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MG Midget and Sprite Technical - Rear wheel issue

Hi all,

Please can anyone advise what may be causing the issue I have with regard to the lack of drive to the rear wheels on my late 67 Gan 4 midget.

When I was out driving the car last it lost the drive to both rear wheels.
The current condition of my car is that the engine starts up and runs fine,
I can depress the clutch pedal and select all gears, the prop shaft rotates but the car doesn't move forwards or backwards.

Other than stripping down the rear of the car, is there a way of testing if it could be a half shaft issue on one side or both sides or something else which may be causing the problem?

John
J Bond

Jack up the rear and spin one wheel. The other one should spin the other way. If not, you most likely have a broken half shaft. It could be a broken pinion gear, but that's rare. It did happen to a Marina I ran (as company car I hasten to add, I wouldn't buy one), but they don't have the same diff.
Les Rose

Sounds like half shaft broken. Looks like half shaft out each side to check.
MG Moneypit

And both halfshafts and diff will have to come out anyway if you want to clean out the debris to prevent it getting into the bearings, or worse - lodging between crown and pinion.
Paul Walbran

Thanks for your help.
I rotated both wheels with the car raised up but there wasn’t any wheel movement on the opposite side.
Removed both half shafts but they both look to be good condition, now looking towards examining the crown and pinion in the differential casing to see if they are causing the drive problems and replace if necessary.
Any tips or advice on carrying out this work will be much appreciated.

John
J Bond

The fact that turning one wheel didn’t make the other turn is inconclusive, unless you had the car in gear to stop the prop turning.

Turning one wheel should either turn the other wheel, or the propshaft, depending on how much drag there is on the brake shoes.

If you put it in gear and repeat the procedure, if the opposite wheel still doesn’t turn, you have a problem with either the sun wheels or planet gears.
Dave O'Neill 2

I had a pinion gear with two teeth missing and a third well on the way (cracked most of the way though). Although it did still work!!

Malc.


Malcolm

It's a bit strange, it must have stripped the teeth off a side gear or sungear, It's a wonder it hasn't been making noises

Your pinion looks a bit sad Malcolm--I remember (quite clearly) that i mistakenly left our old racer in gear on the trailer once, towed it 1000Klm to a race meeting and found it had pinged a tooth off the crownwheel on the way--Desperate to race we pulled the side off the diff and removed said tooth and slapped it back together--He was a tiddle clunky at walking pace but once it got moving it was fine---did all the elimination heats and a 100 lap final---i think teeth are overrated----lol
willy
William Revit

Sounds ominous. Next step would be to drain the oil from the diff and see what comes out with it.

What next depends on available facilities - diff can be removed in-situ on axle stands or ramps, but much easier if you have a vehicle lift. If you don't and the check strap bolts will come undone then it may be better to remove the whole axle and work on it in comfort.

AdrianR

The diff cross shaft can also come out DAMHIK. I didn't hear a thing either but just lost drive after lifting off and when reapplied no drive. Chipped a pinion tooth badly enough it was scrap.
David Billington

This thread was discussed between 14/05/2022 and 16/05/2022

MG Midget and Sprite Technical index

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