Occasional Brake Pedal Vibrations

Hi,

Got an odd one on my 1995 T5 Auto. Basically the brake pedal very occasionally (i.e. twice in the last 5 weeks), when slowing down gently is making a buzzing sound and there was alot of vibration via the pedal for the first few miles after startup (i.e. it sounded like someone been electrocuted!) The car braked fine, but this vibration was unnerving to say the least. It seems to be when the car has stood for one day or there is heavy rain - wondering if this is how the abs works from cold / wet normally or it could be something else. No ABS warning lights come on, and a garage recently checked it and said the left abs sensor was a little suspect and reset this. The ABS control unit was also recently replaced under warranty.

Thanking everyone for their help.

Jon Wong

[Mike Arnold]

Suggestions:

1. faulty ABS sensor or unit.
2. seized caliper
3. thick rust rim build up on disc.

[sheerwater]

Can be caused by certain types of brake pad / disc combinations.
As this happens after rain/wet/and or standing or after washing and standing you may find that the disc is rusting in a certain pattern albeit small. A look at your discs may reveal marks vertically as opposed to the concerntic rings. These will show up as black lines and show where the pad has sat overnight on several occasions. Dont ask me why it happens on some cars but not others but it does!!!. My 740 sits for weeks rusting on the disc but this grinds off in a few miles and is then smooth. My 940 on the other hand had genuine volvo parts and suffered the symptoms you describe and they took ages to wear away. Cheers Nigel

Guys,

Thanks for the feedback - I suspect the sensor is the culprit. It happened again this Friday after about 20 - 30 mins of driving so it is intermittent. The garage did say the sensor was suspect. Question is will it damage anything driving with this (the sound is very worrying!!)?

Jon Wong