Hydrovac Care

[joel gopan]

Do not forget to give your Hydrovac a shot of OHT (Available from RAM, a popular and knowledgeable character appearing on another forum) this adds life to your Hydrovac.
I was taught by a gentleman from Maine who worked for Bendix and helped develop their Hydrovac in the early thirties, to pump the brake pedal several times after engine shutdown, to exhaust the vacuum still in the Hydrovac. What could happen is that the seal for the relay rod may be worn and that would allow the brake fluid to be drawn into the Hydrovac can. Has anyone had the fluid in their CCKW Master cylinder disappear overnight, and not find any sign of leak? Now you know. Cyril Morrison was a Motor Sargeant in the Pacific, and instructed his drivers to practice this habit. Cyril was a gentleman and worked into his eighties repairing brakes, he gave me many tips on the care and adjustment of brakes on GMC and Jeep.

[dr deuce]

Good idea (bleeding off the vacume) that most of us forget to do....

Remember to set the parking brake if you do this as you will have no brakes until the engine starts.

If you have had a leak (engine eating brake fluid), check the check valve on the manifold. I may be all gunked up inside and allow fumes to enter the hydrovac. I had one a couple years ago. I could not believe how much gunk was in it!

Steve AKA Dr Deuce

[Brent Delaney]

Thanks Joel and Steve,
Good tips, our cckw 353 B1 is losing fluid and I suspected the hydrovac to be the culprit, quite annoying as it is a nos straight out of the silver paper.

Just to note that this truck stops on a dime when the brakes are working ok, I will be changing my H1 brakes to a dual circuit when the time comes as a friend of mine has done, he used a japanese late model dual circuit master cylinder I think he also used a modern booster as well

But I look at it this way, if the truck was still in active service what do you think they would be doing in the year 2005 Yep modifying and updating components that made the vehicle more safe/reliable and the parts are bought over the counter. Not NOS that has long dried out and perished (found that out the hard way) some NOS parts are only good for looking at or worse

Ah that feels better, I had a bad day at work damaged the breakpress in the sheetmetal shop honest mistake easyfix thankfully.

Cheers,

Brent Delaney

[joel gopan]

FYI, the Bendix 3rd Series Hydrovac is still a current and modern Hydrovac used on a lot of vehicles, it is BENDIX PN 374750, and the factory rebuilts are done with fresh present day components. I will upgrade 1st Series as soon as the 1st indication of leakage or failure is evident, maybe sooner.
Joel

[Frank Bogers]

What's OHT Joel ??
And how can I tell if the one on my '43 353 is a series 1 or a series 3?
And are they interchangeable?

Maybe it can be read on the thing itself ... I must admit that I haven't looked yet
I've only recently bought this truck and I've started overhauling it.
I'll have and want to overhaul the brake system too.
My brake pedal can be pressed to the floor and stays there (with the engine running).
But the brakes do function and when I pull back the brakepedal by hand, the brakes release ... so my guess is a brake pedal linkage or even a master brake cylinder concern.

I'll keep you posted on what I find.

[Fernando Mendes]

Do not forget to give your Hydrovac a shot of OHT (Available from RAM, a popular and knowledgeable character appearing on another forum) this adds life to your Hydrovac.
I was taught by a gentleman from Maine who worked for Bendix and helped develop their Hydrovac in the early thirties, to pump the brake pedal several times after engine shutdown, to exhaust the vacuum still in the Hydrovac. What could happen is that the seal for the relay rod may be worn and that would allow the brake fluid to be drawn into the Hydrovac can. Has anyone had the fluid in their CCKW Master cylinder disappear overnight, and not find any sign of leak? Now you know. Cyril Morrison was a Motor Sargeant in the Pacific, and instructed his drivers to practice this habit. Cyril was a gentleman and worked into his eighties repairing brakes, he gave me many tips on the care and adjustment of brakes on GMC and Jeep.

[Fernando Mendes]

Who knows OHT?