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MG MGB Technical - suspension vibration

I bought a 78'MGB several years ago that needed much work, I have rebuilt the engine, replaced the rear suspension with tube shocks, replaced the bushings, hubs, wire wheels and tires, had the driveshaft straightened and u-joints replaced, and so many other repairs too numerous to mention. The car oriiginally had a bad vibration at 30 mph, now after the replacement/rebuild of these parts, the car has a noticable vibration at 60-75mph. About the only thing I've not done is replace the wheel bearings. The vibration doesn't really seem to come from a corner of the car, thus my original thought of a bent drive shaft. Before I had it rebuilt the u-joints were just trashed. Anyone with similar problems or ideas?
Rick Gray

a wheel out of balance, or out of true?

double check all nuts and bolts?

Wear in the rack and pinion?

that's all I can think of at the moment.
glg gimbut

I just replaced the wheels and hubs because previous wheels were out of round. I had the wheels checked for out of round/untrue and actually sent two of four back to the factory because they were out of true. The wheels are all balanced well, I spent quite a bit of time with the wheel guy. The wheels were balanced in accordance with wire wheel spec's. I've not done anything other than replace the boots on the rack & pinon. The car runs as true as can be even at high speeds when the vibration is very obvious. All the nuts & bolts have been checked & double checked. I just can't figure this one out & I can't turn the radio up to get rid of the simptoms.
Rick Gray

Rick, you mentioned not replacing the wheel bearings. I've read in a past thread where someone's front end vibration was cured by replacing the old wheel bearings. May be worth a try.
Joe Ullman

Yeah, as Joe says, what the heck! Put in new bearings and races.

And as I think of it, might it be possible that the front spindle nuts are not torqued to spec? (or, that there's been some wear in that area.)

Really, this should not be a major or serious problem, (unless the floors and sills have rusted some, that being that the structure has been compromised by corrosion).

Jack up the front so both wheels are free and wiggle them, to and fro, back and forth.
That might give some indication.

Good luck and keep on posting till it's fixed.
glg gimbut

I have a similar problem with my 69 B. The vibration occurs at the same speed and the vehicle tracks true. My front wheel bearings have been replaced, but i know for a fact that my wire wheels weren't balanced correctly and they are untrue. But my car also has in excess of 132,000 origional miles and no front end rebuild.
Robert

Rick,

I recently cured a 60 mph vibration by replacing my driveshaft. There was a lot of play in the spline. I would think the people who straightened yours would have checked this, but it only takes a second to double check it yourself.

Also, you may want to check your rack and pinion and tie rod ends for play. I'd also check for a broken tube shock, or lever shock out of fluid.

While you're down there, check for broken or loose motor mounts or gearbox mount, and for loose mounting anywhere on the crossmember.

Believe it or not, check that your brake drums and disc rotors are not out of round. I once had a warped brake drum that would just barely rub the shoe twice per rev. Once you got on the highway, there was one speed where it would set up a noticeable vibration.

Matt Kulka

Out of round tires can cause a vibration. I get my tires trued up after riding on them for about the first 100 miles and you can't believe what a difference it makes. You also can't believe how out of round the tires are - every brand and not just on the same car. Also an out of balance brake drum can cause a nasty vibration. I went nuts on a 240Z I restored to figure out where the vibration was coming from and then a lightning bolt hit and I found the problem. BTW, does the vibration have the same rotational speed of the wheels or at a higher rotation rate like from the driveshaft? You can usually tell from the seat of your pants
M Landskroner

Rotate you tires front to rear one side at a time, see if you get any change in the way it feels-Ric
Ric

Rotate them one side at a time and see if it changes.
After two trips to the tire shop and them telling me they were balanced, that fixed mine. Or, showed that they were wrong anyway.
There is a special mounting needed to balance the wire wheels. Most shops don't have it or don't have someone that know's how. For the most part, they don't want to spend the time it takes to make them right. They want to blame everything else but their work.
Been through it many times with a Xk120, TR6, MGA and now the MG

Kelly
Kelly Combes

Is the vibration at the steering wheel ir in the car as a whole? I had steering wheel vibration at the speeds you mention for the life of one set of tyres despite repeated rebalancing, no problem before or since.
Paul Hunt

Rick,
I have vibrations in my car aswell. I traced my problem to non centered bores in the front wheelhubs. "Ìnherant from factory". On my car the problem is visuable as different thickness of the material surounding the center dust cover. Spin the rotor with wheel off and check for radial runout.

Good luck
Erik
Erik

Erick is right on.

This is somehting that is fairly unique to our cars rostyle wheels and even good alignment shops miss it often.

This problem will cause the ballance weights to actually make the wheel less ballanced as the center of ballance is calculated at the incorrect moment.

The center hub hole under the cap is not actually true to the outer rim. The lug holes were the point of reference when they were manufactured.

Please check the archives, there is a long discussion of this there.

To verify this, you can try a couple things.

1.) find a place that offers 'on car' wheel ballancing. (rare anymore, more common in europe) The reasoning for that it takes the rotors and all rotational weight into account. The guy sits on a litte cart with a spinning wheel. I have seen it done, but for the life of me can not figure out the physics behind it. (There were several who reported finding places in the archives). Terry in New Orleans was the closest to me in Pensacola.

2.) go buy a spacesaver spare tire from a junkyard from a saab 900. (good replacement for the spare and frees up space in the boot) Move it to all 4 corners until you isolate the wheel with the problem. This will only work if you have only one bad wheel.

3.) If you are in a club, find a friend who might be willing to allow you to swap on a set of wheels to isolate the problem. (gonna be a good friend.)

Hope this helps.

If you rule this out, I vote for the rack, and kingpins.
Craig Amos

I appreciate everyone's advice, I have thought more about some of the advice and have previously ruled out some of it. I'm fairly sure the problem is not the wheels. I just replace the WIRE wheels and bought new tires yet the car has the same symptoms as before so I've swapped out tires & wheels. I replaced the rear hubs recently but that didn't have any affect from the previous set. (The old wheels and tires needed to be replaced for other reasons.) I feel certain the problem isn't engine related because without the driveshaft there is no vibration in same gear at same speed. It also has new motor mounts and all bolts have been checked. The car vibrates from the seat not the steering wheel, the body has a noticable shake at high speeds. I have ordered wheel bearings and will try that angle. I still feel the problem is driveshaft or axles, I haven't noticed any odd brake wear. There is slight play in the wheels once jacked up. Is there suppose to be any play to & fro? This is especially true on the front wheels. I haven't checked torque on front spindle nuts yet. There just isn't enought time in the week.

Thanks for the ideas.
Rick
Rick Gray

This thread was discussed between 23/04/2003 and 29/04/2003

MG MGB Technical index

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