930 steer when braking, suspension?

Falk930 · 05-05-2011, 09:43 PM

Hello,
I have a 87 930 which steers/drives strange to the right side
when I push the brake.
The easy answer is, that the left front brake has problems.
But, on the brake test roll ( if thats the correct word?) the brakes
are 100% ok and identical left to right.
Probably because the wheels can`t steer on the brake tester.

I suspect a problem with the suspension.
Anyone discovered something similar and can give me some ideas
where to start?

Falk

piggdekk · 05-05-2011, 10:10 PM

I'd start from the front arm bushings.
luca

wildcat077 · wildcat077's Garage

Falk,

Go for a short drive without going too crazy on your brake pedal and then feel if there is a difference in heat between your rotors ... maybe you will see if one side is dragging more than the other ...
Could also be a corner balance issue,how's your ride height ?

Cheers!
Phil

IROC · IROC's Garage

Quote:

Originally Posted by wildcat077

Could also be a corner balance issue,how's your ride height ?

Yeah, look for obvious things first - alignment, tire pressures, loose or worn suspension components, etc. Then I would inspect and bleed the brakes and if that doesn't solve the problem it would be worth checking the corner balance.

Falk930 · 05-06-2011, 04:57 AM

Thanks,
my car is more or less fine corner balanced, no problem from that side.
I am not sure, but during a fast check it seemed the Bilstein shock
has some play inside.
But we was not able to see it again...

The front arm bushings are worth to check anyway.

Falk

KTL · 05-06-2011, 05:55 AM

Bad shocks can cause some weird things to happen that you wouldn't intuitively expect. In these struts, if you've got Bilstein struts, there are bushings that periodically wear out. If one is bad and you've got some play there, it could cause some wandering of the car's direction.

I agree you should take a close look at your tire wear and see if anything jumps out at you. Tire wear is a good indication of problem sources.

Is the steering wheel centered, or has it gone off-center to one side, when driving straight ahead? Does the car track straight ahead when not braking? When you apply the brakes, does the car want to turn sharply or does it slowly veer to the right?

Falk930 · 05-06-2011, 11:27 AM

The right tire has unequal wear.
Steering wheel is centered during driving.
When I push the brake, it feels more like a sharp turn,
sure all depends on speed and brake force.
But, emergency braking, what should be possible with a 930
is really strange. A lot of steering force is needed to keep it on track.

*can the Bisteins be repaired by myself or do I need to send them in?

Falk

Chuck Moreland · 05-06-2011, 10:10 PM

Quote:

Originally Posted by Falk930

Thanks,
my car is more or less fine corner balanced, no problem from that side.Falk

How did you measure the corner balance?

Does the car pull when the brakes are not being applied?

Falk930 · 05-07-2011, 05:15 AM

Corner balance was done on...how to say in english?
Just with a balance under each wheel and a digital main unit.
Its a professional system owned from a friend who prepares
cars for different racing series here..

The car is going straight without braking, only when I apply the brake
it pulls to the right.

I will check the Bistein struts + A-arm bushings when I find time.

Falk

Flieger · Flieger's Garage

I would suspect brakes. Oftentimes the inside piston will gum up first. Check the pads and see if the inside and outside pads are worn evenly.

johnsjmc · 05-07-2011, 03:07 PM

I first thought corner balance but I think that has been done properly. I would look for a bent strut. I had a similar experience years ago the alignment and corner balance were correct when sitting on the machine but the strut was bent . As it compressed while braking the camber changed more on one side than the other causing a pull.

JJ 911SC · JJ 911SC's Garage

Next time it rain (a down poor is ideal), see if it steer to the left?

If it does, its the brake.

ivangene · 05-07-2011, 04:09 PM

air in the lines or a single piston repair where the set resting point is slightly off from the other side........

that or a sticking caliper would be my guess

Falk930 · 05-12-2011, 11:01 AM

hmm,
I do not think its caused from bad brakes.
When testing brakes on the roll, they are perfect balanced.

Guess I need to rebuild my front suspension.

Falk

RoninLB · 05-12-2011, 02:26 PM

wild guess is that if these are new brake pads and rotors they may need some time to wear

johnsjmc · 05-12-2011, 02:47 PM

Still would look at bent strut. Mine was bent rod down inside.My car had new brakes Car was aligned and corner balanced. It ran straight but pulled when braking. We eventually found a bent strut. Alignment had compensated by repositioning the top .Strut compression when braking allowed camber change, more on one side than the other causing a pull.