The Stovebolt Site Forums The Parking Lot Big Bolts 1950 chevy 2 ton truck hydrovac

I have repaired many problems on the truck that the previous owner did not do right. the problem that I am working on now is after bleeding the brakes and rebuilding wheel cylinders the brakes stay applied I emailed this question before and a person said make sure the the brake pedal was coming all the way up it was not the spring was off I replaced the spring and now it comes all the way up. I thought maybe the master cylinder was not assembled right the previous owner said he rebuilt it. so I removed it. I went to the rear wheels and still could not turn them with the master cylinder off the truck. so I broke the line loose on the hydrovac and left the pressure bleed off. then I could turn the wheels the previous owner installed new brake lines I was wondering if he put them on the wrong places or is there a hydrovac problem? the line in the back of the hydrovac that goes to the frame goes to the wheels I don't have a book I am sure someone here can tell me thanks for any help. the line near the center of the hydrovav goes to the master cylinder.

In what order did you bleed the hydro-vac and wheel cylinders?

Did you you use a pressure bleeder?

started with the furthest wheel from the master cylinder and worked towards the master cylinder did not use a pressure bleeder ive done this many times on other vehicles and never had a problem

A pressure bleeder for brake line bleeding on big trucks is not called-for in the Shop Manual until 1951.

Before bleeding at the wheel cylinders, did you bleed the hydro-vac unit at the two bleeder valves?

I only saw 1 bleeder on the hydrovac I will check tonight for an other 1 I tried to post a picture on this site but I could not figure out how

There may only be one bleeder on the hydrovac in 1950 - all I know about your year (1950) is shown in this multi-year Shop Manual.

The hydro-vac in my 54/55 GMC 2-ton did not work correctly until I followed the suggestion for a pressure bleeder (Chev shows pressure for 1951 and later, so you should be OK) and the bleeding sequence shown in the GMC maintenance manual. I think the GMC sequence might be different - maybe due to the location of the hydrovac?

I found the second bleeder I will probably have to wait till the weekend to try it I also have to put the master cylinder back in and I am pretty busy this week I will let you know how I make out thanks for the help

You can't post pictures here. You have to link to them. Refer to the note in lower left column of this page.

I installed the master cylinder and bled the hydrovac and system the way the link said to the brakes still are locked the picture of the hydrovac in the link looks the same as mine I am still wondering if the lines are in the wrong place on the hydrovac but I cannot find a diagram on the internet showing that hydrovac with a description of where the lines go

Hy 29tons, the input to the Hydrovac from the master cylinder goes into a port just below where a cylinder projects out of the flat plate at the end of the vacuum reservoir, the output to the wheel cylinders goes in the end of the cylinder which projects out from the flat plate, hope that helps.

I have been looking into Hydrovac retrofits recently (for a Canadian military Chevrolet but a Hydrovac should work the same no matter what it is hung on). One of the common problems seems to be that people retrofit a Hydrovac (containing a check valve) onto a vehicle that has a check valve included in the master cylinder. The two check valves in series typically cause the brakes to lock on. The standard solution given is to either swap out the master for an equivalent master without the check valve or to remove the check valve from the existing master cylinder. Another thing to be aware of if you don't trust the previous owner's maintenance skills was that Bendix published guidelines for the bore and stroke that master cylinders should have for the various Hydrovacs depending on the weight of truck they were installed in (and how many wheel cylinders were involved).

all the wheel cylinders stay locked. Last week end I bypassed the hydrovac to see if the truck would work like a manual system and it dose.so some thing is wrong with the hydrovac. but at least I can move the thing around under its own power while I am working on other things