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MG Midget and Sprite Technical - Diffs and Gearboxes and Oil - Oh My!!

I admit it right away - I'm confused.

Perhaps I am going blind, but I just can't find the drain plug for the diff in my 1979 US midget. It is in the middle of a LHD to RHD conversion here in Australia.

All the diagrams, etc in my Bentley manual (as well as the diagrams on Moss) tell me that there should be a bolt with a "square hole" at the exact bottom of the diff . . . . but the bottom of my diff is smooth, no indentations or bolts. Very confusing.

I am also changing the oil in the gearbox while the engine is out of the car, and need some advice on the bottom drain plug. It won't screw all the way in, and leaves some thread sticking out of the transmission tunnel. Is this right, or am I just setting myself up for some extra oil leaks??? Don't want to force it, in case I do damage.

Photo attached of the drain bolt for the transmission.

Oh my . . .


w butler

I have to admit I took the transmission bolt out to drain the gearbox when I took out the engine a few months ago, and can't remember how it looked at that time.

Oh my . . . !!
w butler

according to the drawing in my factory Parts Catalogue the drain and fill plugs for the gearbox are square male

so looks like someone has changed that one at least but no problem as that plug is easier to fit, as long as the thread is the same and you'd know by now if it wasn't

no they don't go in all the way

same with the r/axle drain and fill plugs which were square female, now 3/8" hex female

the replacement plugs I have for r/axle stick out a long way and only go in a couple of threads

might sound silly but do you have the rear axle right way up

best way to drain oil if possible is to get it as warm as possible so as much oil and muck comes out as possible
N Atkins

perhaps you have a non-standard or different r/axle as the drain and fill plugs are quite obvious

my factory Parts Catalogue is (1976) marked February 1977 and lists overseas variations but I don't think the r/axle casings change after that anyway (?)
N Atkins

something the handbook probably doesn't tell you is that the later 1500 axles did not have a drain plug; either the improvement in oils over the decades meant it could be pronounced 'sealed for life' or they realised they had developed a 'constant loss' system and you just keep topping it up ;-)
David Smith

I was looking in the factory (76) Parts Catalogue

I suppose it changed when they changed ratio sometime in 1500 run

I've only got the 1275 owners Handbook, if either of us had the correct Driver's Handbook I'm sure the information would be in there :)
N Atkins

I'm not sure exactly when it was deleted, but I've had a couple of late 1500s without a drain plug.
Dave O'Neill 2

David . . . now I've got my sanity back - there is no drain hole.

I have three manuals and none of them mention the lack of drainage???? The Bentley especially gives information on the 1979 US Midget, and even it doesn't mention the lack of a "plug".

Is there any way of knowing what oil I need to keep topping up with? I've got EPX80W/90 ready to go but not sure of mixing oils??

Thanks everyone on the information on the plug not "screwing" all the way in. I can now fill up the transmission with the EPX80W/90 and start fitting all the bits'n'pieces ready to put the motor back.

w butler

if you look in the archives there a big debate on what goes in gearbox and r/axle

the ones with a plug now get EPX80w/90 - or a long debate other opinions are available

personally if it's fill for life (bet they didn't allow for 32 years, or care about it) I'd empty out as much of the present stuff as I could and top up with something fully synthetic - they'll also start a debate
N Atkins

Let the debate begin. I can use some sort of syphon to get as much oil out as I can. I wonder if mixing with whatever was put in there "for life" will cause problems with the new stuff.

Might even be worth starting a new thread to see what happens. I actually bought the EPX80/90 through reading that long debate.


w butler

This thread was discussed between 18/10/2011 and 19/10/2011

MG Midget and Sprite Technical index

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