Brake discs.

[matt2223]

At what point do other testers on here fail a brake disc for being seriously weakened? For me I’d take it as being water thin or cracked. One of my testers likes to fail them for being pitted. What’s your opinions on this?

[Deleted]

The government don't want brake discs failing the test unless they are seriously weakened. I take that to mean that if the NT considers that the discs/brakes would become damaged as part of brake testing, then a refusal to test brakes would be the correct option. This means "Abandon the test" at the end before testing the brakes, the presenter can then get the brakes fixed and another test completed. You are correct that if a disc is wafer thin or cracked then abandon the test.

[Noberator]

I got two advisories last week on my ST.

Brake disc,pitted or scored,but not seriously weakened Nearside Front [3.5.1i]
ion thro
Brake disc,pitted or scored,but not seriously weakened Offside Front [3.5.1i]


I was half expecting it as I am getting slight vibration through the steering wheel under normal braking which is more pronounced under heavier braking.

I was advised to get new discs/pads fitted.

[rpm]

I can't remember the last time my Mot station failed a disc

Had no end of advisories, and loads that I deem unsafe and insist on changing. But they have to be really bad to fail ?

[matt2223]

May 11, 2018 13:01:55 GMT 1 rpm said:

I can't remember the last time my Mot station failed a disc

Had no end of advisories, and loads that I deem unsafe and insist on changing. But they have to be really bad to fail ?

In my opinion reading the manual they would have to be really bad. I’ve tested one this morning where in a service look you would say it needs discs but I couldn’t say they were seriously weakend however I know one of my testers would of failed it straight away

[Karl]

You effectively can't fail a brake disc

It has to be so bad that it would be a dangerous to carry on with the test

Just being worn below minimum thickness/badly lipped/ or pitted or corroded isn't a reason for rejection

[Karl]

If the brakes are truly bad they are going to hopefully show up during RBT

Expect he fails them for binding on the ramp too

When it's only a fail if picked up in rollers

A common mistake

[dave]

I dont understand that people would skimp on brakes or tires then happily put their kids in the Car
But I also think that 75 percent of the people out there are retarded so it' probably just me 

[Deleted]

May 11, 2018 19:16:08 GMT 1 dave said:

I dont understand that people would skimp on brakes or tires then happily put their kids in the Car
But I also think that 75 percent of the people out there are retarded so it' probably just me 

You been doing your homework then 

[Deleted]

May 11, 2018 14:36:43 GMT 1 Karl said:

You effectively can't fail a brake disc

It has to be so bad that it would be a dangerous to carry on with the test

Just being worn below minimum thickness/badly lipped/ or pitted or corroded isn't a reason for rejection

Actually yes a brake disc or drum can be failed as stated below;


the condition and security of brake drums and discs

i. a brake disc or drum in such a condition that it is seriously weakened or insecure

The problem for some NT's is in the understanding just how bad this has to be. If the NT chooses to apply the above fail criteria, then if the NT backs that up with a RBT, then DVSA staff know the NT made the incorrect decision, this is because the DVSA staff do understand the forces involved when carrying out a RBT to gain efficiency limits of 16 and 50 or 58% respectively. If a brake disc or drum was significantly weakened then you would cause damage to the presenters vehicle, but it is more than unlikely to be very rare occurrence for an NT to see this, this being because the presenter has to drive the vehicle to the Test Station over some miles, and the damage has not occurred during normal driving, so the condition must be severe to be honest to fail and abandon the test. 

[Karl]

That's what I said
Or should have said
Need to be dangerous to the point of damage during RBT to abort the test .

But how many do it the right way ?

Brake test performed last

[Deleted]

May 11, 2018 21:59:01 GMT 1 Karl said:

That's what I said
Or should have said
Need to be dangerous to the point of damage during RBT to abort the test .

But how many do it the right way ?

Brake test performed last

Me and you of course 

[valhalla]

Loads of failures here on Skye for discs that are not effective across the width of the brake pad, i.e. the disc surface has rusted across enough of the face to constitute a serious loss of braking surface area.

It's a moot point as to how much surface area has to be lost to constitute a fail..... I work on 50% as a limit on the front discs (main braking forces) for my services, but I will advise customers well before then.

Only structural failures I have seen are not on MoT's, they have come in as severe judders or imbalances, where the ventilation area of the disc/s has/have parted company.

[Deleted]

May 12, 2018 21:52:10 GMT 1 valhalla said:

Loads of failures here on Skye for discs that are not effective across the width of the brake pad, i.e. the disc surface has rusted across enough of the face to constitute a serious loss of braking surface area.

It's a moot point as to how much surface area has to be lost to constitute a fail..... I work on 50% as a limit on the front discs (main braking forces) for my services, but I will advise customers well before then.

Only structural failures I have seen are not on MoT's, they have come in as severe judders or imbalances, where the ventilation area of the disc/s has/have parted company.

In the mot test for the UK the surface area does not matter, the whole rubbing area that the pads rub against can be completely rusty, in other words no visual surface area left. From the mot standards that brake disc or discs on "Condition" has past the mot test, however the RBT is another thing all together!

[remmington]

We have seen several ventilated brake discs that have parted - ended up in two bits thru corrosion.

Nasty mess!

Not nice for the person driving either...