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MG MGB Technical - vibration at 2500 rev

My 1967 mgb roadster has developed vibration at around 2500 rev but stops when I take my foot of the accelerator. It could be many things but any ideas to solve this would be appreciated, it started about six months ago all of a sudden I stopped the car as I thought it was a flat tire, but it now is getting worse.

Thanks Bob.
RR BLACKSHAW

Bob, is this engine speed or car speed related? Does it happen in neutral, clutch in / out? How did it develop, suddenly or gradually?Guys here need such info to help you.
Art Pearse

Yes more info; it started suddenly, 6 months ago getting worse, at 2500 rpm but not in deceleration, ( engine related? drive train under load.) Sounded like a flat tyre, so bad enough to worry about? So we need to know; does it happen with car standing still ( perhaps removes some drive train out of the equation.)Try then the clutch in/out bit. etc Mike
J.M. Doust

Bob. Different car but same problem. Vibrates when engine under load but not when foot of throttle. My daily runner a little Ford Laser does that, I have tracked it down to loose baffles in one of the mufflers. I'll replace one day!

Tony
Tony Oliver

The easiest to check and easiest, cheapest to cure fault is a propshaft UJ, more likely the rear one.
Allan Reeling

Is this a physical vibration felt more than heard or the other way round?

Propshaft was my first thought as well, although that would be more road speed related than revs. If it's in 3rd and 4th at least at 2500 rpm then it's got to be engine/clutch/gearbox. Have you checked the mechanical fan? Does it happen at a constant speed or only when accelerating by a significant amount? If the former does the vibration continue if you leave your foot on the throttle but dip the clutch? And of course if the former does it do it when revved at a standstill?
PaulH Solihull

Just had this happen this summer with my '71 B. Leading up to the eventual failure, it had me really wondering what on earth it was... and it was the prop shaft (drive shaft).

It finally gave up the ghost when the U-joint knuckles blew apart, dropping the shaft on the engine side. I'd been greasing the U-joints, but I guess it was just their time to finally go.
Dave Cardoza

This thread was discussed between 06/11/2011 and 08/11/2011

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