My main frustrations with working on an older truck have come from finding parts, and there are some things that I don't want to get used. Master cylinders, and brake parts in general, fall into this category. In my view, running is good, but stopping is essential. My truck is a 1966 GMC 5500 (HM according to the VIN). In the bigger picture, this is not really all that old (I could have driven it new), but parts for this particular year and model seem hard to find. With that off my chest, here is the situation.
The truck has a dump bed that came with tall racks (mostly bolted together but also welded in a few spots) that limit its use. After removing the rotted plywood, I wanted to move the truck under a tree branch to lift off the heavy steel frame parts. This should have been easy, since the truck was running when I parked it a couple months ago. Starting was not a problem, although the idle problem hadn't fixed itself yet, but then the brake and clutch pedals went to the floor with no resistance - not a good sign. A quick check of the master cylinder found it empty of fluid - also an unpleasant surprise. And there was no sign on the ground where the brake fluid might have gone (hopefully not into the hydrovac or past the wheel cylinders with no pressure on the brakes).
After adding fluid, the brakes pumped up without a problem, but the clutch refused to be primed by pumping the pedal. OK, I already knew the clutch needed adjustment because it didn't disengage until just before the pedal reached the floor. This makes replacing the slave cylinder seem like a good place to start. I was able to find this part on-line. In fact, I found more than one, and they look different. So now it is time to take the old one off in order to know which new one to get.
And since removing the old slave cylinder will probably drain the old master cylinder (again), I might as well replace it at the same time. But this is easier said than done. After checking both retailer and manufacturer websites, no one seems to be carrying, making, or providing rebuilding parts for my 1966 medium duty truck master cylinder, and none of the pictures of dual brake/clutch master cylinders match what I see in the truck.
So where does one go to find a new or rebuilt master cylinder (or rebuilding parts) for a medium duty truck? I am getting used to having to search for parts, but this seems so unlikely that it must be from some shortcoming on my part. The only next step I can think of is another trip to the local Napa dealer and trying to explain what I need to the nice, and smart, young man at the counter who isn't old enough to know from experience what I am looking for.
I am old enough to be cantankerous about having a hard time with things I think should be easy. And this more than qualifies. Any help would be greatly appreciated!
JRMunn
