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wayne.yl · 01-24-2007, 08:44 PM

Now that I have I newer T/V I must adapt it to accomodate the Hydra-vac brake system on our 77 sovereign. I am needing to find a vacuum port on the suburban 8.1L manifold and am hoping someone has knowledge of this engine. I think I can "T" into an existing vacuum line also if I can find one but now its still a mystery. Anyone with thoughts on where to look?
Thanks,
Wayne

Buttercup · 01-24-2007, 08:46 PM

You can use a Vacuum pump if you REALLY need. I got rid of my old hdy/vac system but I know that this was an option I could use if needed.

wayne.yl · 01-24-2007, 08:57 PM

Actually I bought a vacuum pump to mount on the trailer tongue and I almost did last summer but..... Something inside my stubborn brain said, "if you do, it will compromise the original trailer. I know your thinking this is a minute variation from the original but I am just not ready to pull the trigger on the vacuum pump. I know its sick but I want to go this route first.
thanks
WP

davidz71 · 01-24-2007, 09:20 PM

Wayne, I guess you didn't find the hex plug on the back of the manifold? It was hard for me to find but I was told it was there. Maybe they didn't have it on your '01 8.1 like I have on my '01 2500hd.

wayne.yl · 01-24-2007, 11:41 PM

Craig,
Its going to take more daylight and some mirrors. They literally poured that beast into the Suburban. Where you told me to look is so far up under the fire-wall that visibility is minimal. I will keep looking. thanks for the additional pics though.
Wayne

wayne.yl · 01-27-2007, 09:42 PM

I have given up on trying to access manifold vacuum for my brake system and am going to use the vacuum pump I bought previouly. My question is whether anyone is using a vacuum pump for their hydra-vac system and if they have incorportated a vacuum resevior to store additional vacuum? Does anyone have experience with how effective the pump is at providing enough vacuum?
thanks,
WP

ROBERTSUNRUS · 01-27-2007, 10:03 PM

Quote:

Originally Posted by wayne.yl

I have given up on trying to access manifold vacuum for my brake system and am going to use the vacuum pump I bought previouly. My question is whether anyone is using a vacuum pump for their hydra-vac system and if they have incorportated a vacuum resevior to store additional vacuum? Does anyone have experience with how effective the pump is at providing enough vacuum?
thanks,
WP

Hi, No I haven't done this, but as a quick service mechanic for many years and have repaired many vacuum systems, I would recommend a vacuum storage tank and a vacuum check valve for sure.

wayne.yl · 01-31-2007, 12:29 AM

I take it from the lack of response that this is not a common brake set-up.
Oh well, I will try another question anyway. Would it be better to mount the vacuum pump on the trailer or the tow vehicle?
I am thinking the Trailer because I would have more options on t/V's to pull with.
But I am wondering if this would prevent emergency braking of the trailer since there would now be no vacuum loss if the trailer disconnects from the T/V. I thought I read somewhere that a disconnected trailer and subsequent vacuum loss to the system would automatically engage the trailer brakes. Was I dreaming this?
Wayne

overlander63 · 01-31-2007, 06:37 AM

For a vacuum reservoir, you can get an old "tomato soup can" reservoir from an older Ford or Chevy. or a newer "vacuum ball" type that mounts under the hood. The ball type is available from the dealer.

davidz71 · 01-31-2007, 07:25 PM

Wayne,
The vacuum reservoir is already on the trailer under your HydraVac system. All you need is either a constant vacuum source or one that turns the pump off at a premeasured amount of vacuum. If you mount it under the rear bumper and hook it into a female 1/2" industrial coupling, if/when the trailer breaks loose from the vehicle, the hose from the trailer is pulled loose and you lose vacuum to the reservoir. Brakes are then engaged. If the pump is mounted on the trailer tongue, i'm not sure how a breakaway switch would be mounted to cause vacuum loss in the reservoir. Someone on here would probably be able to let you know how.

ZoomZoom · 02-01-2007, 05:49 AM

Your coach already has a vacuum storage tank under the floor just behind the "a" frame.

SilvrSausage · 02-10-2007, 11:49 AM

If it was me, I'd put the vacuum pump on the trailer. Put a tee in the vacuum line, and run a vacuum line to the hitch terminating in a barbed hose fitting, larger diameter the better for rapid vacuum dumping. The line would be attached to the tow vehicle, and in case of separation would dump the vacuum and apply the brakes, even with the vac pump running. This is simpler than fabricating a dump valve on the trailer with a cable lanyard.

If you want to get fancy, consider the dump valve found at the brake pedal of most cruise-control equipped vehicles, $5 or less at the junkyard.

Excella CM · 02-10-2007, 02:25 PM

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.

wayne.yl · 03-04-2007, 08:24 PM

It finally stopped raining long enough for me to work on the trailer.
I mounted a vacuum pump on the trailer tongue hoping this would provide my vacuum source needed for the brakes.
The pump includes a shut-off valve and switch that turns the pump off at 20 inches of mercury. The switch is designed to activate the pump when the vacuum falls below 14 inches. After installation I can't get the
pump to shut off though. I have checked the wiring at least 5 times and I know the switch is working because if I disconnect it from the vacuum booster and plug the valve with my finger, It shuts the pump off.
I have concluded I have a leak in the booster somewhere but I have checked all the fittings.
Any thoughts about where the leak is or if I am missing something.
Thanks for your help.
Wayne

davidz71 · 03-04-2007, 09:00 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, 09:34 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 · 03-05-2007, 11:15 PM

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, 11:59 AM

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, 08:54 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 · 03-06-2007, 11:02 PM

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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