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 MGB Technical - Knocking/Rumble - Please Help

Hi all,
Help, please. My cars not had any problem like this before but I have a noise that started this morning on my '77 mgb roadster, there's a knocking/rumble coming from the underneath of the car what sounds to be towards the rear. Symptoms are, no noise when accelarating away from a stop, however on decelaration i.e. slowing down at a roundabout or approaching lights is when the sound is heard. The noise is audible but not loud & is faster or slower dependant upon the speed of the car at the time of slowing down (no more that 30mph in the morning around Swindon anyway). I have checked the wheel bearings, well moved the wheels back & forth no undue movement on the wheels, suspension feels ok.
Any ideas or suggestions as to what to look for this evening or weekend???
Thanking you in anticipation for your help.

Barry
Barry Simmons

Wheel bearings usually make a pretty constant noise IME, but can be noisy long before any untoward play is felt. The diff or possibly UJs will make different noises according to whether you are accellerating or decellerating or off load. If the noise is independant of which gear you are in i.e. same sound at a given speed whether in 3rd or 4th then it is almost certainly after the gearbox/OD. Axle secure? Exhaust pipe not resting on something? Oil level in diff?
Paul Hunt

Paul,

Thanks for all that info I will put it with the other info I have from "the other side" (MGOC site). The sound dosen't change as to which gear i'm in, only on decelaration through gear change or just slowing down. Most comments point at the mo' to the UJ's, hopefully so & nothing more expensive. But I will also check out the other areas you highlighted & the wheel bearings when I jack the car up.

Cheers

Barry
Barry

First you should remove the drive shaft and have it rebuit as opposed to doing the U-joints yourself. I Jax it costs about $35 to have the drive shaft redone and ballanced. I have rebuit two on different cars. If this doent do it then go to wheel bearing. I bet you dinner that this fixes it.
Drew

It was UJs on mine. Boy, were they shot. I was looking at reconning the UJs, but was told that if the UJs have gone, the splines on the prop (it's telescopic for some reason best known to BL) are probably not far behind. Further inspection proved this to be a fair assesment of the truth. New, not recon, props are available and are not expensive...
Tim Cuthill

It is splined because, as the rear axle moves up and down and the engine moves back and forward under acceleration & braking, the distance between the gearbox and axle flanges changes - a solid shaft would strain the UJs.
Chris Betson

this has the sound of the exhaust touching a part of the frame, as suggested by Paul Hunt

it produces a characteristic buzzing type of noise and often occurs on the overrun as a result of torque reversal moving the engine and those bits attached to it in an anti clockwise direction viewed from the rear

If it has suddenly appeared Check for broken or perished engine front mountings as well as obvious exhaust misalignment (often where the downpipes just make the turn rearwards)

Christopher Storey
chris

This thread was discussed between 21/11/2002 and 22/11/2002

MG MGB Technical index

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