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Car stutters/jerks forward when pressing the brakes

When I press the brakes to slow down, my car jerks or stutters forward. Not sure if it’s the brakes or something else. It’s kind of like when you ride a bike and keep pressing and releasing the brakes and it jerks you. Any ideas?

Warped brake rotors.

Tester

That won’t show up on a diagnostic scanner will it?

No.

Tester

Ok, last question, how do I know if it’s the front or back rotors? Thanks for your help

What kind of vehicle?

Tester

2001 Porsche boxster s

Nine times out of ten the front rotors cause this problem.

But to find out for sure, a dial indicator is used to check the run-out of the rotors.

Tester

I’ll just buy new rotors and replace them, Thank you for all your help

Buy new brake pads, too.

3 Likes

If you have a parking brake that you can apply and release with one hand - like the between the seats lever with a release button on its end - that works only the rear brakes. You can apply/release it while driving and see if the rear brakes are working smoothly or not.

1 Like

It is typical with modern cars that they have disc brakes all around, but that they have a tiny set of brake shoes (i.e. drum brakes) inside a hat-shaped mechanism attached to the rear rotor. If this Porsche has rear discs with a separate drum brake mechanism inside a “hat”, your suggestion will not produce any valuable results.

Does the OP know whether his Porsche uses the disc brake mechanism for the parking brake function, or if it uses a separate set of brake shoes for the parking/e-brake function?

Yeah, you’re right. I was thinking of the rear drum brakes on my Honda and even older cars.