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MG Midget and Sprite Technical - No power to rear wheels

My 1978 1500 midget suddenly stopped sending power to the rear wheels. I was pulling into traffic. The engine kept humming along through 1st and 2nd gear, but the car might as well have been in neutral.

The clutch is relatively new (12,000 miles) and I have even fewer miles on a rebuilt differential. It still goes smoothly in and out of all five gears without any grinding or complaint.

With the rear end up on jacks, I put it in 1st gear and the prop shaft spins and the rear wheels do, too. But back on the ground it just revs in 1st without turning the rear wheels.

My fear is that oil gotten on the clutch disk or pressure plate (or both?) and it's now slipping, but that's just a guess.

Any ideas?
D Steves

It's probably a half shaft that's broken. Much simpler to repair!
d cusworth

Have an assistant sit in the car and, while you watch the prop shaft, put the transmission into first gear and let out the clutch. If you see the prop shaft moving and the rear wheels are not, you have twisted off an axle. Not an uncommon problem with the Sprite/Midget.

Les
Les Bengtson

If the prop shaft is turning then it would be either a half shaft broken or the diff Kaput

However if the propshaft does not turn then the issue is the clutch
Bob Turbo Midget England

>>while you watch the prop shaft, put the transmission into first gear and let out the clutch.

Hi Les

How does DS watch the prop under these circumstances? A hint would be good!

A
Anthony Cutler

"Have an assistant sit in the car and, ...put the transmission into first gear and let out the clutch."

Les assumes that DS has better eyes than Anthony!

FRM
FR Millmore

You don't need an assistant.

You already know it's not going anywhere, so start the engine and put in gear, let clutch out, and get out of car. Lean down and take a look.

Was the sudden lack of forward motion of the car accompanied by a loud bang or similar? Each time I've snapped a half shaft, that's what I've heard, but that was on other cars.

Amazingly I can't recall the last time I snapped my sprite half shaft(s). But then again I no longer drop the clutch like a rabid teenager trying to impress with squealy tyres and smoke. :) I still keep a couple of spares just in case though.
Lawrence Slater

When I snapped a half shaft there was no bang, just lost drive. It happened on a straight bit of road while accelerating when inside rear wheel slipped over a manhole cover. Very undramatic.
frogeye Gary

You don't have to start the engine to do this test though. After jacking up the car (and supporting it safely on jack stands), rotate the driveshaft with one hand while you hold one tire still with the other.

Because of the open differential, one tire will rotate and one will not, if everything is OK. With a broken halfshaft, the side that is broken will spin free, while the other one will have noticeable resistance still coming from the differential.

With a broken halfshaft, there is possibility of broken metal pieces loose in the differential gear oil, so be sure to flush out the rear axle housing real well too, before you drive the car again.


Norm
Norm Kerr

Even worse, with a broken diff (usually spider gears seized to their shaft then one shatters) there are bigger bits of teeth flailing round that can wedge themselves in the CW&P, ruining them too. Don't ask how I know, all happened too quick!

So for that reason I do the engine-off test. Jack one side at a time with the car in gear. If only one wheel turns and propshaft doesn't, then it's that halfshaft.
If both wheels will turn (when only one in the air at a time) and propshaft doesn't, then it's the diff.
If the propshaft turns it's the gearbox or clutch.

As per others, safe money would be on a halfshaft.
Paul Walbran

Just a little elmers glue and all is good agian...ahahah
Prop and the Blackhole Midget

I can't believe I'm saying this, but I am rooting for a broken half-shaft!
Lawrence: No loud bangs or anything to signal that I was in trouble...just a matter of no longer getting any forward movement with the car in gear.
I'll try the recommended tests and report back this weekend.
D Steves

Hi,


Is the speedo registering still? If it's a snapped half-shaft the prop is still turning and the speedo will work even tho the car is standing still!


No speedo equals clutch/gearbox problems.





SR Smith 1


Just back from following all the recommended tests. Most point to the diagnosis of a broken half-shaft (Most likely on the left/driver side). Based on all your input and what I found, here's why I'm leaning that direction:

-With engine on, both wheels off the ground, and car in first gear, prop shafts moves and the L wheel does not spin. The R wheel is spinning pretty weakly and haltingly -- I can stop it with my hand. (Les's and Bob’s test)

-With engine on, both wheels on the ground and car in first, prop shaft moves and the car stays put (Lawrence’s test)

-With engine off, and both wheels off the ground when rotating the prop shaft, the L wheel spins free and the R side resists. (Norm's test)

Everything points to the L side half-shaft, right?

However, I get results that point to a different diagnosis when I jacked one side at a time with the car in gear and the engine off (Paul’s test).
My results: Prop shaft turns with either side lifted. L wheel spins free and the R side spins, but with some resistance. Following Paul's thinking, that would suggest a problem with the gearbox or clutch.

And when I did SR’s speedo test, the needle jumped to about 10 mph, but didn’t behave as if the car was actually running down the road…even when I revved the engine, the needle just hovered around 10 mph.

So what do you guys think --- disregard the somewhat contradictory (or at least, non-confirming) results on the one-side-at-a-time test and the speedo check, assume that there’s sufficient evidence to point to the half-shaft and pull them out to take a look?
D Steves

Just do a couple of test cos I am not sure of what you are saying.
Put car in gear and jack oneside

Try spinning that wheel that you have jacked up
if it turns freely then it is a fair bet it could have a broken halfshaft, if it will not turn then everything would seem to be ok

Do the same with the otherside

If both wheels turn when jacked up and car in gear then it could be that the diff is damaged and stripping is required. Removing the halfshafts and diff is not difficult so no worries
Robert (Bob) Midget Turbo

Hi again,


Fortunately removing the half shaft is easy on a spridget.


Wheel off, brake drum off, undo the screw holding it in and gently prise it out, be ready for a bit of oil spillage.


The broken one will be obvious, three quarters of the spline will be stuck in the diff!


You'll have to take the diff out to tap out the broken bit, but not a tough job.
SR Smith 1

I had a friend who broke his half shaft but not the usual 2/3 of the spline. His flange broke off of the shaft. Easy fix since he didn't have to pull the diff. But that's the only time I seen a half shaft break that way. My four required diff removal.
Martin Washington

Easier to pull the rear axles than the engine and transmission. Hence, start at the easier point and, if necessary, progress to the harder. Be unfortunate to pull the engine and tranny, replace the current clutch, then find the problem still exists. Have not hear of Bob's method of checking for a broken axle before, but it makes sense and is easy to do.

Les
Les Bengtson

I'd say Bob's test is definitive, with the addition that if the wheels turn with some drag and the propshaft turns, it is forward of the diff. If the wheels turn and propshaft does not turn, it is halfshaft or busted diff. If the speedo only goes to 10mph in gear running, wheels off ground, then the drive from the engine is slipping. Most likely clutch driven plate is dead, or possibly pressure plate, but that should feel odd to the foot.

FRM
FR Millmore

If the prop turns with no drive to wheels:
Jack it up, take a wheel off, pop the brakedrum off, remove the screw and slide the halfshaft out to check, then check the other side.
If its not a halfshaft, must be the diff.
Quicker than drive tests.
Bob T

Thanks to all of your advice. Pulled the left-side half shaft and it was indeed broken off. Guess I'll be fishing some metal bits out of the dif and then getting on with getting my Midget back on the road.


D Steves

Bottom one is too short - you been cheated!
Seriously. wash the other and examine under magnification, or get a dye penetrant crack test kit, or best, take it to a machine shop and have it Magnafluxed.
Fairly deep wear notches (crack starters) at the spline ends, though it hasn't been abused much. Still easier to know and get two now.

FRM
FR Millmore

A strong magnet is useful for collecting bits of metal from the axle casing.
Dave O'Neill2

This thread was discussed between 29/06/2012 and 05/07/2012

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