Saturday, 27 July 2013

Handbrake fails MOT.

Handbrake adjuster
This is a stressful time for the motorist; it is where you hand over your pride and joy to a third party to be poked, prodded and shaken into revealing those profitable faults for the garage. If you are a owner maintainer you should be able to minimize these unexpected failures because you regularly service and put right problems as they show up. I know in practice this is not always the case. But it is better and more cost effective if you do, than to be thrown in at the deep end when you are at your busiest.

MOT testers are human and have pet hates. As an ex tester mine were lights not working and torn wipers. To me this indicated that it may have other MOT issues which proved to be the case on many occasion.

Brake fluid
I am not immune from the unexpected. Having checked the van over and put right the sticking hand brake again, I was confident that it should pass it's MOT. The van and tester had other ideas. It failed! I was expecting him to say it was a ball joint but no it was that damned hand brake again. Apparently the brake machine showed that its effectiveness was outside the permitted balance parameters - (MOT speak), and it was the offside that was less effective or put another way the nearside was still sticking.

With the vans 'back end' in the air and the wheels off, I started to check everything again. But this time more thoroughly than before. I started by loosening the hand brake cable at the adjustment in the middle of the van. Then removed each cable from the caliper first checking to see if the handbrake lever was at rest. They were both holding off by a finger nails width even though the cable was very slack.
Surprisingly with this
poxy system this small amount can make the brake bind badly. I freed off the arms as described in a previouspost. Then checked to see how free the movement was on each hand brake cable that ran from the caliper. The OS one was very rough and stiff as the cable moved back and forth in the sleeve. The NS one was less so but on the way. So I changed both to be on the safe side. So what's next? The brake pads are not that old but I checked them anyway. The near side looked OK and the piston moved freely the same for the offside but the pads had an unusual wear pattern. It looked like the centre of the pad had crumbled away meaning that only the outer portion was in contact with the disc; could this be the problem? I checked the brake disc carefully, the surface was reasonably flat and I could not see any reason for the center wearing faster than the outer edge. The only way to be sure is to replace them. I know! more expense!

Now to fit them. I started by winding the piston back into the caliper. This needs a special tool but if you do not have one you can get away with using an adjustable wrench ( the type that bites your fingers if it slips off - ochhh!!) and a G clamp. It is slow and a pain but saves on the price of the tool. Basically you wind in the adjuster several turns and then use the G clamp to push the piston back. Before you start this you should pop the hood and take the cap of the brake fluid reservoir and place a cloth over the top to stop the brake fluid pouring all over the engine bay. This may happen if the fluid has been topped up. Once it is wound back clean the mounting bracket area where the brake pad sits and then put a little copper grease on the edges of the pad that sit on the bracket, this prevents sticking. Push the caliper into place, always use the new guide pin bolt provided with the brake pads and tighten to 35 newton meters (26 lbf ft). You should only remove one pair of pads at a time this allows you to reset the piston for the new pads by pumping the brake peddle also reducing the chance of the fluid reservoir overflowing. Spin the disc to make sure it is free and then apply the hand brake with your hand on the lever to make sure it works and releases properly. Then do the same to the other side.

Adjustment settings
Now attach the hand brake cable to each side and adjust the cable. I usually put a bit of copper grease on the adjuster thread to stop it freezing. Wind the adjustment nut up until you obtain a clearance of between 0.1 and 0.5 mm between the operating lever and the stop on the back of the caliper body. You can check this by using a feeler gauge. Now spin the discs, if it feels like it is binding then back the adjustment off until it stops. Hop in the cab and pull on the hand brake several times checking how many notches it come up - one or two is about right but not set in stone. Then check again to see if the discs are binding now the cable has been settled in. If OK it's time to box it up.

It is a tense time back at the MOT station as they check the hand brake on the brake machine. Has it passed? it looks to me as it's within parameters. Yes! A 'thumbs up,' great news! back to the day job. 

Update to post 18/8/13.

The handbrake is still working properly with no sticking to date. I have noticed that the mpg has increased since sorting out the brakes by as much as ten miles to the gallon which is astounding. So all those bits I replaced will have payed for themselves.