The Stovebolt Site Forums The Parking Lot Big Bolts Hydrovac internal leak

I"ve been scratching my head for some time now on where my brake fluid is going -- master cylinder is about half empty every time I run her but no leaks in the lines, wheel cylinders, master cylinder -- nothing. Brake pedal takes a pump or two at first but then holds a nice pedal and the truck stops just fine. Until yesterday that is when I put on the brakes a little heavy and so much white smoke billowed out the tailpipe I couldn't see the end of the truck. My guess is the hydrovac is dumping brake fluid into the vacuum system and the engine is burning it up. I understand that some parts are still available for the hydrovac although I've not yet started my search.

Questions: 1) How much boost does the hydrovac give? Mine is a parade truck and, although I totally agree that stopping is mandatory the most I haul is the wife, a cooler and a couple chairs. Can I just bypass the hydrovac at least temporarily, and still stop reasonably? 2) I like to consider myself a decent antique mechanic but I've never been into a hydrovac before. Any advice for a first time rebuilder of such things?

Thanks

Pete P.
Harborcreek, Penna.

Hi Pete, I rebuilt all of my 6 wheel cylinders and the master cylinder, replace all steel lines with cupro-nickel and all new rubber hoses. I have no leaks and a great peddle. I bypassed the hydro-vac by running the line from the master directly to the first tee. My truck weighs 7200 lbs. empty and I haul 110 bales of hay a couple of times a year and I'm happy with the brakes. You have to get used to them and keep an eye on traffic 'cuz you won't be locking up the brakes but no trouble bringing it to a stop. With that all said my truck tops out at 45 MPH due to the 7.20:1 rear axle so speed is a factor here.

What year and size is your truck?

If a child runs in front of your truck during a parade you'll be glad you have a working hydrovac.

The Hydrovac provides a 35% increase in line pressure, so if 78buckshot uses 100 pounds of leg pressure to stop his truck you'll get the job done with 65 pounds of leg pressure.

NAPA used to carry rebuilt units...and there are companies that rebuild then for you. For me for the ~$300 cost, it's not worth not having it working.

Mike B

Hey Pete. It’s there for a good reason. As someone who works around heavy equipment, and I know it’s different, safety isn’t something worth gambling on. The Berns Company (Gary Kirpluk) sells rebuild kits for $75 (although that was probably more than five years ago now). There are parts to deal with but the rebuild itself is pretty straight forward. If you need any help or detailed pics of anything, let us know! And once done, there’s almost no maintenance associated with (maybe a couple drops of mineral oil in the drum each year). #stovebolt.com #payingitforward

Derek

The hydrovac system is fail safe to resorting to normal brake operation if it fails.
Often on old trucks the hydrovac is long inoperable junk but the brakes still work okay
I have three farm trucks In this state, 2 tons and up all factory hydrovac all haven’t had proper service in perhaps 40 years and the basic brakes work with no assist.
These trucks are not drive on the road obviously.
With no load good brakes will let you lock up the tires no problem in panic braking
So don’t worry about Sunday parades
It’s safe for that without the hydrovac
You want the hydrovac when you are tailgating In modern traffic with a full load
Which you shouldn’t be doing in the first place
-s

We had our hydrovac rebuilt at a company in Chicago. "Rebuilders Inc.". They did a great job, and I highly endorse them.

Steve

By the way, our hydro also leaked into the vacuum side and down to the check valve.

Steve

PeteP Fix your hydrovac for safetys sake,once done a little bendix vacuum cylinder oil 2x a year and you''ll have brakes.My 2 are 71 yrs. old and with service work fine,read the service book use hydraulic jack oil from your local flaps. Always fun to climb on the brakes and know you can stop !!

Rock Auto will set up an RMA with A1 Cardone in TX and will provide you a shipping label to send your hydrovac in for a rebuild. Takes a few days. The hydrovac makes a HUGE difference in braking. I don't mean to sound like a nanny, but I can't imagine the conversation with the insurance company if you get in a wreck and disabled your factory brake booster and that's why I had mine rebuilt.

Sorry, forgot the truck particulars -- it's a '46 2T (6400.)

Sounds like parts aren't that expensive and the rebuild is, hopefully, straightforward. I'm pleasantly surprised that there are still commercial rebuilder options available too.

As I mentioned above, I agree completely with the 'stopping is mandatory' logic. If repair were impractical that's one thing but it sounds like this won't be that bad.

Thanks all,

Pete P.
Harborcreek, Penna.

PeteP I was trying to figure out what bendix vacuum cylinder oil is (hydraulic jack oil is the same thing wont hurt rubber) My local parts store told me to call a place in Evansville Indiana. That guy mentioned that if your booster uses fluid he could fix that problem,he however didn't know what bendix vacuum cylinder oil was. Jim Carter himself told me ...Jim is a great guy ! That booster leather cup gets dry !!

PeteP message for you try no.2

I remember one time when I was working for a school bus fleet. I was just 20 years old. Our wrecker was a 1964 Chevrolet C-60 (could have been a 50 also, there was no emblem.) Anyway, I was towing a 66 passenger bus home from a distance of about 90 miles away. I just got back within about 3 miles from the shop when I came upon a late changing red light. It picked that time for the hydro-vac to fail. I did just about everything I could to slow that rig down. It was a highway, and I was running about 45 mph. I grabbed the parking break, stood on the brace pedal, double clutched and dropped it into 2nd gear, and ran that red light blaring the horn at 15 to 20 mph. Boy that was not a good feeling. Fix that hydro-vac!

Steve

I just had the hydrovac rebuilt on my Chevy 1960 C60. Big difference. Now I can stop. Proportioning valve requires my attention. I also had bypassed it for general yard usage. The same person did the vac for my 1977 International 1600 the week before.
Now I need to wear a belt to keep from hitting the windshield! (just kidding). Power Brake exchange in San Jose. I highly recommend them. The old Bendix Aircraft Co, South Bend Indiana, vac is somewhat complicated and expect to pay $300.
You gotta have good brakes around here when that new Tesla cuts you off! lol

The sleazy ambulance chasers who hire me to inspect wrecked vehicles for non-standard parts and other defects so they can hang people out to dry who think they are smarter than the manufacturers. They will give a jury a sob story and try to take everything you own, plus a piece of every dollar you ever hope to make in the future, and laugh all the way to the bank, or at least the closest high-dollar speakeasy to the court house. They particularly love to zero in on steering, suspension, or brake modifications, and the quality (or lack of it) won't make a shred of difference. "IT'S NOT ORIGINAL- - - - - -WHERE ARE THE RESEARCH AND DEVELOPMENT RECORDS?"

I have two brothers- - - -one does computer modeling for automotive manufacturers on a contract basis. He designs a part on a computer, and runs it to failure on the same computer, using a program he wrote to predict the cost of manufacturing and failure rates during the warranty period. His fees are reasonable, $1K per day or so, depending on the complexity of the part. If he saves the manufacturer $1.00 a part on a run of a million items, they will pay his fees gladly. Even a 50 cent saving is profitable to them.

My other brother is a criminal defense attorney. He defends robbers and murders, so he's not quite as sleazy as an ambulance chaser! Get to know both of those guys before you start butchering on steering, suspension, or brakes, It might come in handy!
Jerry

https://www.fleet-products.ca/

The company above is where I purchased my new hydrovac. Even without hauling heaps of weight I'm happy I have a hydrovac on my 55 2ton

https://www.fleet-products.ca/

The company above is where I purchased my new hydrovac. Even without hauling heaps of weight I'm happy I have a hydrovac on my 55 2ton

I need to rebuild mine on a 57 one ton GMC or get a new one.
First step is to pull it and see what model it is and then go to our local NAPA and see if they can help me.
What do you folks think is the best and safest way to go?

Thanks
Don

OK, I just found the tech tip on Hydrovac systems. I’ll read that and then have an idea on how to move foreword and still stop.

Don