Intermittant brake pedal softness

[Bicyclops]

I'm really happy with Brembos all around and the pedal feel with a higher pick point on the pedal, but... lately I have been getting a soft brake on the first push. Not all the time, just sometimes. Never gone to the floor tho. When it happens, one pump and it's back high and braking action has never suffered. I re-bled them. I pumped a liter of Dot 4 through and it's the same. Sometimes, but not every time, I have to pump once. Seems like it's happening more frequently and I'm beginning to get spooked. Could this be from having a master cylinder with 230K+ miles on it? It's not leaking externally and I've never had to add fluid. I guess I could replace the MC and see if that fixes it, but I don't like just throwing money at it and not knowing why.

Ed

[David Ferguson]

On a race car, we might suspect brake pad knock-back. This is caused by less than perfect wheel bearings (and/or high cornering forces). The rotors actually push the pads back some, and the next brake application has a slightly longer pedal. Race drivers will sometimes compensate for this at the end of some non-braking esses, by a slight tap of the pedal before the next braking zone. The solution is floating rotors, which allows some hub movement without transferring that to the pads.

My advice, check the wheel bearings are properly tight and not worn.

[Bicyclops]

David,

What a great call. My right front wiggles. Yikes!

Ed

[Bicyclops]

That's it for sure. When I wiggle the rotor, the pedal wants one pump. Thanks for the tip. I didn't think of it. Saves replacing the MC. I've ordered some OEM wheel bearings. These TRQ bearings didn't last 5K miles. Might be wise to replace the driver's side while I'm at it or at least check it more often.

Ed

[Bicyclops]

New wheel bearings did the trick. The brake is high and tight. I also discovered a sloppy sway bar rod end bearing. The ball is tight but the shaft can move back and forth inside it. Replaced that and the annoying rattle that I couldn't find is gone. Hard to believe how little travel on that bearing caused how loud a rattle! It's always something.

Ed

[Ray from Long Island]

Nice work "Detective Dave" !
Ray