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MG MGB Technical - Bad vibration

I've been having a bad vibration in my 74B for about a month now that seems to be getting worse. There is a low pitched rumbling sound and I feel the vibration thru my seat, steering wheel,pedals,shifter,and the glove box door rattles terribly. Its getting almost undrivable. It seems to come on at 40mph and above with 40-50 mph being the stongest resonance. I've revved up the engine while parked upto 5000rpm with no vibration but under no load. When I take my foot off it on the road it lessens. I'm pretty sure its in the drive train and suspect eithr universal joints or a wheel bearing about to go. I have some fluid getting into the right side drum andhave replaced the axel seal a couple times in the last 15000 miles or so. If these symptoms sound familiar I'd sure appreciate any feedback to see if I'm on the right track.
Bob Ekstrand

Could be a wheel bearing going bad. Causes vibrations, noises and a wobbly feeling in the steering and else where. Antidote: Listen to the Beach Boys more often to get rid of the 'Bad Vibrations' Sorry, I just couldn't help myself or Rhonda.
Mike MaGee

Is it at all sensitive to engine load? If it happens coasting in neutral at speed, but is better under braking then its a wheel bearing. If it is worse under engine load it could be a rusted, seized u-joint. A badly bent driveshaft might do it, but then given the position of the driveshaft in the car bending the driveshaft seems a hard thing to do.
Andrew Blackley

Yeah, bearings, driveshaft, unbalanced tyres, a slightly skwed rear axle, or maybe even a few loose bolts. Or any combination of those or others.
glg

Could be a belt slipped in a radial tire.
CW Strong

Bob - I just had the same symptoms on our 67 MGB. Several weeks ago I started noticing a vibration accompanied by a rumble. The next day the vibration and rumble seemed to have gone away and I forgot about it - bad move. Last week on our way home from Seattle (70+ miles), late at night in the rain, the vibration and rumble came back and preceded to get worse as we continued to drive. By the time we reached the half way point, it got so bad, we stopped and called AAA for a tow home. The next day I got under the car and tried the U joints and both seemed fine (no slop in the rotation), then I pulled on the back of the drive shaft and got almost a quarter inch of movement side to side. Seems that one of the bearings had pushed out and allowed the cross to move back and forth. I suspect that if we had tried to drive on home, I would have ruined a drive shaft. The rear U joints on our cars seem to be rather short lived, so I would check that first.
Good luck - Dave
David DuBois

Sounds like prop-shaft UJs to me. When my front one seized anything above 40 caused a bad vibration, below that only the gear-lever went up and down!
Paul Hunt

I have been down that road. I would say if you drop your driveshaft and check your U-joints your will find the trouble. My U-joints looked fine until I got the driveshaft down. One, just one cap had NO bearings in it and just a little dust. A new set of U-joints front and rear may fix you up.
MY BEST
THE BRITT
Dale
Dale & Barb Mast

This might be another idea. Check the retaining nut that holds the drive flange to the transmission main shaft. The lock washer may have failed and the nut has come loose. See if there is excessive play on the flange itself. This happened on my B and I drove it 300 miles at 40 mph in the middle of the night to get it home. Lucky it didn't grenade on me and there was no significant damage when I repaired it.
Kevin

Thanks for all the input. I pretty sure now the trouble is in the u joints. Not to long ago I replaced a u bolt on the axel but I did not tighten it enough resulting in rear end steer problems and I was hit from behind as well recently. I think with the age of the u joints the additional stress and torque loads may have done em in. Is replacing them an easy job? I got an estimate of $175 from a local shop if no other work was needed. That seemed high considering the parts are about $30 from Moss. Anyway thanks again all!
Bob Ekstrand

Bob - The replacement of U joints is more fussy and dirty than hard. I normally pull the drive shaft myself and take it and a set of U joints into a local drive linen shop. I just did this and having him replace the u joints and balance the shaft came to about $65. I suppose that you could look at the remaining $110 of the estimate to be labor to remove and replace the drive shaft (also a dirty and fussy job). Good luck - Dave
David DuBois

This thread was discussed between 13/12/2003 and 15/12/2003

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