The Stovebolt Site Forums The Parking Lot Big Bolts Dead hydrovac?

When I first brought my '46 Chevy 2-ton home, one of the 1st repairs I performed was replacing the rusted-through brake line between the MC and hydrovac and then bleeding the system. After this, I could lock the rears up (in gravel)and feel the fronts at least trying to grab through the steering wheel without too much pedal effort.

Now, all of a sudden, I have no brakes at all! The pedal is all the way up and hard as a rock. Also, when I step on the pedal, I can hear a momentary puff of air (don't know if it's positive or negative pressure) coming from the "breather" behind the seat I didn't hear before, but only when the engine is running.

I'm thinking ultimately, I'm going to end up using a Hydroboost system when all is said and done but that's a ways in the future. For right now, I just want to get it stopped reliably without pulling on the hand-brake!:D

Thanks all.

You can buy a factory remanufactored hydrovac at Alretta Truck Parts.

Hy Dieseldude03, your brake lines may be rusted on the inside, and they are clogging the lines. You already replaced one rusted through line, so maybe they all need replacing, replace all the flexible lines as well. The noise you're hearing is the atmosphere valve allowing air into the power side of the Hydrovac. Rebuilding or replacing all the components is the safest thing to do.

Thanks to both of you. I thought about rusty lines and replaced all the steel ones a few days back. I can crack the bleeders on all 4 corners (one at a time of course lol) and push clean fluid through them rather forcefully with the pedal like one would expect. Could a blockage still be a possibility?

If your hydrovac has one, pull the plug on the back of the hydrovac and check to see if brake fluid dribbels or pours out. If it does, you need a new hydrovac, or a rebuild.

If you want to wait, you can just bypass the hydrovac with a piece of brake tubing and rebleed your system. You'll have to push harder on the brakes, but it won't effect the brake system.

Jeff

Hy Dieseldude, you could have siezed up wheel cylinders, or brake shoes that are siezed that's about all I can think of that would give you "no" brakes. It sounds like you have hydraulic fluid flow, so something is impeding the application of the shoes. better pull things apart and see what's going on.

IF you hear application thru the breather, the HV is working, with your foot on the brake pedal and with pressure, when you start the engine does the pedal go down a bit, if so the HV is working, if you have a lose of fluid from the master cylinder either the HV is using it or a leaky wheel cyln, as stated above remove a plug or hose off of the bigger part of the HV if fluid runs out it needs to be rebuil. Front brake hoses could very well be swelled up inside,replace them, this can cause front wheel problems. The HV works very well, no need to change to a hydro boost system.

Well I finally got a chance to look things over a little more. I climbed into the truck for the 1st time in 2 weeks and stepped on the brake pedal. It's still all the way up and hard as a rock. I pushed on the pedal pretty hard and started the engine. The pedal moved less than 1/2 inch down. Still hard. Checked level in MC. NO fluid loss. I then climbed underneath. I don't see a plug on the back of the Hydrovac unit anywhere. I asked Wifey to come out and step on the brake pedal when I said OK. I then took the line off the back of the hydrovac and told her to push the pedal down HARD. Brake fluid shot the entire length of the truck so there doesn't appear to be any restriction inside the unit itself. With her foot still on the floor, I re-connected the line, then topped off the MC. Took the truck down the gravel driveway and jammed the brakes as hard as I could, resulting in a slow coast to a stop.

when i got the 51-720 series gmc rescue truck back in 2006, i was told that the brakes didnt work and the hydravac was the issue. since the M/C was bone dry i filled the system and bled all the wheels which took some time because due to the size of the truck each wheel had two wheel cylinders per wheel. i had a full hard pedal and very little stopping action. after i got the truck home i thought i had the issue corrected until i saw i blew a rear cylinder with all the fluid on the inside of the wheel. i was brake checking it and i put all the pressure i could on the pedal. after i disassembled the cylinders i found out why they didnt work. every wheel cylinder was frozen. how could this be? i had to use the pedal to blow the cups out. i dont know what it was but each cylinder had solidified with what ever the previous owner had used for fluid for the previous 55 years. i had to actually dig out the crap. after getting the cylinders lined i found out there was nothing wrong with the hydravac. maybe this is your problem

I could definitely see that happening. Thing is, they worked fine after I bled them initially after replacing the steel lines. Could lock up the rears on gravel without any undue stress on my part. Then, all of a sudden, hard pedal and no brakes at all.

Dieseldude......It is now April 28, 2014, and I am having the exact same issue that you did. I just installed a new master brake cylinder on my 1960 Viking 2 ton, and now the brake pedal is rock hard, and only moves down an inch or so. I loosened the two front bleeder screws, and get no fluid coming out when I hit the brake pedal. When I take the top off the MBCylinder, fluid does squirt upward when I hit the rock hard brake pedal. MBC is not leaking any fuid, and when it sits for a week, there is no loss in fluid.

Did you ever discover what your problem was? I would bet I have the same issue. Do I need to try bleeding the Hydrovac, or could a bad check valve do this?

Many thanks for any suggestions.

dwight

Sounds like one of the rubber lines collapsed. I think that's the case with Billy W's '60 Viking bus. After replacing practically everything else,this might be the cause. Solid pedal.Leave the bus ,come back two weeks later, Pedal still solid,even with engine off. I guess we'll find out...

wetwilly.....thanks for your input. When you say one of the rubber lines may have collapsed, which lines are you talking about? The metal brake lines leave the MBCylinder and about a foot down they convert to a larger rubber line which goes downward toward the Hydrovac. You referring to these, or maybe some rubber lines "inside" the Hydrovac?

If you are referring to the rubber line below the MBCylinder, guess I can go to the Hydrovac and open the bleeder, and if nothing comes out, then there must be a clog from the MBC to the Hydrovac.....but my gutt tells me the lines are fine.

Hope that I dont have to rebuild the Hydrovac just yet.
dwight

I would start with the line that comes out of the master cylinder. Crack the line loose and see if you have fluid. If you have fluid move to the next connection which should be at the hydrovac. This should tell you where you have fluid and where you don't have fluid.

There are two flex lines on the front,)axle)and one rubber line on the rear,usually located above the differential. These lines deteriorate,(from brake fluid,combined with rust from the steel lines), from the inside-out,like the steel lines,but they collapse,sometimes completely restricting flow. There are rubber lines that attach to the hydrovac, for vacuum assist.I'm replacing all of my lines,brake and vacuum,(rubber and steel). Most are as old as the truck,and need replaced,anyway. There is a vacuum check-valve,located on the vacuum manifold. it,(manifold),is attached to the firewall. If this becomes inoperative,it will eliminate vacuum to the hydrovac,and 2-speed,(if so equipped). We think that's part of the problem,with Billy W's '59 Viking 60,bus. We'll find out Tuesday!

Don.....10-4....as soon as these torrential rains are over, I will check these brake lines as you say....go from one to the next until I discover the problem.

I didnt get your entire message, but I see that I need to check all the hoses coming to/fro the Hydrovac. Will do when the weather clears, and I will post what develops.

Thanks.
dwight

Here are some pics to help everyone see my situation, and to help with my Hydrovac questions:

Pic 1: My 1960 Viking with new Master Brake Cylinder under hood.

http://i950.photobucket.com/albums/...0Repair/VikingMasterBrakeCylinder002.jpg

Pic 2: Closer shot of Master Brake Cylinder
http://i950.photobucket.com/albums/...0Repair/VikingMasterBrakeCylinder003.jpg

Pic 3: Pic of Hydrovac. This is the brake line coming from the Master B. C. and going to the Hydrovac.
http://i950.photobucket.com/albums/...0Repair/VikingMasterBrakeCylinder008.jpg

Pic 4: Hydrovac.....Is this the bleeder screw for the Hydrovac?
http://i950.photobucket.com/albums/...0Repair/VikingMasterBrakeCylinder009.jpg

Pic 5: Hydrovac....is this the fill plug for the Hydrovac? If so, how much mineral oil do you fill in this rascal?
http://i950.photobucket.com/albums/...0Repair/VikingMasterBrakeCylinder010.jpg

Pic 6: This shows that the brake pedal is only going 1 inch before hitting a stone wall.....it is rock-hard, and will not go any further....but I am not getting any fluid to the Hydrovac.
Pedal Up:
http://i950.photobucket.com/albums/...0Repair/VikingMasterBrakeCylinder021.jpg

Pedal Down:
http://i950.photobucket.com/albums/...0Repair/VikingMasterBrakeCylinder022.jpg

Today I loosened the line going from the Master B. C. to the Hydrovac, and I got fluid running out. However, when I push on the brake pedal, I see no increase in the flow rate. I later loosened the line at the MBC which feeds the Hydrovac....I loosened it while someone pushed the brake pedal slowly, and I got fluid coming out. I closed the line and then let my helper release the brake pedal. We did this about 7 times, and I felt that all the air was out of the MBC. I then went back to the Hydrovac and loosened the line and had my helper push the brake pedal......and got nothing coming out.

Now, some more info. to help you experts diagnose the problem: The brakes have been bad for a few years, and I have been driving around the farm using the emergency brake whenever necessary. I have been refilling the MBC quite often, and I would get alot of leakage whenever I hit the brake pedal since the fluid was shooting around the shot seals in the MBC, and leaking down the inner firewall. I never noticed any fluid coming from any of the wheel cylinders, and am thinking that perhaps alot of the fluid would slowly leak downward and into the Hydrovac. Maybe it is half full with brake fluid, and that is why it runs out when I loosen the brake line from the MBC, but am getting no fluid when I hit the brake pedal. Does that make sense? Im thinking that maybe I need to totally drain the Hydrovac of all fluids and then fill up with the correct amount of mineral oil, and then attempt to bleed the lines from the MBC to the Hydrovac.

Please let me know if anyone can solve this mysterious Viking problem. I really dont have the time now to remove the Hydrovac and tear into it searching for the problem.....hoping it will be a simplier fix.

Also....what if I am not getting enough vacuum to the Hydrovac? Years ago I would hear a nice "air release" sound when I touched the brakes, but now I can run the engine, let the vacuum build, and tap the brakes....and I hear no air release sound.

Help.......
dwight

I would pull the drums and see what is going on. Look for a stuck wheel cylinder, broken return spring or stuck adjusters. You could also have a flex line collapsed.

Dwight,
If I recall correctly, you indicated in another thread that you had drilled and tapped a separate line from the hydrovac into the master cylinder resevoir. I think I see that line going into the side of your master cylinder in pic #2. Is this the line that you say "feeds the hydrovac"? I don't understand the function of that line. There should only be one line from the master cylinder to the hydrovac and then one line from the hydrovac to the wheel cylinders. Perhaps you can clarify what your connections are.

Your hydrovac vacuum chamber may full of brake fluid, which might explain the loss of "air release" sound. There are internal valves that can leak, filling up the vacuum chamber, causing loss of fluid from the master cylinder, without apparent external leaks. If that is the case a rebuild is in order.

If your brakes have been bad for several years, you may have multiple problems. If wheel cylinders are not "exercised" they will seize, so you may have one or several cylinders that are not functioning, as Don Stocker has indicated above, in addition to possible hyrovac problems. Good luck and let us know what you find,
Kent

Kent,

Yes, when I ordered the replacement Master Brake Cylinder, it did not have the hole in the side for a third line (one line for the clutch, one going to the Hydrovac, and this one....I think it is a return from the Hydrovac, but I need to double check that). So, I took it to a machine shop to have it drilled and tapped.....and the mechanic laughed and said that he just did one for another guy last month who was restoring an old Chevy Viking firetruck.

(I just checked my shop manual for the 11" MultiVac brake unit, and the third line is indeed a return line from the Hydrovac.....seems this system has fluid going in, and fluid coming back to the MBC when the brake is released).

When I take the top off the MBC and gently hit the brake pedal, fluid squirts upward and it may be coming from this third line.....but I am not sure yet.

Yes, I was thinking that the Hydrovac could be full of brake fluid, causing problems. Guess I could open the bleeder and see how much comes out.

My shop manual does not say how much fluid (mineral oil) is supposed to be in the Hydrovac....so, I need to search around and get that info.

I will tackle the brake lines again and try to determine why the fluid is not making it to the hydrovac......either a collapse in that short rubber line, or the new MBC is not pumping.

Thanks for the input.

Don....thanks for the advice. As she stands now, the fluid is not making it to the hydrovac, and none is arriving at the bleeder screws at the front brakes.

Seems like it must be that collapsed rubber line about a foot below the MBC. You have any clue as to why they used this short piece of rubber instead of running metal tubing all the way from the MBC to the Hydrovac?

I guess a quick test is to just disconnect the tube at the MBC and also at the Hydrovac and try running brake fluid or air thru the line.

dwight (pro-russian millitant)

The chassis flexes,from bumps in the road,and especially when used off-road,such as farming. Solid steel lines would tend to kink,causing restricted flow,(poor brakes).The short rubber lines act as a shock-absorber. Hope this helps explain the reasoning.

WetWilly.........OK, that makes good sense.....like a rubber shock-absorber between the MBC and the Hydrovac.

I hope to have some time soon to remove that entire line and look for a clogging issue.

dwight

It has been mentioned that the brake goes in an inch or so, my brake pedal goes all the way to the floor and is very easy to push that pedal down. The master Cylinder is losing no oil, it did have slight bubbles when we first pumped the pedal but they have now gone. Still losing no oil.

Could this be the Hydra Vac also?

Thanks

John.

John,

Are your shoe adjusted to a heavy drag? If not that could be the problem.

Mike B

Hi Mike B,
Thanks for that, I will be checking that today. I am sure there is no drag at all as I have the front up on stands and the hubs spin too freely.

Thanks you.

Don't forget to apply the brakes a couple times as you make adjustments to re-center the shoes to the drum.

Let us know if that fixed the problem...

Mike B

Hi Mike B.

Whew, what a day crawling under that truck. Been a while since I used to help dad with the brakes and get oil up to the elbows.

Thanks Mike. B All worked well with your advice. Re the trick with the brake pads, yes, dad was all over that and made sure I did it, well he did it as I was the grease monkey under the truck. Like you, he knows all these little tricks I would not think of. Bled some air and water from the lines. Great peddle now.

Tackled the park brake also, had to pull the adjusting bolt that hangs down for the inner shoe facing of the brake drum. It was gunked up pretty well. Now she adjusts fairly well.

Brakes-check
Electrics-check
Starts/stops/runs-check.

Photos to come soon,

Thanks
John.