Pulsing Brakes MOT failure?

catflea

Hi guys

Our 97 Transit campervan has been left laid up since Glastonbury last year and its now MOT time...

Took it out for a spin today and have found that the foot brake is pulsing as you drive, the brakes are still very good indeed though so is a pulsing pedal going to mean that the MOT is a failure?

No ABS and its pulsing when you apply light pressure when you actually hit the brakes there isn't really anything noticable

Its likely to fail on something else anyway knowing my luck but....

Ebe_Scrooge

If it's not got ABS, then my guess would be the discs are slightly warped. You can check them easily by using a straight-edge ( something like a steel ruler ). If this does turn out to be the case, it's not necessarily an MOT fail so long as the braking efficiency is within the prescribed limits - though it may fail if they're excessively warped.

The good news is that new discs and pads are pretty cheap, and dead easy to fit - DIY-able if you're reasonably familiar with working on cars, or a very quick and easy job for a mechanic.

Stigy

I have done a bit of copy/pasting....I think the two threads will probably be merged anyway though to save confusion.

Me_in_other_thread wrote:

From experience as long as there's no imbalance during the brake test done on the rolling road, and the brakes appear to work effectively when the system is pressurised (an assistant will either pump the pedal or apply maximum foot pressure during the test) you should be fine, maybe an advisory at best. MoT regulations have changed somewhat since I was in the motor trade so I could be wrong here, but I'd think you'd be okay as long as they work effectively (same goes for being too sharp...).

As far as a fix goes, it's more than likely the front brakes have corroded and are not as 'true' as they were before it was laid up....Was it garaged? Being discs up front, corrosion is far more common on front brakes than rear on Transits of that era (your Transit would have drums at the rear unless converted for discs, or a 'Custom' model).

You_in_other_thread wrote:

Yes. Sorry

If a mod could close this then I will repost in the correct place...

And stiggy yes, the discs were definitely nicely corroded

Me_in_other_thread wrote:

Give it a good run and use the brakes a lot, try and burn some of the corrosion off, at least for the benefit go the MoT. In the long-term, new discs and pads are more than likely needed. It's a relatively easy DIY job if you're that way inclined, and will probably save you about £100 in garage fees.

forgotmyname

Are you sure its not flat spots on the tyres?

Maybe just working the rust off the discs.

Strider590

Are the discs getting really hot?

On a vehicle that old, left unused for some time, it's possible the brake calliper pistons are corroded in their bores and seizing. This causes overheating which boils the brake fluid and leaves an uneven layer of pad material on the discs (which then causes the symptom you describe).

Old Fords suffer this quite a lot, as the calliper pistons used to be chromed steal, the chrome used to blister and allow rust underneath. Newer Fords have stainless steal calliper pistons.

Jack the front and check the wheels spin, also check the brake light isn't stuck on permanently, as this is another tell tale of that fault.

Stigy

Strider wrote:

On a vehicle that old, left unused for some time, it's possible the brake calliper pistons are corroded in their bores and seizing. This causes overheating which boils the brake fluid and leaves an uneven layer of pad material on the discs (which then causes the symptom you describe).

That's a good point, and worth noting also that it's not always immediately evident that the calliper is seized/partially seized under normal driving conditions

Strider wrote:

Jack the front and check the wheels spin, also check the brake light isn't stuck on permanently, as this is another tell tale of that fault.

The brake light switch is on the brake pedal arm/bulkhead (can't think why or how it would be anywhere different?), so the brake lights should be off until the pedal is pushed regardless of the calliper situation. The lights would stay on if the pedal itself was sticking down, as the brake light switch relates directly to what the brake pedal is doing, rather than what the mechanical parts of the braking system are doing.

AdrianC

It's been sat for a year. Almost certainly it's just corrosion on the disks, where the pads weren't. It'll clean up in no time.

And, no, it's not going to be a fail. MOT only really looks at the maximum retardation.

Stigy - there are vehicles out there with brake lights working from hydraulic pressure, but they're mainly a lot older than this.

catflea

Like my moggy minor

arcon5

A corroded disc will fail.
Surface rust on the other hand will scrape off in no time. More than likely though just sticking brakes

Joe_Horner

arcon5 wrote: »

A corroded disc will fail.
Surface rust on the other hand will scrape off in no time. More than likely though just sticking brakes

You'd be surprised how much corrosion is allowed as long as the brakes still perform ok.

Guidance, with examples of what should pass, courtesy of VOSA (as was) / DVSA:

https://www.youtube.com/watch?v=xVpgCKz8oWs&t=2m25s

OP, pedal pulsing in itself won't fail but if the brake effort is also changing significantly as the wheels rotate then it can fail for that.

Strider590

Stigy wrote: »

The brake light switch is on the brake pedal arm/bulkhead (can't think why or how it would be anywhere different?), so the brake lights should be off until the pedal is pushed regardless of the calliper situation. The lights would stay on if the pedal itself was sticking down, as the brake light switch relates directly to what the brake pedal is doing, rather than what the mechanical parts of the braking system are doing.

When the calliper pistons seize, the brake fluid doesn't return to the master cylinder as it would normally, the weight of the brake pedal causes the pedal to rest on the brake light switch and as a result the lights can get stuck on.