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Author Topic: Where to connect air line for toad assist braking  (Read 1891 times)
Melbo
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« on: October 02, 2008, 08:31:32 PM »

I am ready to attach an air line for M-G engineering toad assist braking.

I am posting a picture of the brake can.

Which line should I attach my air line to the toad to.

There are three lines attached to the can ( originally I thought there were only two -- sorry Sammy )

One line is near the bottom of the can -- there is a line in the middle and one near the top or close to the actuator.

I have the air diagram for my MC8 but have not been able to sort out which line is the main pressure line to the brake can.

Thanks.

Melbo
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buswarrior
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« Reply #1 on: October 02, 2008, 09:28:12 PM »

Hello Melbo.

The air for applying the brakes via the brake pedal is the middle portion of the DD3 brake chamber on your bus.

However, you need to be careful to not disrupt the balance of air delivery by just plumbing a T off one side, and you want to consider the effect of a leak in the toad system.

It is doable to brake the toad with air, but some things to wonder about...

Observers will be shocked at how slow adding extra tubing on one side will make the associated brake apply, and even longer releasing. Imbalanced braking.

And don't get the signal and delivery lines mixed up at the relay valve, carving into the signal line to supply a chamber in the toad will have unintended results in the force at which the relay valve is commanded to apply to the chambers, the effect will be to weaken your brake application for a much extended time, if it ever recovers in a practical length of time. Carving into a delivery line disrupts the time it takes to make the brake application you call for with your foot, but you'll eventually get it, once enough air fills the extra lines and parts.

Still, there's problems: Teeing in at the relay valve in order to fill the line to the toad will affect the timing in application and release of that axle in relation to the front. All the lines and valving have been sized to fill the chambers that are there, not an additional mileage of hose and another chamber.

I would also be hesitant to run air lines between vehicles without some form of air system protection, such that is found in the two line plumbing on the back of tractor trailers. Without some form of protection, if the toad line or the components failed, you compromise the bus portion of the system you plumbed into, again harming the ability to stop properly.

Unless there is engineering direction as to a simpler way to keep the bus system working properly, putting the supply of air in the toad that applies the brake in the toad, and running a signal line to a relay valve, imitating a tractor trailer style of air delivery, would eliminate the simpler "what ifs"

What method is the MG unit using for brake-away braking?

This is a great topic you've unearthed!

happy coaching!
buswarrior
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johns4104
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« Reply #2 on: October 02, 2008, 09:34:25 PM »

Maybe add a small air tank for breakaway and use a signal off of the brake lights to actuate a solenoid for the towed assist.
As mentioned I certainly would not tap into the existing brake system on the bus!

John
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quantum500
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« Reply #3 on: October 02, 2008, 09:35:22 PM »

Great indeed.  What are the alternatives to this method?  How are trailer brakes used in comparison?  Great thread!
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luvrbus
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« Reply #4 on: October 02, 2008, 09:44:49 PM »

Melbo,mine is supplied from the rear brake relay it has a service port if your doesn't the instructions tell you to tee off the port that supplies the brake chamber fwiw M-G has a diagram on their web site not for sure but I think it is www.hotrodparts.com/rv/mg-brakes.htm
« Last Edit: October 02, 2008, 09:53:35 PM by luvrbus » Logged
Nick Badame Refrig/ACC
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« Reply #5 on: October 03, 2008, 03:48:50 AM »

Hi Guy's,

Here is SMI's site. It works off a self contained vacuum system with no air line connections.
http://www.smibrake.com/Items.aspx

Nick-
« Last Edit: October 03, 2008, 03:51:24 AM by Nick Badame Refrig. Co. » Logged

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luvrbus
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« Reply #6 on: October 03, 2008, 05:23:33 AM »

Hey Nick that link shows that to be a air system working off the coach air also   good luck
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JackConrad
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« Reply #7 on: October 03, 2008, 05:30:07 AM »

   We installed a T in the line to the right rear tag axle brake line. We ran 1/4" DOT nylon tubing from the T to a female quick connect fitting we installed under the rear bumper of the bus. We also installed a female quick connect fitting under the front bumber on our toad. This fitting is connected to the M&G through a solenoid valve and also fills a small tank controlled by the solenoid via a break-a-way switch which is connected to the bus. A coiled nylon air hose with 2 male fittings is used to connect the 2 female quick connect fittings.
   We added a 3# PSI pressure switch on the M&G that is wired to a flashing red LED on the dash of the bus.  This not only shows the M&G is working when the service brakes are applied, it also shows if the break-a-way switch has been activated (intentionally or accidentally).
    I was concerned about what would happen in the event of a failure in the system we added. To test this, I installed a male quick connect fitting in the female quick connect fitting on the bus (creating a 1/4" diameter "air leak") and went for a drive in the bus.  I was still able to stop the bus normally as well as a hard "emergency" stop with no problem. Although air was leaking, it was not leaking fast enough to set the DD3 before the bus was stopped. Once stopped, I set the DD3 parking brake and the air pressure immediately built back up. Only time air loss was noticiable was when applying the service brakes. This works for us, YMMV.  Jack

PS: here is a link to M&G website for more information   http://www.m-gengineering.com/index.html
« Last Edit: October 03, 2008, 05:35:05 AM by JackConrad » Logged

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Melbo
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« Reply #8 on: October 03, 2008, 06:09:27 AM »

Jack that is what the people at M-G told me also

Tap into the brake system with the 1/4 in od  dot brake line and it would not affect the braking if it were left open.

I asked about tapping into the tag axle air line and was told to go to the drive axle because the tag air is regulated down.

They said that the small volume of air would not affect the brakes but would operate the toad brakes just fine and I did get the breakaway system as well.

Thanks for the information.

Melbo
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CindyandJohn
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« Reply #9 on: October 03, 2008, 06:48:45 AM »

Hey Guys,

FWIW - I instlled the SMI Air Force one on my Eagle. The system works great. It has the extra tank for the toad, taps into the vacuum assist on the toad, has a break away valve which shuts the air supplies, etc. It was very easy to install. I tapped into the service line at a vavle area not directly off the can. That's probably the same affect of t'ing off the can but I would honestly say that I haven't seen any issues with braking... I would recommend the system without question... It is expensive but once installed you don't even see it in the toad. We have a 2005 Jeep Liberty. I had to modify the plastic under the dash just a bit so that the air vavle wouldn't rub and had to make a mount for the air tank under the hood - other then that, the install on the bus was quite easy.

John
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« Reply #10 on: October 03, 2008, 07:22:19 AM »

I have a 2003 liberty and its plumbed the way M&G describes, works great with no problems.>>>Dan
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Nick Badame Refrig/ACC
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« Reply #11 on: October 03, 2008, 07:46:28 AM »

Hey Nick that link shows that to be a air system working off the coach air also   good luck

Yea, The Air Force One is but, the Stay In Play works entirely from brake signal and vacuum.

Nick-
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luvrbus
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« Reply #12 on: October 03, 2008, 08:36:55 AM »

Sorry Nick didn't read about that type but a question for you were does the vacuum pump draw from for power I have a vacuum over hydraulic system on my gooseneck and the pump draws from the truck  battery and if it is left on in 2 or 3 days the battery is dead   good luck
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JackConrad
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« Reply #13 on: October 03, 2008, 10:03:42 AM »

I asked about tapping into the tag axle air line and was told to go to the drive axle because the tag air is regulated down.
Melbo

We tapped in before the tag axle brake pressure regulator. Jack
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Nick Badame Refrig/ACC
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« Reply #14 on: October 03, 2008, 11:15:09 AM »

Sorry Nick didn't read about that type but a question for you were does the vacuum pump draw from for power I have a vacuum over hydraulic system on my gooseneck and the pump draws from the truck  battery and if it is left on in 2 or 3 days the battery is dead   good luck

The brake system has it's own little vacuum pump in a small box that mounts in your engine compartment of the toad.
This system always stays in place and the acuator arm is also always in place. There is vurtually one connection when
hooking up the toad.
Nick-
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