Pulsing Brakes MOT failure?

AdrianC

Strider590 wrote: »

The only way the pedal is going to return is if it's not actually attached to the piston from the master cylinder.

Well spotted.

I assume everyone here understands why the brake pedal drops slightly when you turn on the engine, versus the car not running??

With your foot resting on the pedal, overcoming the spring? Absolutely.

Stigy

Strider590 wrote: »

Oh really......

Less that one year ago I replaced two seized brake callipers on one of my cars, it did not fail an MOT for seizing callipers (because it's not an MOT fail), it failed because the seized callipers had caused the pedal to fall on to the brake switch, causing the brake lights to show constantly.

I could get the brake lights to turn off by using a brake calliper opening tool to force the pistons back, thus forcing fluid back up into the master cylinder.

In the end I fitted new callipers, flushed through with new brake fluid and no more problem.

Your brake calliper couldn't have been seized to that great an extent, as if it was your brakes would have been binding in to the extent that it WOULD fail an MoT and you certainly wouldn't have been able to wind the piston back. I'm assuming as you used a winder it was a rear calliper? As most cars these days have push back Pistons on the front these days.

The brake pedal isn't pushed up by hydraulic pressure in the same way as a clutch pedal often is. Think about it, if you have a leak in the system does the pedal fall to the floor? No, it stays up at its default position until you operate it. Only then do you realise there's a leak when the pedal feels spongy and then is the only time it goes to the floor, but only when operated.

salubrious

For the OP - It's likely to be surface rust on the brake discs.

Unlikely to fail on the disc itself, but if the brake is fluctuating when applied (which it is atm) then it will fail.

With it standing 12 months there could well be other issues on the brakes anyway, as other have already explained.

Strider590

Stigy wrote: »

Your brake calliper couldn't have been seized to that great an extent, as if it was your brakes would have been binding in to the extent that it WOULD fail an MoT.

Brake binding isn't an MOT fail. As long as they stop the car to the standard specified then it's a pass.
It can only go down as an advisory and for as worrying as that may be, that's the way it is.
Even the tester was surprised when the system would not let him fail it for binding brakes.

The tyre's were also barely legal, less than 2mm tread, 20+ years old and hard as a rock, these couldn't be failed either.

I got new tyres from a motorsports supplier (some nice road legal semi-slicks), then I replaced the callipers + pads + discs and pressure bled the system when the parts arrived a week later.

AdrianC

Strider590 wrote: »

Brake binding isn't an MOT fail.

Wrong.
http://www.motinfo.gov.uk/htdocs/m4s03000702.htm
Reason for rejection: The braking efforts at the road wheels do not reduce at about the same rate when the service brake is released gradually.

Stigy

Strider590 wrote: »

Brake binding isn't an MOT fail. As long as they stop the car to the standard specified then it's a pass.
It can only go down as an advisory and for as worrying as that may be, that's the way it is.
Even the tester was surprised when the system would not let him fail it for binding brakes.

The tyre's were also barely legal, 20+ years old and hard as a rock, these couldn't be failed either.

I got new tyres from a motorsports supplier, then I replaced the callipers + pads + discs and pressure bled the system when the parts arrived a week later.

You sure it wasn't their rolling road at fault? If ever there was a cause of a brake imbalance, a seized calliper is a prime example, to the extent that there really aren't many other causes! If the seizure is such that it's only partial, or on the rear and not too severe that braking isn't affected then fair enough, but the vehicle will usually be unbalanced under braking with a seized calliper.

Strider590

Well I guess both were equally as bad..... In fact I know they were because I stripped them down afterwards with a view to reconditioning them.

Joe_Horner

AdrianC wrote: »

Wrong.
http://www.motinfo.gov.uk/htdocs/m4s03000702.htm
Reason for rejection: The braking efforts at the road wheels do not reduce at about the same rate when the service brake is released gradually.

You're right that it's a fail, but more likely under RFR 3.7.1:


1. A significant braking effort recorded on a road wheel, even though the brake is not applied, indicating that a brake is binding.

Although your RFR could work for a calliper that's sticking very slightly and releasing fully but slowly

Strider590

"Significant"

The road wheels could be rotated by hand, with a little effort, when they should move freely.

THAT is not significant..........

Are you really going to sit here doing the keyboard warrior dren, picking at slightest thing where I don't write a f**king essay to describe it to the n'th degree?

My bad, i guess i should have measured the force required to turn the wheels by hand.

Stigy

Strider590 wrote: »

"Significant"

The road wheels could be rotated by hand, with a little effort, when they should move freely.

THAT is not significant..........

Are you really going to sit here doing the keyboard warrior dren, picking at slightest thing where I don't write a f**king essay to describe it to the n'th degree?

My bad, i guess i should have measured the force required to turn the wheels by hand.

There should be a little resistance, although minimal on rear braking systems. This is only the case for rear brakes where the handbrake is connected. On older Vauxhalls you had to be careful as the slightest over-adjustment saw the brakes overheat and the brake fluid boil up, causing constant brake fade.

Most are automatic adjustments now, but where the adjustment is manual, the less resistance the worse the handbrake becomes. You should be able to freely rotate the drum but it should stop by itself, almost instantly as a rule.