Restoring #1566

Brake Master Rebuild

We are restoring the US-style brake master cylinder for the Magnette Mk. III. The difference between the US and rest-of-world style is the addition of a large seperate tank. The US and UK cylinders are identical in all other respects and even use the same rebuild kit.

This is an overview of all the parts of the brake master. Again, the US version has this additional tank, pipe, and bracket shown. It was originally painted black with a blue "Girling" sticker. I have not been able to locate a sticker for it. I have chosen to powder coat the tank rather than paint it because the powder coat is more resistant to brake fluid.

Here is the US style tank, before sand blasting.

I chose to shot blast the can because of the curves around the cap. There was also a great deal of hardened "something" around the inside edge. It is surely a blend of evaporated brake fluid, paint, and the remnents of the rubber seal under the cap.

Whether you end up painting or powder coating your can, it is best to put a wire hanger on the inside and hang the can from a wire when applying the finish to avoid contact marks from touching the ground or your fingers.

Here I am preheating the can, just to get the chill off in the below freezing garage.

Here I've powdered it.

And now its done.

The cap gets a similiar treatment, but I de-rusted it on the the wire wheel. I prefer to use the wire wheel whenever possible because I don't have to have the compressor running to use it!

Here is it, completely de-rusted and paint free. It wouldnt' look like this for long though if we didn't give ti a protective coating.

Here is the cap, done. I have powder coated it because 1) you do not have to prime, 2) you can powder coat in freezing weather, 4) it dries in about two minutes rather than a half hour, and 4) powder coat is resistant to brake fluid because it is not paint, it is plastic powder melted to look like paint.

Here is the actual brake master. UK versions look slightly different, with an interagal fluid resevoir. Boy does it look ugly!

The master cylinder is easily taken apart by removing the circlip on the inside of the cylinder orifice. The remaining components are removed (in this case) by plunging them back into the cylinder body to break them loose, and then banging them on the workbench to get them out. A professional would use compressed air I guess, but nobody is really reading this anyway are they?

Here are all the insides, all layed out.

The body needed work. I removed all the rust and scale on the wire wheel. The cylinder would soon however become ugly again if you didn't atleast shellac it. I have, in this picture, plugged the threaded ends with high temp silicone plugs for powder coating. You can plug them with masking tape if you are only spray painting.

"Clear" powder coating goes on dry in a white color. But once it is heated and cured, it turns clear.

From my manual: Lift the the thimble leaf over the shouldered end of the plunger. Depress the plunger return spring to allow the valve stem to slide through the elongated hole of the thimble and release the spring tension. Remove the thimble, spring, and valve complete; detach the vavle spacer, taking care of the spacer spring washer located under the valve head. Remove the seal from the valve head. Assembly is mainly a reversal of the dismantling procudre, but note: Make sure that the flat side of the valve seal is correctly seated on the valve head. Locte the spring washer with the somded side against the underside of the vavle head. Parts Key: 5- Valve Seal, 6- Valve Stem, 7- Curved Washer, 8- Valve Spacer, 9- Spring, 10- "Thimble", 11- Plunger Seal, 12- Plunger, 13- Some plungers have a space for this additional seal.

Here it is, all done and on my desk.