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Old 03-24-2024, 10:09 PM   #1
58ApacheGuy
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1958 Apache 3800 Hydrovac

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.
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Old 03-25-2024, 01:15 AM   #2
leegreen
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Re: 1958 Apache 3800 Hydrovac

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
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Old 03-25-2024, 11:05 AM   #3
dsraven
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Re: 1958 Apache 3800 Hydrovac

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.
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Old 03-25-2024, 11:36 AM   #4
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Re: 1958 Apache 3800 Hydrovac

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
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Old 03-25-2024, 12:16 PM   #5
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Re: 1958 Apache 3800 Hydrovac

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.
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Old 03-25-2024, 07:38 PM   #6
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Re: 1958 Apache 3800 Hydrovac

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.
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Old 03-25-2024, 09:39 PM   #7
58ApacheGuy
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Re: 1958 Apache 3800 Hydrovac

Quote:
Originally Posted by leegreen View Post
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.
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Old 03-25-2024, 10:56 PM   #8
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Re: 1958 Apache 3800 Hydrovac

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.
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Old 03-25-2024, 11:02 PM   #9
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Re: 1958 Apache 3800 Hydrovac

It looks like it is special order with a 50 buck core charge from most vendors and several say out of stock.
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My ongoing truck projects:
48 Chev 3100 that will run a 292 Six.
71 GMC 2500 that is getting a Cad 500 transplant.
77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.
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Old 03-26-2024, 12:10 PM   #10
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Re: 1958 Apache 3800 Hydrovac

Quote:
Originally Posted by 58ApacheGuy View Post
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
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Old 03-26-2024, 12:27 PM   #11
dsraven
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Re: 1958 Apache 3800 Hydrovac

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.
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Old 03-26-2024, 01:30 PM   #12
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Re: 1958 Apache 3800 Hydrovac

Quote:
Originally Posted by dsraven View Post
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.
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My ongoing truck projects:
48 Chev 3100 that will run a 292 Six.
71 GMC 2500 that is getting a Cad 500 transplant.
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Old 03-26-2024, 03:34 PM   #13
1project2many
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Re: 1958 Apache 3800 Hydrovac

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
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Old Yesterday, 07:23 PM   #14
Grey beard
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Re: 1958 Apache 3800 Hydrovac

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.
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Old Yesterday, 07:40 PM   #15
58ApacheGuy
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Re: 1958 Apache 3800 Hydrovac

Thanks for the visual. Mr48chevy (fellow forum member) gave this recommendation.
Now after seeing, looks very doable.
Again, thanks
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Old Yesterday, 08:02 PM   #16
dsraven
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Re: 1958 Apache 3800 Hydrovac

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.;
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Old Yesterday, 09:58 PM   #17
1project2many
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Re: 1958 Apache 3800 Hydrovac

Quote:
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.
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