Tightening handbrake

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Eric Brough
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Tightening handbrake

Post by Eric Brough » Sun Mar 11, 2007 6:06 pm

I've just acquired a BX19D Estate. All in reasonable shape, with new front pads and discs. However, the handbrake pulls up almost to the limit of its travel and then barely bites. I've encountered this effect on other BX's, but have never fully worked out the cause.

I assume may be something to do with the need to rewind the caliper pistons - as you should do when fitting new front pads. If this were not done, would this lead to the 'floppy handbrake lever' effect? I'm not entirely sure about the internal anatomy of the front calipers and how the 'automatic' handbrake adjustment is effected.

Or do the handbrake cables just stretch?

Can anyone shed any light? Thanks, Eric.
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jeremy
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Post by jeremy » Sun Mar 11, 2007 6:55 pm

I expect the self adjusters are a bit sticky. You can usually get them to work by pressing the pedal hard down with the engine running - then pull the handbrake on and off a few times. Usually tightens it nicely.

If this doesn't work - examine the cables - they can break - usually when a support bracket chafes through the outer cover - in which case replacement is the only answer. Some cables (Quinton Hazell) have a thick plastic cover which prevents this chafing. Garden hose split and firmly attached may achieve the same result.

New cables - £12 - £15.

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Eric Brough
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Post by Eric Brough » Fri Mar 16, 2007 10:32 am

Thanks for that Jeremy, I've tried it and its made a small improvement.

I'm trying to get an idea of how the hanbrake mechanism works in the front caliper. It seems to be along the following lines (based on Haynes and a dose of imagination):-

* The handbrake cable attaches to a lever on the caliper. Taking the LH caliper and looking down on it, then when the handbrake is applied, the lever is pulled towards the rear of the vehicle.
* The lever is mounted on a vertical pivot rod. So again, on the LH side when the handbrake is applied, the rod rotes anti-clockwise.
* The rod has a rachet notch in it. An intermediary peg sits between this notch an another rod, the 'piston locator/adjuster'. When the handbrake is applied, this has the effct of moving the piston locator/adjuster todands the brakepad.
* The 'piston locator/adjuster' is the central rod that runs through the middle of the piston. It runs though a seal into the piston chamber. The piston end is threaded and the piston itself is screwed onto the end of it. It is this thread that is screwed back when the piston is rotated.

That may be inaccurate, so I'd be interested to see a better explanation.

I still cant see where the 'automatic adjustment' gets into the system. Somthing in the system compensates for pad wear. I cant see how this happens. The 'piston locator/adjuster' seems to be stopped from turning by the way it engages with the ratchet. The piston is stopped from turning by its outer face notches engaging with a notch in the brake pad. There are some spring wahers mounted on the 'piston locator/adjuster' whose function is not entirely clear to me.

Any improvements on this account?

E
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ken newbold
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Post by ken newbold » Fri Mar 16, 2007 7:28 pm

Have you adjusted the excessive slack out of the cable, by means of the adjustment and locking nut at the end of the cable?

Also it pays to pack grease in behind the rubber boot on the back of the caliper to keep the self adjusting mechanism lubricated. If you pack it now, each time you service the car in future you can give the boot a little squeeze which will push more grease into the mechanism. :)

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Post by Stewart (oily!) » Fri Mar 16, 2007 9:35 pm

Its also wrh noting that you only adjust the slack out of the cable, the lever on the caliper must return to the forward end f its travel otherwise the self adjuster cannot work.
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Eric Brough
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Post by Eric Brough » Sat Mar 24, 2007 2:20 pm

Further investigation revealed that the lever on one caliper was sticking intermittently. It was not returning freely to the 'handbrake off position'. So a bit of WD40 and some exercising seems to have freed it for the time being. Then, after some application of the footbrake and several good tugs on the handbrake, the whole lot seems to have tightened up.

So thanks for your replies - it seems the solution lay, in part, in all your suggestions.

I still do not understand how the 'self adjuster' operates in the front caliper. But it seems something must happen. Why, otherwise, would we need to wind the pistons back in when renewing pads. One day I will take a front caliper apart...

E.
<------------------>
BX 16TXi saloon
C3 1.6HDi
C5 Estate
<==========>