Drifting MGB

Hi

I'm looking for advice as to why my 74 MGB wants to go left all the time.

Since restoration years ago this has been a problem. It's had new calipers, tyres and springs. Tracking checked numerous times to no avail. No history of a crash that I'm aware of. Measurements that I have done seem OK - length from hub to hub each side within a millimetre or two. It was recently in for some other work at Edinburgh Sportscars and thought front bushes looked OK. Driving on road with opposite camber doesn't eliminate the problem.

The problems are:
1. Drifts to the left all the time, more noticeably at motorway speed.
2. The steering wheel feels 'neutral' when turned slightly to the left.
3. There is bumpsteer - hit a bump and the steering wheel jerks round to the left.

I'm looking for hints as to where the problem might be. The rack or other steering components? Or something else?

As an aside, I've also had real problems getting the tyres balanced recently. I've gone from a very minor vibration to a major shake despite having it redone three times at two different garages. This is new, quite sudden after the first rebalancing, and not related to the drift. Just wondered if this was a problem you have come across before?

Many thanks in advance

Chris Kissack

What kind of rims do you have?
Does the vibration change if you switch the tires front to rear?
Are the rims bent?
When you replaced the calipers, did you replace the rubber brake lines?
Are you sure the left caliper is not sticking? (just because a part is new, don't always assume it is good)
Are the front tires showing funny wear?

I get that "bump steer" too ('73 Midget). I've been working on the theory that it has something to do with some of the (on the Midget) non-adjustable alignment settings -- like castor.

I'm very interested in hearing what others think.

What kind of rims do you have?
Does the vibration change if you switch the tires front to rear?
Are the rims bent?
When you replaced the calipers, did you replace the rubber brake lines?
Are you sure the left caliper is not sticking? (just because a part is new, don't always assume it is good)
Are the front tires showing funny wear?

Thanks for replying.

With regard to the vibration problem:

This is sudden inset after balancing and seems to be a problem with balancing. Don't think the rims are suddenly bent. I suspect it's a difficulty with balancing wires and just wondered what experiences others had had.

With regard to the pull:

The car has pulled for a long time, and has been through two new calipers each side during that time without any change. Brakes overhauled last year including new rubber brake lines. Wear on tyres is compatible with age, and tracking has been set numerous times during the cars life without altering the pull.

Thanks

CK

Chris,
"Since restoration years ago this has been a problem."
Was the steering rack, front crossmember and rear axle assembly removed during reatoration? You imply the car steered straight prior to restoration, is that a correct assumption? Have you measured the corner heights of the car? Measure from the bottom of the chrome strip on the wings to the center of the wheel caps. Are those measurements equal, side to side within say 1/8 "?
"Wear on tyres is compatible with age, and tracking has been set numerous times during the cars life without altering the pull."
I'm not familiar with what is actually checked with a tracking check in the UK, our common language isn't always common. In the USA a wheel alignment can be either a front end alignment or a four wheel alignment. A simple front wheel alignment should check toe in, wheel camber and castor. Toe is adjustable but camber and castor are not other than replacing worn or damaged parts.
A four wheel alignment checks how the rear wheels track the front wheels along with rear wheel camber or toe which should be at or very near 0 on an MGB.

Bump steer may or may not cause the car to pull. . If the track rod ends have been changed the new rod ends should be installed so that each rod is the same length. The best way to do that is count the number of threads when installing the end, usually around 18 turns and adjust each side equally to get the correct toe in. Getting each track rod equal will usually correct bump steer problems unless you have lowered the suspension, made some modifications to the front suspension or have wheels with non stock off-set.

You mentioned you have checked wheel base. You need to check if the rear wheels are following the front. Tie a string on a stand positioned behind a rear wheel, extend the string to another stand in front of the front wheel. Pull the string tight so it contacts the tire/tyre sidewalls in the front and rear. You may have to move the steering to make the front sidewalls parallel to the string. You should have a tight string contacting the front and rear sidewalls of the front and rear tires. Don't move the car or the steering wheel, move the stands and string to the other side of the car. Pull the string tight again. If toe in is near 0 the string should contact the front and rear of the front sidewalls and be straight. For accuracy move the front string stand away from the car and slide it toward the tyre sidewall stopping it when it first touches one sidewall. It should touch both sidewalls on the rear wheel and may touch onlt one on the front depending on amount of toe in/out. If it does the front to rear tracking is close. It should be obvious you can check your toe in with a string. Naturally these checks should be done on a level floor or drive.

The MGB has has lots of built in front positive castor. A quick check of castor can be made with a carpenter square. Turn the steering wheel to the left until it stops, set on the short length of the square on the floor and slide the other length to contact the left tire sidewall, it should contact the top sidewall, measure the distance to the bottom sidewall and record the figure. Without moving the steering wheel go to the right side and do the same check, the square should contact the lower sidewall. Measure and record the distance to the top sidewall. Now turn the wheel to right lock and measure again. If the measurements are close on each side the castor should be ok.

To make a rough chack of camber turn the wheels straight ahead and slide the square against the front tyre sidewalls. Both sides should be equal. If the square touches the bottom and not the top you have negative camber. The MGB should have ) to a small positive camber.

If you are still with me an done these checks wilh reasonable accuracy you should find what is causing the steering pull. I know it's lots of work but you can spend $$$$$ trying to get it sorted out at a shop.

On the wheel balance you need to find someone that knows wire wheels, any other place is a waste of money.

Good luck, Clifton

You mentioned wires. Jack up the car and spin the wheels and see if there is a wobble. As far as balancing, a cinder block can be balanced but won't roll. Your rims should be trued and balanced by someone who is experienced with spoke rims. Motorcycle shops may be able to recommend someone.

Clifton

Many thanks for that detailed and instructive reply, which must have taken some time. It is much appreciated.

The string test wasn't totally reassuring, The right hand side lined up fine, but then on the left hand side the string hit the tyre wall at the back of the front tyre before it hit the front wall of the rear tyre (it was about 2-3mm away) - so as if the rear tyre on the left side was angled slightly to the right. I thought maybe the axle might be shifted, but then why did the right side line up fine?

The Castor measurements seemed OK - each side within a couple of millimetres, which is probably explained by tyre pressure - the right tyrewall bulging slightly more than the left at the bottom.

The Camber, however, is out. I have a marked negative camber, with the bottom of the tyre wall sitting 0.9 and 1.2 cm further out than the top of the tyre wall on left and right sides respectively.

Any suggestions where I go from here? It seems like I've come across two problems in the measurements I've made.

Many thanks

Chris Kissack

Chris,

The rear left wheel rim may not be straight. A string alignment will not correct for bent wheels or tires that have a high spots. Another possibility is the left rear axle tube could be bent, not a common problem unless the car has been in an accident. To check the wheel you can jack the wheel off the floor and place a pointer on a stand near the wheel rim and spin the wheel. Measure any differences in rim distance from the pointer and try to center the wheel between the minimum and maximum distances, that may help. The front measurements at the front show that you have 2 to 3 mm toe in. Specified toe in is 1.5 to 2.3 mm so you arent that far off. Of course all measurements should be with the tyres at proper inflation pressures.

Your camber should be between 1 1/4 degrees positive and 1/4 degrees negative. I'm assuming your car doesn't have negative camber wishbone arms. There is enough differnce in your side to side camber to cause a left drift. I didn't suggest this in my first post but it may be a good idea to switch the front wheels with the rear wheels and see if your steering changes, unless you have already tryed that. I had some new tyres that caused a steering pull. In your case it sounds like you have some wear in the front suspension. Original wishbone arms to inner wishbone pivot bushes wear quickly and could be the cause of the problem. About the only way to check is to eyeball the wishbone arms eyes and big washers under the pivots. If the bushes are badly worn the eyes will be off center from the washers. MGB V-8 bushes solve the problem. Jack up the front wheels, check for loosness by placing one had on top and the other on the bottom of the wheel and try rocking the wheel in and out. If there is loosness it could be bearings, kingpins, upper or lower trunion pins or bushes or loose damper mounting bolts. Hope this information helps.

Clifton

Chris, there have been a number of great replies to your question. One item that I would like to add, is to check the wear on the front suspension lower A arms. the holes that mount the arms to the king pin wear over time, becoming oval in shape. This can allow the kingpin and swivel axle to take an improper set. Replacing the lower A arms is th esolution. Some folks will weld a washer to the A arm to get a proper hole, but you have to be spot on for the alignment to be right. Just another thought to the many great ideas already listed. Hope that you are able to solve the problem.

Take it to front end algnment shop have them set toe-in.that's all thats adjustable but they can inspect for worn frnt end parts while there.mgbss63