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Hydro-Max Brake Assist *pics added* (long read)

spicergear

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For the amount of times that 12v boost motor is going to run, why worry about getting a 24v motor? Slap a couple of wires to a switch or whatever from one battery and call it a day. It really is only a momentary draw and not like something always eeking away juice from one battery.
 

jesusgatos

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Still on the hunt. Have been all over the place, literally, and online, and on the phone. From one place to another to another to another. Everyone has been really helpful, errr, tried to help. But no luck on that 24V booster pump yet. Waiting for calls back from a few places. Hoping someone might have some good news for me.
 

SuperJoe

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Not to sound like a stick in the mud, but perhaps a different search criteria is in order. Instead of looking at every place that makes the parts you want but with the wrong options, look first at what trucks were 24v to start, then focus on only those parts suppliers. I believe 24v system went away quite a while ago, so most available parts now will not accommodate your needs. Just a suggestion

Joe
 

jesusgatos

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For the amount of times that 12v boost motor is going to run, why worry about getting a 24v motor? Slap a couple of wires to a switch or whatever from one battery and call it a day. It really is only a momentary draw and not like something always eeking away juice from one battery.
Oh, of course you're absolutely right. Like I said, this isn't a deal-breaker. Would just rather use a 24V backup pump if I can find one. What it really all comes down to is that I like making informed decisions.
 

jesusgatos

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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.
 
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jesusgatos

Active member
2,689
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Location
on the road - in CA right now
Not to sound like a stick in the mud, but perhaps a different search criteria is in order. Instead of looking at every place that makes the parts you want but with the wrong options, look first at what trucks were 24v to start, then focus on only those parts suppliers. I believe 24v system went away quite a while ago, so most available parts now will not accommodate your needs. Just a suggestion

Joe
So what vehicles were equipped with 24V electrical systems and Hydro-Max brakes? I have no idea.
 

SuperJoe

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No idea. Just thinking that would be an easier info to find about certain vehicles opposed to the specific brake parts. My deuce is the largest truck i have worked on so i will be no help in that aspect
 

spicergear

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Residual valves, does the stock system have them? Yes or no? Would you need them, ...there's your answer. Residual valves hold a small amount of line pressure so the system basically doesn't have to start from scratch as far as line pressure to actuate the brakes. I believe drum brake residual valves hold more pressure than disc brake systems because drum shoes actually pull away from the drum where disc pads are basically right there.

Oh, quick question; why the huge brake line MC?
 

jesusgatos

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on the road - in CA right now
My understanding is that residual valves might not be necessary, but can help to keep the pedal from going soft when a vehicle sits for a while, but more importantly, the the small amount of line pressure they maintain (10-15lbs?) can help to keep the wheel cylinders from leaking. Didn't spend much time talking about that with Tim, as it seemed like kind of a trivial detail, so can't give you any more definitive information about that right now. Maybe someone else will have a better answer.

Not sure what the deal is with the larger brake lines on the older MC.
 

jesusgatos

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on the road - in CA right now
Don't have any Hydro-Max parts yet, but was looking through the PDF's and they recommend a pedl ratio of about 3:1. Stock pedal linkage is more like 5:1, so might have to mount the master cylinder a few inches lower and extend the lever arm. Looking forward to getting into all this. Hoping to have all the parts ordered by tomorrow.
 

jesusgatos

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on the road - in CA right now
Did a little bit more research this morning and looks like the stock master cylinder is only 1 3/4", so am tempted to try the 1 3/4" Hydro-Max 1 master cylinder with the Hydro-Max 2 booster. Tim is putting together some parts/prices for me, and am hoping I might be able to start working on the brakes next week.
 

Lonesome715

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I found a dump truck in a local salvage yard with six hydro disk brakes on it. I have been thinking about going back and getting all the parts.
 

spicergear

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Disc brakes are gradually starting to show up on more and more heavy trucks. When I was in the whole hydroMax search and info search on it PLUS Rockwell retrofit search, I saw a lot of info about them outlasting drums and air calipers, more resistant to fade, and other positive info.
 

jesusgatos

Active member
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Location
on the road - in CA right now
Ordered all the Hydro-Max parts from Precision Rebuilders this morning. They have to build a custom master cylinder for me because it's a unique configuration, with all of the specific features that I want to have for this application (50/50 1 3/4" master cylinder, with a pressure differential switch, and remote master cylinder with 3/8" NPT fittings, etc.). Tim's also going to send me an assortment of different pedal rod-ends so I can figure out which one will work best with the stock pedal linkage. Parts should ship tomorrow or Monday, so looks like I'll be able to start working on the brakes by the end of next week!
 
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