Strange brake / ABS issue

[John V]

I'm having a strange issue that I'm wondering if anyone has come across. The brake pedal has for lack of a better term, a slight "notchiness" to it. It's as though something is binding and causing a feeling that the pedal catches, then releases. It is audible as well - it causes a reasonably loud click when it occurs.

I inspected the pedal mechanism and the booster and with an assistant pumping the pedal I can't feel it in the linkage or the booster - but I feel it in the high pressure brake line out of the master cylinder leading to the ABS unit.

The brakes function normally, I have proper brake assist and the ABS seems to work correctly.

Has anyone ever noticed this before? I haven't checked to see if a caliper is binding, and I flush the brakes once per year. Would air in the ABS system cause this?

[John V]

Nobody, huh? :(

[Loren]

Have you checked the brake booster for water?

http://www.renntech.org/forums/index.php?s...ost&p=79485

[John V]

Have you checked the brake booster for water?

http://www.renntech.org/forums/index.php?s...ost&p=79485

I forgot to list the year of my car, but it's a 2000 Boxster S. I don't think this problem affects my car.

But regardless, I don't have an issue where the brakes won't release, and the clicking noise is not originating from the booster. So I don't think that is the problem. My best guess at the moment is air in the ABS unit.

[John V]

I was finally able to look into this more. It appears that there is a brake proportioning valve off the master cylinder of my '00 S that has failed. When the pedal is depressed, this valve gives out a loud "click." It's part number 2 in the attached PET diagram. part 986.355.305.00. I verified that the sound is not coming from the master cylinder or brake booster, which is also not full of water.

Tool Pants / Loren, have you heard of this part failing? Fortunately it is not expensive, but I find it a strange failure. It looks like the valve can be disassembled, so I'll have to take it apart when I get the new one.

[Loren]

I have not heard of problems with this valve before - but there is always a first.

[John V]

I am not sure I would call it a failure, but it definitely was faulty. I disassembled the valve and found a large amount of grit inside. There is a spring-loaded mechanism inside which limits flow in one direction once a certain pressure has been acheived.

New valve, no noise, and better braking performance.