5008 Parking Brake (handbrake) Low Efficiency

[BadMojo]

Hello All

First post and asking for your help and guidance.

My 5008 has just failed it's MOT with low efficiency on the parking brake (handbrake). It only scored 12%.

The garage removed the rear wheels and had a thorough look at the cables, calipers, cleaned, etc and it still failed. They commented on how good everything looked and that there was nothing obvious they could see to explain the low efficiency. They let me take it away, but were totally flummoxed as to what the cause could be. They actually said google it and if you find a fix, let us know! Hence my visit.

Test Results
Service brake Front
L353 kgf R411 kgf 16% Imbalance

Service brake Rear
L268 kgf R270 kgf -1% Imbalance

Service Brake Total
1302 kgf Efficiency 72%

Parking Brake
L110 kgf R104 kgf 22% Imbalance

Parking Brake Total Force
214 kgf Efficiency 12 %

A month or so ago I changed the rear pads, front discs & pads, but didn't do anything with Diagbox. A couple of weeks ago I changed the handbrake switch as I was getting faults. (I changed the battery first, but it didn't fix it.) During this process I used DiagBox and went through the parking brake calibration process a couple of times. More of a precaution that anything else, in preparation for the MOT.

I was hoping someone would have some ideas on what I could try to improve the efficiency and get me through an MOT.

Keywords
Handbrake, parking brake, efficiency, inefficient

[GiveMeABreak]

Do they realise that they have to test the handbrake with the ignition off? Or they can hold the handbrake control up and that will apply full force or ‘Dynamic Braking’.

[BadMojo]

Coincidentally, I've just been reading about this very point. I'd forgotten about 'maximum application' by a long pull of the switch (for when parking on hills or when towing) and have also just read about having the engine off too.

I have no idea if he knew about either of those points, or how he performed the test. My wife took it in and they guy was very helpful and said he was more than happy for us to research, fix and take it back for a re-check before a re-test. I'll get her to give him a call in the morning. I'll be really annoyed if that's the reason for the fail. If it is, we'll be asking for a refund!

So is it an and/or when it comes to long pull/engine off?

[GiveMeABreak]

Well all I’m saying is that Dynamic Braking is used in emergencies when driving. Say the worst happened and you were a passenger in a moving vehicle and the driver became unresponsive. The passenger could pull up and hold the electronic brake control and that would apply dynamic emergency braking which would bring the car to a standstill using the ESP system for stability control. So with the engine running and without forward motion, it would simply apply maximum braking force used for parking on hills or when parked and connected to a caravan or trailer.

So you Could just ask them to keep the engine running and hold the handbrake control on whilst doing the test and the will apply maximum force.

They should be aware of the procedure though as it will tell the, on the computer prior to the test of any special requirements.

If there was a problem with the brake callipers themselves, I would expect that to show as an issue with the normal brake test.

[RichardW]

It's common for these to fail on the handbrake - but it works in reality, so it must be something about the way they test it. If it was really only doing 10% then it would roll away on an almost imperceptible hill! Our C4 Picasso got a fail on a reading like this, but it would hold it on the 1:10 hill on the way home from work so it was working - the trick seems to be to make sure that they know to hold the switch for a couple of seconds till it applies the extra load, and this should put it over the required level. I did wonder if the main cable was getting a bit sticky, and this was confusing the sensors in the motor - I had planned to change it on ours, but I sold it instead!

[BadMojo]

Spoke with the garage owner and he was aware there may be an 'extra' handbrake boost, but it appears the tester may not have known how to apply it to the 5008. She was trying double pulls of the button (Audi require this) but not a long pull. The engine was running during the test. So there's a chance a re-test with a long pull on the button will get me the extra few % I need for a pass. We're waiting for a call back and hopefully a re-test this afternoon.

I was going to run Diagbox for one last check for errors, but it's decided to stop working. But that's a different issue...

[GiveMeABreak]

It's annoying that they do not check their systems properly - the Audi system is not the Citroen system and completely different. They should know this! It shows complete ignorance and a 'can't be bothered to check' attitude that would have me walk away from that place I'm afraid.

[BadMojo]

We're taking it back at 1500 for them to recheck. They're now claiming to have applied the 'full power' handbrake after saying they didn't know how to. The main thing is, I hope it passes. We can argue about why they didn't do it right the first time, later. But I suspect they'll claim it's something I've done to 'fix it'.

[GiveMeABreak]

Good luck - let us know how it goes

[BadMojo]

They retested, applying the handbrake as instructed by us and the results literally jumped to 17% efficiency and I got my MOT pass. The tester was adamant she'd applied the handbrake correctly, but she obviously hadn't. My wife argued for a refund of the £35 they charged us to strip and clean the rear brakes and the manager agreed.

[GiveMeABreak]

Well done, great news on both fronts. At least you will be prepared in future if the same thing happens.