Diff dilemma?

Post by **lynda** » Fri Mar 20, 2009 10:12 am

Hi,

I'd like to make my car a bit quieter, and lower the revs for motorway cruising. He currently has a 1275 engine, probably originally from a Midget, and standard Minor gearbox.

I'm thinking of going for either the 3.9 or the 3.7 diff, but I don't want to lose too much power at low speeds as there are a few hills round here. What do people think would be the best one to go for? Also any recommendations for suppliers would be welcome, thanks! I'd rather get a new / recon one that works, than risk a second hand one from ebay!

Post by **callyspoy** » Fri Mar 20, 2009 5:50 pm

from my experience (with my dads 1275 powered 3.7 diff car) it pulled it fine. I think it only really would become noticeable driving on a motorway at say 70 and going up a steepish slope then, but at lower speeds it really isn't a problem. incidently he now has a 3.6 Marina diff, and it still pulls great with a standard 1275. revs are around the 3000 mark at 60, which is not too different to a lot of modern cars and doesn't stress the engine, good fuel economy too.
that said, if not driving on the motorway that often, it is probably more worth while going for a 3.9 for the added "zip".

Post by **Kevin** » Fri Mar 20, 2009 7:03 pm

I'd rather get a new / recon one that works, than risk a second hand one from ebay!

Hi Linda that might be a problem without having one to give in exchange and I expect they are not cheap as the 3.9's often sell for £100 and quite a bit more for the 3.7.
If you go to an second hand MG specialist you may get some sort of guarentee.

Post by **PSL184** » Fri Mar 20, 2009 7:19 pm

NOS 3.7 diff's run at about £350 - £400. Recon ones are about £275 but as said you will pay a premium without an exchange item. They are easy to check for wear so if you find one on ebay (about £100 usually) just check there is not any excessive backlash and that the gears turn without a grating or clicking noise. Look at the gear teeth for wear and feel for play / movement in the bearings. If all this is good then it will be OK.

Post by **bmcecosse** » Fri Mar 20, 2009 11:28 pm

May as well go for the 3.7 diff, if you can find one at fair cost! Easily fitted - and there is a handy Mini speedo that swaps in and keeps the readings accurate. You may have to pay ~£100, but it's something that will always hold it's value, so not money down the drain!

Post by **lynda** » Sat Mar 21, 2009 10:00 pm

I think I've got a 3.9 diff around (well, attached to the traveller the engine came from) that I could use as exchange if necessary... and no, it's not any good otherwise I'd have already used it on my car

Still by the sound of things a 3.7 may be the way to go... will have a look at the price difference!