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MG MGB Technical - Body Gyrations at speed

Two years ago, bought 77 MGB with bad suspension. never had the car over ~ 45-50MPH. Finally got suspension parts replaced and a ~$45.00 alignment.

at ~ 65MPH the body gently gyrates. no feel in the steering wheel, just the body.

after market wheels 185X65X14 tires. The mechanic noticed deep scar marks on the inside of the front wheels because of the old tie rod ends.

don't want to replace tires to find out it is the wheels or replace tires and wheels to find out it is something else. anyone else have a similar experience?

Ron

First and foremost, if you have deep scar marks, I'm surprised the mechanic let you out of the shop without replacing the tires. You should consider replacing them out of safety.

Second, you've probably already ruled this out, but just in case: Are all of your highways grooved pavement? Some tires are worse than others about following the grooves and this can cause some odd sways and darts.

Third, have all of your wheels balanced. If you don't feel the gyration in the steering wheel, then if it's a wheel balance problem, it's probably a rear tire. But it doesn't cost much to balance a wheel, so why not do all four and make sure.

If after this, it still gyrates, then roll your car in neutral down a gentle hill at about 5 mph. Make it a gentle enough hill that you don't have to use brakes. If you feel a sway like riding in a railroad car, then chances are good you have a bent wheel or bad tire.

I checked my wheels by getting the car off the ground, then attaching a long zip-tie to a jack stand and using that as a pointer against the rim. Point it to the base of the bead area (not the very edge of the rim). Turn the wheel slowly and check for side to side runout as well as out of round.

A wheel whose cords have been damaged internally (like by a hard thump to a curb or pothole or possibly gashing by a tie rod end) will often show it with bulges in the sidewall or tread, or occasionally with a tread that snakes side to side. While you're checking the wheels, eyeball the tires for these symptoms as well.

Hope this helps. If not, you can always sign the car over to me. You wouldn't want the headache, and I'll take it off your hands free of charge.
Matt Kulka

Track rod ends rubbing on the inside of after market wheels is not unheared of. At one time you used to be able to get smaller track rod ends to solve this.

You say it gyrates. I assume this is a low frequency rocking motion. Possibly a slight rotationalor diagonal rock with no noise associated with it. If so I would sugest you check your dampers.

There are a number of ways of doing this. The easiest is pushing down on the corner of the body and letting go. Alternativly, at the back you can disconnect the drop links and push the leaver arm up and down. If there is little resistance or it differs from one side to the other you will need new ones. When new they are quite stiff.

You don't say if you used new dampers or not.

David
David Witham

This thread was discussed on 31/08/2004

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