Drum Brake Wheel Cylinder Service

Contributed By: Dennis "Doc" Fariello

Relining the rear brakes is not within the scope of this article. It will be covered in another article at another time. This article assumes that you are at the proper point in rear brake service (old shoes removed, new shoes not yet installed, brake assembly clean and dry).

This procedure is also for doing the wheel cylinder while still installed in the vehicle. It is sometimes easier and better to remove the wheel cylinder, but if you haven't damaged the wheel cylinder, it isn't really necessary. Replacing the wheel cylinder is EXTREMELY easy, assuming your brake line isn't totally rusted and fused into one piece with the wheel cylinder. This procedure is for the real cheapskates among us, those who would rather spend $4.00 for a rebuild kit than $20.00 for new cylinders.

1. Pull the brake pins out of either end of the wheel cylinder. Just pull them straight out the ends, they'll come right out.
2. Pull old end seals off wheel cylinder. You may need to pry them off, if you do, be careful not to nick the sealing surfaces.
3. Stick your finger in either end of the wheel cylinder and push the piston assemblies out the other end. Catch the pistons in your other hand, otherwise the spring may cause them to go sailing off into the sunset.
4. Discard all the rubber pieces, and the spring. All you'll need to re-use are the aluminum pistons and the pins.
5. Clean pistons and pins, using alcohol, brake fluid, and/or brake cleaner. You can use a brass wire brush to clean deposits off the piston, and a wire wheel to clean the pins if you like. Be careful not to gouge the pistons.
6. Wipe out the cylinder with a clean rag soaked in brake fluid or alcohol. If you're going to be converting to silicone (DOT-5) brake fluid, then you will need to use alcohol throughout the entire procedure, in addition to flushing out you master cylinder, brake lines, and front brakes with alcohol before filling with the DOT-5 fluid. This will not be covered in this article.
7. Inspect wheel cylinder. Slight discoloration may be removed with crocus cloth if brake fluid doesn't remove it. There are hones available for wheel cylinders, but I've never needed to use one. If the cylinder is that bad, it's easier to just replace it, and they don't cost THAT much.
8. Rinse wheel cylinder again with clean brake fluid.
9. Ok, you've got your rebuild kit in hand. It should have two piston seals, one spring, and two rubber end seals. Make sure of this.
10. Install one end seal, on the end away from which you're going to be inserting everything. It's ok to use a piece of wood and a hammer to knock it into place, just be gentle.
11. Insert one piston, open end in first, into the open end of the cylinder.
12. Take one piston (cup) seal, soak it thoroughly in brake fluid, and insert it into the cylinder, open end toward the end you're working from.
13. Insert spring.
14. Insert other piston (cup) seal, open end inward (toward the spring). By this time, you'll have to be pushing on the spring, be careful to not shove the already installed piston out the other end. You may want to hold that end seal with your other hand, if possible. If the end seal is installed correctly, and you don't push on the spring too hard, it shouldn't go flying, hopefully.
15. Insert other piston, open end out.
16. Install other end seal, just like the first one.
17. Now install the pins, one to each side. They just slip in and contact the pistons.