Sat Oct 22 07:28:56 CAT 2016

one for home mechanicS

By unknown | May 12, 2010 | COMMENTS [ 0 ]

ONE of the few repair jobs the average home mechanic can still do on a modern car is overhauling the drum brakes that are used on the rear wheels of many cars.

ONE of the few repair jobs the average home mechanic can still do on a modern car is overhauling the drum brakes that are used on the rear wheels of many cars.

I recently had the opportunity to go through this familiar routine again when a friend called me to say his four year old Opel Corsa, which up until now had never put a foot wrong, had developed the disconcerting habit of losing brake fluid.

He had been alerted to the problem when the brake warning light on the dash was triggered by the low fluid level in the reservoir.

The two of us decided to go DIY on the brake problem.

So Friday evening found the two of us under the Corsa with a droplight, looking for the leak. It was easy to spot: the brake back plate on the right rear wheel showed the telltale dampness, while the one on the left-hand side was dry and dusty.

Off came the wheel, followed by the brake drum. On this car the brake drum is integral with the hub containing the roller bearings that run on the stub axle.

To remove the drum the nut holding the hub on the stub axle has to be undone (it is secured with a split pin), allowing the drum-hub unit to be pulled off.

The drum slid off easily, revealing a right royal mess.

Brake fluid had leaked from both ends of the wheel cylinder for some time. Furthermore the linings on both shoes were soaked.

It is almost impossible to salvage linings once they have been soaked by brake fluid, despite numerous purported remedies. The shoes had to be exchanged for relined ones at the local clutch and brake specialists, even though the linings showed minimal wear.

Fortunately the brake guys were open on Saturday morning, so by Saturday afternoon we were ready to resume battle. First the old shoes were removed, after a few close-up pictures had been taken on a cellphone to show the arrangement of springs, levers, handbrake cable and so on. Then we clamped the flexible brake hose feeding the right rear wheel, with vise-grip pliers, taking care to fold a sturdy strip of rubber over the hose to prevent the jaws of the pliers biting into it.

The wheel cylinder could now be taken off without a major loss of fluid from the brake lines.

The pistons were extracted from the cylinder, and when their rubber cups were examined under a magnifier, we could clearly see how their sealing edges, which are supposed to be sharp, were worn away.

The reason for this became clear when the bore of the cylinder was wiped clean: rust had formed on the bore where the cups move to and fro as the brakes are applied and released, and the abrasive effect of the rust had worn away the sealing edges of rubber cups.

Fortunately the rust was only superficial, so we could smooth out the bores with 1000 grit water paper and methylated spirits.

Then everything was scrubbed clean with an old toothbrush and meths, and new rubber cups were fitted to the pistons. All that remained was to reassemble everything using the relined brake shoes.

When the brake drum has been put back (and the clamp removed!) the brake line to the wheel has to be bled, but you will need very little brake fluid for this.

Knowing that if one side starts leaking, the other side is bound to follow soon, we repeated the job on the left rear wheel the following weekend - just in time, because the first trickle of brake fluid had already appeared at the wheel cylinder.

The cost of the entire job (both sides) came to less than R140 for replacement parts, including half a litre of brake fluid. Of course, the real satisfaction of doing it yourself comes from knowing that it's a job well done.

You need little more in the way of tools than a couple of sockets, some standard ring and open-end spanners, a pair of pliers, a screwdriver and a vise-grip.

An interesting question is why the wheel cylinders started rusting so soon. One doesn't expect to find this on a four year old car. I maintain it would never have happened if the brakes had been bled through with fresh fluid once every two years. (Brake fluid slowly absorbs water from the air over time.) Herein lies a lesson for all car owners.


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