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Old 01-24-2007, 09:44 PM   #1
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Needing manifold vacuum for brakes

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?
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Wayne
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Old 01-24-2007, 09:46 PM   #2
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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.
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Old 01-24-2007, 09:57 PM   #3
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vacuum question

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
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Old 01-24-2007, 10:20 PM   #4
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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.
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Old 01-25-2007, 12:41 AM   #5
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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
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Old 01-27-2007, 10:42 PM   #6
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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?
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Old 01-27-2007, 11:03 PM   #7
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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.
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Old 01-31-2007, 01:29 AM   #8
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Another vacuum question

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
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Old 01-31-2007, 07:37 AM   #9
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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.
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Old 01-31-2007, 08:25 PM   #10
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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.
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Old 02-01-2007, 06:49 AM   #11
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Vacuum Tank

Your coach already has a vacuum storage tank under the floor just behind the "a" frame.
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Old 02-10-2007, 12:49 PM   #12
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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.
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Old 02-10-2007, 03:25 PM   #13
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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.
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Old 03-04-2007, 09:24 PM   #14
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Vacuum pump won't shut off

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
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