ABS with tantrums?

nielstroll · Post by **nielstroll** » 17 Jul 2011, 07:35

My V70 AWD with 300 k on the odo sometimes gives a slight whirring sound while driving. As it says in the song, this means "there's trouble ahead": when applying the brakes I get a loud sound and vibration around the front wheel which I associate with a ball bearing with a broken ball, or stopping a bike with a piece of wood in the spokes. The "feel" of the brake pedal also changes; there is vibration feedback to the pedal. This sound also occurs without the whirring precursor.

The vexing part is that occasionally I can drive a few hours without this phenomenon and everything seems normal. Wobbly brake discs, worn out wheel bearing, brake control box have all been eliminated as possible causes. Theon/off nature of the problem makes it hard to diagnose. Anybody with a good suggestion?

Post by **Ozark Lee** » 17 Jul 2011, 17:36

Is the ABS or TRACS light on? The system is normally pretty good about illuminating a warning light if it is unhappy about something.

In some cases dirty wheel sensors can cause the problem but in most cases the ABS module itself is having issues. There are only two kinds of ABS modules on the '95 and later cars; Those that have failed or those that are going to fail.

I have no experience with the AWD versions but cleaning the sensors and the reluctance rings is fairly easy on the FWD versions. On the rear brakes you need to remove the caliper to get to them but on the fronts they are very accessible.

...Lee

nielstroll · Post by **nielstroll** » 18 Jul 2011, 02:33

Sofar the ABS and Tracs warning lights have only come on once. Drove to the nearest motorway stop, switched off, started and warning lights gone......The rattling sound has on dozens of times by now.

A run with the car with a laptop with diagnostig software plugged in did also not give any pointers. The garage is muttering about a new car ( since they cannot find the problem), but with engine and body believed to be in good health, this seems crazy to me.

nielstroll · Post by **nielstroll** » 21 Jul 2011, 01:38

Have decided to write off driving substantial distance without problem as a fluke, since it now occurs 30-40% of every brake action. As I will work on the car again next week, I will concentrate on user experiences with this phenomenon WITHOUT the ABS/TRACS lights coming on.

Using the search "ABS module; noise", I counted hundreds of instances, but most with indications that the lights came on, or no mention of lights in their posts.

In the meantime, Ozark Lee, thnx a million.