The Stovebolt Site Forums The Parking Lot Big Bolts Hydrovac

My 54 4400 wrecker has the hydrovac disconnected. For pleasure cruising I would think this to be alright. I drive them because I like too, not worried about perfect restoration. Safe enough this way? Opinions?

kb3csw!

As usual, Ralphy has good knowledge. I have a 46 2 ton and I'm not sure if the Hydrovac is working as I haven't had a load on the truck that required much in the way of brake power. I have driven it about 3000 miles and have no problem with brakes. The manual tells how to service/overhaul that Hydrovac unit but it's kind of a 'fussy' thing so why bother if the brakes work OK.
Cheers, George

Thanks for the replys it's unlikely to see any real work. Saw it and liked it so hauled it home.

To check the Hydrovac, push on the brake peddal with the truck OFF (do this when the engine has been off for a while so all vacuum is gone), then start it up. As the engine vacuum increases you should feel the brake peddal creep down a little...if it does then it's working.

Good luck !

Looks like I'll be tearing into mine soon. I've just finished doing the rear wheel cylinders and am getting new 9x20's mounted this week. The passenger side had been seeping for some time now and I just couldn't stand it anymore. ' looks like I'll be needing new seals and bearings back there too.

While I'm at it I notice that everytime I let up on the pedal the master cyclinder bubbles back. Might as well get a kit for that too while I'm there.

And since I'm under there doing that I might as well go ahead and...

Hey John,

Since your doing all that work, now would be a good time to replace the steel and rubber lines if they have never been done before. They like to rust from the inside out, so they can look good but are really bad!

Regards,

Mike Boteler

There is a lot momentum even when a truck that size is running without a payload. Bashing the Lexus that cut you off suddenly will not be a good way to end a pleasure cruise.
If the hydrovac was disconnected, I would suspect that it went south before that. They can be rebuilt, sometimes NAPA carries rebuilt units depending on available cores. At the risk of suggesting something besides bone stock, I would recommend a diaphragm type Midland brake booster like was used on '70s GM trucks. I can't give you a model # off the cuff, but they were common on motor homes, RVs, and one ton and up trucks. On split systems, one was used for front, one for the back. One of these would give good performance when replacing the hydrovac. You would need to fabricate a frame mount for the unit. If you wanted to go with a dual master cylinder, there is also a unit which has dual boosters offered by ECI hot rod brakes. They could give you more information on that.
If I find the model #, I'll post it here as I level my table top.

I would have to agree that the hydrovac probably doesn't work or else why would they have disconnected it.

Hook it back up!! The brakes are something you just don't mess with, I have heard but would never recomend someone rebuilding one on your own unless you had a way to test and inspect it by a PRO.

I sent mine out to Karp's in CA, they did a bangup job. www.resleeve.com

Anybody know on the 46 2ton, does the hydrovac work on the front, back or both front and rear brakes? I have one that I am just getting to know.

Mike B I plan to replace all the lines rubber and steel that way I know what I have .I just wasn't sure about the Hydrovac. For the other Gents on the 46 question I believe if you have the original style brakes the Hydrovac would operate on both front and rear looking at one of the previous post in this thread where Stovebolter was talking about updating to split systems

While we're talking about steel lines, I'll be hauling my 54 4400 home soon and will need to do the same thing. Do you buy tubing and bend your own? Does NAPA carry the steel tubing?

I drove my 54 for 5years w/out hydro working. Brakes bled OK,pedal up, just took more pressure, specially after a few gravel loads! Every winter I would park it and start once in awhile, sometimes move. Most times brakes grabbed bad when doing this or getting out for spring. One winter, thought that's what happened, but instead the hydrovac started working! Wow! Super power brakes! Had to get used to pedal pressure w/out flying through window after that. Still don't know what happened to make it work, but was glad! Too bad I sold the truck a few months later after all those years together.....Wahhh!

With my 38 I bent the lines myself. Get the proper tool or you'll crush the lines and waste your money.Also my bends didn't always match the factory routing but it worked ok

I just started tearing into my brakes, too how much brake line did it take to do the 38? where did you get the tool? ahh.. prolly should start my own thread with these questions...

-Mike R.

When I purchased my 49, 6400 truck a couple of years ago, I had to drive it about 250 miles to get it home. I did not know what a hydrovac was at the time. It took a lot of pressure to stop the truck on the way home. The hydrovac had been bypassed. I soon got into the hydrovac, had it rebuilt, cleaned up my brakes, replaced the rear pads and put wheel cyl kits in all 4 wheels. What a difference in braking. This truck weighs about 8000 lbs unloaded, so I am all for keeping the hydrovac working.

Jim

FAHR it's been close to 10 years since I did any serious work on my 38 so I con't remmeber lenghts if I ever knew the total. I just dove in and started doing. You'll need a tubing bender. tubing cutter, and a flaring tool and patience. They are found at most places that stock automotive tools, and some hardware stores as you can use them for old copper plumbing pipe