55.2-59 1958 Apache 3800 Hydrovac

[58ApacheGuy]

Looking for Hydrovac unit. It mounts under the cab on the passenger side then brake lines travel to front and rear brakes from there. It has a vacuum source feeding it from the manifold.

[leegreen]

Any hydrovac or OEM 1958 bendix hydrovac?

newer medium duty cabover trucks often have them

or you might find an old one and a rebuild kit on ebay

Its probably cheaper to buy an aftermarket kit to put a dual master and booster where the stock master is

[dsraven]

if you're having brake issues for sure look into a dual circuit master cylinder upgrade if it isn't already done.
like LG says, many medium duty trucks used a hydrovac so maybe something newer could be made to fit.

[jwhotrod]

0first of all a hydroboost setup does not use vacuum, its operated by hydraulic pressure from the power steering pump. if you are looking for a source for a hydeoboost unit this guy builds a very good unit. He was recommended to me by ECI an old friend and trusted brake supplier/
Im planning a LS engine in my truck and they dont generate enough vacum to run the power brakes properly.
www.hydratechbraking.com

[leegreen]

He asked about hydrovac, not hydroboost.

"Im planning a LS engine in my truck and they don't generate enough vacuum to run the power brakes properly"
Apparently GM did not know this when they put vacuum boosters onto millions of LS powered vehicles.

[dsraven]

hydrovac is different than hydroboost. hydroboost uses hydraulic pressure, hydrovac uses vacuum. it can be a little confusing if you haven't seen or heard of a hydrovac unit. mostly medium size trucks used them and called them that. just google it for a bunch of history, diagnosis, repair info. you might even get to hear the dude that gave the shop class video narrative from the 70's. hha.

[58ApacheGuy]

Originally Posted by leegreen

Any hydrovac or OEM 1958 bendix hydrovac?

newer medium duty cabover trucks often have them

or you might find an old one and a rebuild kit on ebay

Its probably cheaper to buy an aftermarket kit to put a dual master and booster where the stock master is

Thanks. Have been considering this resolution. Problem is with frame mounted master cylinder, if I mount the vacuum booster combo, I'd either have to convert to automatic transmission, or convert manual clutch to hydraulic clutch, which I haven't even begun to research.
Right now trying to find an acceptable Hydrovac, even if I can find a rebuild kit.
But, again that's what makes groups like this great. Thanks for the suggestion.

[mr48chev]

Rock Auto Shows a booster that they are out of but a search shows that other vendors do have them. The same unit fits 48 to 64. Remembering that one of the 51 4100 trucks I bought a few years ago had one on it. I have no idea if that is all you will need but if you are attempting to cobble this together you would be far better off to place a regular booster behind the transmisson crossmember, fab a seriously heavy duty and long push rod and go that way.

[mr48chev]

It looks like it is special order with a 50 buck core charge from most vendors and several say out of stock.

[leegreen]

Originally Posted by 58ApacheGuy

Thanks. Have been considering this resolution. Problem is with frame mounted master cylinder, if I mount the vacuum booster combo, I'd either have to convert to automatic transmission, or convert manual clutch to hydraulic clutch, which I haven't even begun to research.

does this work with factory clutch setup?
https://www.holley.com/products/brak...ORN755DISCDRUM

[dsraven]

Forgive me if I'm wrong here, but the hydrovac boosters I remember had a master cyl that was foot pedal operated and that sent a signal to the hydrovac booster mounted somewhere else and it also has master cylinder on it that operates the brakes. Really, a hydrovac from a newer truck should be able to be serviced on your old truck. Just do a bore size comparo and go from there. Maybe also run a vacuum reservoir tank with one way valves so you don't run out of vacuum. Really though, if using the brakes, the throttle should be closed causing a higher vacuum. It depends on rpm then as to what vacuum you actually see.

[mr48chev]

Originally Posted by dsraven

Forgive me if I'm wrong here, but the hydrovac boosters I remember had a master cyl that was foot pedal operated and that sent a signal to the hydrovac booster mounted somewhere else and it also has master cylinder on it that operates the brakes. Really, a hydrovac from a newer truck should be able to be serviced on your old truck. Just do a bore size comparo and go from there. Maybe also run a vacuum reservoir tank with one way valves so you don't run out of vacuum. Really though, if using the brakes, the throttle should be closed causing a higher vacuum. It depends on rpm then as to what vacuum you actually see.

You are correct in how they work and I'd say correct in that one off a later model would work and might be a better option.

[1project2many]

Hydrovac is a brake power booster that is operated by a remote master cylinder. They work well as long as the brake system is in good condition. They do not usually survive if the brake system is allowed to sit empty for any period of time.

Many, many trucks have used Hydrovac. C50, C60, C70 trucks in '70s and '80s used them. They can be rebuilt but IMO if you don't like working with small parts its better to buy a reman. Both Midland and Bendix made Hydrovac boosters. There are also different styles of Hydrovac.

Hydrovacs can become badly corroded internally. This makes rebuilding challenging. If you are just looking for a replacement, maybe consider getting a unit that's already rebuilt and submitting your as a core.
https://www.powerbrake-drivetrain.com/hydrovacs/

This unit is listed for a '62 C50 and may work for your truck also?
https://shopbumpertobumper.com/en/p/.../c50/1962/6261

[Grey beard]

Could you run a push rod from your pedal to a hydraboost/master cylinder ? Here's how I did one with a vacuum booster that I later changed up to a hydraulic hydraboost set up.

[58ApacheGuy]

Thanks for the visual. Mr48chevy (fellow forum member) gave this recommendation.
Now after seeing, looks very doable.
Again, thanks

[dsraven]

there are a few alternate setups like that here. some use the hydraulic style hydroboost but they require a power steering pump for hydraulic power. if you run a vac booster like the pic from greybeard, you may wanna instalk a check valve and vac reservoir inline with the vac hose to the engine. a steel line may also help as it has no flex, doesn't break down with time like rubber does and takes less space. just a thought, someone here used an old master cylinder, bored right through as a forward mount for the booster, the pushrod went right through the master cylinder in it's stock location and followed along a space to where the booster was located further back.;

[1project2many]

someone here used an old master cylinder, bored right through as a forward mount for the booster, the pushrod went right through the master cylinder in it's stock location and followed along a space to where the booster was located further back.;

That's an ingenious solution. Very creative.

[hogfarm]

I just went thru the Hydrovac experience. I have a 1982 Ford F700 dump truck. I had to replace the Hydrovac unit as well as the dash mounted master cylinder. My Daughter who is the manager at my local O'REILLY's was able to get me a rebuilt Hydrovac for about $200.00. I'm glad I went this way rather than changing to a different type of brake system, the brakes now work great. But bleed the system was a little tricky. There is an extra bleeder valve under the cab that needs to be bled first, then farthest wheel working your way to the nearest. I did use a pressure bleeder

[dsraven]

to bleed a hydravac you need to first bleed the firewall mounted master cyl at the line fittings. then bleed the bleeder screw on the hydravac unit and if possible use a clear tubing so you can see if there are bubbles coming or not be patient as this can take a lot of time to get the air bubbles from the firewall master all the way down to the frame mounted unit. you're gonna need a good supply of brake fluid. once you are absolutely sure there is no more bubbles from the first part then tighten that bleeder screw and go to the furthest away wheel and do that one next. a pop bottle partially filled with the clear line set into the brake fluid and held there so it can't come above the fluid in the bottle is a decent way to bleed them so no air gets in. a tight fit on the bleeder screw to the tubing is also good and don't back the bleeder screw out a whole bunch thinking you will get more flow because that also leaks air into thee system when the brake pedal is released.some guys I know will try the reverse bleeding method where presure fed brake fluid is forced backwards through the system from the bleeder screws. i personally prefer the old fashioned pedal pump method. also ensure you have a helper to keep an eye on the master cylinder level so you don't suck air from that end. you gotta start over

[dsraven]

adjusting the brakes prior to bleeding also helps because the wheel cylinders don't use up a bunch of fluid trying to move the shoes outward to the drums. not that there will be a bunch of pressure when you bleed.

[dsraven]

check this site for details. f**d, I know, but same principle.
https://www.ford-trucks.com/forums/8...ke-system.html

[dsraven]

revised bleeder how to. forgot about the second bleeder screw on the booster. some have it and some don't.

Originally Posted by dsraven

to bleed a hydravac you need to first bleed the firewall mounted master cyl at the line fittings. then bleed the bleeder screw on the top of the hydravac unit that looks like it is oposite of the supply line that comes from the master cyl on the firewall and if possible use a clear tubing so you can see if there are bubbles coming or not. be patient as this can take a lot of time to get the air bubbles from the firewall master all the way down to the frame mounted unit. you're gonna need a good supply of brake fluid and also keep checking the master cylinder fluid level. once you are absolutely sure there is no more bubbles from the first part then tighten that bleeder screw and go to the next bleeder screw on the unit which is close to the outlet where the line leaves the booster and heads off to the wheels. then when thats all good clean fluid with no bubbles go to the furthest away wheel and do that one next. a one man bleeder is handy for this as sometimes the "pedal man" and the "bleeder man" can get out of sync and that can allow air to enter. a pop bottle, partially filled, with the clear line set into the brake fluid and held there so it can't come above the fluid in the bottle is a decent way to bleed them so no air gets in. a tight fit on the bleeder screw to the tubing is also good and don't back the bleeder screw out a whole bunch thinking you will get more flow because that also leaks air into thee system when the brake pedal is released.some guys I know will try the reverse bleeding method where presure fed brake fluid is forced backwards through the system from the bleeder screws. i personally prefer the old fashioned pedal pump method. also ensure you have a helper to keep an eye on the master cylinder level so you don't suck air from that end. you gotta start over

[hogfarm]

I would never bleed the brakes again with out using a pressure bleeder. Did not spill a drop, just have a friend make sure the tank is full and pump it to 10psi. then just go from bleeder to bleeder, it comes with a catch can and clear hose. About $50.00 on amazon. If you want to do the job you need the tools.