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MG MGB Technical - poor handling of lowered R/B

Hi,

I have a 78 MGB, US spec.
I lowered her, using shorter springs. I also fitted Chrome bumpers.
A reconditioned steering column was fitted a couple of years ago. No play in the column.
I fitted new v8 disc brakes last week.
Her handling was already pretty poor, but now it is even worse. When I go faster than 60 mph, steering is very very vague, also on smooth roads. It almost feels like there is no downforce on the front wheels..
If I drive on bumpy roads, alreadyh from 30-40 mph the steering wheel is constantly flipping from left to right and it feels like I am driving a kart.
Looking at the wear of the tires, it seems that alignment is not ok. The outer sides of the front tires wear more.

So my questions are:
What can be the cause of this? Could it be just from fitting shorter springs? Did I do something wrong when fitting the discbrakes?
How can I improve this handling? Does anybody have suggestions.

Thanks,

Rik (netherlands)
hpm rik

Rik

Did you get the toe in corrected after the lowering? If you drop the front of the B the steering tierods have to slope upwards to the outward ends. This will pull the toe in quite significantly hence the problems you're experiencing. Once you get this sorted it will improve things but you'll still get a bit of extra bumpsteer (google this for a definition)
Stuart Robson

What state are all the suspension bushings and mountings in?

Mine is also an ex US 78B I am going to lower at some point so I'd be interested to hear how you sort yours out.
Simon Jansen

Rik, stand outside the car and watch the front tires WHILE you turn the steering wheel back and forth. You should see response in the tires at the smallest turn of the wheel. If there is a lack in response, have someone else turn the wheel and you watch from the front. Check the outer tie rods for slop or play. If there is slop in any parts or in the rack, repair as needed. Also check the lower control arms. The outer U-channel pieces should be straight - no bends or warpage throughout their length. The only bend should be near the pivots on each end. Are all the A-arm bolts tight? Are the wheel bearings tight? Is there a clunk when starting and stopping?

When you lowered the car, did you shorten the bump-stops? The car could be hitting them, preventing full suspension travel. You will need to shorten the bottom one. You could also purchase a shorter one that does not use the aluminum spacer.

Are your tires properly inflated? Try a different gauge to double check. How much air pressure do you use?

Of course you need the alignment to be spot on. I use a piece of old metal fuel line to check mine. Its about 40" long, with a 5" extension bent out at almost 90 degrees on each end (shaped like this [ .) It fits nicely under the car and makes a great measuring tool to adjust the toe. You want the front measurement approximately 1/16" smaller than the rear, while measuring at the midpoint of the rim. It sounds like your tires are severely toed inward, the front measurement will be MUCH smaller than the rear.

Sorry so long winded, but somewhere in here you should find the cause of your issues. There's nothing on this list that you can't repair yourself!!!
Jeff Schlemmer

THANKS for these replies.
Here some answers to some questions already:

Toe in is not corrected yet: So #1 to do, that makes a lot of sense.thanks for the tip Stuart and Jeff.
Regarding Toe-in measurement: I assume you measure distance between L/R Frontwheel on front side of axis and back side of axis. Difference in measurement should be approx 1/16" JEff?


All bushings / mountings are ok

Good response when turning wheel, no play whatsoever.
Bump stops are shortened already.

Wheel bearings:
these might not be as tight as described. My MG parts supplier told me I could remove the metalbush close to the wheelbearing and remove the shims. Then just fit the wheelbearings without the bush. So there is no endfloat at this moment, but torque on the wheelbearing. Because this is a lot easier to mount, I decided to mount it this way, after having fitted the discbrakes. This can be a reason as well, jee, I should have thought of this myself.

So I have some things to do and check.
Keep you posted when I find out more.

Rik
hpm rik

I am about to redo the front wheel bearings myself so I looked in the archive. There seems to be a bit of debate over if you can leave out the spacers or not. The general argument for leaving them out being a lot of cars like the MG don't have them. Personally I will be putting them in. That's what the factory manual says you should do so seems reasonable to me. And it doesn't seem that hard to do, just a bit repetitive setting up the shims.

How did you lower the back of the car out of interest?
Simon Jansen

Rik
It sounds like you might be getting a little bump steer.
have someone bounce the front end up and down, or jack it up and down and watch and measure your toe in. If it varies substantially as the suspension goes up and down, you have bump steer. Hit a bump and your car darts one way or the other.

There are various archives that talk about bump steer.

Barry
Barry Parkinson

Where can one purchase bump stops which do not use the aluminum spacer?
Thanks, Dave
Dave

dave, I think you can get them at www.brittek.com, or you can cut down and re-weld your own. I don't think you would actually even have to weld the two pieces back together. Just bolt them back into position once you cut out the approx. 1/2" section where the spacer used to be.
Jeff Schlemmer

Toe will definitely affect the feeling of vagueness. A lot of people try to tell me that nowdays, no one uses a toe in. Well, on my car, at least, zero toe causes it to fell vague and it wanders a bit. The simple 1/8 in. toe in seems top make that disappear.

Regarding the spacers on the front wheel bearings, the mechanical engineer in me tells me that the idea of spacers/shims and then torquing the nut down is a good one. This allows one to put a proper pre-load on the tapered roller bearings. However, there is not a lot of info on what the pre-load should actually be and most folks (or shops for that matter) don't have the tools necessary for measuring the pre-load and accurately determining the thickness of shims required. This makes it a guessing game and that is what you have when you leave the spacers out.

I have never had a good feeling about the 'tighten it up until it feels right and stick a cotter pin it' process. Just doesn't seem secure enough to me (relying on the cotter pin). I rather like the extra security of being able to really tighten the nut.
Richard Smith

Forgot to mention as well that the lower CB cars usually do not benefit from a rear sway bar whereas the RB cars do. A lot of people do not recommend a rear sway bar for CB cars.
Richard Smith

Spacers and shims were a requirement on cars using the ball type wheel bearings to prevent excessive side loading on the bearing. Tapered roller bearings have been used without problem for years without spacers or shims. Preload is set by tightening the retaining nut until it stops, then backing off to the first position where a cotter pin can be installed.
Rik, you are correct with your description of the toe measurment.
Bill Young

There should be no pre-load on the roller bearings in the MGB. However there *is* end-float (free play) and this is achieved by adding shims between the inner race of the outer bearing and the distance tube, and torquing the nut down to the correct figure. Lots of argument as to whether this makes the stub axle stronger or not, but it certainly stops the inner races spinning on the stub axle and welding themselves to it. There is absolutely nothing to be lost by setting the bearings up in the way the factory always recommended, a number of things to be lost if not.
Paul Hunt

Hi Rik,

I've tried various different front springs on my Chrome bumper V8 (which have the same ride height as the rubber bumper cars) When you fit shorter springs you alter the angle of the steering arms relative to the lower A arms with the result that the ackerman angle is affected and the front suspension is put into a position where you get bump steer. The ackerman angle effect is most noticeable in slow 1st and second gear corners giving a "plowing on" feel to the front suspension. The bump steer effect will cause the toe in angle to increase when the front suspension is compressed. You gain handling through less roll but lose out bump steer and the ackerman angle effect. Having tried two different spring rates in both lowered and standard height I've settled on standard springs with a much thicker front anti roll bar as the best compromise. Giving less roll but nice simple feedback messages through the steering wheel.

Having said all that if you've changed the springs but not reset the toe in your front end will feel downright horrible.

Have fun

Phil
Phil

I discussed the poor riding with some other Local MG guys.

Besides the already mentioned toe-in, one moer interesting thing came up.
We found the following:

The steering arms are not horizontal but are relatively moved upwards, I say about 1,5 to 2".
One solution that a guy did was mounting the tie-rods UNDER instead of Above the tie-rod. He used so called Rose joints for that. I saw this and his steering arms are pretty much horizontal again.

Does anybody have experience with that? Or other suggestions that may get the steering arms back to a horizontal position?

Rik
hpm rik

If you wanted to put the tie rods under instead of above couldn't you swap the arms on the swivels over so the tapered hole is up the other way? I don't know if doing that is advisable though.

Simon
Simon Jansen

hpm-

I think you've heard (and apparently believe) an old wives tale about horizontal steering arms. That is, that the steering arms need to be level for 'good handling.'

This is not the case. The distance relationship between the inner upper, lower, and steering shaft pivots must be similiar to the relationship betwen the outer upper & lower pivots, and tie rod end. In addition, when the wheels are centered the steering shaft pivot should fall on an imaginary line drawn between the inner upper and lower pivots, and the tie rod end on an imagonary line between the outer upper and lower pivots. Arbitrarily moving the tie rod end over an inch out of position is certain to introduce some significant bump steer characteristics.

For instance, say the distance between the upper and lower inner pivots is 9" and the distance between the steering arm and the lower pivit is 3"- the rakationship is 3:1, that is the upper pivot needs to be 3 times the distance from the lower pivot as the tie rod end (Measured to the center of axis, which is not obvious on a tie rod end.) If the kingpin assembly is 12" from upper to lower pivot, the pivot center of the tie rod should be 4" above the lower outer pivot, retaining the 3:1 ratio.

This is a good general rule- frequently minor changes can be made from this starting point to optimize bump steer, but if you start with the above, you'll be fairly close


There is some risk with just flipping the steering arms side for side- this moves the tie rod end toward the wheel, and depending on what wheel you run, it can cause problems.

Based on the comments so far, though, with wear on the outer section of the tires- generally that sounds like to much toe in, but that generally leads to a stable condition.

The first thing you need to do is find out where you are- what's you're toe setting
greg fast

Thanks Greg and Simon for feedback.

I will first measure and set the toe-in, and let you guys know the handling results.

However, still this general question:

When one is lowering a RB car to CB spec using different front springs and lowering blocks at the rear, what are the things or steps to do to obtain proper handling, besides setting toe-in?

Rik
hpm rik

Hi Rik

As part of the toe in adjustment, make sure that the tie rods are of egual length.

You will need to pull back the large end of the boot at each end of the steering box to expose the inner ball joint, measure from the same part of the ball joint on each side to the centre of the outer ball joint bolt at the steering arm.

Set these two lengths equal, and then adjust toe in by rotating the tie rods an equal amount untill the correct toe in is achieved.

Also check that the steering arms are not bent.

As others have said - setting the tie rods horizontal should not be done. This will upset the relationship that is built into the suspension/steering design and you will get bump steer.

Cheers
ian F

Ian Fraser

This thread was discussed between 15/05/2005 and 25/05/2005

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