MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

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 - Then it went bang - differential?

Having just reinstalled fuel tank, sender unit, lines and re-calibrated fuel gauge took my 57 for a quick spin 5 or 6 miles topping 60mph at one point. Heading home, smiling with a now functioning petrol gauge and how well the car was going as a I changed down to 3rd for a road junction - BANG (literally) and the car coasts to a halt. engine re-starts fine but car wont drive away, revs drop to a near stall in any gear. On a slight incline I let the car roll backwards into a drive way. Starting the engine I tried pulling off again but same as before engine revs drop but no movement. Tried reverse and going through all the gears I hear/felt a knock from the transmission , now in gear I can release the clutch completely with zero effect . My thoughts where that the clutch had disintegrated but RAC patrol guy jacking up the car and rotating each wheel in turn declares the problem to be with the differential maybe half shafts. Car is towed the short distance home no problem with wheels turning. I had, had the car jacked up one side at the rear for a couple of weeks while gradually sorting out the fuel tank so maybe a problem with lubrication in rear axle after this time - one side dry because of the angle. Anyway can anyone suggest any easy tests or sequence of tests please? My first move was going to be to remove and check the shafts but is it more likely to be part of the pinion set?

Kevin
K Garner

Does sound like a half shaft. If you jack up the rear of the car, turn the wheel on one side and the other should turn in the opposite dirrection, if it doesn't, it's going to be a half shaft or something in the diff. A half shaft is easy to fix though a little bit expensive at around £100 from Moss.
Lindsay Sampford

I had something similar happen two years ago. I upshifted from second to third and suddenly found myself coasting to a stop. Putting the car in gear with the enging running, the drive shaft turned freely but the car didn't move. Everybody told me it HAD to be an axle. Turned out that the casting of the differential "pumpkin" had a defect and picked that day to finally let go. I had a second pumpkin in with a box of parts, and one of the sides of it was cracked loose, too. This, supposedly, NEVER happens. :-)

The upside to this story is that when the differential went out, a friend and I had just gone past a local Mom N' Pop grocery store. So we walked back and got some beers to enjoy while we waited for the tow truck. Another local MG owner drove past and saw us, and came by with even more beer. So something good can come of any situation...


David Breneman

I am a little confused at your comment that "revs drop to a near stall in any gear". That doesn't sound like a broken half shaft. A broken half shaft would put no load on the engine so it would rev freely in any gear but the car would not move. Sounds like something is locked up. If you are saying that initially it wouldn't move and bogged the engine down, but now it revs freely but won't move, then unfortunately that sounds more like a broken diff.
Jeff Schultz

Dave my diff broke just like yours did on my coupe back in 1975. Dumped the clutch going around a corner and it went bang. Picked up a used assembly for $15.00.
Those were the days.
R J Brown

RJ, add two zeros to your amount, and you'll approximate what it finally cost me to get my car back on the road. I had the work done professionally, thinking it was just the axle, and my garage wasn't wide enough to pull both axles out. At least I got a nice 3.9 gear ratio out of the deal.

I lost a differential in the late 70s on my 68 MGB in much the same way. I had parked, got distracted talking to my friend (needless to say, not on a cell phone) put it in reverse, forgot I hadn't shut off the engine, and released the clutch quickly with my other foot firmly on the brake. At least I could limp home in the forward gears. I bought the whole rear end at a junk yard for about $100. (Contemporary photo, taken in my parents' car port, attached...)


David Breneman

Agree with Jeff's observation, but it is possible that the rough edges are enough to load it. Could also be a gearbox failure, same idea.

I broke the carrier casting on my '57 ZB in '68, had a clear casting defect in it. I was still able to drive it, but it sure thrashed about. A spare MGA one was at hand.

Start it up and have someone look under to see if the propshaft is turning while in gear - if so, it's the diff or axle. If not, gearbox. Not recommended that anyone actually be under the car, in all or in part, while doing this!

FRM
Fletcher R Millmore

Regardless of where the problem is you will need to remove the prop shaft so do that first. Once this is done you will be able to tell whether it is g'box or diff. The cast iron diffs on MGA era BMC cars had a propensity to fail (my Worseley 15/60 diff failed many years ago) no so sure about aluminium diff centres on MGAs.
Mike
Mike Ellsmore

Thanks for the suggestions, yes Jeff your interpretation was correct at the first bang the engine stalled and then it seemed as if the whole transmission was locked up there was no way I could pull off - like trying to pull away with the handbrake full on. Strangely the car would roll back, it was only when I tried pulling off in reverse that I felt another slight nock through the transmission thereafter I could release the clutch completely with no effect. Back in the garage I ran the engine up and clearly the prop shaft is turning through all the gears but no effect on the axle but a definite rumble from the diff. Have just removed both half shafts and they are fine and splines intact. So I’m assuming it something like you experienced with the diff casting David - comments welcome. This is all new territory for me so any advice would be useful. I’m assuming prop shaft and differential removal are next steps - is this within the realms of a novice mechanic?

Kevin
K Garner

With the axles out it is easy to do now. Just undo all the bolts around the pumpkin center section and withdraw the housing. You will see the problem then. Be certain to completely clean out the housing including the axle tubes. Those little pieces go everywhere.
Sandy
SANDY SANDERS

EASY job.
When mine broke in 75 all I had going for me was my Autobooks manual and a lack of money. I had to fix it if I was to drive.
Cleaning out the housing will be the hardest part of the job. With the axles out you are more than half way apart.


R J Brown

May be too late with this: with the car on jack-stands, disconnect the prop-shaft. With the car in neutral you should be able to turn both the prop-shaft and the pinion coupling by hand. The one that will not turn is where the trouble lies.

David Werblow

I found a couple of degreaser spray packs discharged into banjo housing from the ends and from the main opening followed up by the garden hose (or garden sprayer) stuck in each end removes most of the gunk. (a broom handle with a bottle brush on the end can help). Make sure you put a large tray under the diff drain plug to catch all the waste.
Mike
Mike Ellsmore

Diff removed this evening and image below is what I found left in the banjo housing. Image in second post shows what I assume was the culprit pinion shaft.


Kevin


K Garner

Image of parts below, looking at the Haynes Manual I assume this is the pinion shaft that has sheared in half. Casing marked 10/43 so assume this was standard MGA ratio. Looks like I will be looking for a re-built unit.

Kevin


K Garner

For What its worth:

A. Could have been worse. At least its not in the gearbox.

B. You now have the option of changing your gear ratio.

Good luck.
Lmazoway

Kevin, just remember, at least you have the comfort of knowing that this mode of failure NEVER happens! :-)

Sorry -- Welcome to the club.

My nephew who was an engineering major took my pumpkin to a professor at his university. He pretty much confirmed my speculation that it was a bad casting. It just took 50 years to finally fail. Alas, my nephew now designs golf clubs, not cars...
David Breneman

Kevin,
Just curious, did the car exhibit any symptoms leading up to this? I shudder to think what is would cost if this happened on the way to a GT. Maybe pulling the rear-end down and getting is crack checked is not a bad idea...
GTF
G T Foster

Hi GTF absolutely no warning, just a sudden clunk (I thought one of the batteries had fallen off the tray) and the engine stalled, luckily I was only doing 20-25mph. There’s no trace of the pinion shaft locating pin, no sign of debris of the pin in the shaft hole or cage housing, the pinion casting looks fine, but I see some clash damage on gears. Have been directed to a local transmission company by MGA specialist Bob West to check things over.

Kevin
K Garner

This thread was discussed between 05/06/2010 and 08/06/2010

MG MGA index

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