MOT parking brake performance

The message from "AstraVanMan" contains these words:

Teehee! Newton would have been proud.

Conor wrote on Mon, 19 Sep 2005 04:43:01 +0100:

ROFL

Yup - sin x and tan x approximate to x (* constant if you're not using the appropriate units) for small x, which is any reasonable gradient.

cheers, clive

Interesting. The handbrake on my E39 BMW is truly pathetic despite being correctly adjusted. If it were a manual it would be a pain doing hill starts. I know it's no longer needed as an emergency brake, but still needed for hill starts etc so should still be efficient?

When I bought the car at two years old, it wouldn't hold the car stationary in drive no matter how hard you pulled it on. Had to investigate this for its first MOT and found the adjuster on one side jammed on minimum. Must have been like it from new. Had to remove it to free it. Not seized through corrosion, etc but merely jammed on the end of its thread. And the handbrake cable on that side had been adjusted incorrectly to try and help. So much for BMW servicing and warranty as it had already had a service where the handbrake should have been checked and adjusted, and had also gone in once for rectification on this point.

So one brake working wouldn't hold the car in drive or reverse at idle but both just do. There was a note at MOT time that it was poor. The tester said they all were.

Dave Plowman (News) ( snipped-for-privacy@davenoise.co.uk) gurgled happily, sounding much like they were saying :

That'll be your famed BMW quality, that will...

I doubt any car with the drum in disc handbrake is any different. And at least it's a simple system which can be 'fixed' without new calipers.

But then I don't *expect* any car to be perfect. BMW just get closer than most. ;-)

Dave Plowman (News) ( snipped-for-privacy@davenoise.co.uk) gurgled happily, sounding much like they were saying :

Oh, I dunno... I'd expect most to be delivered with it working, or - at least - to be fixed by the dealer when the owner complains...

Yes, yes, yes, Dave, whatever...

Both the cars I have with drum-in-disc handbrakes have crap handbrakes. But at least the Toyota is an auto, so I put it in Park and forget about the handbrake until MOT time!

I'd always assumed that a drum-in-disc handbrake would be miles better than the ones that try to do both on the disc alone. Drums need so much less force to operate. Much nicer for cable operation.

One of the wheels was stuck to the disc on the Saab, so I freed it by driving backwards with the wheel-bolts loose and yanking on the handbrake - Definitely no problem with efficiency. I need new tyres now as well ;o)

Cheers,

Colin.

Colin Stamp ( snipped-for-privacy@stamp.plus.com) gurgled happily, sounding much like they were saying :

How very odd.

The XM uses the front pads for park brake, with a foot pedal for operation

- so nice and easy to put PLENTY of pressure on them. It's now 9yo and 120k miles (half of them with me), and is still on the original cables. The handbrake works fine. It's not even needed looking at - other than pad/disk replacement as per usual - since I've owned it. I live on a hill, so the park brake is used all the time.

Working it by foot certainly seems a good way round the force issue.

The Sierra, combined calipers on my kit-car are particularly bad for force. You need arms like Popeye to lock the back wheels up on that.

Cheers,

Colin.

Citroen also got it right on the BX - with a normal handbrake lever. Good thing too - adjusting the tiny separate pads on the CX was a complete PITA.

cheers, clive

Clive George ( snipped-for-privacy@xxxx-x.fsnet.co.uk) gurgled happily, sounding much like they were saying :

A bloke I used to know had a CX where he'd modified the handbrake mechanism, replacing everything with sealed bearings - and he reckoned it took all the hit-and-miss out of it all. It kept the adjustment for ages.

Hmm. But part of the problem was that there were too many degrees of freedom - principally cable length vs adjustment position. Just like adjusting cantilever brakes on a bike - I hate them.

Still, if it works then well done to him.

cheers, clive

How well a parking brake works is down to the mechanical advantage of the layout - ie how much force and travel the handbrake has, and how this is translated into force (and possible movement) on the shoes. The BMW (and others)_drum brakes aren't self adjusting, so they have to allow the handbrake lever to move far enough to take up possible wear. If they were self adjusting, they could be much easier in operation by providing more leverage. But that would cost pennies more. ;-) My impression is they're made for the US market where near all cars are autos, so a handbrake doesn't matter.

LOL. Auto cars tend to need the handbrake mechanism freeing off every MOT. THe one on my Capri has seized from doing the same as you.

"Conor"

Shouldn't any periodic maintenance during the year of taken care of this problem? These sorts of mechanical failures, as you say, are found on vehicles whose owners leave defects to be identified by an MOT tester. The same owners clearly don't give thought to other road users and may even have their own children in the same vehicle they have neglected to maintain properly.

John

Nope. The lever on the backplate is exposed to the elements. Tried greasing up and everything...

Never owned a classic have you?

No lack of maintenance here which is why the only thing this 20 year old car can potentially fail on is the handbrake.

"Conor"

Actually I have one, a 26 yr old vehicle of which the parking brake works fine.

Any forseeable MOT failure is a lack of maintenance.

John