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MG MGB Technical - Vibration in front suspension

I have a 69' MGB with 130,000 miles on it. When the vehicle reaches about 70 mph (yes, that is the speed limit on I26) it starts to vibrate violently. At 68mph it is smooth whith no rattles or noise. The vibration dies off at about 75mph and comes back around 80. (I recognise the answer is easy- slow down, but it is the principal of the thing!) Most of the vibration seems to come from the front end. The tires are new and were balanced less than a year ago, all weights are still in place. I just thought this was an odd situation and was looking for some insite. The front end has never been rebuilt, could this be the problem? or more likely an untrue wheel? The car has wire wheels for what its worth.
Robert

Probially the wheel balance. You should have the tires speed balanced on the car. This would cause a vibration @ 70 MPH. As for the front end, if you have 130,000 miles on it I would suspect at least the rubber bushings are worn, if not the spindles too. You can check the wheels by jacking it up and spinning them as fast as you can. If you have a good eye any signicant amout of warp should be present.
J Arthurs

I had bad steering wheel wobble for the life of one set of tyres, it was fine both before and since. Also if there is vibration *without* steering wheel wobble it could be a shock absorber gone one side, although IME this also causes pulling to one side under heavy braking. Balancing on-car seems a lost art, at least in the UK. And modern wheels are meant to be balanced using the centre hole, Rostyles just weren't manufactured acurately enough for a technique that hadn't been invented then and must be balanced on the stud holes. Neither can the modern machines balance centre-lock wheels accurately unless they hold the wheel on the inner cone on the inner face but the *outer* cone on the outer face. The machines often can only hold the wheel on the inner surface both sides.
Paul Hunt

As strange as this may sound, a member of our club recently had new tires (tyres?) put on his TR6. Couldn't get one balanced....Tire appeared to be okay...A tech in the shop told the balancer guy to ensure he was balancing the tire while it was spinning in the direction the wheel would travel while on the car...Balanced out perfectly.

John
John Staub

I had a similar problem once after some tyre fitting. Turned out that in the "musical chairs" exercise with the wheels one had ended up on the front that wasn't exactly straight. Finally spotted this on the third rebalance when the guy lifted the cover on the machine before the wheel stopped rotating. It was then obvious that there was a very slight but distinct "wobble" on it.
Tim Cuthill

Robert,

From what you say, it may be a bit of both - the wheel/tyre and the front end. My 79 had wheels rebuilt and new tyres - put on & balanced by the same people who did the wheels, but this only reduced, not eliminated the 70 mph vibe. What fixed it fully (at about 120k miles, not too different from yours) - and increased the driving pleasure 100% - was a front end rebuild (rebuilt kingpins and V8 bushes, etc).

It's obviously worth rotating wheels around the car to see if this makes a difference - after all, with 5 wheels, you must have some variation.

FWIW
Kevin Kelleher

"balancing the tire while it was spinning in the direction the wheel would travel"

But they *always* put the wheel on the machine the same way regardless.
Paul Hunt

Robert, I don't have wire wheels but some people I know with wire wheels have taken or shipped
their wheels and tires to Hendrix Wire Wheels in Greensboro, NC. They all say that after Alan does
the wheels there is no shake at any speed you want to drive. The on car balancer works if you can find
someone that can use one. Most shops that have one would have to look for the balancer and blow the dust off and try to find someone in the shop to use it. Look for a senior citizen owenr mechanic because the younger guys don't normally know how to use them. If you really want the shake out it's best to let
the shops that service wire wheels do them, not cheap but they get rid of the shake.
http://www.hendrixwirewheel.com/
FWIW, Clifton
Clifton Gordon

Thanks alot, your suggestions are certainly worth a try, I greatly appreciate your input. I have a feeling that my wheels aren't true because I can hear one in the rear squeaking. If one is untrue then inevitably the rest arent also. And with a meager 130,000 miles on the car a front end rebuild is probably also a very good idea. Again, thanks alot.
Robert

This thread was discussed between 03/10/2002 and 06/10/2002

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