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MG MGB Technical - 'Clang' not a 'clunk' in rear end

Hi all
I purchased my 1973 MGB GT in April this year. It has Rostyle road wheels and was fitted with the 4 speed non o/d gear box. A couple of months ago I noticed a noise coming from the rear end, more of a hollow "clang" than a "clunk".

The noise occurs at every gear change and also upon acceleration/ decelation. It is also very noticable if the car is placed in 4th. gear and rocked back & forth.

I replaced the 4 speed box with a reconditioned 5 speed unit from a Toyota Supra and fitted a new prop shaft with new universals.

The noise still persisted.

I pulled the diff cover and checked the thrust washers. They were like new but I replaced them anyway along with a new pin, new vinyl diff washers and wheel bearings.

Still the "clang" persists.

I have searched through the archives but cannot find any thread that exactly mirrors my problem.

Any ideas from the experts?

Regards

Graham

G.J. HOYLE

Have you put it in fourth and rocked it with your ear next to the spot while someone else rocked it back and forth? Granted it is low to the ground, but find a spot that is a little higher for the rear so that you can get down there. Just to narrow it down to the spot that the noise originates from.
Mwhitt

Graham,

While I'm not sure the noise you report matches, have you checked to see that your rear shock bolts are TIGHT! They do loosen on MGBs, and under the best of circumstances, need to be checked at least occasionally.

A "clang" as you put it, might be caused by something inside a brake drum striking it. I know percussionists consider the brake drum an "instrument" because of the "clang" it produces. I'm hard pressed to think of something inside that could produce a noise like this (broken adjuster???), but it might be worth your time to pull the drums and see if there's anything broken inside.

Loose splines on a drive shaft could cause a "clang" but since you replaced the shaft, it seems somewhat unlikely that this is the problem - unless you swapped one worn drive shaft for another. At any rate, with the rear of the car on secure jackstands, and with the parking brake released, you might try grasping the drive shaft and smartly turning it back and forth to see if you can recreate the "clang". If it's in the splines, you may see the slop between the shaft and the drive flange as you hear it. Are the splines greased? Pumping grease into it is not a fix, but if it alters the "clank" you have located the problem.

And now I'm out of ideas. Please keep us posted.

FWIW,
Allen
Allen Bachelder

Hi Graham . I hade a clang in my 66 roadster on acceleration and deceleration and found the splines worn on the axels good luck. Alan
alan

Alan,

Do you have wire wheels or road wheels?

Graham
G.J. HOYLE

Have you had the pinion out of the axle case. If so the preload on it may have been messed up and it may be shifting in mesh with the crown wheel.

Although I hope it is something much simpler.

David
David Witham

Check for worn U joints.

My '74 did the same thing you describe when I first got it if I didn't shift 'just right.' My U joints were very worn. Replaced them and the noice went away.


Paul
PR Peterson

Oops. Disregard the above. I see now that you mentioned you have new U joints. You've probably checked already, but be sure all the bolts are tight.
PR Peterson

New parts can fail--never assume something's good just because it's new. Recheck your driveshaft and U-joints.
R. L Carleen

After digesting all of the advice, which is much appreciated, I raised the rear wheels and tried to replicate the noise by turning the road wheels by hand.

No appreciable noise on take up, definately no clang.

Lowered the car to the ground again and, while the car was in 4th. gear I crawled underneath as far as I could and had an assistant (wife) rock the car back and forth.

The clang seems to be coming from the front of the diff but as others have said, it could be resonating from another source.

I have discussed the problem with two MG mechanics and they are at a loss for an explanation.

Unfortunately, an exchange diff/rear axle does not appear to be an option for me where I live.

I'll investigate further over the weekend.

Thanks

Graham
G.J. HOYLE

It is rare, but I have seen diff's where someone has removed the pinion nut to replace a leaking grease seal and then not torque it to specs and crush the preload washer behind the yoke. The result being the pinion getting very loose back there and flopping around excessively.
mwhitt

Oh, to check it for looseness. Out of gear and take hold of the end of the differential where it attaches to the driveshaft and see if you have any movement in any direction. You should have none up and down or side to side, but you may have some in rotation.
Mwhitt

Graham.
wire wheels on the 66 roadster

Alan.
Alan petersen.

Just a thought, do the nuts and bolts joining the driveshaft to the diff have lockwashers on it? Doesn't a clang usually resonate up thru the driveshaft when it is loose to the flange of the diff?
mwhitt

WORK AS MECANIC IN THE LATE SEVENTIES
THIS IS PROBERLY THE PROP SHAFT JIONT UNVERSAL JIONTS

JACK THE CAR UP AT THE BACK AND APPLY THE HAND BRAKE ON
AND START ENGINE AND SLOWY LET THE CLUTCH UP AND DOWN

howard

JUST ADD IF IT STOPS THE PROP OR ENGINE ON GEARBOX MOUNTING, EXHAUST PIPE HITTING SOMETHING ETC
GET SOME TO SLOWY LET THE CLUTGH UP AND DOWN WHILE IN GEAR
AND HAVE LOOK UNDERNEARTH
HOWARD ENGLAND

Graham - were in QLD are you? I used to live in Brisbane and there is a MG restorer/shop on the kangaroo point / southbank side of the river (can't remember the places name or adress at the moment).
N.C. Nielsen

N.C.NEILSEN - I live in Bowen which is about 1000klms north of Brisbane on the coast. There are a number of dedicated MG workshops in Brisbane, many of them I am on a first name basis!

MWHITT - One of the MG mechanics also suggested that the preload washer might be the problem so I will check it for looseness this afternoon.

HOWARD - The uni joints were new when the propshaft was fitted. The clang existed before fitting the new shaft and uni joints.

I jacked up the rear of the car on the weekend, put it in 4th. gear and gave the wheels a good wrench forwards and back. The clang was very apparent.

Regards
Graham
G.J. HOYLE

ive got this problem developing, i checked the UJ's and they have worn a bit but not massive play, and all the bolts were tight. i have wire wheels, im pretty sure that the diff needs adjustment. i dont have time and need the car until thurs. then i have to finish my land rover S1 engine conversion so i can repair the B
d buck

This is probably a silly suggestion but when I had a "clang" in my GT (I also had a "clunk" but that was loose damper bolts) it turned out to be the jack rattling about next to the spare tyre. Wrapped that in an old towel and the noises all went away.

Simon
Simon Jansen

Hi Graham,
I spent a lot of time looking for the clang (more correctly a loud ping)on a customers car about 20 years ago. Rebuilt diff gear thrusts etc. All to no avail. Later on when trying to find thge same noise on another car I found that the diff pinion flange was moving just a few thou on the pinion spline. Removed flange, applied a couple of drops of loctite and reassembled. tried it out 2 hours later & the noise was gone. I have performed the same operation many times since. It is more prone to happen on '77 on cars cos the diff is more rigidly located.
Garth
Garth Bagnall

This thread was discussed between 15/12/2005 and 22/12/2005

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