Hot Rods Hydraulic over hydraulic brakes. Has anyone done this?

I was helping a friend with a 36 ford 3 window project. We were mounting a modern booster and master in the firewall, and I hate the way it looks.
I have had a brake line split once on a single system (that ****ed), and I have delt with underfloor mount problems as well. So I was trying to figure our what else could work.
As I was thinking of alternatives, the thought of building a hydraulic over hydraulic system came to mind. I am wondering if anyone has done this, and if there is something that I am missing.

The way it would work is to use an old style single " jam jar" master cylinder on the firewall. That would be plumbed to a remote mounted clutch slave cylinder which would activate a modern dual master cylinder that is plumbed to the brakes.
Advantages would be that if it's sized right the slave cylinder could run a bell-crank that could act and feel like power brakes without needing a booster (or it could still run through one if there was room)
Many cars don't really have room under the car where a master cylinder can mechanically be tied to the pedal. With this system the master could be mounted anywhere (like behind a roadster seat).
The single master on the firewall looks and fits so much better on most early cars.
And it would get all the "experts" concerned when they see a big hemi engine and "inadequate" brakes. (I like messing with "experts")
As far as safety, my thoughts are that big truck air brakes are a couple stages, many trailers are electric over hydraulic and have been for decades. The single line from the master to the slave could be protected (all the failures I have heard about were caused by rusty lines) and e brakes are a separate system for safety.
So again, my questions are; Has this been done before? Am I missing something?



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There are remote power brake boosters that work like that. They came stock on Jaguars and possibly other cars, and are a common hot rod accessory.

 

https://www.impalabrakeparts.com/proddetail.asp?prod=7984#.VASZPVy9LCQ

Yeah you can do that.
Similar set ups were factory that way.

Not so sure that you can get a power brake feel with out the extra boost of a booster though. You'll have to play with that one. Pedal ratio will weigh heavily on it. Every time you trade travel for force you'll need to increase the other.

I was thinking the same thing the other day. I want to move my master cylinder back and on the Trans side of cross member to gain some exhaust room. but there's not enough room for a regular master there. So this is a good option as there is a bunch of room further back for a big *** booster too.

 

I was thinking that if a single master has enough hydraulic fluid transfer that it can activate 4 drums, it should be able to replicate maybe double the travel and foot pressure needed for the double cylinder. With some leverage I could maybe get the feel of power brakes. I don't think a clutch slave would have enough travel, may need a regular small cylinder to ensure the right specs.


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Do some calculations.
You aren't going to get something for free when it comes to hydraulics and force vs travel.

Most manual brake pedals have a lot of travel and height because of the pedal ratio than power brakes. No matter what, the master needs to stroke the same and the floor board isn't moving. What makes it up is pedal height and travel. Like I said play with it and see.

100% sure that it will work fine. Not so sure that you'll be able to duplicate power brakes with out a boost into the system. A bell crank can change direction of force and act as a medium to exchange travel for force. Changing of bore sizes can also exchange leverage for force. Draw it up and play with it. Your goal is to decrease pedal travel and increase force at the pads. See what happens on paper.

 

Thanks, I forgot how much brake pedal travel the old systems had. Adding a booster if I can mount it anywhere won't be a problem anyways.


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No gain what so ever. IMHO this is over-engineered and has absolutely no advantage over a single pot system, as it still is a single pot system.

 

Still one line away from total failure.

 

I am nowhere near the engineer the guys on this site are. I just wanted you to know that there is a retrofit/aftermarket brake/booster combo with (I think) an 8 inch booster. They are for a 59 Chevy truck and tuck away against the frame under the floor board.

 

Single pot system master has a bunch of lines, 2 tees, 3 or 4 hoses and 4 wheel cylinders
And about 16 fittings.

A hydraulic over hydraulic with a single pot master would add 2 fittings and 1 line. Way different no ?

 

It's not the same as a single line system, as the vulnerable lines under the car are split from two reservoirs and the line from the single cylinder would be short and without the multiple fittings(failure points) that the single line system has. The advantage is that you can hide a modern booster/ master where it fits and is accessible for maintenance, and you don't have an ugly street rod looking master cylinder/ booster taking away from the looks of your flathead or competing for space on the firewall. 99% of what we do is about looks over pure functionality or comfort and that's the prime focus here.


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60's and some early seventies GM trucks ( 40 series and up ) had a system ( hydrovac ) your describing that worked real good as the firewall pedal was a single pot and the power booster or the secondary master which on some was a smaller bore had a drive cylinder that amplified the pedal effort to it to supply the fluid volume and pressure needed for the big drums . they hid them under the running boards on the drivers side of the cab . google hydovac brakes image and they show pictures to give you a idea how it works

basically a single pot driving a clutch slave cylinder to push the dual pot master would be the kind of set up your looking for , as you can increase the secondary pot application pressure by using the laws of hydraulics with bore sizes . the only problem is the stroke length

 

Over engineered with no gain ?

Yes it's still a single pot actuated system but its quite a bit simpler.

 

I've been mulling this idea for a long while; glad someone brought it up. Every system ultimately has a single point of failure, so I'm not sure that's an issue with this one. Here's the hydrovac layout, and, like PKap, I'd have a dual reservoir master hidden wherever it fits.

 

That's still a one-leak equals total failure system.

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Night and day difference

If you can't see that difference as well as the one similarity you do see - then no amount of explaining will help.

Yes 1 failure in 1 line that has only 2 fittings that can be ran in a premium spot will mean a total failure.

That really can't be compared to a single pot system with multiple lines, 16 fittings, 3 hoses and 4 wheel cylinders sprawled out to the 4 corners of the underbody exposed to every hazard there is.

 

My point is that how is that any different than a broken bolt or a push rod or a mounting bracket? I'll repeat: Every system ultimately has a single point of failure. Which failure are you most worried about?

 

I have had 6 vehicles experience a brake line, hose failure, or other hydraulic failure in the last 25-years. All were dual circuit.

I have had zero vehicles experience a bracket, bolt, pedal, or any other related component failure, of any kind, in the last 25-years.

Your mileage may vary.

I do not own, will not own, and will not drive, any vehicle capable of a single point hydraulic failure.

Had I not held this policy. I'd already be dead.

 

PKap, this is taken from your post,

99% of what we do is about looks over pure functionality or comfort and that's the prime focus here.

No it's not, you are trying to make modern stuff appear vintage or something other than what it is. You like messing with the experts?? How old are you?

Complexity is the enemy of reliability

 

PKap; Aussie A-body Mopars equipped with slant 6 engines had just the system you describe. Due to being right-hand drive, there wasn't room on the firewall on the right side for a master, let alone a booster. With the slant leaning that direction, things got even tighter. Ma Mopar solved it by leaving the master/booster on the left, mounting a small, single master on the right, that was plumbed to the left, and actuated a small hydraulic cylinder that did the pushing on the booster/master combination on that side. You might want to research it a bit, but the system has been used, and many A-bodies down under are still on the road.

Roger

 

I can appreciate the idea, the theory, but still nothing is really gained and some things are lost. What is lost is probably the most important aspect in driving a vehicle. That is feel.

A dual pot system will occasionally fail just like a single pot can. The first sign of problems in a brake system is felt by the foot. When you have come up with the old style system, you pay attention to this, as one pump may be all you have. With this system that "feel" is at least dulled. No longer is there a direct mechanical connection to the system that you can feel.

I my opinion a simple single pot system would be better than this double system. A least with the old single system, you can feel it and have less points of failure. The system you are contemplating is basically two systems piggybacked. That means the chances of failure are doubled.

If there is is a problem, which system is at fault? Which has the leak? Which is out of adjustment?

You have to ask yourself why is this not a common fix? Although I just learned Chrysler did this on Aussie Slant 6 cars but that was a factory stop gap to sell cars. It does not mean it's a good idea.

If you want the braking advantage of a post 66 system, then use that system as it was designed to be used.

 

I don't think I would want you doing the maintenance on my vehicles, that is a lot of failures, you ought to keep the brake systems up in shape. I have only had one brake failure in the last 40 yrs., and that was a duel system, and the pedal went plumb to the floor, no brakes. It was the master cylinder at fault.

 

Ok, here is what I am doing, it is an off topic vehicle, (tandem axle pick-up) but I think the ideas apply. I didn't want to rely on a single dual master cylinder to work all 6 wheel cylinders plus I wanted double redundancy. I am actuating both sides of a 60 Chev master with the brake pedal and a balance bar. (these were the parallel master that worked brake with one side and clutch with the other) From this master I will have 2 slaves that actuate 2 Hydro-boost dual master cylinders, one controlling the front axle the other both rear axles.
To stay in the realm of traditional use the 61 Chev master then underneath the car, 2 clutch slaves actuating 2 fruit jars. You have your double redundancy with parts that were available in the day, by using a balance bar you have adjustable brake bias. This is a pic of the 60 Chev pick-up master that I stole here on the HAMB, I don't know anything about the pedal set.


You are looking up at the underside of the cab

 

Customer cars are often delivered in a disagreeable state of repair. None have been on my personal vehicles.

Oh, and it is dual, which means two, not duel, which means a one-on-one battle, often to settle a grudge, frequently with swords or pistols.

 

As far as how old I am, close to 50.
As far as the "experts" I like to mess with, it's the ones that think they know everything, and anything they don't know or didn't think up can't be right.
EVERYTHING on the Hamb is about looks over function. We drive and build old cars cause they look cool and they are fun. Almost every new car drives better,cheaper, and is safer than any car on here. I don't care. I drive my 72 international 1210 instead of my diesel f 350 because I choose to.
Complexity being the enemy of reliability has it's limits. We are not going to go back to a mechanical model t style and that's as simple as it gets. I also saw a full on abs system installed on a pro touring car. That was infinitely more complex, but I would bet its reliable. I believe good design and fabricating creates reliability.

The reason for this post is that I want the size and look of the original style brake system, but not the lack of power brakes. I think that the proposal has uses where a normal type installation won't work. My truck is on a later frame, so it doesn't work to under mount, and I have a channeled cab with a 472 caddy. I have very little firewall room. The 36 ford had about two inches of space between the booster and the valve cover and looks ugly.
All I was asking was if it had been done, and it's cool to hear that it has been by oem builders in the past. There have been some good points that I had not considered, and that's what I love about this place. Like any thing on a road driven vehicle, I will not run anything that has not been looked at and backed up with guys that know more than I do, and maybe there is a redundancy factor that could be designed into this somehow. Thanks for all the comments on the idea (good or bad). I think there is still room in this hobby for different ideas (otherwise we may as well all build 1-800 street rods)
Paul


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I had dual remote boosters on a '70 BMW. It was a RHD 2002, and I think there were space issues compared to the LHD spec, leading to the use of this set-up. It could be erratic in use, but so was the entire hydraulic system including the clutch, these being my student days when I lacked the funds to get the necessary work done (not that I have the funds now ...)

 

single pot or dual pot when a master fails it doesn't make a difference , I have seen a pick up truck ( late model GM ) come in with both the front and rear brake lines blown out , guy had a panic stop and one let loose and when the abs kicked in the second side blew out , rust between the frame and pipe at both failure points ) that' s why the oems use a cable emergency brake system and every car should be equipped with them and working ( my o/t pick up I have used it 2 times , when the line rusted out in a spot where I couldn't see it ( behind the fuel tank next to the frame and when the spring shop kinked it and then tried to it straightened out over the axle perch when they replaced the leaf springs ) and its used to adjust up the rear brakes too ( little known fact of bendix brakes ) so its always in good working shape.
always have a redundant system incase the first one fails , planes and semis have redundant brake systems , my 50 they cut the front e brake cable when they installed the nova/camaro clip ( don't know why as it was not in the way , but I replaced it and hooked it up to the new rear end ( 8.5- 10 bolt ) with a little work and right now it hold the car in place as there isn't a drive train in it .

 

Agree that you will not have a power ***ist, either travel or force, no free ***ist.

Can it work, yes. I think it is overcomplicated for a solution. Even you orig post states that lines are the main failure point. So just keep up those in good shape, the single vs dual master is not really an issue.

On my old 37 Chevy pickup, prev owner had installed a remote power booster. Biggest POS thing ever. Dead feel and not really much power ***ist. Took it off and redid lines to get rid of that and with no booster it was fine. Disc front and drum rear. No power ***ist was needed. Many hot rods do not require a power booster, not sure why it is such a common perception.

 

Common because of pedal travel distance. So unknowingly they build a pedal ratio that is closer to 5:1 as with power brakes because it fits the car better. Now It won't stop because they need a power booster. See how that worked ?

That manual brake pedal rides pretty high and it can be a drag sometimes to get your knee up high enough to get your foot on to the pedal. You may even actually need to lift your heel off the floor board - oh my!