Needing manifold vacuum for brakes - Page 2

davidz71 · 03-04-2007, 10:00 PM

Wayne, is your brake controller hooked up? My service manual says that the trailer embellical cord should be hooked up to the vehicle electrical system before testing to see if the vacuum system will get the tank to hold vacuum. It says that the synchronizing valve is powered by that cord. It also says that the brake controller must also be operating correctly.

Excella CM · 03-04-2007, 10:34 PM

It sounds as though you may have a leak in the HydraVac somewhere-possibly the diaphragm. Did your old TV mysteriously pick up a little idle speed when the trailer was hooked up?

wayne.yl · 03-06-2007, 12:15 AM

Thanks fellas,
Turns out it was a leak in the sync valve at the bottom of the actuator. Luckily I had a spare one in my parts bin so the down time is minimal. I switched them out in less than 3hours. Two years ago my wife complained about me buying other people's junk off the internet but today that junk paid off for me. I am only bragging because it rarely if ever turns out this way for me. Anyway thanks for helping out.
Wayne

**Action** · 03-06-2007, 12:59 PM

Wayne,

Congrats!!!!! On using the pump. On finding the issue. And on having a spare part that worked! My wife is kinda the same way. I have parts squirreled away in different locations so she doesn't see the entire load of things I have for all the different toys I have listed below. (Including a couple I don't have listed)

Using the pump and if you haven't yet a tank with a check valve should provide you with the supply that you need to stop your trailer. For safety this will be better than "teeing" into the engine. Should the vacuum system to the trailer leak when brake appplication is needed the manifold vacuum leak would cause a significant rise in engine RPM. So the TV would have to stop a trailer with no (vacuum to the) brakes, and over come high engine RPM assuming you have an automatic transmission.

This kind of situation usually leads to a darker colored seat cover in the drivers position.

And yes your system is quite rare. It did not work well so many units have been converted to electric.

Should you wish, you could mount (conceal) the vacuum pump on the TV some where and Tee into the TV looking like the original system.

>>>>>>>>>>>>>Action

davidz71 · 03-06-2007, 09:54 PM

Gee, I kind of take exception to the statement that the Hydravac system did not work well. It was complicated, not many people understood how it worked and many just wanted to use what was readily available in RV and horse trailer shops. Andy from Inland RV helped me with my questions and I was fortunate to have not only a 1977 standard Service Manual but also a Dealer Service Manual which had coated sheets, larger pages and additional pages for the Excellas. That disc brake system puts the electric drum brake system on my '25 Sovereign in the dark ages because it would stop my 2500hd on a dime without the use of the truck brakes. The discs were huge and the brakes pads easy to replace. To be honest, I wish I had that system on my current trailer.

wayne.yl · 03-07-2007, 12:02 AM

I agree with Craig on the benefits of this system. It is true, by now I am well schooled on the subtleties of this one, but this only serves to fuel my commitment to it. After studying the 1977 service manual, particularly the brake actuator hose schematic, I thought fairly certain I could diagnose and fix the problems. I also agree that this forum is invaluable in both helpful information and encouragement. I have received so much good advice and numerous PM's over the years by fellow Airstreamers who are just wanting to help and who have even sent me parts (at the cost of shipping), that they no longer needed. You all know who you are and I thank you. But I must add that much of the mystique of my AS is in the fixing and tinkering. If I can't go on the road with it, I simply enjoy working on it. It's a kinda of therapy I can afford and I think its working. I guess I am in trouble the day I get everything fixed. Oh well, that day is long off.
Again thanks for all the help....again.
Wayne

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**Action** · 03-07-2007, 08:33 AM

Quote:

Originally Posted by Action

And yes your system is quite rare. It did not work well so many units have been converted to electric.
>>>>>>>>>>>>>Action

I amend my statement to be:

It was not a well understood system by owners so many units were converted to electric operation.

>>>>>>>>>>>>>>>Action

JimGolden · 03-07-2007, 09:32 AM

Why not pitch the vacuum unit into the weeds and get a good electric over hydraulic unit to power the system? The Towbrake unit is excellent.

Since you've got the old system working, I guess it makes no sense to get an E over H unit now. I have the same system in my trailer, but I'm going to dispense with the hydravac altogether and get the Towbrake unit to power the system.

I have a diesel and have no easy source of vacuum either. It just seems to me that we get a battery to power a vacuum pump to create force to move a piston. The Towbrake unit uses battery power to move a piston. It simplifies things.

But what the hay, there's many ways to skin a cat

**Action** · 03-07-2007, 10:21 AM

Jim,

Slightly off topic.

Your diesel most likely has a vacuum pump too. To power vacuum driven accessories if not the brake booster in your vehicle.

If you are going to remove a working hydravac system or any parts from your A/S, I bet there would be others that would want any thing that your remove. So I would suggest not pitching any of those pieces. If not for you at least for others that could use those parts.

>>>>>>>>>>>>>>>>>>>Action

JimGolden · 03-07-2007, 11:24 AM

Action,

Rest assured, anything that I remove from this coach will go on here for cheap or for free.

Being a frugal buzzard, I'm going to try to reuse as much as I can when I do my rebuild, but what I don't I will certainly try to see that it goes to a good home!

Actually, I should have realized that my truck has a vacuum pump. Doh! Maybe I can use the old Ausco's then.

I was planning to switch out everything to either Dexter or Kodiak and use the towbrake E over H. I'm not quite there yet

This summer though

Take care,

**Action** · 03-07-2007, 03:33 PM

Quote:

Originally Posted by JimGolden

Action,

Rest assured, anything that I remove from this coach will go on here

Kool!
>>Action

wayne.yl · 03-07-2007, 10:18 PM

Quote:

Originally Posted by Excella CM

One thing you might consider, even if you mount your vacuum supply on the trailer, is a "T" in the vacuum line with a ball valve to atmosphere. This allows you to set the trailer brake by hand when you are at the hitch. I find it very conveient to "blow down" the system when I stop to adjust or inspect or park for a short period. Having the 4 wheels locked tight is added safety. I would fabricate a pump electrical over-ride to shut the vacuum pump off when the ball valve was open using a micro-switch or momentary off spring loaded button switch (you want this so you wont forget to turn it back on). This would also give you a way to shut down the vacuum pump easily. Lastly, a nice, bright L.E.D. (s) to indicate power to the vacuum pump might be good to have. I sure others can think of ways to add work for you to do, too.

Before I finish this project with the ball valve and switch, I have two more questions. I have wired the pump to a fused line to the battery but the vacuum switch needs a 12volt line also and I am wondering if I can tie into the electric jack circuit. Is it reasonable to assume I can add a switch to this circuit that would alternate power to either the vacuum switch or the jack? Is there ever a time when I would need power to both simultaneouslly?
Thanks,
Wayne

JimGolden · 03-08-2007, 09:25 AM

Wayne,

I think you'd be fine like that. Just remember to chock the wheels before you raise the trailer off the ball. I can't see why you'd need the brakes when you're stopped and chocked.