Hi 235 Kidd,
My truck is a '44 CCKW (2-1/2 ton). It too, utilizes the Hydrovac. With that said, not sure how much of the following applies to civilian models, so take it for what its worth.
If you already have the system torn apart to rebuild the wheel cylinders, I personally, would not even consider putting it back together without removing, inspecting, and rebuilding the master cylinder. If it's pitted, (which it likely is) you can either replace it or have it sleeved. Same goes for the wheel cylinders.
As mentioned previously by HotrodLincoln, now is also the time to inspect hoses and lines. Replace them if they look even remotely suspect. They are not that expensive.
The Hydrovac on the other hand, is a somewhat different matter. If it worked previously, does not show any signs of internal or external leakage, and the brake fluid is not heavily contaminated, I would consider leaving it alone. Otherwise, I would replace it. As 78buckshot mentioned, NAPA has them. They were rebuilds from Midland the last time I checked. They were also not cheap.
I just went through all this on my truck several years ago (all new hoses, lines, 6 rebuilt wheel cylinders, master, hydrovac, etc.) so I know it is a lot of work. Brake systems, however, (especially on big trucks) are something that one should never scrimp on IMHO. About a year after I got my truck back on the road, a guy in a teeny little compact car made a sharp left turn from the right shoulder directly in front of me. He was so close that I could barley see the roof of his car over the top of my hood. All ten wheels locked, tires screeched, and my passenger nearly banged her head on the windshield, but I did not hit him. I was glad that the system was working correctly. If it had not, I would have creamed him.
I did not, BTW, have access to a pressure bleeder at the time. I followed the TM, used a hose on each bleeder connected to a small reservoir of fluid, and went at it one bleeder at a time. It bled satisfactorily. However, if you have do access to one, it will obviously make your life much easier.
With regards to running without a hydrovac, my truck uses the Huck design which is pretty anemic in the way of self-energizing. I once disconnected the vacuum supply just to see what would happen. Pedal effort was
really high, so I could not imagine driving it without assist. Try carrying a load and it would be a nightmare to stop. BTW, if your truck also has the Huck system, let me know and I can give you a few extra tips that may make your life easier.
Good luck!!
Best Regards...
p.s. Hey 78buckshot, where in SE MI do you live? I think we might be neighbors.
p.p.s. If anyone is interested in learning more about Hydrovacs, TM9-1827B covers them in detail. It does not show the Type 3, which is the replacement for most older units, but it does show theory and operation.
A freebie download can be had here:
https://archive.org/details/TM9-1827B
