The Stovebolt Site Forums The Parking Lot Big Bolts Replace hydrovac with late model brake set up?

I was thinking of replacing ( non-functional) hydrovac on my 54 two ton with a late model power brake unit perhaps from a 1970's-80's c30 which I can most likey pick up from the bone yard for about $20.00 or so. I realize this means a firewall mount but that does not look too difficult. Has anyone done this and if so what parts did you use and do you have any advice?

Thanks,

Pappy

Nobody said you had to put it on the firewall.....
It'll look better hidden under the cab. Make a bracket to mount it to and run a push rod back to it.

Grigg

Would a brake unit from a c30 be appropriate for the stopping power needed for my truck (54, 6400)?

My guess is NO it won't work.

The MC bore is not the same for 1 ton and 2 ton trucks. The bigger trucks have larger wheel cylinders that require more fluid to engage the brake shoes. If you use a small MC the pedal will be on the floor before the shoes hit the drums.

Mike B

I already did this and it worked awesome. I used a on the firewall vacuum boosted master cylinder from a 96 chevy HD. 40mm bore, That's over 1 1/2 inch, the original was 1.25 inch,(Napa 390278 or NMC P3305) this number is for the master-cylinder, The vac- booster is ( 54-71046 )Invest in a line bender. Take your lines across the top of the firewall and drop down on the passenger side, I put some coils in the line to give it some give, then, at the frame is a three way that came from rear and split for the two fronts. I put the line from the front of the master-cylinder to this splitter, then hook the line from the rear to the rear master-cylinder line. Then I pulled out the old hydroboost (actually pulled this out first),and connected the lines on back to the rear.
As for the peddle and master-cylinder mounting I marked the holes needed and pushed into place, had to pound in the inner fender just a tad to clear. On the inside I used inch and a half angle and put these on the bolts of the master cylinder to spread out the pressure to the firewall of being pushed on and these also are what I welded a swing bolt to for the S-10 peddle I used. Also a return spring and brake light sensor. I then hooked up the vacuum at the firewall that went to the Hydroboost with a flexible brake vacuum hose, put in new front brake cylinders in the wheels(back seemed to be fine, bled it and and WOW did it work.
The first time I tried it out, I had just armoralled the seat and I hit the brakes at about 20 MPH, I was then spat on the steering wheel like a bug on a windshield. I have carried about 2 tons on it since and it works strong. I'll try to post pictures. Bob

Bobb,
Don't get your HydroVac confused with a HydroBoost.
A HydroVac "sucks" and a HydroBoost uses power steering pump pressure.

Grigg

There are a couple shops that can rebuild a hydrovac unit, you might think about doing that against trying to put a hole lot of stuff together for cheap and something not work right, then you start paying, I have a company here in Ca that ha sbuilt several hydro vacs and no problems, prices have ranged from $180 to $240, with a proper hydro vac and good shoes,drum, and cylinders they work just fine.

Sorry, Your right Grigg, got my terminology wrong.
The original vacuum system on both of my 6400's sucked, they worked and didn't leak, but sucked. But I didn't know that until I changed them. They are just not as good as a modern on the firewall set up and are not split systems, so not as safe either. Yes the ultimate is the hydro-boost but I found them higher priced and I don't even have power steering, so that would be another box of worms. Did the on the firewall set up in little over a day and it is screaming good compared to the original. But to confess I really did the conversion because my neighbor convinced me that I should have a split system for safety, especially hauling loads, it's not just my life I am risking.
And I think if you read the original question he is not so concerned about being original if it's hidden under the hood, if you look at my bucket pics , I only had about $250 into the conversion andI think it looks pretty natural since that is where they have been since the 60's. My opinion, Bob

We've had 2 ton trucks since the 40's when my dad started farming a 47,53 and a 61 GMC plus my grandfathers 57 Chevy, never once did we have a master or wheel clyinder fail on us on the road, the mountians or anywhere, over loaded with sugar beets, cattle or what ever would fit on those poor old trucks and not one failure, all equiped with hydrovacs, in fact I still have and run the 61 when we need it, these trucks worked for a living in their day, and you guys worry about failure on a empty toy truck.
In fact Grigg may have seen the 53 Chevy 2 ton moving van at the Pleasenton show last may, I just rebuilt the brakes and hydro vac on that truck and empty it may weigh 11 to 12,000 #, I started it today and moved it and remembering this thread tagged the brake pedal, and found myself up against the steering wheel, I don't know what more a person would want.

Following

I installed a 80s chevy G30 truck master w/ a 7" universal corvette style booster under the floor of a 52' 4400. Installed new wheel cylinders and shoes on the 14" drums. the GVW is 14,000, and the truck stops like new ,even with a huge load of wood.. Very little rework on the brake lines and the master ended under the seat, but its worth the trouble.

I'd stick with what you have, it is hard enough to find a parts store that knows what a medium duty truck is, let alone how to find parts for one that hat been modified.. I found a place named Reman Inc that will have anything you need to rebuild or buy a rebuilt HydroVac. Google Reman Inc for contact info. If you insist on going with a later brake master cylinder setup, be sure you get acquainted with brake pedal ratios, wheel cylinder diameters and master cylinder diameters. There's a lot more to this than bolting on parts. There is an excellent reference article on Pirate 4x4.com, written by Billavista. Good luck.