speed ... 240%3A1318

Post by **NIGEL15** » Sat Feb 14, 2009 10:11 pm

I wondered if anyone could help me on the subject of diffs.
Having got the minor back on the road after 20 years of restoration, well alright 19 years in the pub and one year restoration I fitted 14'' alloys to it with 185/60r14 tyres as supplied by Bullmotif. The trouble is that its now all revs and no top end speed. The speedo is inacurate aswell but I can handle that. Does anyone know which diff would sort out the problem or would it be better to fit a 5 speed box ?

Post by **bmcecosse** » Sat Feb 14, 2009 10:28 pm

Can't see the tyres will be that much different to standard tyres - although 60 aspect ratio is a bit too low - 70 would have been much better. 5 speed box conversion is very expensive near 4 figures unless you can engineer/do it all yourself. Just get a 3.7 diff (~ £70) - it slots straight in -took me about 2 hours in total to swap mine. Then look for a 1248 tpm Mini speedo - mine cost ~ £3 from ebay, and fitted in about 1 hour. It works !

Post by **mike.perry** » Sat Feb 14, 2009 10:34 pm

Depends how much money you have and how much work you want to do.
A 5 speed box will probably cost getting on for £1000 with all the bits and pieces although a 2nd hand one will be cheaper. There is probably a lot of work involved in fitting it. Can't be specific because I've never fitted one.
You can pick up a Midget diff for £50 -£150 and it will take less than 2 hours to fit including cups of tea.

Post by **bmcecosse** » Sat Feb 14, 2009 11:25 pm

Here's a 3.7 diff on ebay! http://cgi.ebay.co.uk/MG-midget-Sprite- ... 240%3A1318

And - here's a 3.9 - they tend to be cheaper! http://cgi.ebay.co.uk/morris-minor-3-9- ... 240%3A1318