# Rusty & pitted brake discs



## HARRYH (May 18, 2005)

Hi
2007 Swift / Fiat
Having just had an MOT failure on my wifes Honda Jazz brake discs, due according to the Honda Garage the low mileage 8500 in three years allowing rust pitting. The car does 20-30 miles most days.
My motorhome concern is that by comparision it stands unused more.
Has any one had any problems with disc rust pitting and is there any precautions /prevention?
It seems that discs rust out before pads ware out these days and a bit of hard brake pedal use maybe a good thing to keep the rust at bay & repair cost down.


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## 96410 (Sep 30, 2005)

I would get a second opinion, if car is used daily then than would clear all the surface rust, Looks like they may be looking for work.


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## Zebedee (Oct 3, 2007)

HARRYH said:


> Having just had an MOT failure on my wifes Honda Jazz brake discs, due according to the Honda Garage the low mileage 8500 in three years allowing rust pitting. The car does 20-30 miles most days.


This is not logical Harry.

20 to 30 miles each day should be enough to keep the disks in good condition, irrespective of the mileage. It's frequent use that makes the difference, and low mileage with almost daily use should make them last longer, not accelerate the wear!!!

As for the M/H query - I don't think there is an easy answer. Someone may have a tip for both of us?? 

Cheers

P.S. Subaru beat me to it. Damn!!!!!


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## mangothemadmonk (Aug 6, 2006)

The only thing that knackers up disk brakes is if you have worn the linings/pads down to the metal.

This can happen if the calipers have been sticking but it would be a rare thing but not unheard of.

I would ask to see the discs before work was done on them.

I had to renew mine on the Hymer when I bought them as the pads were starting to crumble so i repalced the discs and pads at the same time.

This was due to lack of use.

Johnny F


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## aultymer (Jun 20, 2006)

I have been advised by 2 different garages to run with the handbrake partly on for about 10 minutes every week to clean up the seldom used back brakes on 2 different motors. It appears that modern brake management systems seldom use the back brakes and that rusting is the most common cause of MOT failure.
My own thoughts on the matter are that pitting in itself should not be a reason for failure, unless so bad that failure could occur before the next MOT, since pitted discs are not that different from vented discs.

I have just heard that our BMW Mini 02 plate (now with my son) has just passed its MOT in an independent garage in spite of the BMW dealer telling us at the last 3 services that the discs needed changing!!

Maybe changing your MOT station would be cheaper than changing your discs in future. 
I try to never use a main dealer for consumables or MOT simply because their overheads lead to ridiculously high charge-out rates.

I am not a mechanic and can only tell you of my experience so when in doubt consult a professional (but maybe not at a main dealer).


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## AberdeenAngus (Jul 26, 2008)

Couple of tips.

Don't store the van with salt on the discs, give them a hose down with fresh water.

Don't let the van stand for ages with the pads resting on the same place.
Each time you do a spot check onthe van, move it forward or backward slightly.

Bit off topic but important. When in storage never just start the engine then shut it down. Give it a good 10 mins and let it get up to operating temperature.
Couple of reasons:
Repeated short starts & stops can glaze the cylinders of a large diesel with low operating hours (i.e low mileage)
You need to replace the juice you took out of the battery to start it.
Heating the engine right through, drives condensation out of the oil and engine bay.
Oh, and run the air-con too, or the seals may dry out and crack.


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## HARRYH (May 18, 2005)

Thank for you advice
A bit more on the Honda story. I did not accept the garage tale and after a bit of argy Honda UK paid £100 of the bill to the Bolton garage for the discs but it still left me/my wife feeling we had been ripped off and about £80 down.


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## johng1974 (Jan 17, 2007)

> since pitted discs are not that different from vented discs.


what does that mean aultymer?

re: surface rust on disks, if you can, before an MOT, on a vehicle that's been left a long time, give the surfaces a quick wire brush.. I know it's a hassle but a few mins spent is better than an uneccessary £200 bill..
I appreciate working on a MH is a taller order...

otherwise, a decent drive should normally clear it...

just my 2p

:lol:


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## rowley (May 14, 2005)

Quote from aultymer--I have been advised by 2 different garages to run with the handbrake partly on for about 10 minutes every week to clean up the seldom used back brakes on 2 different motors. It appears that modern brake management systems seldom use the back brakes and that rusting is the most common cause of MOT failure. 

I would not do this on the X250 chassis as I understand that the handbrake is on a drum whereas the foot brake operates discs on the rear.


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## AberdeenAngus (Jul 26, 2008)

Quite a few larger vehicles run with this arrangement now i.e. combined rear hub & disc


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## CliveMott (Mar 10, 2008)

When you wash the wheels / wheel arches etc take the vehicle for a short spin to dry off the brakes. Its leaving it stood up wet is the worst (apart from wading in the sea!) . The water gets retained twix pad and disk and you get nice pad shaped rust holes.

C.


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## SpeedyDux (Jul 13, 2007)

I had my California serviced not long ago at the local VW franchised dealer. They didn't put it through the MoT as requested because they said they were too busy. They also didn't re-gas the aircon as requested. Before asking me to make a new appointment for the MOT they told me the back disks were corroded and needed replacement before the MOT, otherwise it would fail. Would I like to book it in for that work as well?

Hell no. I took the van to my non-franchised garage/MOT station next day, and it passed. They said there was slight pitting on the back disks but nothing to worry about.

I'm not going back to the VW franchised dealership. The T4 forum posters often refer to them as "stealerships". I wonder why.

SD


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## aultymer (Jun 20, 2006)

> I would not do this on the X250 chassis as I understand that the handbrake is on a drum whereas the foot brake operates discs on the rear.


Thanks Rowley for bringing that to everones attention. As I said my story was about my vehicles and there will never be an X250 in that group given the problems and lack of support their owners get.


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## inkey-2008 (May 24, 2008)

*rusty brake discs*

I remember reading an article from an MOT trainer and he said that It did not matter how much they where rusted .They should not be fail on a sight test, only if they failed the brake machine test. As it has been said surface rust can be polished off by driving with the brakes on. I had this on my old van but it was only as a recommendation not a failure I did change the discs but only when they failed the machine test.


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## teensvan (May 9, 2005)

Hi.

As stated the look of surface rust or light piting on a disc is not an MOT failure. The disc can only fail the test if it is below a manufactures stated thickness as measured by a micrometer / callipers twisted through overheating runout or very severe pitting allowing it to fail the brake test. Most main dealers use this as a money making job as the average owner does not know what they are looking at when it comes to disc problems. I have built and owned that many cars vans and motorbikes i cannot count them and have never had one MOT failure due to disc faults. 

steve & ann. ------------- teensvan.


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## GerryD (Sep 20, 2007)

teensvan said:


> Hi.
> 
> As stated the look of surface rust or light piting on a disc is not an MOT failure. The disc can only fail the test if it is below a manufactures stated thickness as measured by a micrometer / callipers twisted through overheating runout or very severe pitting allowing it to fail the brake test. Most main dealers use this as a money making job as the average owner does not know what they are looking at when it comes to disc problems. I have built and owned that many cars vans and motorbikes i cannot count them and have never had one MOT failure due to disc faults.
> 
> steve & ann. ------------- teensvan.


The MOT test does not allow for micrometer checking of the brake disc. A disc would not show any rust provided it has been driven before the test. The first application of the brakes would remove any surface rust build up. A disc could fail the MOT if the tester felt that braking efficiency was reduced due to wear of the disc but the only check would be a sight test based on feeling the wear ridge at the edge. The only actual measurement taken and enforced in the MOT is exhaust and brake efficiency. The examiner is not allowed to utilise any other service tools. It is even not allowed to remove wheels so discs cannot be measured.
If you want a true and fair test, always use your local Council or VOSA testing station.
Gerry


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## teensvan (May 9, 2005)

The measuring of discs is allowed by a micrometer at an MOT as there is a minimum thickness stamped on a set of discs i am looking at that are fitted to one of my motorcycles.

steve & ann. ------------- teensvan.


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## GerryD (Sep 20, 2007)

teensvan said:


> The measuring of discs is allowed by a micrometer at an MOT as there is a minimum thickness stamped on a set of discs i am looking at that are fitted to one of my motorcycles.
> 
> steve & ann. ------------- teensvan.


You may be right about a motorcycle, the disc is a much lighter and more fragile affair, but on a car or commercial vehicle it is not possible to reach the brake disk to measure it without removing the wheel. It is not permissable for the vehicle examiner to remove any part of the vehicle.
Gerry


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## wizza (Jun 27, 2008)

Discs can be advised for slight corrosion, pitting, or worn and can be failed for excessive, corrosion, pitting or worn nothing can be removed from the vehicle not even a wheel trim and is a visual inspection only but some of the ones i have seen and failed you would not want on the road


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## Wizzo (Dec 3, 2007)

aultymer said:


> I have been advised by 2 different garages to run with the handbrake partly on for about 10 minutes every week to clean up the seldom used back brakes on 2 different motors. It appears that modern brake management systems seldom use the back brakes and that rusting is the most common cause of MOT failure.
> My own thoughts on the matter are that pitting in itself should not be a reason for failure, unless so bad that failure could occur before the next MOT, since pitted discs are not that different from vented discs.


The brakes should always operate on all 4 wheels when you apply the brake pedal, if it doesn't then it's faulty!

I think you've confused a vented disc with a drilled disc. A vented disc has the inside and outside edges separated by a space. Drilled discs were often used on motorcycles for lightness and to try and disperse water. The Japs in their infinite wisdom used stainless steel discs in the 70's which had the same buttock clenching properties in the wet as pedal cycle brakes.

JohnW


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## aultymer (Jun 20, 2006)

> The brakes should always operate on all 4 wheels when you apply the brake pedal, if it doesn't then it's faulty!


There are awful lot of faulty brakes out there. Look at some - front used and shinny - back dull from lack of use. The back discs on many cars will only get used when real pressure is put on the brake pedal and most people now drive to minimise hard brakeing.
The brakes work as designed just not hard enough on the back to keep the discs from rusting.
Not my reasoning but advice from 2 different garages who weren't working on the brakes for 2 different makes of car (Pug 406 and BMW Mini).
Maybe I just don't brake enough and it's just my cars affected this way.


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## Wizzo (Dec 3, 2007)

aultymer said:


> There are awful lot of faulty brakes out there. Look at some - front used and shinny - back dull from lack of use. The back discs on many cars will only get used when real pressure is put on the brake pedal and most people now drive to minimise hard brakeing.
> The brakes work as designed just not hard enough on the back to keep the discs from rusting.
> Not my reasoning but advice from 2 different garages who weren't working on the brakes for 2 different makes of car (Pug 406 and BMW Mini).
> Maybe I just don't brake enough and it's just my cars affected this way.


The pressure would certainly be different front and back but the brakes should always work on all 4 wheels. By the very nature of disc brakes there is always some contact of pad on disc so even the act of the wheel revolving should clear any surface rust. If you have any surface rusting that isn't cleared then I suggest that you have a sticking caliper.

JohnW


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## 110227 (Feb 27, 2008)

teensvan said:


> Hi.
> 
> As stated the look of surface rust or light piting on a disc is not an MOT failure. The disc can only fail the test if it is below a manufactures stated thickness as measured by a micrometer / callipers twisted through overheating runout or very severe pitting allowing it to fail the brake test. Most main dealers use this as a money making job as the average owner does not know what they are looking at when it comes to disc problems. I have built and owned that many cars vans and motorbikes i cannot count them and have never had one MOT failure due to disc faults.
> 
> steve & ann. ------------- teensvan.


Brake discs cannot be failed due to being "below manufacturers stated thickness" as discs are not measured during an MOT test. The only items measured during the test are tyres. The discs are tested visually for condition and the efficiency of the brakes are tested in the rollers.

As with many of the items tested during an MOT, servicability of brake discs is a matter for the personal opinion of the tester concerned. The view of VOSA is that the tester should be trying to pass the vehicle where possible. The reality is that in many Main Dealers the bonus schemes in place mean that there is considerable pressure to upsell where possible. Brakes are an easy sell as most of us put safety before cost.

Regards

Mick 
(An MOT tester)


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