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Old 11-16-2005, 07:23 PM   #15
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Question...

I am curious about something. Towbrake is a servo actuator that basically does what the brakes on the tow vehicle does except that instead of a pedal operating a piston, a servo of some sort does the piston actuation, sort of like the old vac/hyd units. If this is correct then I have a safety concern...

Standard vehicle has 2 separate circuits for the brakes. One for the front and one for the rear. A trailer does not have anything like that (as far as I know). If a leak develops in the brake system on a trailer, all the brakes will fade away with a servo system. Correct???
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Old 11-16-2005, 07:34 PM   #16
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Terry,

I think Jim was going to go either the Actibrake or the Towbrake actuator. Both are commercially available. I think the confusion was whether he would keep the original hydraulic disk brakes, or go with new hydraulic drums. Maybe Jim will confirm this?
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Old 11-16-2005, 07:41 PM   #17
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Quote:
Originally Posted by Buttercup
. . . Standard vehicle has 2 separate circuits for the brakes. One for the front and one for the rear. A trailer does not have anything like that (as far as I know). If a leak develops in the brake system on a trailer, all the brakes will fade away with a servo system. Correct???
Buttercup,

Neither the Towbrake, the Actibrake, or the Brakesmart system operate like the old vac/hyd units. All take the electrical signal from the brake controller (like a Prodigy), and use that to turn on a motor which pressurizes the hydraulic system.

The difference is that the Brakesmart and the Actibrake use multi-piston pumps, while the Towbrake uses a linear actuator, which is really just a big single piston.

The Towbrake system does have a dual circuit, I think it is so that in dual axle systems the second axle can be delayed so it doesn't lock up. I don't know if the Actibrake or Brakesmart have dual circuits. Maybe I can look it up on your chart.
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Old 11-16-2005, 09:11 PM   #18
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O.K. So the Towbrake does operate like I thought. I don't think I expressed it quite right.

The Actibrake states that it is dual circuit 6 piston pump but I am not sure if that means that it can be ported so that 1 axle is pumped separately from the other.

One point about these systems that use a pump as opposed to a servo operated piston... The pump system I have waits until the brake controller outputs 2 volts or greater before the pump starts. Once the pump is going, the voltage signal from the brake controller to the pump is used to tell the pump to modulate the pressure by some means such as a variable bypass valve or such. The pump speed remains constant but you can hear the difference in sound the pump makes as the pressure increases or decreases. I played with this during the installation process.

But what I am getting at is that the pump is not directly operated by the output from the brake controller as in electric brakes. In that system the output drives the electromagnets directly.

In my system the output from my brake controller is used as a control signal only for the hydraulic pump. The power for the pump (in my case) comes from the trailer battery.
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Old 11-16-2005, 10:06 PM   #19
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Has anyone tried this sytem? http://www.sensabrake.com/page.cfm?id=3
It looks like a way to decrease response time.

They advertise the coming availability of ABS brake systems for trailers.

They also have a pressure sensitive pad that you mount on your brake pedal. It senses the amount of pressure you are putting on the brakes and modulates the signal to the trailer brakes.

What will they think of next!
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Old 11-17-2005, 04:55 PM   #20
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I don't think Airstream is using Actibrake any more on the new trailers. They are using Dexter axels and the Dexter disc brake system.

So, we have many choices as does Airstream.
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Old 11-17-2005, 05:38 PM   #21
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A/S is stilling using Actibrake

Speaking as the GM of an A/S dealer, I can confirm that while A/S switched to Dexter axles (all models) and Dexter disk brakes on the Classics (not based on engineering, but other factors), they are still using Actibrake Actuators. I have a 34' Classic SO Limited manufactured less than a month ago and it has the Dexter Actibrake combination. There are factors that I am not a liberty to discuss that lead me to believe that Airstream will be staying with Actibrake even with pressure from Dexter to use their actuator.
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Old 11-17-2005, 06:46 PM   #22
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See the back cover of Fall '05 Airstream Life...

It's an ActiBrake ad, as "installed on the Classic Airstream Trailer."

Interesting comment dtbw. Not surprising in light of competitiveness, axle supplier upheavals, Airstream keeping their options open...
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Old 11-17-2005, 09:14 PM   #23
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Hey Everybody,

I never meant to stir up any turmoil on here. Let me try to straighten things out a bit.

First, thanks to all of you for your responses. I appreciate them all.

The best thing I can compare a linear actuator to is a servo that you had in your radio controlled airplane when you were a kid. What it amounts to is an electric motor hooked up to a gear-set which is connected to an arm. The magic of the thing is that it works proportionally. So if you move the stick half way on your radio control unit, the arm of the servo moves halfway. If you move the stick 3/4 the way, the arm moves 3/4 of the way. It's proportional. This arm had a pushrod hooked to it on the plane which attached to the rudder or elevator or aileron. This way you could control the amount of deflection you gave a control. So, it wasn't just all or none (like the really old R/C units were), but you could linearly vary the amount of movement you input.

On the TowBrake unit, it's the same thing. If you tell it to move halfway, the servo motor (linear actuator) moves the piston halfway. Tell it 1/10 the way and that's what you get. It is proportional. They work basically instantaneously. There is no lag. We use them in factories all the time for automation type stuff. Things where you need to be able to control how much a thing moves, not just move or be still.

Towbrake offers two models, a dual port unit and a single port unit. The dual port has two pressure outputs. With that, you could hook up each of the tandem axles independantly. They told me, however, that most RV guys buy the single port unit and just hook it up to the exiting (if you had one) brakeline system. I'm undecided on that issue. I think the single port would probably be fine, but the dual port is tempting, although it'd add a bit of complexity.

I didn't fully understand how the other units worked until after I originally posted this and then really started reading up on it. I see now that most (if not all) of the other brands out there use some type of multicam pump to pump up the pressure required. Not a thing wrong with that, just two different approaches.

I've read test results on the ActiBrake and the Dexter. Both of them seemed to work just fine. I also read the test results on the TowBrake unit, and it did just fine as well. It's two different ways to "skin a cat". Which one is better? I don't know. The linear actuator seems simpler to me. It works just like the brakes in a non power assisted car. Except you have a linear actuator working as your leg to "push the pedal"; it is what supplies the muscle to push the piston on the master cylinder.

TowBrake does sell a complete kit. That is what Trailer Life tested. I am not sure if it is compatible with Airstream. However, the Electric over Hydraulic unit they sell is compatible with any disk brake system.

For my own use, here is what I am leaning toward currently:
New Axles (mine are 5 degrees UP)
Kodiak disk brake setup
Either ActiBrake or TowBrake brake control unit.

Both the ActiBrake and the TowBrake units have some good testing behind them. I've not looked at the warranty on the TowBrake units yet...

I do not feel that this will be a cobbled together setup. On the contrary, I want to choose a good disk brake system that I will be able to get parts for, and a good electric over hydraulic unit to power this system with. Two separate parts of the system. I had considered rebuilding my Ausco's until I looked into it. It costs more to rebuild the old system than to go brand new. That's no exaggeration either! In addition, you can't get certain parts for the old system. That option, for me, went out the window. That narrowed it to new drums or new disks. After looking at the testing, I want to stay with disks.

It's a tough pill to swallow, but I've always wanted a 31' Airstream and now that I've finally been able to get one, I want to turn it into the best unit that I can. It's going to cost me as much to put new axles with a new disk brake system on the coach as what I paid for the trailer itself. But, I'm a good mechanic, and the way I see it, I'll probably have less than $10K in this unit by the time I get it done (not counting my labor of course) and it will be the equal of a new one and will be customized to my personal tastes. So, I want to do it right. That being said, it's going to get new axles with a new disk brake system.

I do agree; assembling a collage of mismatched parts is a recipe for disaster. But I'm not going to do that. The Ausco's are history. I'm going to go brand new. I'm just trying to decide which brakes and which brake unit. I'm currently leaning toward new Henschen axles with Kodiak brakes, and either the TowBrake or the ActiBrake EoverH unit. I think that'd make a great setup either way you look at it. I'm also looking hard at the Jordan brake control unit (although that's a different issue...the idea of having the trailer's brakes work as a function of how much I depress the brake pedal rather than a pendulum swinging makes a lot of sense to me).

I'm also going to reinforce the frame and do a new floor and put in new appliances and upholstery...oops those are different threads

I want to build the best '77 Excella possible. A lofty goal in the company of those on these forums, but I'm going to give it my best shot. Somebody had a post on here about "...why did you choose an Airstream". I just like them; they have character; I've always wanted one. My dad's fifth wheel with three slides has five times the room of my "little" Excella, but I'll take my silver palace over his monster any day. My buddy used to work for Prowler. He was checking out my 28 year old trailer last week and said "The fit and finish on this thing looks better than the ones we sent out the door last month." Says something about Airstream's build quality...

But I digress. I want to assemble a well engineered braking system. It won't be cheap, but I'll spend what I must to get a good setup. I just want to be sure I'm doing the best I can.

Thank you for your guidance,

Jim
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Old 11-17-2005, 10:32 PM   #24
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Jim,

i don't think you have to worry about being appologetic on this topis. it is an important one. And the most important thing is that you are comfortable with what you get. Afterall, how comfortable will your trip be if you are unsure about something like your brakes.

Whatever you do I hope that you will share your experience both good and bad with the forums here so that we all can learn.
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