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MG MGB Technical - Shakes at 55mph

I have a 74 B that shakes at around 55mph. I've rebalanced the wheels (Rostyle), rotated the tires, checked the alignment and replaced the drive shaft. The front end was rebuilt less than 10K back, including rebuilding the shocks.

I'm coming to the conclusion that I have either a ply seperation or a bent rim. This leads to a few questions - first how do you check for a bad tire and second how much runout is allowed on these wheels (and where do you measure). And finally, what else might I being missing. This problem is getting real "old"!
Thanks!

Cheers,
Jim
Jim Budrow

Try swapping front wheels to rear and vice versa. See if that changes things. If not, it's probably not the wheels or tires.
Steve Simmons

Jim here's part of one of my mga entries. You'll find many many threads on this in the mgb archives.


The ft end shakes at 55-60 mph. Sometimes it's so bad it feels like the steering wheel is going to come off - then, on the same drive it's fairly smooth. Below 50 it's smooth and above 65 it's smooth. It'll do 80 easy with the B engine. The problem is, it's very transient and it seems to be worse climbing a hill, or driving into a strong wind???

I had them spin balanced on std machine and was told the rims were out of round. Still shook

I had them spin balanced at another place using the proper adapter. Still shook

I trued the rims to +- .040 which is within the factory spec according to Hendrix Wire Wheel. Rebalanced. still shook

Checked the tie rods, shocks, pinions, alignment. shakes

I shaved the tires to take off the high spots. Still shakes

Balanced them on a gravity balancer and balanced the ft brake drums. still shakes

Rebushed the steering column, which helped a bit but not really. Still shakes

Installed all new ft bearings and used lock tite sleeve lock. Very nice stuff, took all the play out of the ft bearings from worn hub I.D.s, but still shakes

New steering dampers now on order but it will still shake because it's gotta be the rims or tires.

Throw in a few more balances, shaves, and about 50 ft wheel removals for kicks and it still shakes.

Either my car is sitting to high, the shocks are actually bad when I think they're ok, the tires are bad, or the .040 spec is B.S. The tires conform to the out of roundness.

Here's my plan.....
1. bleed shocks and/or install heavy duty valves
2. Install new dampers(good luck)
3. Send rims to Hendrix Wire Wheel this winter(if entire ft end holds together that long) for their "ride on a Cloud) treatment
4. Get BOLT ON alloy rims(cop out)- but probably the ONLY real solution(if I want to drive it as much as I do i.e. long journeys, track tours at R.A. and turn #1 down the block.

A local SCCA mgb racer said, "get rid of those wire wheels" as his solution. He's usually right!

P.S. read the mgb archives under "shake", "ft end shake", and "dreaded 55 mph shake"!

Update - 7/2/03 last night I installed one of the steering rack damper pistons and I THINK much of the shaking is gone, but most of the test drive was either too slow or too fast to really tell.




Fred Horstmeyer

Jim - Rostyles have been known to be out of round. Simply jack the car up, pick a fixed point on the ground and have someone spin the wheel. The bottom of the tread SHOULD not move up and down - but it might. Reproduces an out of balance condition. Perhaps someone knows of a cure for this, other than sorting through racks of wheels for a centered one.

Also be sure your steering rack's rubber gaiters are not split. They should be full of grease. While your front end was rebuilt 10,000 miles ago, I take it you've kept that greased as well?

Old timers used to balance wheels while on the car, so that the rotational masses of the wheels, tires and brakes are all taken into account. Traditional technique was somewhat unsafe, according to many, so finding someone to do such a balancing act will be difficult.

Bent rims should be visible to the eye. I've had internal ply separation in the past - I believe that tire removal is the only way to conform a diagnosis - again, I could be wrong.

That's the simple stuff - hope it's one of them!
John Z

Jim, The MG shop manual reads as follows;

"Check the wheel wobble. This is the lateral variation measured on the inside vertical face of the flange and should not exceed .55"." I'm sure it should be .055".
"An additional .015" is permissable at the welded joint."

"Check the wheel lift. This is the difference in height between the high and low points measured at any location on either tyre seat on a truely mounted and revloving wheel. The difference should not exceed .055". An additional .015" is permissable at the welded joint."

You will need a dial indicator and some method for mounting it to measure the run out.

Good rostyle wheels seem to be hard to find. I don't think the center hole for the cap is the true center of the wheel. To balance them correctly they should be bolted to an adapter rather than using a cone in the center of the wheel. Most tire shops will not use or have an adapter. If you can find a shop that uses a on car spin balancer that would be the best way providing the operator knows how to use it.

How do I know this? On my 74 roadster I spent around $150 having wheels balanced and changing tires from bad to what I thought were good wheels. I replaced almost new store brand tires with Michelin rian force tires and still had the shakes. Then I dug deep into my pockets for a set of LE wheels, problems solved.

Hope you find the problem with having to buy tires and wheels. Good luck, Clifton
Clifton Gordon

Jim,
Some cars have a sympathetic vibration at certain speeds. Convertibles can be worse because they lack the additional strength given to hardtop models.

I (temporarily) owned a miata that did the same thing, shook around 55 mph. Supposedly Mazda added additional body bracing in later models to deal with it.

Dave
David Steverson

Jim,

I had a similar symptom in my 74 1/2 "B" Roadster when I bought it. Did all the balance etc, with little result. Finally adjusted the front wheel bearings per manual & help from Paul Hunt's site. Front end smoothed right out!

Cheers, Doug
Doug Keene

Hey! Before expending large quantities of cash, sweat and swearwords --- check the u-joint.
Dan

Did you make sure that the wheel assebmly is intact. Ie. bearings and king pin?
Thomas Nolan

I know that you said that you replaced the drive shaft, but make sure that the yokes are aligned correctly and hat there is no play in the U-Joints. Loose U-Joints can be responsible for some really disturbing noises and vibrations.
Steve

What type of tires do you have on the car. Sounds like the tires are seperating at some speeds or out of round when they get warm. Had a similar experience on a Jag. Recommend going to Costco and replacing all tires with Michelin MXV4 Energy, 185-70-14. In my opinion these are the best made tires and always in balance. I've had no problem with my cars since fitting these tires.

Andy
Andy Preston

Thanks, I really appreciate the response. There are some great ideas here. Wife and I have a lot planned for the long weekend but I'll grab a dial indicator from the tool room and make a couple of checks over the weekend.

I have a pair of Goodyear and Firestone radials. I've swapped the fronts to the rears, etc. without any noticable change. I believe the driveshaft yokes are in the correct position and I replaced the u-joints.

Thanks again and have a great 4th of July!

Cheers,
Jim
Jim Budrow

I've had a terrible time getting someone to balance my Rostyles correctly. The tip-off is that they'd come back and say the wheels were out of round. Yet when I bolted them to the car and spun them, they're straight as an arrow. This told me that the technician simply didn't mount them on the balancer correctly.

A month or so ago, I had a flat repaired at a new shop. I let them know the trouble I had with balance. I told them that I had checked the wheel for straightness on the car, and asked that if the wheel seems to wobble, then it's just not on the balancer correctly. Lo and behold, when I got that wheel back, it was balanced beautifully. Just this weekend, I took the two rear wheels to the same shop, and asked for a balance, giving them the same warnings.

As hoped, the wheels came back beautifully balanced, and the rear of the car is as solid as a rock. I just got back from a drive on a new interstate, and they were smooth up to 80 MPH.

The lesson is that most shops can't balance a Rostyle.

On the other hand, it's not always tires. Earlier this year, I found the splines in my driveshaft were loose, giving a horrible vibration. When I replaced it there was a serious improvement.

Also, check the play in your front wheel bearings, kingpins, steering shaft u-joint, inner tie rod ends and the play in your steering rack itself. Make sure your shocks are in good shape.

Best of luck.

Matt Kulka

Well, I've now got two rostyles that won't balance. I've watched them on the machine and there's a fair amount of "wobble" on both of them. They're not out of round but they are out of vertical true in both cases. One of these was on the front of the car and fine until the other day when I removed it to work on the brakes. I guess that it "relaxed" when the tension was off the retaining nuts, having taken a knock since it was last bolted on. I was a bit suprised to be suddenly confronted with the 55 mph shimmy on putting everything back together. Move it to the back, all OK now.
So, out of the five that I own, I now have two duff ones. It's no wonder the shops don't try too hard to balance them, they've probably seen so many shot ones it never occurs to them that the problem could be on their end.
I'm now trying to scrape together enough cash for alloys....
T J C Cuthill

TJCC:

I mis-stated when I used the phrase "out of round." I did mean the same as you - the shop claimed they were out of true side to side, not egg-shaped.

Please take a minute to mount the bad wheel on the front of the car and give it a spin. This will tell you if it's really out of round or if you're a victim of the same syndrome I was.
Matt Kulka

Well I checked the wheels and found that 3 of the wheels were out of square by less than .03" TIR. These same three were out of concentricty in the rim area by less than .015" TIR so I think they are okay. The 4th wheel is out of square by .055" TIR and off center by .03" TIR. I'll see if my spare is any better and try it in place of the questionable wheel.

The 'bad' wheel is now on the rear axle but I still get the shake, so I wonder if I'm really chasing the right problem. Anyone have a set of mini lights I could borrow?!?!?!? Yeah right!

Also it might be my imagination but the 'shake' seems to vary with road temperature and roughness. Temperature makes me think tires while roughness equates to suspension....????

I'll keep looking as time permits. Again thanks for all the suggestions!

Cheers,
Jim
Jim Budrow

This thread was discussed between 02/07/2003 and 07/07/2003

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