"Tom" wrote in message
...

"Chris Whelan" wrote in message
...
Michael Chare wrote:

When my VW Passat was last serviced I was told that the front disks had
corroded. This is true and there has been some corrosion at the edges. I
have been reluctant to change the disks, as neither the disks or pads
are
near their wear limits, even after 45,000 miles and 5 years. The brakes
work fine.

However, the car is now due for its MOT, so my question is: Is the state
of the disks an MOT failure point?


Reason for rejection:

"a brake disc or drum insecure, cracked or excessively scored, pitted or
worn"

See here, section h:

http://www.motuk.co.uk/manual_350.htm

Corrosion is not specifically mentioned. The friction material wear limit
(WRT the MOT) is 1.5mm. I would imagine you would not get a fail.

Chris

--
Remove prejudice to reply.

Corrosion on a brake disc tends to remove friction material from the pad,
in much the same way that sandpaper/ emery paper removes material. Once
the material is removed from the pad this relieves the pressure on this
part of the contact area, thus allowing the build up of further rust,
removing further brake pad material and further reducing contact surface,
thus enhancing brake pad wear. In short, it's a descending spiral, a
matter of judgement as to how far you are along the way and hence the need
for replacement.

Last one I replaced had a greatly differing amount of wear across the
pads, with the most worn pad bearing on only about half the designed width
of the disc, due to rust build up = MOT failure = urgent disc and pad
replacement.

Pads will not remove corrosion from discs in the course of use, it's a
fallacy.

If you can see the reduction in contact area of the pad (bright part on
the disc) so can the MOT man and he may say, "Do that and bring it back
when you have".
I have now examined the disks.

There is a rust area of about 1/4" across the pad starting from the centre
of the outside surface of one disk. On the other disk there is a rust area
on the inside surface for about 1/4" starting from the outer edge. The rust
areas have polished peaks.

Question is, is rhis bad enougth to fail an MOT test?


--
Michael Chare

I have now examined the disks.

There is a rust area of about 1/4" across the pad starting from the centre
of the outside surface of one disk. On the other disk there is a rust area
on the inside surface for about 1/4" starting from the outer edge. The
rust
areas have polished peaks.

Question is, is rhis bad enougth to fail an MOT test?


--
Michael Chare

I think it will come down to whether braking efficiency is up to scratch.
You might well get an advisary though.

Michael Chare was thinking very hard :
When my VW Passat was last serviced I was told that the front disks had
corroded. This is true and there has been some corrosion at the edges. I have
been reluctant to change the disks, as neither the disks or pads are near
their wear limits, even after 45,000 miles and 5 years. The brakes work
fine.

Corrosion on the no (pad) contact areas of the disk is normal and no
reason for concern.

However, the car is now due for its MOT, so my question is: Is the state of
the disks an MOT failure point?

If the all the pad contact areas are clean, with no extensive grooving
and the thickness of the disk is within spec., you have nothing to
worry about.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk