/ Car help - why is my parking brake efficiency so low?

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Ben Sharp - on 10 Jul 2013
I just got my car back from it's MOT and it needs a few things, one of the things it failed on was having a rear park brake efficiency of 8%. Which I thought was pretty low?

I parked the car on a really steep hill last night and the hand brake held it fine (like a really steep hill. I was wondering how the score can be so low yet the handbrake seems to do the job in practice. I always thought if it held it on a hill then it would pass the MOT...guess not. So how do they test it?

Also I've been lazy in the past and just tightened the cable from under the handbrake gaitor before, is this a bad idea? I'm guessing if that would have passed it then they'd have done that instead of suggesting taking the drums apart. Is it possible that I've stretched the cable to the point where it is that that's causing the problem?

Cheers

Ben
James90 - on 10 Jul 2013
In reply to Ben Sharp:

Not an expert but on my old car i had 2 problems with the parking break (for MOT)

for one of them i just had to tighten the cable as you describe.

For the second one i can't remember what had broken but it resulted in covering the break drum (on one side) in a lubricating fluid. this only affected one side (But i always replace break parts in paralel)

the reason i say this is that in the first case it wasnt holding in the second it was, i wasn't being ripped of by the garrage as I did the follow up work myself.
John W - on 10 Jul 2013
In reply to James90:
> (In reply to Ben Sharp)
>
> Not an expert...but it resulted in covering the break drum (on one side) in a lubricating fluid...

It might be just me misreading this, but I'm guessing it wasn't "lubricating fluid".
Richard Wilson - on 10 Jul 2013
By taking the slack up in the cable you are stopping the auto adjusters in the back brakes from working.
Slacken the cable off & take the drums off so you can clean & if needed un seize any linkages.
When refitting make sure the auto adjusters are working & have taken up any play inside the drums before you tighten the cable.
Ashley - on 10 Jul 2013
In reply to Ben Sharp:

I'm not an MOT tester but my understanding is that there has to be travel left in the lever after the handbrake is fully applied so maybe they pulled the lever to where they deemed to be sufficient additional travel and then measured it? When you apply the hand brake do you pull the lever nearly to the end of its travel?
Blue Straggler - on 10 Jul 2013
In reply to Ben Sharp:

Consider not simply tightening the cable, but looking at the handbrake compensator. This basically equalises the load to left and right wheels. If the compensator gets stretched, one wheel will not receive as much "braking" if that makes sense. I had my compensator (on MG Zt-T) replaced recently - that phase of Rover-MG was notorious for having compensators made of some steel that was more akin to margarine. I had to pull the handbrake lever right up to the max to be sure of the brake being good. So the cable was fine but the compensator was not. Now I have a solid steel compensator that will never need replacing, and we set everything so I don't need much lift on the handbrake lever.
It may not be your problem, but look into it at least (I guess just Google "handbrake compensator [Ben's Car]" :-)
Blue Straggler - on 10 Jul 2013
In reply to Richard Wilson:

Yours sounds more likely than mine (and you sound more like you know what you are on about than do I! :-) )
teflonpete - on 10 Jul 2013
In reply to Ben Sharp:

Is it that the efficiency figure is low because the handbrake is only working properly on one wheel? It would still work in practice but would show up on the brake tester in the MOT.

My Focus Estate on the other hand passed its MOT handbrake test but merrily rolls down hills with the handbrake applied!
James90 - on 10 Jul 2013
In reply to Ben Sharp:

just remembered something else, in MOTs there supposed to pull the break lever up to a certain height, if efficiency is that low as they say and it is still holding is it possible you are pulling much higher then they are?

jkarran - on 10 Jul 2013
In reply to Ben Sharp:

Ineffective handbrake is only likely to be a slack cable (excessive lever travel) or something slippery in the rear brakes.

What on earth '% efficiency' means in the context of a handbrake test I have no idea?. With all numbers like this you have to ask yourself 'is that actually big/small?", it could be fairly normal (as hinted at by a pass and the fact it works).

jk
teflonpete - on 10 Jul 2013
In reply to jkarran:
> (In reply to Ben Sharp)

> What on earth '% efficiency' means in the context of a handbrake test I have no idea?. With all numbers like this you have to ask yourself 'is that actually big/small?", it could be fairly normal (as hinted at by a pass and the fact it works).

He said it was one of the things it failed the MOT on.


To the OP, they test the handbrake with the car wheels running on driven rollers, same as the way they test the (foot) brakes. I believe the brake tester measures the resistance the car's brakes provide (via the wheels and tyres) to the rotation of the driven rollers when the brake is applied.

To JK, could it be that the % increase in force (or rather, torque) required to keep the rollers turning when the brakes are applied is represented as % efficiency on the brake test document?

wilkie14c - on 10 Jul 2013
In reply to teflonpete:


> To JK, could it be that the % increase in force (or rather, torque) required to keep the rollers turning when the brakes are applied is represented as % efficiency on the brake test document?

I think thats exactly it Pete. You don't need 100% or near it to pass either, IIRC handbrake needs to reach 25%
jkarran - on 10 Jul 2013
In reply to teflonpete:

> He said it was one of the things it failed the MOT on.

Ooops, my bad for not learning to read properly.
jk
Craigyboy13 - on 10 Jul 2013
In reply to Ben Sharp: could it be the rear brake cylinder?
Martin W on 10 Jul 2013
In reply to James90:

Dear James

The correct spelling of the name of the device which slows down, stops or immobilises a vehicle or other moving object is: brake

A break is something that a psychopathic pedant might inflict on the legs of someone who does not respect this simple fact.
Ridge - on 10 Jul 2013
In reply to Martin W:
> (In reply to James90)
>
> Dear James
>
> The correct spelling of the name of the device which slows down, stops or immobilises a vehicle or other moving object is: brake
>
> A break is something that a psychopathic pedant might inflict on the legs of someone who does not respect this simple fact.

Glad it's not just me.
jonathan shepherd - on 10 Jul 2013
In reply to Ben Sharp: If you have drum brakes on the rear it could be that you have self adjusting brakes that don't self adjust. My handbrake started to lose its holding capacity despite me having adjusted the adjuster nut under the center console so the handbrake was fully on with a minimum of lift. I mentioned it to my local garage and he said the brakes probably need adjusting in the drum, I said i thought they were self adjusting brakes at which he smiled and implied they never work properly. I took the drum off and adjusted them myself and the problem was solved. What happens is when the shoes wear down they move further away from the drum outer, the adjuster is meant to compensate for this by moving them back nearer the drum outer as the shoes wear but if they don't work properly the gap between shoe and drum increases and if your handbrake is already adjusted to the maximum or close to it there is no more room to adjust.
teflonpete - on 10 Jul 2013
In reply to Ridge:
> (In reply to Martin W)
> [...]
>
> Glad it's not just me.

It's not just you, it hurts my eyes, but alas, I have not the energy to smite the perpetrators of such heresy.
Ashley - on 10 Jul 2013
In reply to Craigyboy13:
> (In reply to Ben Sharp) could it be the rear brake cylinder?

Probably not, hand brakes almost never use the hydraulic system, they're normally mechanical and pull on one pair of the rear brake shoes (even if you've got rear discs, the hand brake is normally a small drum brake mounted in the rear hubs), also the OP said he'd adjusted the cable which would suggest their hand brake is a mechanical linkage.
Ben Sharp - on 10 Jul 2013
Thanks for everyone's replies. Had quite an extended fight with the drum tonight - rusted, one of the pins sheared etc. It was the offside drum that wasn't holding properly, the other side is fine. I took it off with great difficulty and the whole thing was seized up.

Nicely cleaned, greased and new pads on and it all looked perfect but it's still not holding the wheel properly when the handbrakes on so I'm guessing it's something along the lines of that cable being stretched or the compensater as suggested. Having spent over 3 hours getting the thing off and on again though, I've run out of time/patience and it's booked into the garage tomorrow for the retest so I'll have to admit defeat on this one.

Thanks again for everyone's help
wilkie14c - on 11 Jul 2013
In reply to Ben Sharp:
The shoes/pads are going to need bedding in mate and then they'll improve massively. A run around with the handbrake 'slightly' on will speed up the process but be gentle as you can overheat and glaze the friction material.
Ben Sharp - on 11 Jul 2013
In reply to wilkie14c: Cheers, I gave it a run around the town last night with the handbrake on a little but it's just that when it's up on jack stands with the handbrake on the offside spins and the nearside locks up fine.
Richard Wilson - on 11 Jul 2013
In reply to Ben Sharp:
> (In reply to wilkie14c) Cheers, I gave it a run around the town last night with the handbrake on a little but it's just that when it's up on jack stands with the handbrake on the offside spins and the nearside locks up fine.

Sounds like its seized somewhere.
Cú Chullain - on 11 Jul 2013
In reply to Ben Sharp:

Not sure on the make of your car but most motors have a 'nut' on the rear discs that allows you to adjust the distance bewteen the brake shoe and the drum, this prevents you from having to ratchet the handbrake lever up full tilt or having to mess around with the actual cable itself.

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