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Posted by David Sherman on Thursday, February 26, 2009 at 04:07:32 :
In Reply to: 1965 WM300-Locking Brakes posted by mike murray, NJ on Wednesday, February 25, 2009 at 18:43:47 :
If all the wheels lock up, it's probably a problem with the M/C, not a wheel cylinder or brake line.
First, loosen the push rod a lot, so it's very sloppy, but the brakes still work. If it still locks up, it's almost certain that the tiny bleed port in the M/C is clogged. If you haven't rebuilt the M/C, do so, making sure to clean the innards of the MC out thoroughly and clean out the bleed hole. If you did rebuild it, one small flake of rust can still get in and clog the hole (speaking from experience). If you take the cover off the M/C you will see a 1/8" hole drilled all the way from the reservoir into the cylinder itself. That's the main port. An inch or so behind it, you'll see another 1/8" hole, but it's only drilled part way through. The remainder is drilled with a #72 drill. That's very small. A #72 torch tip cleaner will just fit in it. If that size tip cleaner won't go through, you might clean it out with a tiny X-acto drill. You might be able to do this without removing the M/C from the truck, but the risk is that the speck of dirt you pushed down into the cylinder will find its way back to the bleed hole eventually. One time I had to remove the M/C, put acid in the reservoir, and let it sit overnight to eat through the rust.
Summary: First loosen the push rod. If that doesn't work, clean the bleed port.
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