OK, so here’s today’s brain teaser that I am hoping one of you experienced mechanics will be able to help me solve.
A few months ago my trusty LS400 developed a soft (long travel) brake pedal. Pads and discs at the time looked ok, but I do remember the travel increased after a particularly hard breaking episode on the M5 due to some numbskull in a 5 series BMW (say no more).
Checked brake fluid and this was pretty black so changed and bled the system but without improvement. After about a week the ABS pump started to kick in every time I set off (within 10 yards) after starting the ignition. A slight rumble of the ABS pump with vibration in the pedal and then same level of travel on the pedal, this only ever happens once until you restart the engine. The pedal does come hard after pumping three times and then softens upon release. The ABS ECU has no recorded fault in its memory, the ABS light does not come on and all wheel sensors are reporting correctly. The ABS rumble only happens once after engine starts and the car moves, if the car remains stationary the ABS does not kick in. So I am thinking that this is something electro-mechanical that is linked to the wheel speed sensors which is causing the ABS pump to kick in. The problem has not got any worse over the past 4 months and my driving style has adjusted to the long pedal, but I would really like to find a solution.
I am just about to change the front discs and pads as they are now a little warn. Whilst this is likely to reduce the pedal travel I do not think it will influence the overall issue.
Any ideas?