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Author Topic: Towed brake connection, serious safety and legal issue  (Read 3062 times)
Jerry Liebler
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« on: August 29, 2007, 11:08:43 AM »

I have a Brakemaster 9160, by Roadmaster that I've installed in what will soon be my towed.  This is an air cylinder that activates the towed's pedal and it has a 'breakaway' reservoir and switch.  It connects to the coach by a single air line through a 'quick connect' fitting.  The installation instructions tell one to use an extra port on the rear brake relay valve to supply the quick connector, or if no extra port put a 't' into any of the lines that has air flow only when the treadle is pushed.  There is no mention of any form of 'tractor protection' and I believe there is a federal law making it a crime to hook up a trailer without.  In the event of a break away, the towed would have it's brakes applied but the bus, on the other hand would have a 1/4" tube draining it's air so braking would be severely limited.  I sure don't like this situation.  I looked into tractor protection valves but they all depend on the trailer's connection by a supply/emergency line and a control line.  Since they sense reduced pressure on the supply line to shut things down they won't work with the Brakemaster's single line.  Then I found  http://rversonline.org/ToadInstall.html
Neat. by adding a relay valve and a pressure protection valve at least 85 psi of bus air will be available for braking even if the towed breaks away.  The 2 valves add less than $100 to an already expensive system.  I'm adding in an r4p pressure protection valve (85 PSI) and an r-12p relay valve to the installation and think anyone who doesn't add similar parts is taking a huge unnecessary risk.
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Jerry 4107 1120
 
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Nick Badame Refrig/ACC
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« Reply #1 on: August 29, 2007, 11:16:22 AM »

Hi Jerry,

I think members here have mentioned that this kind of brake needs to be tapped from the tag axle to not

disrupt the drive axle brakes. But, if you don't have a tag axle, what do you do?  Huh

Nick-
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DrivingMissLazy
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« Reply #2 on: August 29, 2007, 11:54:55 AM »

Great article. I wish I had known about it ten years ago. That was always one of my main worries about that same braking system that I installed back in the 90's. The other problem that I saw was that it was difficult to do a static test of any kind to see it it was actually working.

And Nick, if you disrupted the braking of the tag axle, then you would defeat the purpose of this system, since the tag axle does a significant amount of braking also. At one time my tag axle pressure was not adjusted properly and I could see my tag axle tires smoking during hard stops. Needless to say, I got that corrected promptly as it made flat spots on the tags. LOL
Richard
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« Reply #3 on: August 29, 2007, 12:21:59 PM »

Alternately, couldn't a breakaway cable and pin be installed on the bus and connected to the toad... sort of the reverse of what the toad has?  When / if the toad breaks away, a solenoid or some mechanical spring-loaded valve would cut the air to the toad brake connection.  It seems like this might be much easier to install, cheaper, and possibly more reliable.  Of course, if a line connecting the toad to were to rupture, this system wouldn't help.  If an electric solenoid valve were used for the breakaway, the rear air connection could be disabled from the driver's seat.  I guess this would be just a trailer air control, but it would also be automated in the event of a break away.

David
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JackConrad
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« Reply #4 on: August 29, 2007, 04:00:32 PM »

  I have been thinking about this also.  Our present system is an M&G brake unit that fits between the vacuum brake booster and the master cylinder on our Grand Cherokee.  It is operated by air from the tag axle brake line. I also installed a small air tank (4" x 4.5") under the hood of the Cherokee. It is tied into the air line from the bus tag axle brake through a Tee, check valve and a solenoid. I also installed a pressure switch on the M&G. This pressure switch controls a flashing LED on the dash of the bus. Anytime the M&G is applying the brakes, the LED Flashes.  When we connect the toad, part of our pre-trip check is to make a hard brake application and watch M&G flashing LED to confirm toad brake application.  This also pressurizes the tank for break-a-way operation.This serves 2 purposes. First, it lets me know the brakes are working. Second, if the break-a-way cable should catch on something and activate the solenoid, applying the brakes, the flashing LED will let me know the Cherokee brakes are being applied. Hopefully, if that should happen, I will see the Flashing LED and stop, preventing a toad fire from an overheated brake.
    When I installed the M&G, I filled the tank to 40 PSI, temporarily connected a toggle switch to replace the break-a-way switch and drove down our road at about 45 MPH. Put transmission in Neutral, let loose of steering wheel and flipped the switch. Brakes did not lock, but a very quick stop in a straight line. Did this 4 times off the little tank before there was not enough pressure to apply the brakes.
   I have thought about installing another solenoid (N.O.) in the read of the bus. The wire from this solenoid would go through a break-a-way switch installed under the bus rear bumper and connect to the toad with a cable (similar to the break-a-way switch on the toad).  My biggest concern was finding a solenoid the could handle 85 PSI (max brake application pressure I can generate with hard service brake application) and have a large enough orifice. When the brakes are released, all the air to the M&G has to vent back through the bus tag axle brakes.
   As far as smoking the tags, I have under HARD braking (darn quick traffic lights!).  I have noticed tags never lock up with less than 40 PSI brake application pressure. Normal braking is 10-20 PSI.  I have though about installing a pressure regulator in the line to the tag brakes limiting tag brake pressure to 30-35 PSI.  Jack
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« Reply #5 on: August 29, 2007, 04:34:01 PM »

I don't have a tag axle or a sure mental picture of how one would be 'plumbed' so I'm unsure if this solves the problem.  The thought of another breakaway system, kind of in reverse occurred to me as a way to use a 'big rig' tractor protection valve I dislike it because it would require a pneumatic break away device that would be new and different.  I also considered the solenoid valves but they aren't certified for use in air brake systems & might cause legal problems if I somehow had to go through a DOT inspection.  A beauty of the solution with the pressure protection valve and relay valve is these are both certified air brake components.  I'm sure it also will work with Jack's system Too.
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Jerry 4107 1120   
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DrivingMissLazy
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« Reply #6 on: August 29, 2007, 06:20:23 PM »

Jack, my tag axle tires smoked because the torsalastic on the tag needed adjusted to put more weight on the axle. This is how I found out it needed done. LOL
Richard
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« Reply #7 on: September 01, 2007, 11:18:46 PM »

Jerry,

I am not any sort of tecnichian on this subject..... but i installed a product called Air Force One by a company called SMI... I beleive it has the necessary connection to block off the air on both the bus side and toad side... it has a quick disconnect on a the controller box which attaches to the bus - on the disconnect they suggest you cover the connector with a little black plastic cover - after unhooking the toad i have forgotten to put that little cover on - and no air pressure is lost... the toad has that reserve air tank and its own controller as well... just a thought - i am sure you already have a fortune invested in a setup - but maybe this will give you some ideas. just do an internet search on smi or air force one brake controller.... I bought it because I liked how small the acuator was for inside the toad and that once it was installed you can't even see it inside of our jeep liberty. 

Also - the method for install on the bus (1989 Eagle 15) was to hook up to the service line on one of my air canisters. I installed a tee on that line and ran my air hose from there... very straight forward installation.

For what its worth.... just some added info.

John
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Jerry Liebler
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« Reply #8 on: September 02, 2007, 06:31:48 AM »

John,
   Yours ,I think, is really the same set up as I'm talking about.   Sure the female quick connector blocks the air flow when it's taken apart 'properly'. BUT  what happens in a breakaway is the tubing will either break or pull out of the connector, leaving an open air line.  This ABSOLUTELY will reduce the coach braking ability.
I've talked to Roadmaster and they insist it's still safe.  How do they know how safe MY bus is in this case.
I strongly believe they haven't been sued only because breakaways are very rare.    By adding the pressure protection valve and relay valve I know that I'll still have 85 PSI.
Regards
Jerry 4107 1120
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Jerry Liebler
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« Reply #9 on: September 02, 2007, 06:44:17 AM »

Well after looking at the SMI 'Air Force 1. They certainly claim the coach air is 'shut off' in the event of a break away.  No details but definitely the claim.  Regards
Jerry 4107 1120
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JackConrad
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« Reply #10 on: September 02, 2007, 07:02:06 AM »

Jerry,
    Are you saying the relay valve and pressure protection valve are standard air brake parts?  Do you have Bendix part # for these items?  Jack
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« Reply #11 on: September 02, 2007, 07:48:45 AM »

Jack,
    YES, they are standard air brake system components.   I'm using a Bendix R-12P relay valve and a PR 4 pressure protection valve.  At this moment I only have the pressure protection valve in my hands, its PN is BX286500B1  When I get the relay valve (I just ordered it) I'll post it's actual PN as well.
Regards
Jerry 4107 1120
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« Reply #12 on: September 02, 2007, 07:55:03 AM »

Great discussion this one!

Some thoughts:

tapping into the existing bus air system needs to be done in a way that maintains air pressure balance and timing. Tapping into one service line will significantly delay the application and release of the brake that has added mileage to its plumbing. You need a relay valve with sufficient ports to assign the toad its own.

You definitely need to have an automated way for the air system to protect itself from a rupture of the toad plumbing.

For connecting the two vehicles, maybe just use gladhand couplers like the truckers do, mounted correctly so they pull apart instead of tear the guts out of the install, in the case of a break away?

You may also add the second dash mounted plunger and the tractor protection valve for the pain of running one airline from front to back.

From a liability standpoint, mimicing a tractor trailer install would be easiest to defend, and raise less eagerness on the part of an enforcement officer to challenge your install. If they recognize the bits, they won't think to get suspicious?

But there is not nearly the fun in "rolling your own" by going with conventional strategies.

As a sometimes "smoker", (oh, but I don't inhale... Wink)I do like the pressure protection/relay valve concept.

If you cut the toad airline, as long as air stops leaking out the cut line sometime soon, and the coach has enough air pressure left to stop properly, and of course, the poor toad has a realistic chance of stopping itself, and you didn't build it out of McDonald's straws, good for us! A bonus would be having a way of verifying the performance of the toad brakes while underway, but that's sounding too much like a tractor trailer set-up again....

Maybe convention isn't that bad?

happy coaching!
buswarrior
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« Reply #13 on: September 02, 2007, 08:00:51 AM »

I have had the Brake master system and don't feel it's ability is poor on power brakes. As you know when there is no vacuum the force required to push on the brake pedal is large and from my use it never feels like the toad is doing much brakeing. Jerry
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Jerry Liebler
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« Reply #14 on: September 02, 2007, 08:11:55 AM »

Here is a link that states the law.
http://www.cvsa.org/resourcecenter/documents/2005_02_tractor_protection_systems.pdf
As I read it a commercial vehicle towing a towed with the brakemaster system installed according to the maker's instruction would be placed out of service if inspected.  What I'm installing still doesn't fully meet the stated requirements as they include ability to activate the 'trailer' emergency system from the cab.  But it certainly does meet the safety issue.
Regards
Jerry 4107 1120
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