Hydrovac tandem brake booster- parts/rebuilt

[PSW Fix-it]

Looking for leads for this brake booster

1. A take-off (core) to get rebuilt
2. Parts kit to use to rebuild
3. Lead on rebuilders to get ours rebuilt

[mowerman]

I’m surprised nobody’s responding. They’re pretty basic. Try Google search good luck.

[Geoff Weeks]

https://powerbrakes.com/hydrovacs/bendix/

https://www.accupart.com/vacuum-brakes/bendix-type/hydrovac/?page=4

 

Edited Friday at 06:27 PM by Geoff Weeks

[PSW Fix-it]

Correct, we were thinking if we could find an old unit off a junked chassis (cheap), it could be sent out for rebuilding, saving some time.

Rebuilds are running a minimum of $850+ and shipping

The other option to find a kit & rebuild it ourselves?

The particular unit we need is not seeming to be very popular & some of the crosses are the same

Thanks

 

 

[mowerman]

Well, at least we gotta start… truck parts are all a fortune nowadays, good luck

[mowerman]

It the past few months I was able to save tons of money, just by shopping around a bit and asking a lot of questions

[Geoff Weeks]

What are the symptoms? I have 80+ year old hydorvac's and they still work. You have to bleed them in the correct order, or they may not function properly as air gets trapped around the vacuum control valve if it isn't bled 1st.

Also another "must" is a check valve in the vacuum supply between engine and hydrovac. It keeps combustible gases from being drawn into the hydrovac when the engine is shut down

Edited Friday at 09:42 PM by Geoff Weeks

[PSW Fix-it]

Those are good points. Before condemning the unit, we do need to check those points.

Are you familiar with adding lubricating oil to those units? Per the manual, it is required periodically. Is there a possibility the main piston has seized & isn't moving due to lack of lubing?

TIA

[Brocky]

Try BEPCO,inc 2475 South Stratford Road, Winston Salem NC 27103   336-760-0749  or 800-735-1154

It was May of 2007 when I dealt with them for a unit for my 1955 F-600 Ford..

[Geoff Weeks]

1 minute ago, Brocky said:

Try BEPCO,inc 2475 South Stratford Road, Winston Salem NC 27103   336-760-0749  or 800-735-1154

It was May of 2007 when I dealt with them for a unit for my 1955 F-600 Ford..

That was the name I was looking for!

[Geoff Weeks]

13 minutes ago, PSW Fix-it said:

Those are good points. Before condemning the unit, we do need to check those points.

Are you familiar with adding lubricating oil to those units? Per the manual, it is required periodically. Is there a possibility the main piston has seized & isn't moving due to lack of lubing?

TIA

Again, What are the symptoms? Oil will not solve a problem. It is PM.  It can not cause no brakes, only no power assist.

[Geoff Weeks]

Original 3rd series could have a leather piston, so neetsfoot oil would be appropriate, but COULD have a rubber one, in which case jack-oil would suffice. 

On the hydraulic side, brake fluid should pass through from the master to the wheels. If it is leaking brake fluid into to vacuum line back to the engine, then you have to address the hyd side of the hydrovac. 

Again, I have 80+ year old unit that are still function. WHAT ARE THE SYMPTOMS??? 

[PSW Fix-it]

High pedal pressure on level surface, on a downhill grade- feels like there is some boost happening.

Like you mentioned, we need to look at the check valve & at the control valve, etc.

[Geoff Weeks]

Check the breather line (not the vacuum line) for a constant draw of air into the hydrovac. If the the control valve is faulty, there will be a constant air intake anytime the engine is running. 

Under no braking, both sides of the piston are under engine vacuum. If the piston is leaking, there will be no intake of air when the brakes are released, but continuous air intake when the brakes are pressed. In normal use when the brakes are pressed, an amount of air is allowed in but should stop if the pedal is held a some position between the floor and released. 

The hyd cylinder section can also leak brake fluid internally so even though the U cup moves it doesn't build pressure beyond what the master cyl already provides.

 Also don't overlook the brakes themselves. My Hy-Torque style brakes on the rear have siezed up requiring complete disassembly and cleaning + lubing of the pivot points. Once that was done, the brakes would plant your face on the windshield empty or loaded, if you jumped on the pedal hard.

 Needless to say, these units require a good vacuum source AND a good source of clean air. Some units have their own aircleaner (either dry or oil bath types, I've seen both). If the air intake is not filtered, all bets are off of how much dirt and dust has got inside a clogged passages, or even mud dubbers. Some installs have the air inlet plumbed to the clean side of the engine air cleaner. 

There should be two bleed screws on the Hydrovac itself. You start by bleeding to the screw by the control valve, then the one on the outlet, then the furthest brake from the master and working your way back to the closest brake.

Another problem I see, is people don't use vacuum brake hose (which is required by law) but heater hose or hyd hose that is not rated for vacuum brake service. This can collapse, and prevent proper operation. I use as much "hard line" either steel or aluminum, and only use short sections of vacuum brake hose to make connections. 

 If the truck already has steel vacuum tubing  (1/2 or 5/8") make sure it doesn't have pin-hole rustouts in it. 

Edited Saturday at 03:02 PM by Geoff Weeks

[PSW Fix-it]

Thanks for the suggestions, will look into

[mowerman]

On 10/10/2025 at 4:08 PM, Geoff Weeks said:

That was the name I was looking for!

Off the  subject but I read your post and why does that sound familiar? Oh yes, I had a 55 Ford F 600 also it was a flatbed through the years . I did not have it long. Kind of a long story kind of a coincidence but yes, I do remember it had a power brake booster. You could  hear it activating. And feel it in your foot.From what I remember and sorry that was for brocky