Replacing Leaky Wheel Cylinders

The braking system is my least favorite part of a car to work on. It combines all annoying elements: Liquids, Rubbers, Springs, Dust. All plenty annoying to work with/around on their own, but here packaged together into a perfected system of frustration.

In any event, leaking wheel cylinders are a common problem for any car that's been parked or neglected for many years, particularly if you live somewhere wet or humid. Brake fluid absorbs the moisture, the moisture then corrodes the bores of the wheel cylinders, the rubber wheel cylinder cups then won't seal in the cylinder, and brake fluid leaks out. Sometimes the leak is so small and slow you won't notice a puddle on the garage floor (often the puddle will form under the tire and is hidden until you move the car) and then the brake pedal will just go to the floor when you try to stop. Not fun. Here's how I replaced leaky wheel cylinders on my 1969 SAAB.

note tell-tale radiating streaks on the rim and tire - brake fluid that's been flung off by the spinning wheel when driving.

Before starting, I of course made sure I had everything I needed to do the job. New wheel cylinders, brake parts cleaner, brake fluid, new cotter pins for the axle nuts, appropriate sockets, tools etc. Nothing is worse than pulling things apart and realizing you don't have the right tool or replacement part to finish the job. A cheap door mat is a good idea for saving your knees.

First I chocked the front wheels, raised the car with the jack, and used a jack stand to hold it. Then I removed the wheel to get at the drum.

After that I pried off the dust cap, removed the cotter pin from the axle nut, and got out the breaker bar and freed the axle nut. At this point I made sure the parking brake was released, and proceeded to back off the shoe adjustment until the brake shoes were full retracted from the inside of the drum. Sometimes one may simply pull the drum off by hand at this point. However I was facing a somewhat stubborn drum. So I replaced the axle nut to protect the axle threads while I used a large screwdriver and a hammer to gently tap the drum free from the back. If this didn't work I would have had to resort to a drum puller. Luckily it only needed a few taps before it came loose. Then the mess inside the drum was revealed to me.

Brake shoes were soaked in fluid - those have to be replaced. Better have remembered to have some before you started!

This was a good stopping point for a break, because after this things were going to get pretty messy and nasty. After my short snack break, I came back to finish the filthy job. There are a lot of special tools that make working on drum brakes a cinch, but some of these tools can be improvised. To remove the brake shoe retaining clips I used a small socket on an extension to push the retaining spring down with one hand, while I twisted the clip loose from behind the backing plate to release it. I've also learned to stop trying to pry the return springs off the shoes. On this car anyway, it is easier to just pull the shoes apart by hand, and lift them off with the return springs still in place - also makes putting them back on easier.

At this point, the backing plate was bare except for the old wheel cylinder. Before separating the brake line from the wheel cylinder, I put some plastic wrap between the lid of the brake reservoir and the cap. This slows down the dripping of brake fluid once the line is removed - prevents having to bleed the master cylinder by keeping it from draining. On other cars one may clamp the brake hose, but on the 95 the brake hoses for the rear are hidden in a recess up above the axle where nobody can get to them... a hard line is what plugs into the wheel cylinder. Removal of the old cylinder is pretty straight forward. I removed the retaining clip, removed the bleed screw, and undid the hard line. The cylinder then just pulls right off of the backing plate.

New cylinder with paper shim and retaining clip.

A good quality replacement cylinder will come with a paper shim that fits between the cylinder and the backing plate. I'm not 100% sure what it is supposed to do, but I have found that it helps keep the cylinder more firmly retained once the retaining clip is snapped into place. Cylinders without this shim tend to fit a little loose even after being clipped in. Plus if a company is going to skimp on a tiny piece of paper... what else would they cut corners on? Anyway, the most monumental pain in the ass of this whole process is getting the retaining clip back on the cylinder. In fact I end up mutilating the new one and having to reuse the old one. I've noticed that these new wheel cylinders come with clips that are basically unusable. The old clips are springy, so when they deform a bit as you press them on, they return to their original shape and hold the cylinder firmly against the backing plate. The new clips (and I've noticed this in good and bad brands) aren't springy at all. Once they deform as you press them on, they stay deformed and just don't do a good job keeping the cylinder firmly retained. A penny here, a penny there... who cares if your customers die when their brakes fling apart?

Reassembly is basically the reverse of disassembly. Once everything is hooked up, new shoes in, drum on and axle nut tightened down, and retained by a new cotter pin - it's time to bleed and adjust the brakes. Which is a story I'll save for another day. In any case, the new cylinders are a success. No more leaks. No more poo when the pedal sinks to the floor.

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