The Stovebolt Site Forums The Parking Lot Big Bolts Hydro Vac installation ???????

I have just bought a rebuilt Hydro Vac unit for my 1952 Chevy 2 ton. I am wondering if there are any pre-installation tips out there like, does it need priming or pre filled with fluid or anything like that?
The master cylinder and wheel cylinders have just been rebuilt and I will put a new vacuum hose to it but it seems like it should have fluid in it first thing but I do not know as I have had NO experience with these. Thanks, Mitchell

You dont need to fill anything. It has a bleeder on top of the fluid valve. Bleed it there & then loosen the line/s & bleed it there. That should get all the air out if it.

Hy guys, actually there are two bleed screws on a hydrovac, one at the highest point on the unit, and one on the end of the hydraulic cylinder, there is a special bleeding procedure for bleeding a truck with a hydrovac, which involves bleeding the hydrovac before everything else, hope that helps.

3B's reply leads to the following question:

Have you checked out in a Shop Manual for the procedure for "replacement" of a hydrovac unit? Your 1952 would most likely be the same as for a 1951 (in the linked-to manual).

I followed a similar procedure for a 54 GMC hydrovac and it works fine (my first experience with a hydrovac).

You need to fill your Hydrovac with oil, some 30ml of oil through a rubber plugafter you have mounted it in the truck and before starting to use it.

I changed on my 59 to a factory remade, and the instruction said, add oil before use.

Thanks for the info and especially the link to the manual. Should be no problem now. MH

DO NOT use regular oil for filling the hydrovac. It will most likely eat the seals up over time leading to premature failure. Use a non-petrolueum based oil. It only takes a little.

Jeff

I was told to use mineral oil to lube the hydrovac, but I bought a new one and it came with oil already in it, if I remember correctly.

I got an instruction from Alretta Truck Parts together with my remanufactured hydrovac.
.
It says 30cc or one oz for a singel piston 5 1/4".
Same for a 6 3/4" piston.
For a singel piston 9 1/2" it shall have 60cc or 2 oz.
Same volume for a tandem piston.

He added USE HYDRAULIC JACK OIL with a ink pen.

So I followed that advice.

I found this thread and hope some of you are still around. I’ve replaced all the wheel cylinders and master cylinder with new and all new brake lines. The manual I have is for my ‘54 that doesn’t have hydrovac, so no instructions on bleeding the Huck brake system on my ‘52 6400. I’m told bleeding Huck brakes is different than Bendix brakes. Anyone know how?

By the way, I’m going to try the original hydrovac before buying a replacement. We’ll see if it is any good. The bolts holding it are rusted and I couldn’t get the vacuum line off so I figure I’ll give it a try. Does the vacuum line need to be steel and that big?

It helps to adjust the shoes snug against the brake drums before bleeding- - - - -that pushes the wheel cylinder pistons to their fully retracted position and forces any air in the cylinder close to the bleeder screw hole.
Jerry

You can use thick-wall, fiber-reenforced hose no problem, as long as it won't collapse on itself while under vacuum. For longer stretches of hose, it might be worth finding hose that is wire-wound so it has some rigidity - perhaps even hydraulic hose?

Try to at least match your hose inner diameter with the pipe inlets of the hydrovac. Larger hoses mean better flow from the air leaving the vacuum chambers, and your hydrovac will respond faster.

Another mod to consider is attaching a reservoir to the circuit so you have the maximum amount of vacuum available to operate the hydrovac in an emergency. A ten or twenty pound propane tank would work nicely.

Another good source for a vacuum reservoir tank is an empty Freon drum. HVAC shops will probably give you all of them you're willing to haul away, since most of them aren't refillable. They come in various sizes, and some of the smaller ones will tuck inside a big bolt frame channel pretty nicely- - - -maybe more than one in tandem with each other.
Jerry

Thanks for the info, I’ll look for some Freon tanks. Will I need one way valves or anything like that?

Yes- - - -On the smaller (3/8") vacuum lines I use plastic check valves that plug into grommets in firewall mounted brake boosters. I believe there's a spring loaded brass check valve that's used for bigger lines. That allows the vacuum in the reservoir to stay there for a couple of powered brake applications if the engine stalls. I use a small hole saw to pierce the tank to install the grommets.

www.ebay.com/itm/276655911960?

Jerry

oldieoldie, if your truck was equipped with a Hydro-Vac as original, it should already have a check valve on the firewall in the engine compartment. I added a 30 lb. disposable refrigerant canister to my '57 when I installed the 2 speed rear. The vacuum reservoir needs to be open to vacuum in both directions and the original check valve will keep the whole piping system under vacuum as long as the check holds. The tank is just tee'd into the existing vacuum line after the check valve.

That makes sense. I found a drawing showing a check valve, tomorrow I will look for it.

On my '59 Canadian GMC 9600, the check valve was on the firewall immediately below the voltage regulator, and there was a 3/8" hose connecting it to the engine intake manifold. It is a brass casting about 2 inches square.

Mine actually contained two check valves in one casting - one supplied the two-speed axle circuit while the other supplied the hydrovac.

It might be worth taking the check valve apart and cleaning it - old oil might gum up the springs and affect how much vacuum it supplies.

My check valve is slightly different than Puffie40 describes but the same theory, and of course my truck is a Low Cab Forward and not as heavy rated as the 9600. Hopefully with oldieoldie's truck, the original piping is still in place, the check valve will be pretty apparent. I'll try to post a picture.

I’m down to the last few brake lines in the rear and just realized I’ll need something to block off the second wheel cylinder port on each rear wheel. Is there some special plug for this, threaded 7/16-24? I bought and installed four of the same wheel cylinder for the rear since they all had the same part number and just noticed that one of the old ones from each side seams to have a permanent plug. Ideas?

This has convinced me never to do a Huck brake truck again. Until the next great deal. LOL

Is this white thing the check valve? It is hooked directly to the intake, but I don’t see how to take it apart.

I broke the big vacuum line to the hydrovac and haven’t been able to source a replacement. How bad would the brakes be without the boost of the hydrovac? I’ve seen dual chamber upgrades without any boost so I am wondering.

Buy a short piece of double flared brake line that will fit the wheel cylinder, cut both ends off, and crimp and silver solder the tubing stub closed. Install them in one of the ports on each cylinder. Use the single input cylinder on top so the air can purge itself during bleeding.

Did you break the rubber or the steel line? The metal line can be replaced with sweat-soldered hard copper tubing and fittings- - - -the same stuff that's used in some household water systems. (and it never rusts) Flex lines can be fabricated with threaded fittings from hydraulic hose by someplace like NAPA- - - -WAY overkill on pressure/vacuum rating, but they will last about three days past forever!
Jerry

oldieoldie, the factory check valve is directly behind the white item, it's mounted to the firewall. Maybe the original wasn't holding vacuum and someone fabb'd in the plastic one. Hard copper pipe will have a different diameter than the original steel line, I used soft copper (Air Conditioning/Refrigeration) for a short section due to the 1/2" od being the same as the steel. As long as you secure it so it can't vibrate, it should hold up quite-a-few years.

The Hydro-Vac makes a big difference although I did get my truck on the road without the booster, I just bypassed the Hydro-Vac and ran the brake line from the master to the first tee. I then disassembled my Hydro-Vac to see what kind of condition it was in, then ordered a rebuild kit and did the work myself. You will appreciate the boost.

Line diameter has exactly zero effect on vacuum, and "bigger is better" where a hydrovac system is concerned, so the system can flow sufficient volume.
Jerry

Jerry, I included that info for oldieoldie, if the 1/2"od copper is used, he won't have to make any special reducers or fittings, the original steel line is 1/2" od. 1/2" refrigeration soft copper is 1/2" od. 1/2" od hard copper is available but unless he has contacts in the building trades, he may have to purchase a 10' stick.

I like to run new hard line all the way to the hydrovac. No point in betting one's life on a 75 year old piece of steel tube that's subject to rust. Over several decades of fixing others' potentially deadly mistakes I've come to have the opinion that where safety related systems like steering, brakes, and headlights are concerned, the very best I can do is just barely good enough. Ask any ambulance chaser lawyer how he likes to approach a traffic accident involving serious injury or death- - - -he will literally drool over finding some sort of mechanical malfunction or shade tree modification involved. I spent many years investigating situations like that as an ASE certified Master Technician and providing "expert witness" testimony on more than a few occasions.
Jerry

I haven't confirmed it myself, but a video I watched on hydrovac function (www.youtube.com/watch?v=OnuZ1hWMA_M) suggests the hydrovac will allow fluid to pass though itself should the vacuum fail to move the piston. In theory you should be able to plug the vacuum line off until you can repair the lines and leave the hydrovac in the system.

Be aware that because you no longer have the hydrovac amplifying the pressure, the brakes will require more pedal force to stop. It shouldn't be road tested like this.

The line broke right at the connector and I couldn’t get the steel line out of the connector. I plan to use hydraulic flexible line if I can get the right connectors. I have some concerns about bending that big of line to put it back in.

Don't quote me on the numbers, but if I remember correctly the brake system pressure will be about 350 psi with leg pressure only and about 900 psi with the Hydrovac added to the system. If you've ever driven a modern car and had it stall and felt how hard it is to stop the vehicle, that's the same feeling you'd get if the Hydrovac stopped working...it takes WAY more leg pressure to stop the truck. I would consider our big trucks to be un-safe to drive (except in an emergency) without the Hydrovac working, a panic stop would not be fun!

Post a picture of the broken part...

Mike B

The first picture is the connector and the second is where on the Hydrovac it connects. It’s is the large port on the top of the picture.

@oldieoldie regarding the four rear wheel cylinders.. Mine are connected fluid into lower port of lower cylinder, out of lower cylinder upper port to upper cylinder lower port, then upper cylinder upper port to bleeder fitting, so nothing should need to be plugged.

oldieoldie, the tube nut is standard 1/2" inverted flare, the street elbow is 1/2" inverted flare on the female side and if I remember correctly it is 1/4" male pipe thread on the other end, it might be 3/8" male pipe. The street elbow looks ok, the tube nut will be available at your local parts store, you might be able to buy a 1/2"x12" tube with the nuts already on it.

My rear wheel cylinders are left and right with an internal smaller jumper to connect them.

Here is what my rear brakes look like.

I’m going to try to take a brake fitting and weld it shut to make a plug. I’ve spent months trying to find a “made for it” plug with no luck. Anyone have any input on the idea? I’ve already welded them up but haven’t installed. All possible solutions are welcome. I want this on the road in the spring.