I took my car for it's MOT today at a non-VW independant garage and it failed again (see last year) because the front brake disks were 'excessively pitted' (the rears were OK). I decided to have them replaced but I have kept the old discs. On inspection both discs have got corrosion on the inside only, on about 50% of the usable disc. The outsides of the disks are OK.
Bearing in mind that the discs have about 75% usable area do they warrent a fail?
If they are a fail can I draw any conclusions about the quality of the VW discs.
The car is 5 years old and has done 37k.
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Did you notice any problems when braking? Juddering? Loss of braking performance?
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None at all. The brakes passed the efficiency test.
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>>None at all. The brakes passed the efficiency test.
A lot of the time they will pass the efficiency test okay. Its not so much that they aren't good enough to stop the car, but more the fact that the parts construction is beginning to fail.
I have to change the discs and pads on one of the cars that I look after every few years. This is due to pitting, mainly because the car does 1000 miles a year and as a consequence the discs rust and pit. There is little I can do to stop it, but they never fail on the efficiency test and I only change them when they get to the point of it being an MOT fail - its false economy otherwise.
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If they are the original discs then after 5 years they haven't done too bad. Unfortunately pitted discs and what constitutes a failure is down to the opinion of the MOT tester, it is not a straightforward black and white issue. Things such as a light bulbs, they either work or they don't are easy, but your pitted discs fall into a grey area.
Its difficult for anyone to say without seeing the discs but feel free to seek an appeal with VOSA. Although experience says that you are unlikely to get the same result as last year. If I were you I would just replace the discs and pads, then you should be okay for another few years with no problems. If you have done 37k on them anyway you have had a decent proportion of wear from them anyway.
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37k & 5 yrs old id say they don't get used very much im not saying do 20,000mls a year but are you able to remove the discs and give them a clean up with emery cloth? the mileage is low for discs usually they do double that just might save you a few quid?.
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If they are pitted, they will not clean up with emery cloth. Nothing short of having them skimmed will do it, but if you are taking them off then you might as well just replace them anyway.
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Lets ignore the fact that they are pitted. As mentioned, only skimming will satifactorily remove this.
My concern is that they are pitted across 50% of the inside contact area. I can think of two reasons:
1. Your use of the brakes is infrequent and very gentle.
2. The pad on the inside of the disc is not seated parallel to the disc, causing it to contact appreciably only on 50% of the disc. In theory, decent use of the brakes should bed the pad into the disc profile, but this does not appear to be happening.
If you were to put some engineers blue on the discs, you may see that part of the disc is not being used at all. Something appears to be out of alignment.
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SWMBO's 106 gets pitted disks due to short journeys/wet roads/being garaged when wet and brakes cold.
Before MOTs I do an Italian tune up and go to the top of the nearest hill and go down quickly braking most of the time. Twice.
This cleans the disks of any surplus rust and heats the rust so it tends to blacken and be less obvious.
Does it work?
Original disks lasted 5 years.
Halfords replacements (treated as above) have lasted 8 years so far..
madf
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