Dual circuit Hydrovac upgrade?

[overdrivesteve]

Hi,

it's really difficult to bring my truck to a stop when traveling at 35 mph or faster. I have not yet had time to inspect, find and repair the problem, but one of the things I do want to do when I start on the brakes is to install a dual circuit brake system. I am very concerned with a leak developing at one of the wheels causing a total loss of brakes (because of the way the rubber brake lines rub the steering knuckle - another brake problem I May need help resolving).
Unfortunately my truck uses this type of master cylinder:
brake/clutch master cylinder for 60's pickup & Travelall - International Scout parts

So until I have time/money to do a complete brake upgrade, I would like to install a dual circuit hydrovac system downstream of the master cylinder. Is this possible? Do I need to use two separate hydrovacs, and if so how do I equalize the pressure between the two circuits? My concern would be with two separate hydro's, if one works better, or differently, you could create one wild braking problem.

Or is there another way to add power assist and have two independent brake hydraulic circuits resulting?

I read somewhere in one of the posts that there are dual hydrovac models available that look like two smaller canisters attached back to back with the brake line fittings on either end with an independent circuit exiting each opposite ends of the diaphragms. But when I called a hydrovac supplier, he stated they're still not isolated circuits - if a leak develops in one circuit, all brakes will be lost. Was he correct?

Is there any single booster/dual circuit aftermarket brake setups available? What can you recommend with my brake pedal and master cylinder setup?

Thank you.
Steve

 

[FDChappie]

For safety's sake, imho adding more parts and fittings to the system will make things more prone to failure. I'd pull the drums and look for bad seals or glazed shoes before changing things. You could even have some frozen wheel cylinders causing a lack of braking. These systems did work pretty well in their day.

 

[Greg R]

Here ya go:http://forums.IHPartsAmerica.com/brake-tech/1632-hydrovac-unit-dual-mc.html

 

[overdrivesteve]

Yes, thank you for the reply.

I was actually thinking if there was some way to split the output of the hydrovac into two isolated circuits, that would pretty much achieve what I was looking to do, or perhaps split the input (output of the master cylinder) to two hydrovacs.

Seems like either I live with the truck the way it is (after I repair the brake system problems) or I manufacture some type of bracket that will allow me to mount two separate master cylinders (clutch and dual brake) and have one of them offset or stick out from the firewall enough to allow a standard vacuum booster to be installed.
I once had a heavy 1 ton 4x4 panel truck with standard drum brakes and they seemed to work ok after I rebuilt them. Later I added a hydrovac which helped some, but was not that big a deal. I could live with or without it.
If my IH brakes end up working as well as those panel truck brakes, I'm sure I'll forget about adding power assist for awhile.

Just fyi, attached is a diagram of a dual hydrovac system, including part numbers for everything, including every line fitting, etc. Unfortunately it starts with a dual master cylinder. If I had that, I sure would not be using two separate hydrovacs.

Any "outside the box" suggestions for a dual brake circuit, with or without power assist?
Has anyone who had my type of master cylinder initially attempted a dual brake circuit type of upgrade before?

Thanks.

Steve

 

[MarkO]

Back in the day when we were running loadstar chassis school buses with wet brakes we had one line running from the pedal to the hydrovac. From the hydrovac we had a dual chamber mc that went out to the brakes.

On newer model buses they had two hydrovacs that eventually changed into the hydroboost systems that still used today.

Starting in 1967 the round body light line vehicles had a dual cicuit mc with a different mc for the wet clutch linkage.

You should be able to find the part numbers and swap over to a dual circuit without a lot of muss and fuss.

It wasn't until the advent of the square bodies that the power brake booster was used in front of the mc.

 

[Greg R]

split the output of the hydrovac into two isolated circuits,

A true dual circuit is one where each circuit has it's own fluid reservoir, hence the dual circuit master. Just splitting the output is no different from a front/rear junction block on a single circuit with one reservoir for both front and rear.

split the input (output of the master cylinder) to two hydrovacs.

Same story.

Your diagram is a true dual circuit in that it starts with a dual master. The redundancy here is that with 2 wheel cylinders for each wheel, even with a circuit loss there is still f/r braking; though the primary design is for increased braking effect on large chassis trucks.

It's just a small truck or Travelall, it didn't come broke when new. So you have few maintenance problems, fix them and they'll be fine stock. But when you decide to upgrade, go with a standard dual master and a warning switch junction block. You'll have to reapportion your firewall's real estate with 2 masters plus move and adjust the new pedal linkage and brackets.

 

[overdrivesteve]

a true dual circuit is one where each circuit has it's own fluid reservoir, hence the dual circuit master. Just splitting the output is no different from a front/rear junction block on a single circuit with one reservoir for both front and rear.

I understand and agree totally. I was just wondering if there was some way to isolate the circuits to make them dual. But apparently not unless a dual master is used.

back in the day when we were running loadstar chassis school buses with wet brakes we had one line running from the pedal to the hydrovac. From the hydrovac we had a dual chamber mc that went out to the brakes.

So from this second dual chamber mc to the wheels were these two independent isolated hydraulic circuits, such that if a wheel cylinder blew out you would still have brakes at the other axle?

it's just a small truck or Travelall, it didn't come broke when new. So you have few maintenance problems, fix them and they'll be fine stock. But when you decide to upgrade, go with a standard dual master and a warning switch junction block.

Yes, you're probably right. I just want to be sure this old crew cab truck can safely stop when pulling something like an airstream trailer on these mountain roads.

Three times in my life I've had a major brake failure. Once long ago as I recall, a wheel cylinder somehow blew apart in my 49 Chevy pickup - instant total loss of brakes and I hit the car in front of me. Another time someone pulled out suddenly in front of me, I hit the brakes hard and a rubber flex brake line blew out. But this car had a dual brake system and I stopped before hitting the car in front of me. And finally, once on the freeway a big rig truck on my left suddenly pulled into my lane. I quickly swerved onto the right shoulder to keep from being run over. But hitting the hard bumpy dirt at freeway speeds caused my rear tire, axle hub and all to completely break off my car. But I didn't lose my braking ability ;-)

so that's a little background - I'm just anxious to get the truck on the road, but safety and dependability are top priorities.
I have no shop so I'm limited in my fabrication abilities. But adding a rebuilt hydrovac and second dual mc when I put in the new brake lines is well within my abilities. And when it comes to brakes, I'd rather have too much rather than just enough.

If it stops raining this weekend, I'll look again to see how difficult it might be to rework the clutch and brake pedals and mc. That would truly be the best (but most time-consuming) way to go.

 

[MarkO]

The old loadstars dual system wasn't a true dual system because it started up top with a single line. When it got to the hydrovac it split. If you lost one side after the hydrovac it would drain the single line from up top so you would lose all of what you had.

So no, it wasn't a true dual circuit.

I think it was set up to give a bigger % of the braking power to the rear. I know that when the buses were empty and the roads were the least bit wet it wasn't hard to lock up the rears long before the fronts ever started to lock up.

I know some who have posted here and other places are adamant about the importance of having dual circuit brakes. I won't minimize the safety aspect of having dual circuit brakes.

But at the end of the day there is only so much time and $$$. And there have been billions of miles driven with single circuit brakes that didn't end up in disaster.

The importance of proper maintenance can not be emphasized enough.

Also, having a working emergency brake is sort of important as well. It May not have the stopping power of a dual system when something breaks but it is better than nothing.

 

[Greg R]

big rig truck on my left suddenly pulled into my lane.

I hear you steve, also nothing exhilarating like the semi in front of me losing it's tire recap on the rear axle. The 'gator must have been 12' long, it unraveled, flew up in the air about 30 ft and even though I braked and tried to dodge it; it did land on the freeway in the right lane next to me just seconds after I went left. The driver must have been sharp, 1/2 mile later he was pulling over. And if anyone thinks a piece of rubber is no big thing; stop the next time you see a moderately sized gator on the road and pick it up.

Going on the things you say broke that caused loss of braking; you've got some preventive maintenance/scheduling issues. Upgrading is for sure in anyone's favor, but stuff should not be breaking during an emergency maneuver. There's a root cause somewhere else.

 

[overdrivesteve]

I hear you steve, also nothing exhilarating like the semi in front of me losing it's tire recap on the rear axle. The 'gator must have been 12' long, it unraveled, flew up in the air about 30 ft and even though I braked and tried to dodge it; it did land on the freeway in the right lane next to me just seconds after I went left. The driver must have been sharp, 1/2 mile later he was pulling over. And if anyone thinks a piece of rubber is no big thing; stop the next time you see a moderately sized gator on the road and pick it up.

Going on the things you say broke that caused loss of braking; you've got some preventive maintenance/scheduling issues. Upgrading is for sure in anyone's favor, but stuff should not be breaking during an emergency maneuver. There's a root cause somewhere else.

Wow, close call, but never heard them called gators before, but that does describes them well.
I had just bought the Chevy and was taking it home when it blew out the wheel cylinder. The other two cars were both honda's. Just can't suddenly hit the dirt going 65 mph in a prelude and not tear off the back wheel assembly.

Between the raindrops today I was looking at the crew cab to see about changing the brake / clutch pedal brackets and mc. Unless there are nearly correct pedal brackets already made, its beyond my fabrication ability. I mean I can design something simple that will work well, but without a shop it would become cost-prohibitive to pay a machine shop to make every piece. So as for brakes, everything is going to stay totally stock, at least for a couple years.

I know some who have posted here and other places are adamant about the importance of having dual circuit brakes. I won't minimize the safety aspect of having dual circuit brakes.

But at the end of the day there is only so much time and $$$. And there have been billions of miles driven with single circuit brakes that didn't end up in disaster.

I've owned two trucks in my life that I really liked that had single circuit brakes - a 49 Chevy 1 ton panel truck and a 57 Chevy 1 ton panel truck. (I had bought the 49 pickup mostly for panel truck parts before selling it). I drove both those panel trucks all over the country and into parts of canada. In all the years I owned and drove them, only ever had two minor incidents with them - once the exhaust pipe broke on the 49 panel when I was in ohio, and once got a flat tire in the 57 panel in the deserts of Nevada. And that kind of dependability is the goal of what I'm doing now with this crew cab.

I'd probably still have both panels except when I was moving, I had the 49 towed and the tow company totaled it on the freeway (fine print says they're not responsible for damages to towed vehicle). And the 57 I sold for part of a down payment on a house. (unfortunately I lost the house and my business in the northridge earthquake).

My goal for the 62 crew cab is to make it a very safe, very reliable, very dependable, fun to drive, nice looking long distance, on and off-road camper vehicle. I would put a write-up in the readers rides build-up section, but it seems self-serving and what I'm doing seems amateurish compared to most others there. I'm not doing big 4-link suspension lifts, frame-off restorations or anything like that. I'm just trying to fix a never-ending list of all the stupid things the previous owners have done to this truck - things like wrapping the fuel line from the fuel tank, around the suspension spring shackle, then to the fuel pump, or cutting a hole in the wheel fender and another one in the side of the cab to run a heater hose into the cab's heater box, just to name two.

I can understand things like the brakes being done wrong as not everyone knows how to do mechanical repairs, but the one that bothers me the most is that the po took some kind of electric sander to the entire body, then did not put even a coat of primer on. It's rained almost every weekend since I got the truck and before I can get it running it has been turning into rust before my very eyes.

I apologize for rambling on, - just trying to share my truck adventures. I do sincerely appreciate everyone's comments and help.

Thank you.

Steve