Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Diff again, sorry

I have at last got hold of a 4.3 diff,(to replace the 3.9 fitted at the moment witch i think coupled to an 1800 engine and type 9 gearbox makes it a little long legged) it was advertised on ebay as mga (stamped ATB 7186) and it does indeed look correct but the chap that i bought it from seems to think that it is the same unit that was fitted to a Riley 1500 and i suspect that it is probably from a Riley, any thoughts?, also and presuming that it is correct any advise on whether or not to renew the bearings (which seem fine)before i fit it and i know this may sound a bit daft but advise on a decent joint sealant and diff oil would not go amiss thank you in advance, Vin.
Vin Rafter

Is your old 3.9 unit an good? Wellseal is the jointing compound to use - wonderful stuff. Try Buck & Hickmans site. Oil - an EP80/90 - lovely smell too.
Pete Tipping

You should check that your half shafts fit the new diff since there are a different number of splines across the years. Can not remember off the top of my head but Barneys site will give all the info. If the new diff is wrong you can swap the little gears in the diff that take the half shafts. Count the splines - dont just see if it fits because one combination will go together but strip the splines when you put power through them.
A J Dee


I echo Pete's comment about Wellseal. I bought a 250ml tin. Quite expensive. Easy to apply with an artists thickish brush.

Before you fit the diff, do check that you have the correct splines in the sun gears. If not, check Barney's site for the swap over. Straight forward job.

Worth changing the front oil seal while you have it on the bench. You may need to make up a steady bar to bolt onto the U/J flange when undoing and tightening the pinion nut. See mine:....


Steve Gyles

Vin, if you do end up taking the diff gears out I recommend that you reach into the diff casing and hand fit them back onto the half shaft splines. This is about the only time you can isolate any possible play between the two. I fitted an MGB diff and found quite a lot of play here so I put my MGA diff gears into the MGB diff and it improved. Can't think why the MGB diff gears should be more worn than MGA.
J H Cole


From memory the Riley 1.5 uses the same diff. as the midgets and is even longer legged! The ratio 3.55:1 sticks in my mind but that's from nearly 30 years ago when I had my first Midget. I think the later Midgets were 3.9 and then 3.72 and the Riley diff. was a way to gain a high cruising speed at the time.
Neil McGurk

Riley 1.5 was originally destined to be the replacement for the Minor & was essentially the same floorpan etc)Pretty sure the Riley 1.5 Wolsely 1500 will have used the same axle as Minor 1000/Midget etc with different ratios. In its day the Riley was considered very lon legged (My Troop Commander had one in Germany in the early 60's & it was one of the few british cars that didn't get hot & bothered on the Autobahn...unlike my 1960 850 Mini which howled along at 5000 plus revs & consumed loads of oil!)
DG Harrison

As Steve says Wellseal is expensive. Just get a tube of it, that'll do at least a couple of engine rebuilds... Keep the top closed to stop it evaporating and wipe it off fingers quick before it dries on, then you don't need any solvent. You can take as long as you like after applying to all faces before assembly as it always stays soft. RR recommend it too.
Pete Tipping

If from a Riley 1.5 it's a A series diff, won't fit the MGA axle.

Best bet is to get in touch with the Farina crowd and get a diff from them.

Don't know how you could fit a diff with the half shafts in place either, as the shafts need to be out to mount the diff in the casing, and there's no way to get hands in unless you have arms like a gibbon.
dominic clancy

Dominic, to get the diff out in the first place the half shafts are withdrawn just enough to clear the gears. With the empty diff casing and half shafts pushed back the splined ends are then readily accessible and you can offer up the disassembled diff gears.
J H Cole

Well it looks like I may have the wrong end of the stick once more, please take a look at the pictures and let me know what you think, the stamp on the top of the housing showa 10 over what looks to me to be a 4 and the top of a badly stamped 3

Vin Rafter


Vin Rafter

1 more

Vin Rafter

I don't know which model A you have but there are 3 spline possibilities I think, 8 spline, 25 spline or 26 spline. So it is worth pulling a half-shaft to find out which. I would also suggest that you check the condition of the thrust washers in the diff spider as they are a known wear item and easy to swap if you have to change the drive pinions.
Tony Mitchell

Did you sort out your 4.3:1 diff Vin?

If not, I have just today seen a 4.3 crownwheel and pinion for sale on UK ebay that may suit your own back axle.
(tried to send you an email but it just keeps bouncing back to me!)
Colyn Firth

I have a 4.3 diff for an MGA, took it out of my car when I fitted the 3.9. I am in North Lincolnshire if you are interested.
Robert (Bob) Midget Turbo

The number 10 stamped on the casing means it could be a 10/41 or 10/43. In either case, read the ratio stamped on the crown gear to be sure what you have. Have a good day!

John Progess

Robert, thank you for the offer but I have just bought one via ebay, vin
Vin Rafter

No problem Vin if you change your mind or have a duff give me a call.
Robert (Bob) Midget Turbo

Hi Bob,
I may be interested in your 4.3 diff. Do you want to e-mail me about it?

David JM

David is you address correct? messaged returned by AOL
I am rjwelchmidget at
Robert (Bob) Midget Turbo

Thanks Bob, for some reason my e-mail address did not come up correctly, it is
David JM

This thread was discussed between 14/12/2010 and 31/01/2011

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.