Brinkley

What is the diagnosis for a car that feels "squirmmy" under heavy braking? The back of the car feels like it is wagging back and forth a half foot.

I don't have the ability to adjust brake bias front to rear, stock braking master cylinder, steel lines, Pagid blacks, Gaurds Transmission LSD.

I looked in the search section but could find anything that matched this description.

I appreciate any help you can provide

APKhaos

There are a few possible causes:

- Too much rear brake bias. Running slightly softer pads [lower torque values] can tune this out.
- Alignment. Many chassis are very sensitive to ride height & rake setup, which can cause the kind of instability you describe. You need to find someone who really knows Boxter setup for advice on this.

HTH

FTS

+1, and uneven surface is another reason that may happen.

Oddjob

Check rear toe settings.

Chris M.

Yep. Also, what tires?

jrgordonsenior

How much preload was installed in the diff and how long ago was it installed. It's relatively easy to pull the diff and check the preload and discs. Toe can also play a big role in what you're describing, but a Guard under 80% decel lockup should pull that car straight....

I just noticed you're running Pagid Blacks f & R. You could try Yellows (RS19) up front to create more rear bias....

PedroNole

Most likely a rear toe issue. Could also be too much camber in your rear tires if you were getting it at turn 1 or the bus stop at Daytona.

986

Guard suggests jacking up one side of the car then put torque wrench on lug nuts or axle nut. If the wheel turns with <65 lbs torque (breakaway torque) you may need to replace the friction discs.

Also agree with others re: rear toe.

Geoffrey

I would check the rear bump steer. It is likely that the rear it toeing out under rebound. In addition, if you have rubber bushings you'll likely feel some amount of instability under braking.

RSRRacer

Check also for loose or fatigued rear toe link. Jack the rear of the car and try to move the tire with your hand as if you are trying to change the toe.

Professor Helmüt Tester

To everything listed above, add "shocks".

Van

Even the car's "rake" could have something to do with it. If the front is a bit lower than the rear, you might be transferring too much weight off the rear wheels to maintain stability.

kurt M

OK, that was simple.

I had this start up on its own in my old car and found that there was a small air bubble in one of the rear brakes. Not enough to make for much of a soft pedal but enough to skew the bias. A burp of the lines and all was back ot normal.

dmwhite

i would say not enough rear bias to keep the rear end planted...i've found that getting the rear of cars to do more braking has helped settle cars down in brake zones (less weight transferring forward keeps the rear end from getting 'light')...of course this is with bmw's so it may be way off for porsches

and as almost everyone else has said, check the rear alignment...

jgrant

I'd also check for the rear tires slipping on the wheels, and your LSD.

We've had issues with both that caused "squirminess", and when those issues were resolved it was a whole new car.

Turned out the tires had too much lube on them from the difficulty of mounting them, so switched to hair spray as a lube, and no more problems.

Had a diff that was improperly assembled, and wasn't working properly on braking. Fixed/replaced it, and no more problems.