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7xp · 08-05-2006, 09:14 PM

I just purchased a 1978, 31 foot Excella 500. The previous owner recently had the brakes replaced. The braking system is disk brakes with a Hydra Vac unit. He showed me the vacuum line from the engine intake manifold, which had some kind of one way valve in the line. He told me this vacuum line was the brake away system, incase the trailer ever separated from the tow vehicle. He also told me that he has had trouble with this system. He said that if he pressed the gas pedal down hard, his vacuum would drop off and the trailer would apply the brakes. (This does not sound like a good situation to me).
Is this common with this system or is there something wrong with his tow vehicle? Should I plan on changing out this system? If so, what system?
I will be using this trailer as a home, while I upgrade a cabin on property in Montana. It will make one 1500 mile trip, unless I find out that I can’t take the winters in Montana, and then it might make one more trip back to California. (Snow Bird, hehe).
I am soon to be retired with limited funds, and do not want to put a lot of money in the running gear, but I do want a safe vehicle for my son to tow.
Thank you for any help you can give me. “Mac”

bryanl · 08-05-2006, 10:36 PM

If that system is the same one I saw on a similar vintage trailer, it uses hydraulic disk brakes. The vacuum just powers the hydraulic cylinder that is controlled by a standard brake controller. I would think you could replace that vacuum system with one of the new electric powered hydraulic pumps like being used on new Airstreams for their disk brakes. That would clean up a lot of stuff if the pump provided the proper hydraulic specifications.

dwightdi · 08-06-2006, 02:34 AM

Most people have found this system is difficult to maintain on the road as very few RV mechanics know how. Company still exists and you can buy some parts but not all. Most parts are very expensive. Inland RV has some new parts and has remanufactured some but they are also pretty expensive. Many owners have converted them over to electric (as I did). It costs about $50 per wheel plus shipping for new backing plates and drums plus shipping. It only takes five bolts per wheel and stringing some new wire. I did it in one afternoon. You can use Dexter or Kelsy Hays depending on who you can get at the best price thru the jobbers.

davidz71 · 08-06-2006, 08:52 AM

I had the Hydravac system on my '77 Excella 500 and wish I had it on my '86 Sovereign. It was an excellent system if you knew how it worked. I used a Hayes-Lemmerz Energize III controller and those brakes could stop the 31' trailer and my 2500hd in nothing flat. The vacuum source is off the manifold and there should be a check valve within the first foot of that source to make sure the engine keeps vacuum if the hose breaks away at the rear bumper. I lost my pictures on the computer due to a hard drive crash but I believe I may still have some of them on disc. I'll look later and post them if I find them. OK, the airbrake line I used ran inside the frame rail of my '92 1500 and later my '01 2500hd. At the end of the bumper I put a 1/2 inch industrial female quick coupling and a bracket which was bolted to the mount holding the 7 pin trailer receptacle. When not hooked up, I had a 1/2 inch male plug inserted. The trailer vac line male connection plugs into the female coupling. When the truck is running, it provides vacuum to a diaphram in the booster on the tongue behind the propane tanks. When braking, an electrical signal is sent to a part on the booster which allows atmospherical air inside the booster which relaxes the diaphram. The result is a pressure on the hydraulic lines which closed the brake calipher pads. Those rotors are massive as well as heavy. A service manual outlines each part and how the system works. Replacing with electric drums would be a step backward in my opinion. I have heard of people who have taken the booster off the tongue and replaced it with an actuator which would be ideal. You would be better off doing that than ever going back to electric drums.

uwe · 08-06-2006, 10:00 AM

For a regularly driven trailer, the disc brakes are far superior in braking power. I would try the vacuum line forst, see if the system works and holds vacuum. The previous owner might have had a bad line, or bad connections etc.
Second best would be to replace the hydravac unit with an electro hydraulic actuator, such as available from Dexter. It can sit right where the hydravac unit resides now.

You would be spending almost as much money converting to electric drum brakes and end up with an inferior setup. I'd dabble with the discs first.
Take alook at the attachment, it was posted on another thread recently and I saved it.

7xp · 08-06-2006, 11:32 AM

I thank everyone for there quick response! I agree with you Craig, I don't think I would want to go back to drum brakes. I checked out Inland RV and they have an ActiBrake actuator on sale for $790.00. (I belive this is what Airstream uses at this time). This is a little more then I would like to spend for a $5000.00 trailer, however for safety sake I would spend it. If this is the route I go, should the brake lines hook up to it or would there be a lot more items I would have to replace? It would be nice if I could get the original system working properly. Has anyone had a problem with this system wanting to apply the brakes when accelerating. I know that even a new vehicle has changes on the vacuum when accelerating. Could it be a weak diaphram in the Hydra Vac booster?
Craig, do you know if the check valve is only to keep the tow vehicle engine running if the trailer seperated from the tow vehicle also I did not receive any manuals from the previous owner so if you find the pictures on your setup and can post them it would really be appriciated.
Thanks "Mac"

davidz71 · 08-06-2006, 01:51 PM

Quote:

Originally Posted by 7xp

I thank everyone for there quick response! I agree with you Craig, I don't think I would want to go back to drum brakes. I checked out Inland RV and they have an ActiBrake actuator on sale for $790.00. (I belive this is what Airstream uses at this time). This is a little more then I would like to spend for a $5000.00 trailer, however for safety sake I would spend it. If this is the route I go, should the brake lines hook up to it or would there be a lot more items I would have to replace? It would be nice if I could get the original system working properly. Has anyone had a problem with this system wanting to apply the brakes when accelerating. I know that even a new vehicle has changes on the vacuum when accelerating. Could it be a weak diaphram in the Hydra Vac booster?
Craig, do you know if the check valve is only to keep the tow vehicle engine running if the trailer seperated from the tow vehicle also I did not receive any manuals from the previous owner so if you find the pictures on your setup and can post them it would really be appriciated.
Thanks "Mac"

Mac,
It is so that it does not interfer with brake system on your vehicle. Most brake boosters get their vacuum from manifold vacuum and you sure don't want to lose that.

davidz71 · 08-06-2006, 02:17 PM

My vehicle install:

davidz71 · 08-06-2006, 02:21 PM

Continued:

Excella CM · 08-06-2006, 04:25 PM

A minor clarification/ampmlification: The vacuum line does two things. It serves as the power source (some % of atmospheric pressure) for the brake master cylinder and doubles as the brake-away emergency trailer brake. If the hose becomes disconnected, the trailer brakes apply full-on. The checkvalve in the vacuum line of the tow vehicle is to prevent the trailer brakes from coming on unbidden when the tv manifold pressure rises due to engine load. If a checkvalve is installed and the system still applies the brakes when you step on the gas, then there is a leak somewhere downstream of the checkvalve.