symptoms of bad corner balancing??

[dickster]

i have the symptoms:

the left front corner "dives" down and that tyre *tucks* under, when negotiating right hand bends.

body roll appears to be diagonal between the left front and right rear corners. because thinking about it when i do left handers the front left wheel goes very light and could be completely lifting off the road surface.

what causes excessive diagonal roll??

what are the symptoms of bad corner balancing??

anyone, i'm desparate

[jluetjen]

what are the symptoms of bad corner balancing??

>>> The car pushes when turning one direction and is loose when turning the other direction. You may never notice it in normal street use unless you are approaching the "limits of adhesion" which would be a bad thing! The same symptoms could also be the result of inconsistant tire pressures which is a lot easier to check. Make sure that you have the correct tire pressures in each corner. It makes a WORLD of difference.

what causes excessive diagonal roll??

>>> A number of things. First you need to define "excessive" because roll is a critical component of suspension design. Cars need to roll unless the over-riding performance constraint is ground effects which is then a completely different subject. But getting back to your question, what causes "excessive" diagonal roll? In no particular order...
- Mis-matched sway bars
- A high center of gravity at one end or the other of the car, possibly coupled with...
- A low roll center at one end or the other of the car.
- Trail Braking
- Accelerating while cornering
- Non-Turbo 911's will lift the inside front wheel when cornering (more so when combined with accelerating) as a result of the rear suspension geometry. In some situations it can have insufficient anti-squat given roll center location which causes it to "lay over". Turbo's or Turbo look 911's had the geometry changed to increase the anti-squat and raise the rear roll center.
- Bad bushings causing too much compliance and as a result poor geometry.

I'm sure that there are a few other reasons as well!

[sammyg2]

Another obvious sign of a bad corner balance is when the car pulls to one side under hard breaking. It can also be caused by several different problems in the braking system, but if one corner is weighted more than the other the car will not want to brake in a straight line under very hard braking.

[dickster]

uncanny guys.

The car pushes when turning one direction and is loose when turning the other direction

and

Another obvious sign of a bad corner balance is when the car pulls to one side under hard breaking

i get both of these! i think we may be on to something, i need to do some research. can i do a balance check without scales?

thanks guys

well done in the footy btw

[dean]

My SC pulled all the time. I put it on the scales and the weights where off by 100 lbs. I got the weight within 10 lbs and the car doesn't pull anymore. It's now a pleasure to drive.
I don't think you can do the cornerbalance without scales. I borrowed 4 digital scales to do it.

[john70t]

Some other things that might affect it: uneven caster, worn t-bars or tires(tyres), ride height, and frame shift for the early types.
Uneven braking force will also throw it all off too.

[jluetjen]

Just to reiterate since I buried the thought in my earlier post. The most common cause of the problems that you are describing is incorrectly (ie: uneven) tire pressures. Since it is almost free to check and fix, have you confirmed your tire pressures?

[Randy W]

You may also have a dead shock.

[sammyg2]

I agree, check the easy stuff first, like tire pressure and condition.
Then check all suspension and steering components for wear and or play.
After all that stuff is proven to be in good shape, take a tape measure ot the fender lips. Compare front to front and rear to rear.
Unless the car has been crashed or damaged, the measurements should be close. This method will not get you a good corner balance, but it might tell you if it is way out of spec.
Note that any and all changes to ride height will require a full alignment be performed. Even dropping one side 1/2 turn and raising the opposite side an equal amount may change the thrust angle in relation to the rear wheels.

My car is set up really well, but it still pulls slightly sometimes. I could not figure out why it only did it sometimes, until my dad (a very experienced mechanic) suggested that the car was so neutral and light that the crown of the road would affect the car. Sure enough, i experimented on several different roads and lanes. The crown of the road was the culprit. He suggested I give it a little toe in to reduce the effect, but I decided to leave it how it is.

[jluetjen]

He suggested I give it a little toe in to reduce the effect, but I decided to leave it how it is.

I did my own cornerweight and alignment this winter and for about a week I drove the car with a little too much toe. I found that it really tightened up the steering to the point were the steering felt heavy and unresponsive. Resetting it to 0 degrees toe immediately returned the light and lively steering feel that is part of the 911 steering experience.

the car was so neutral and light that the crown of the road would affect the car.

This is known as "Bump Steer" and 911's have it because of the geometry of the McPhearson front struts and the height of the steering rack. Lowering the car will make it worse. Basically, by raising one front wheel you cause it to turn in or out (I forgot which). There is a cheap bump-steer kit which is available all over the place (Including our Host -- Pelican) which supposedly goes a long way to curing this. If you put it on, you do need to reset the toe after installation. I don't have it on my car right now, but it is on the "to do" list.

[john walker's workshop]

occasionally the bushing on one end of the steering rack comes out into the rubber boot, causing a lot of flex along the tie rod on that side. a long shot, but strangely enough i've see 2 911s with that problem in the past 2 months.

[dickster]

i'm pretty sure its not tyre pressures but i'll check.

the shocks are new bilsteins.

i measured the fender height a while ago. the only thing i found was the left front is about 1/4 inch lower than right front. does that mean anything?

j w - i'll have a look at that over the weekend.

its weird, and driving me nuts. its quite a sutble handling problem, my girlfriend doesn't even notice, and the po tracked it and never noticed.

i don't wanna "waste" £450 on corner balancing.

thanks for the ideas. (keep um coming!)

good weekend to you all