The Stovebolt Site Forums The Parking Lot Big Bolts hydrovac or not

I have a 46 2 ton and it appears the hydrovac unit is missing, will the brake pedal be to heavy to stop the truck? should i get a new one? advice would be appreciated. thanks Matt

Hi Matt and welcome!

I think the answer to your question depends on what your intent is for the truck -- Are you intending to drive it loaded (heavy)) or just drive around in it as a fun truck (light)? If you plan on carrying loads, you may want to reinstall the hydrovac system. Short of completely upgrading the brakes, it may be your best and safest bet. The hydrovac units are available (rebuilt or kits). If you go that route, just be aware that using silicon brake fluid (DOT 5 here in the US) is not adviseable with the hydrovac system.

If you are mainly going to just drive the truck around for fun (i.e., light/empty) the brake system without the hydrovac system installed should be okay. I drive my '49 4400 around that way and the brakes were sufficient. Having the hydrovac installed on a trrck that will be driven relatively light will give you touchy brakes -- my '65 firetruck has hydrovac brakes and when I have no water in the tank (1,000 gallon capacity), I have to be careful on the brakes and have locked them up on more than one occasion -- which is sort of embarrassing ...

Good Luck!

I say this way to often, but the hydrovac will NOT make your brakes better. All it does is make the brakes easier to depress with your foot.

Jeff

matt d,

Rustednuts is right...

The Hydrovac only makes it easier on the driver.

Chevrolet stated that if you have a hydorvac in the systen and put a test gauge in the brake line, when the gauge reaches 1000 psi the pedal is providing 35% of the effort and the Hydrovac is providing the other 65%.

I like having the Hydrovac's in my trucks...

Mike B

If it had a hydrovac, I would put it back on. Some of the older ones didn't have that much for brakes to start with. Also we are driving at higher speeda and in more traffic these days.
Jim

I had to temporarily disable by power booster
on the 59 fire truck and its a bear to stop.
Got to rebuild the hydro.

Just to confuse this thread some more with a pet-peeve of mine . . .

My '41 fire truck (either 1.5 or 2 ton - not sure which) has a factory-installed vacuum-assist canister for the brakes. In my mind, this is NOT the same as what everyone refers to as a "Hydrovac" - nor was it called such in the factory salesmen's book. Far less complicated, different principal, and different hook-up. Where a Hydrovac can be mounted anywhere on the truck, and just plumbed to the Master cylinder, the Vacuum-assist is a mechanical only deal, that must be mechanically attached to both the pedal and the master cylinder. No brake fluid ever goes to the vacuum assist unit, and it does NOT require "bleeding".

One uses vacuum to push the brake fluid to the cylinders (hence the "hydro"), while the other just uses vacuum to help push the pedal. (gross over-simplification?)

Anyway, this might affect your plans in terms of replacement of the missing unit. I'm guessing your truck, being the same model as mine-ish, may have had the vacuum assist, which mounts pretty much in-line with the master cylinder, just aft of it - if I remember correctly. Guessing a vac. assist would be harder to find. On the other hand, no reason a hydrovac couldn't be installed instead.

How's that for muddying the waters?

-Michael

Just to add my 2 cents sooner or later a situation will occur where you will want all the brakes you can get.......like when that 5 year old kid runs out in front of you.

Worst case scenario yes, but s*%^t happens.

30 years ago I had a buddy that had a 56 Chevy school bus, the engine killed , he had no brakes and flew through a red light. There where probably other issues, but

I have the hydrovac on mine, best brakes on any antique I have ever had. Been playing with antiques quite awhile, most older. But the 47's brakes work well, though still not compared to todays vehicles. I would use it, the more brakes you got the better :-) good luck with yours.

Thanks for the response chaps. I would fit the hydrovac if I had one. I think I will just have to try it without and see how it goes. The truck is going to be driven unladen and probably for special occasions so will see what happens. Thanks Matt

If it originally had one on it, i'd definitely put one back. Too dangerous out there on the road not knowing for sure if you're going to get stopped in time, or not. I drove a 2 ton Chevy flatbed around for a week, or so with a bad hydrovac, & had several close calls. It does make a big difference.

Does anyone know where to get one from. I presume mine had one because i have a pipe from the inlet up and across the baulkhead then down to the passenger side underseat area. I dont know were they were fitted does anyone know or have photos. Cheers Matt

Check with Alretta Truck Parts. (508)788-9409. Ask for Geoff.

You should also be able to get them from your local parts store. I don't know what the cost would be without the core charge for trade in, but at least you could pick one up locally.

Just make sure you get the right size. Too small and it won't make much of a difference. Too big and it won't work until you have the brakes 2/3rds to the floor.

Jeff

hi rustednuts, im in the uk and i dont think my supplier will have a clue wht im talking about.

Does anyone know what size I should have on a 160" 2 ton 46 stakebed then. without the original im lost.

Spanky where abouts is alretta truck parts, if i put the international dialing code in is 508 the state dial code?? Thanks Matt

Hi Matt,

Duh... I didn't even see that!

Jeff

Jeff, do you know what size I would need?? Thanks Matt

Alretta Truck Parts is located in Framingham, Massachusetts (508)is the State area code.

cheers spanky !!

Matt,

Let me look through my books and see if I can come up with some numbers.

Jeff

Matt, I think you would be fine with a 1 1/2 to 2 ton sized unit. Unfortunately I do not know what the exact sizes are. The 2 1/2 ton sizes (GMC only, since I don't think Chevy made anything bigger than 2 ton in '46) and up look identical without perspective, but they are bigger when you set them side by side and I would be leary using one of them.

One I've seen was about 1" wider but the same length canister. Another was several inches wider and longer in the canister. All looking identical without a size perspective.

These things have been used in a ton of makes and models of cars, trucks, forklifts etc., all over the world. Lots of models out there...

Jeff

you might try classic spares. www.classic-parts.co.uk they advertise brake and clutch parts, located kenton, Devon.

past parts ltd. [email protected]

Have you checked local newstands for Classic and Vintage Commercials or Heritage Commercials they may have useful leads.

Jim Carter Also sells Hydrovacs www.oldchevytrucks.com but he requires a core or core charge will apply.