Upon various pedal effort I will at times get a very mechanical feeling feedback throught the brake pedal, a "clunky" feel, not a pulse like a normal ABS system in slippery conditions more like a brief shudder that effects pedal travel. It is very inconsistent, braking power is not reduced and it is not pulling to either side.

It has been happening sporadically for a while before and after a recent rotor and pad change. I am not an expert but I am thinking this is related to either a sticking caliper and the brake booster over compensating or a faulty/ ailing brake booster.

I know I mentioned it is not pulling which may eliminate the sticking caliper but I do have 4 piston Brembos, so my thought is if one piston momentarily sticks the brake will still operate enough not to notice a pull to one side or the other.

I could be completely off target but I am curious if anyone else has experienced this or can lead me in the right direction.

 

Does one rotor feel hotter than the others?

 

I will take a closer look, or feel, next time the car is out but casually there appears to be no noticeable heat variation.

I can say there is no difference on the surface/wear pattern of the rotors, if that means anything.

 

If this is happening when you're investigating the higher performance limits, it could be the DSC system automatically applying / releasing individual brake calipers. Normal behaviour but a strange feel through the pedal.

Graham

 

The other really odd feeling is the emergency brake boost - a giant foot takes over the pedal and the car stops as if you'd driven into a brick wall.
That happens when you stamp extra hard on the pedal.

 

Good point but it usually happens under light braking/light pedal effort. It certainly feels mechanical rather than a hydraulic shudder, almost like there is some type of linkage issue. The only linkage I am aware of is the pedal assembly and the booster to the master cylinder.

 

I have also felt this on occassion with my 2003 XK8, and wondered what it was.

 

Are the Guide Pins (item 2) in good condition?



Any high spots or corrosion and the pads can bind on them.

Graham

 

Yes, I recently thoroughly cleaned the pins with 000 steel wool and brake cleaner.(Perhaps I should have posted that in the OCD detailing thread)

 

It appears this was caused by the wiring harnesses that are zip tied to the upper control arms. Someone has mentioned this before but I was pretty skeptical as my car was giving me intermittent DSC system faults, the ABS light and apparently the related issue of clunky brake pedal feedback. After a lot of cleaning of the sensors, connectors and inspecting the modules I looked at the wiring harnesses as a last resort prior to repacing components. It worked, as I was finally able to cure all the above issues by simply removing the zip ties, adding slack and re-tying them.