[Flathead Fever]

We used to use McKay brake assembly lube at work when rebuilding wheel cylinders, master cylinders and disc brake calipers. Its some real slippery stuff and makes it easy to assemble the parts. Its thick enough that it will stay in place until your ready to add the brake fluid. Its a little tough to press in a disc brake caliper piston past the internal square seal. The piston has to be absolutely straight. You smear this goop around in there. Then you pull the piston in with a "C" clamp. The goop helps a lot. A little bottle should last you a lifetime. We had about 400 vehicles in the fleet at one time, back when we were rebuilding all the wheel cylinders. We just had a EIS box with an assortment of all the different rubber cup sizes. We almost always never used a cylinder rebuild kit. If there is no wear you just spray a little WD-40 or brake fluid in there. Make about one or two passes though them with a ball hone. We rarely had pits in the bores. If there were any they were usually in the center where the seals do not ride so the pits don't matter. If you hone them, clean the bore out real good. Take a paper towel and some brake clean and keep cleaning until the paper towel is coming nice and white. Clean the pistons good, make sure there are no serious scuff marks on their sides. Put a little of this goop on your finger and wipe it around the inside of the bore. Smear it all over the seal and pistons and stick everything back in. Make sure the seal is facing the correction direction or your going to have big problem In 30-years I maybe went through just a few small bottles of this assembly lube, (including the one I took home as part of my retirement package). By then they did not want mechanics rebuilding cylinders because of the liability. I never killed anybody, not even a near miss. There is probably nobody left there now that even knows what lives inside of a wheel cylinder?

You can use brake fluid to assemble your wheel cylinders if don't want to buy this stuff. How often are you going to use this stuff at home? If the cylinders are going to sit for a long time before you use them then I would use the assembly lube. You might need to go to a "real" auto parts store to find it. Nobody at the others are going to have a clue what you are talking about. They can probably order it for you and get it in one day. I'd take the part number with you to increase your chances.

Buy the very best brake line wrenches you can afford. The Snap-On brake line wrenches would loosen the steel lines that other professional wrenches would not. A lot less chance of rounding off the nut. Never-ever use an open end wrench, you will round off the nut. We had some trucks that ran around up in the mountains in the snow. The nuts would rust to the steel tubing. You could heat the nut red hot and most of the time it would brake loose but I really did not feel comfortable doing that to a brake line. What was better was not to touch the line. Leave the cylinder bolted on the truck and hone them on the vehicle ( not broke don't touch).