Just got off the phone with Tim at
Precision Rebuilders, and he is
the man! Spent 45 minutes telling me all about the Hydro-Max system. Have probably called 20-30 people/companies about this stuff over the last few days and he is hands-down the most knowledgeable person I've talked to about anything brake-related. There wasn't a single question I asked that he couldn't answer, and right off the top of his head. Only thing he's got to look into to get back to me about is that elusive 24V backup pump. He's never seen one. But I've got a lot of great information to share with you guys:
Evidently, there are a few different versions of the Hydro-Max system.
Hydro-Max 1 uses a 1 3/4" bore master cylinder, and with 4,600PSI at the pump, generates 1,800psi. Fluid volume is somewhere right around 2.56 cubic inches.
Hydro-Max 2 uses a 2" bore master cylinder, and with 6,300PSI at the pump, generates 1,900psi. Fluid volume is about 3.35 cubic inches.
Tim also told me that while he couldn't endorse it... if a person were to use a Hydro-Max 1 master cylinder (1 3/4") with a Hydro-Max 2 booster, that would result in even higher line pressures, which he estimated might be somewhere around 2,200psi.
All vehicles equipped with Hydro-Max brakes that were manufactured after 1999 are using Hydro-Max 2 systems. Before 1999, both systems were in use.
There are a number of different master cylinders out there, but there are three basic versions that are the most common/popular. There are also 50/50 and 60/40 versions of many of these master cylinders available though, so you really need to do your homework to make sure you get the right parts for your application. Or just call Precision and they can make sure to get you the right parts.
1) Ford and International have a master cylinder that is equipped with an internal pressure-differential switch.
2) GM master cylinders do not have the internal pressure-differential switch, but do have a fluid level sensor in the reservoir.
3) Freightliner master cylinders are equipped with the pressure-differential switch and the fluid level sensor.
4) But wait, there's also another, less common master cylinder that was intended to be used with a remote reservoir, and those are equipped with 3/8" NPT ports. Some of those also had the built-in pressure-differential switch. This is the one that I'm going to use. And Precision Rebuilders has them in-stock, ready to ship.
There was also a 2" bore master cylinder made with internal residual valves, but these units were only made up through the early 80's, and used larger brake lines (11/16-18 &3/4-18 fittings). So while Precision Rebuilders has rebuildable cores in stock, I'm inclined to go with a newer master cylinder and just add inline residual valves.
