Can washing your car destroy your brake discs?

[LotusOmega375D]

My October 2017 Passat lives outside, but doesn't have a very hard life. I wash it myself every few weeks and always try and get a quick drive in to help dry things off, when I have finished. Anyway, I washed it once before Christmas and left it for a day or so before using it again. The electronic parking brake was binding and needed to free itself, and then I got that pulsing sensation through the brake pedal, when applying the foot brake. No bother, I thought, it will clean itself up and any surface rust on the brake discs will disappear after a few miles. The car had done <7000 miles at that time.

In fact I had a couple of long journeys ahead, so I assumed it would sort itself out. Not so, even after 1000+ miles, the sensation had still not gone away. I booked it in with the dealer, where it is today. The mechanic had a drive with me this morning and confirmed that something was wrong. It's a similar vibration sensation you get when driving over rumble strips prior to a roundabout.

Anyway, the car's now been checked over and all 4 discs are knackered. All are out-of-tolerance and badly scored on the inside (outsides look fine). So since these are consumables, I'm faced with a big bill for new discs and pads on all 4 corners. The car's now at <8500 miles.

Has anyone else experienced this? Anything I can do to prevent it happening again (apart from keeping it in a garage and not washing it or driving it in the wet!)?

[LotusOmega375D]

Yes the VW technician supplied a video and refers to "a DTI brake disc run-out test being performed and found to be out-of-tolerance" on all 4 discs. It is clear from the video that the insides of the front discs are badly scored: almost as if the pads were worn to the rivets. They're not: there is 12mm remaining on fronts and 9mm remaining on rears.

[LotusOmega375D]

bobtail4x4 said:

do you sit in traffic with your brakes on?

that causes discs to warp after a run.

Not me: it's a manual and has auto-hold. What's interesting is that it happened that one particular time and then stayed like that. Prior to that the surface rust on the discs would soon get worn away as expected with no issues. Strange.

[LotusOmega375D]

C.A.R. said:

You say Christmas, I wonder if it was exceptionally cold? Was the car driven prior to being washed (could the discs have been warm and rapidly cooled)?

Seems mad.

I don't remember the exact sequence of events, but even if I had driven it first, by the time I'd unwound the hosepipe and filled the car-wash bucket (no double entendres please) it would have cooled down.

[LotusOmega375D]

Thanks for your replies. I think you're right about the lack of use. All replaced now. VW claim only to offer 6 months or 6000 miles months warranty on discs, so no help from them. It's a company car, so my employer will have to pick up the bill. Still rubbish though.

[LotusOmega375D]

I've had a chance to sleep on this now and think I have come up with a plausible explanation.

I was brought up driving a diet of 1960s / 1970s / early 1980s cars. Cars of this ere were infamous for rusting, particularly around the wheel arches. I therefore got into the habit of hosing around the wheel arches to remove any dirt and salt.

I have carried on with this procedure through to the present day. I think this is causing the disc scoring: i.e. some of the dirt and debris from the wheel arches is splashing back onto the reverse side of the discs. This would explain why only the inside of the discs is affected, since the exposed side gets directly rinsed clean with the hose pipe after I have cleaned the wheel rims. Meanwhile the back of the discs remain coated with bits of hidden crap, which eventually ends up scoring the discs when embedded by the action of the brake pads.

What also supports this idea is that I had a similar issue with a 62 plate all-disc brake Polo 3 years ago. I didn't give it much thought at the time, since I bought that car second-hand and it had covered a good deal more miles. I just assumed that I was a tad unlucky and bought 4 pattern discs and pads and got them changed locally.

So, if true, the moral of the story is don't hose out your wheel arches, unless you take the wheel off and cover the disc brake assembly. It also means that it was my actions which led to the heavy scoring on the inside of each disc, so I can't blame VW after all.