MG Midget 1275 Diff (3.9)

[deccle]

HI All,

I have been suffering from a noisy diff for quite a few years now and have changed the diff oil a couple of times, then added some Moly-Slip into the diff casing, which made no massive difference in the noise. The noise is ok less than 40 mph. The car is an MG Midget 1275 from 1971, and I have owned it for nearly 10 years. Last summer I had the gearbox overhauled and I rebuilt the engine myself and bought new carbs.

This year I am going to attempt to address the diff issue, so looking around for ways to do this seemed to be massively expensive, so I decided to try pot luck and get a reasonably good looking one off E-bay, which I did for £140 (3.9 ratio) visually this looks ok, with no visible wear to the teeth. I did spot a possible fibre thrust washer in two pieces under one of the sun wheels.

Now, for the actual question: I was thinking of simply cleaning it and putting it straight in for a try, or should I change the oil seals, thrust washers or measure the pinion to crown wheel back lash?

Has anyone done a walk through on this? And how on earth if I change the pinion oil seal and pre-load the spacer at the front? - just centre pop nut to pinion and change seal

I am fairly experienced on engines and have a good workshop; it’s just that I have no experience of stripping or rebuilding a diff.

[P3steve]

I know what you mean I'm the same with diffs there a bit of a dark art so there's not much I can offer to help only to let you know your PC is working ok as no one else has answered you good luck and keep us up to date on how you get on.

[MinorTC]

I've only changed the diff on my 1970 Morris Traveller, which has the same type diff as a Midget.

It's quite easy; just jack it all up and support securely on axle stands, drain the diff oil, remove wheels and brake drums, undo the screw(s) that hold the halfshafts in and pull them out a few inches - no need to completely remove them, just enough to ensure they're clear of the diff will do.

Then, having dropped the rear of the propshaft, you undo the diff cover bolts and pull the diff out carefully, getting ready to take its weight (they're fairly heavy).

Inspect the inside of the diff casing, and clean it if necessary. Best to use a new gasket when fitting the new diff - carefully remove all traces of the old one if doing so.

Bolt it all up, slide the halfshafts back in and reassemble brake drums and wheels.

Remember to put the correct amount of new EP90 oil in the diff before trying to use it!!!

[outdoorjoe]

ever seen "an mg was born" presented by Mark Evans, they restore an MGB one episode ther recon the diff and was very detailed and helpful! worth getting the series (part of the an ..... was born" series!

[JPB]

The clip's available on youtube somewhere. For a vet he made a darned good diff builder!

Ah, tried to embed it here but only got a load of code.
Have this handy LINK instead. The diff job comes at around 5 minutes in.

[outdoorjoe]

Thats the one! great series caught it when i was off work ill one week, missed the last one so never saw it done but seen a picture.

certainly useful to me so worth a watch as it covers the resto start (from purchase) to finish in quite extensive detail!

[Martin Evans]

In additon to the above, if you look in some workshop manuals, it tells you that the halfshaft gaskets have to be the right thickness, so that the halfshaft grips the wheel bearing but at the same time providing a seal. Most of the gaskets you get these days are too thick and when I asked about grades ones, nobody had heard of them, so I made my own. My Midget has Rostyles; I'm not familar with the set up on wire wheel models and apart from the length of the halfshafts, it's much like the Morris Traveller.

My father has a 1275 Midget and I have pondered about the 3.7 CWP, as a simple way to raise the gearing. I wonder how the 1275 would cope with this. Later 1500s had the 3.7 and were still undergeared (Which is why I fitted an overdrive) but the 1500 had a bit more torque.