Pop one of the old wheel cylinders apart. The diameter will be molded in on the inside of the rubber lip seals. If you can get the bleeder screw open, you can rebuild the wheel cylinders instead of replacing them. Rebuilding them was a standard part of drum brake jobs in the '80s. The advantage is you don't have to worry about twisting off the steel lines. The disadvantage is the rebuild kits often cost almost as much as a new wheel cylinder.
If you don't have a brake cylinder hone, you can clean out the wheel cylinder with an electric drill, and a strip of sandpaper wrapped through and around a cotter pin. We had to use that makeshift tool on Ford Escorts because their rear wheel cylinders were too small for the hone to fit into. We ended up replacing most of those Escort wheel cylinders because almost every one had developed deep spots of corrosion on the bottoms of the bores, between the two lip seals. Brake fluid leaked around the seals in those spots and that resulted in the pistons becoming rusted tight. Check yours for those spots of corrosion. If you don't see that, it is acceptable to rebuild them.
Before you assemble the wheel cylinder, be sure your hands are clean of all wheel bearing grease residue. Wash them with soap and water before touching the lip seals. Any hint of petroleum product mixed with brake fluid will contaminate the entire hydraulic system. The only proper repair for that is to remove every part that contains rubber that contacts the brake fluid, flush and dry the steel lines, then install all new parts that contain rubber. That includes the rubber flex hoses, wheel cylinders, calipers, master cylinder and the rubber bladder seals under the reservoir caps, the combination valve, and for those vehicles that use a rear height-sensing proportioning valve, that must be replaced too. That gets to be a very expensive repair. Easier to just keep contaminants out of the wheel cylinders.
If you prefer to replace the wheel cylinders and the soft metal line nuts are rusted to the lines, do not use any type of penetrating oil to try to free them up. That is also a petroleum product that can get into the system. There's two tricks to get the line off the wheel cylinder. One is to unbolt the wheel cylinder so it can be pulled away from the backing plate, then rotate it instead of the line nut.
The second way is to heat the line nut with a propane torch. Once it is hot and expanded, use a flare-nut wrench to work the nut back and forth until it will spin, then use Brake Parts Cleaner to wash it out as you spin it by hand.
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Sunday, July 12th, 2020 AT 7:08 PM