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Author Topic: Air Brakes - Application Pressure? Related to toad brakes  (Read 9807 times)
rv_safetyman
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« on: December 02, 2008, 01:06:58 PM »

I use a 1.5 inch diameter piston actuator for my toad system (plumbed to the bogie relay valve).  Today I unhooked the vacuum system and then drove around the yard and applied air to the cylinder.  It looks like at 60 PSI, I get some decent stopping.  I have been a bit concerned, since I now tow a service truck that weighs over 8K.

The question is, what does a typical hard stop air pressure go to?  As I recall some folks talked about light breaking resulting in pressures in the 20's.  I know that Jack Conrad played with his system at about 50 PSI.  If the pressures go over 60 PSI on a hard stop, I will feel comfortable with the cylinder I have.

I don't have an application gauge, so I hope some of you have an applied pressure gauge and looked at some of the pressures at various braking levels.

Jim
« Last Edit: December 06, 2008, 05:53:02 PM by rv_safetyman » Logged

Jim Shepherd
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« Reply #1 on: December 02, 2008, 01:13:19 PM »

Jim, a max brake stop will put full air on your brakes.   Most of the time not over 60 lbs. for a highway stop, but in a bang bang stop look for over 90 lbs.
Jack
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« Reply #2 on: December 02, 2008, 01:24:04 PM »

Jim,
I think you will be just fine.  You don't really need the toad brakes until you really need them. 
At 1.5" diameter, the area is 1.76"2,  so at full application of say, 90 psi you will be putting 158 lbs on the brake pedal, probably about what it would be from your foot in a panic stop.

I think the home built that Fred Hobe uses http://users.cwnet.com/~thall/fredhobe3.htm has a 1" x 6" cylinder.
« Last Edit: December 02, 2008, 01:28:39 PM by Len Silva » Logged


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rv_safetyman
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« Reply #3 on: December 02, 2008, 01:31:05 PM »

Thanks Jack and Len.  I had done the math as well and felt that it should be enough, but did not have a good handle on what a full application would give in the way of air pressure.  It makes sense that it would be full system pressure, but I wanted to verify that.

I used this cylinder for a lighter toad and never worried about it.  However, with this big hunk it became more of a concern.

Jim
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Jim Shepherd
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« Reply #4 on: December 02, 2008, 03:38:15 PM »

Hi:

Thanks for jogging my memory with this thread.

I have the 1/4" brake line plumbed now from the relay valve on the tag axle, through a 1/4" ball valve, then to a quick coupler at the rear bumper of my MC7.
My toad is a Geo Tracker 4 dr with power brakes, weighs in around 2200lbs I guess.

Question:

Fred's setup includes an 'air muffler' which I believe is threaded into the 2nd port on the air cylinder. His part number for the cylinder translates into a 1.5" cylinder with a 6" stroke. Our local supplier has these on the shelf. What does the air muffler do, and is it required?

The way I figured it, when the brake is released, the air must travel back to the relay valve to escape.

I am 'assuming' (Oh, I hate that word) that can just plug the 2nd port on the air cylinder.

Any suggestions would be appreciated before I buy/install the wrong thing.

Best regards.

Mark

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Mark Morgan    near Brandon, Manitoba, Canada
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« Reply #5 on: December 02, 2008, 10:29:27 PM »

When I was driving my truck with an application gauge, during normal braking, I made it a rule not to go over 30psi.   As consequence, my brakes have lasted over 300,000 miles.  So in my book, 60 psi would be too much.  Good luck, TomC
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« Reply #6 on: December 03, 2008, 05:06:27 AM »

   We installed a brake application air pressure gauge when we installed the R&M dash in our MC-8. A "slow down" application is usally about 5-10 PSI. A "stop sign ahead" application is about 10-15 PSI. A "S%*T, the light just changed!" stop is 25-40 PSI.  When we do our pre-trip, while sitting still (after releasing the parking brake),  I make a HARD application to pressurize the break-away tank on the toad, (70-80 PSI).
   Our M&G installs between the brake booster and the brake master cylinder. It does require an air line connection to the bus air brake system.  We installed a Tee in the right rear tag axle brake line (before the tag axle brake regulator) and ran a 1/4" DOT tubing to a quick connect female fitting on the rear bumper.
    I did a test by inserting a stand quick connect (open) male fitting in the bumper female fitting and went for test drive.  Although I had a "major" (1/4") air leak when brakes were applied, I had no problem making a normal stop or a "panic stop". Only problem was when I kept the brake applied after coming to a stop. Setting the parking brake and releasing the service brake solved that problem.  Jack
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« Reply #7 on: December 03, 2008, 10:09:04 AM »

Question:

Fred's setup includes an 'air muffler' which I believe is threaded into the 2nd port on the air cylinder. His part number for the cylinder translates into a 1.5" cylinder with a 6" stroke. Our local supplier has these on the shelf. What does the air muffler do, and is it required?

The way I figured it, when the brake is released, the air must travel back to the relay valve to escape.

I am 'assuming' (Oh, I hate that word) that can just plug the 2nd port on the air cylinder.

Any suggestions would be appreciated before I buy/install the wrong thing.

Best regards.

Mark



The muffler allows the air on that side of the piston to escape. It also keeps dirt out.

If you plug the port, you won't like the results . . .
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« Reply #8 on: December 03, 2008, 10:34:40 AM »

This may be an off the wall question, except to those that aren't old truck drivers, but...

Why do you use a shop air quick connect/dissconnect on the air line from the bus to the toad instead of a glad hand connection?

It's always been my experience that the brass or steel connections will eventually start leaking when exposed to the elements, but, while a gladhand connection may start leaking, it only costs about $1.00 to replace the glad hand rubber.

Another plus of the glad hand is, if you mess up and forget to unhook, the gladhand will come apart, leaving you to straighten the lock plate back with a pair of pliers. If you do the same with a quick connect, you'll be replacing either an air line or a couple of connectors.

I'm not saying that your are wrong to use those fittings, I'm just looking for the rationale behind it.

Thanks,

Dallas
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« Reply #9 on: December 03, 2008, 10:41:06 AM »

Can't speak for others, but in my case, I already had the quick connect fittings and one of those 10' coiled air hoses.  Didn't even have to drive to town (25 mile round trip) for any parts.  Jack
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« Reply #10 on: December 06, 2008, 08:34:08 AM »

Even though folks think I might be OK (at least for the panic stop), I went ahead and ordered a 2 inch cylinder.  That will give me about 80% more force.   

Hopefully, it will come before we leave (just after Christmas - have to be in Indio by Jan. 1 -- wish we were heading towards the other coast).  That way I can do some testing at various pressures.

That cylinder will give me much better braking at less that full pressure (touching the brakes going down big hills when the Jakes just can't quite keep up).  My guess is that I will have to put a pressure regulator on it to keep from getting too much brake in a panic stop.

I want to make sure I keep the bus/truck in good control, since I am at about 45K total. 

The truck (3/4 ton)has all disk brakes, so a little extra use will not hurt anything.

Jim
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Jim Shepherd
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« Reply #11 on: December 06, 2008, 09:03:14 AM »

Jim, I use a 2" cylinder myself.  I can DEFINITELY tell that the toad brakes are working when it is hooked up.  Like you, my toad has all wheel disk brakes and I've never had any issues with the toad brakes locking up even on "hard" stops.  The peace of mind with the braking system hooked up is immense especially knowing I'll be okay if I have to make a hard stop while going down a steep grade.  I consider a toad brake essential equipment.
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« Reply #12 on: December 06, 2008, 01:34:58 PM »

Jim,

I have stayed out of these discussions but you disrupted my comfort level.

If you use a 2" cylinder, I am afraid your toad may be trying to stop your bus.   You will have a tendancy to wear-out your toad brakes also.   If you have vacuum in your brake booster, you have the potential of bending the brake pedal bracket.   Dependent on brake system design, the brake pedal ratio is somewhere between 3.3 and 5:1

Years ago, I designed brake pedals, brackets, and systems.  I would be OK with 150# brake pedal effort, under no vacuum, on an OCCACIONAL basis.   We designed for 600# max pedal effort.    Some of you may say that was over design, but we had seen brackets that showed that level of panic braking.

I do not like any of the commercial toad braking systems.  How can a company, supply a brake toad system, that provides effective braking for motorhomes ranging from 12-53,000 pounds, and  toads 3-8,000 pounds?  They can't, or haven't yet. 

Jim, if you have access to a brake decelerometer, and pressure gauge connected to the rear brakes, we can design a relatively effective system for your vehicles.   Aren't you coming to Bussin?

(That said, of the systems out there, I like the M&G the best.)

Ed Roelle
 
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« Reply #13 on: December 06, 2008, 02:26:35 PM »

Jim,


I do not like any of the commercial toad braking systems.  How can a company, supply a brake toad system, that provides effective braking for motorhomes ranging from 12-53,000 pounds, and  toads 3-8,000 pounds?  They can't, or haven't yet. 

(That said, of the systems out there, I like the M&G the best.)

Ed Roelle
 

We are planning on coming to Bussin.  we just ordered an air force one from smi.  it looks the same???  but they specified a pressure regulator which they are going to set before shipping becuase of our power brakes.

any thoughts?
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« Reply #14 on: December 06, 2008, 05:52:14 PM »

Hi Ed.  I wish we were heading to Florida, but we have shows to do in CA the first week of Jan.

I need to do a design check with you.  When you are talking about 150#, I am assuming you are talking about the force at the pedal as opposed to the master cylinder rod.  That would make sense.  When I first started playing with my system I grabbed a bathroom scale and tried some pressures.  Seems like I got to at least 100 pounds.

I want to clarify that I do not have a vacuum pump for the toad brakes, I am careful to pump the brakes a few times to empty the chamber, so we are talking about un-assisted brakes.

The 1.5 inch piston has an area of 1.77 sq. inches while the 2 inch has 3.14 sq inches.  At 60 psi that gives forces of 106 pounds (1.5 cylinder) and 188 pounds (2.5 inch cylinder).  My problem was that the typical non-panic brake application was in the 30 psi range and that is almost no toad braking. 

As I mentioned, I did some testing (seat of the pants) and at 60 psi with the 1.5 inch cylinder, it slowed down reasonably well, but was far short of strong stop.  I was on dry grass, and I was not even close to sliding the tires. 

My plan is to use the 2 inch cylinder and add a pressure regulator.  I will probably set it to 50 psi (157 pounds force) or perhaps 60 psi.  If I understand your numbers, that is right in the design range of the pedal. I will do that testing on dry grass as well (hopefully there won't be snow on the ground Angry).  If I do slide the tires, I will probably try it on dry pavement.  One of the problems is that I do not have the truck fully loaded right now - probably at least 1000 pounds short of the typical load of product and show equipment.

Ed, give me a cross check and see if I messed up in my thought process.

It sounds like it works well for Brian. 

Jim
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Jim Shepherd
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« Reply #15 on: December 06, 2008, 07:04:25 PM »

Tom,  I looked-up the  Air Force One and could not find out how they do what they claim.  A regulator can help to limit the maximum force, but the cylinder diameter sets-up the proportional braking.  All things considered, you would like your toad to brake at the same deceleration rate as your coach.

Jim,  Yes, the 150# is at the pedal.  One FMVSS test stipulated 150# max pedal effort, no power - stopping distance was verrry long.

"My problem was that the typical non-panic brake application was in the 30 psi range and that is almost no toad braking.  "   If it is a non-panic stop, is toad braking necessary for you?

Optimally, if you are stopping your coach alone at a medium decel and there is x psi air pressure to the rear bus brakes, your would like the x psi, operating the cylinder in your toad, to give you the same braking decel - proportional.    I think the 2" is too large.  When I went through the numbers a few years ago, I think the cylinder diameter was to be ABOUT  1 1/4"  to 1 1/2" - as I remember (my paperwork is at home and I am in Florida).  You will not be able to slide the toad tires on pavement under no power, below 150# pedal effort.

Jim, you are on the right track with some testing - light bus braking, ? decel, ? air pressure.  Repeat med bus braking, heavy bus braking.  Now go repeat in toad - light toad braking, ? pedal effort ...  Then it is just sizing of cylinder so a given bus braking/air pressure applies toad pedal force to give equal/proportional decel.

The difficulty in all this for us, is we just don't have decel meters and pedal force transducers readily available.

The difficulty for toad brake manufacturers is the multitude of combinations of coaches and toads.   So, the manufacturers have to design to assumptions.   When I asked them about their designs, they admitted that proportioning meant more toad braking when there was more coach braking - NOT equal proportioning.   

I support having toad braking.  Someone may have a true proportional toad brake system, I just have not seen an effective system available.

Ed Roelle
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« Reply #16 on: December 06, 2008, 08:06:40 PM »


It sounds like it works well for Brian. 

Jim

I also tried a 1.5" cylinder and was not happy with it in the least.  2" provides braking that "feels" right to me.  I know, not much science there.  I wish I had access to the right tools to prove perfect levels of proportional braking, but don't.  So, seat of the pants testing like Jim descibes is the best I can do.  I do know I don't lock up the brakes and I also know there is a noticable difference in bus brake pedal travel/force required if I don't have the toad brake connected compared to when I do.
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« Reply #17 on: December 06, 2008, 08:21:27 PM »

Ed, thanks for the reply.  BTW, I changed the subject to let folks know that the discussion involved toad brakes.

Obviously, the air pressure to the cylinder is the same as the air pressure applied to the bus brake chambers.  Thus the force to the master cylinder would be a direct function of air pressure to the air brake chambers on the bus.  Beyond that I don't know enough about the brake dynamics to say that they would be proportional.  I would think it would in the ball park of being proportional.

For the normal city driving, or to slow for a slower driver, the toad breaking is not a significant issue.  The one place that I am concerned about is really steep hills.  With the 10 speed and good Jakes, I don't have to use the brakes very often.  However, I have been on hills where I have to slow the engine from slightly over 2100 rpm to perhaps 1900 rpm, or to slow for a slower vehicle.  I try to use a moderate stab on the brakes for a perhaps  5 - 10 seconds.  However, I would bet that I never get over 40-50 psi and that does not apply any significant toad braking according to my testing.  In that case, I want as much toad braking as I can get, so that the slowing takes place quickly and does not heat the bus brakes any more than necessary.  I guess the other way of saying that is that I want the heavy truck to share the braking load under less than panic conditions (the truck is about 20% of the total GCVW).  Knowing that it will never be perfect, I want to defer to a bit of overloading the truck brakes.  With the 4W disc brakes on the truck, I don't think I will be doing any significant heat damage and the parts are fairly cheap.

Keep up the dialog, as I want to make sure I am doing the right thing.

Jim
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Jim Shepherd
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« Reply #18 on: December 07, 2008, 08:20:14 AM »

Your case is different from most of us with the heavy truck and four wheel disk brakes.  For me, towing a little CRV, I don't want any toad brakes until I REALLY need them.
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« Reply #19 on: December 07, 2008, 10:04:48 AM »

This may be an off the wall question, except to those that aren't old truck drivers, but...

Why do you use a shop air quick connect/disconnect on the air line from the bus to the toad instead of a glad hand connection?

It's always been my experience that the brass or steel connections will eventually start leaking when exposed to the elements, but, while a gladhand connection may start leaking, it only costs about $1.00 to replace the glad hand rubber.

Another plus of the glad hand is, if you mess up and forget to unhook, the gladhand will come apart, leaving you to straighten the lock plate back with a pair of pliers. If you do the same with a quick connect, you'll be replacing either an air line or a couple of connectors.

I'm not saying that your are wrong to use those fittings, I'm just looking for the rationale behind it.

Thanks,

Dallas

Dallas,
You make a valid point! How ever as a heavy duty wrecker operator I can add one more reason for the use of the shop air quick disconnects. On a system such as our buses not having a trailer valve on the dash would mean that that air line is always "charged". Which is exactly as Jack described on his test run of a "1/4" air leak while holding the pedal down." Unless you used glad hand plugs you'd have the same problem & glad hand plugs are #1) not readily accessible to all & #2) in my opinion are more prone to some kid or clown tampering with than just a female quick connect that is empty.
JMHO FWIW Grin  BK  Grin
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« Reply #20 on: December 07, 2008, 10:18:36 AM »

Ed,

No expert here. However, I too leaned toward an M&G toad brake system. Only problem was they do not make one for my toad (2003 Dodge Ram 2500 4x4). The factory says there is not enough room in the engine area for their unit.

I found the SMI Air Force One on the web and made arrangements to have one installed at a rally last spring. This year we have logged over 7,000 miles and knowing the toad had its own brakes was a comfort to both of us. We even went over the Applachians and Rockies twice without problems. I really learned how to use the Jake also.

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makemineatwostroke
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« Reply #21 on: December 07, 2008, 10:55:00 AM »

I changed over to the M&G system from Brake Buddy for my Jeep in Oct after the unit failed what I don't like about Brake Buddy or the Roadmaster unit they will take a toll on the firewall as the vehicle wasn't design for that type force on the pedal or the seat without power assist so I would me careful in the design of a unit that puts out a great amount of pressure on the pedal, firewall on the floor board.I saw one I don't know who the manufacture was but it ripped the floor board and another at PPL in Houston that stripped the gears in a power seat on a Jeep    have a great day
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luvrbus
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« Reply #22 on: December 07, 2008, 11:27:34 AM »

Jim, I have a Blue Dot vacuum pump for the brake booster new still in the box I bought to go on the Lexus if you want it I will bring it to Quartzsite in Jan I know we can trade for something.But I would be concerned about putting anything on a power assist braking system pedal without one, didn't Ben have a problem with his brake pedal using a air system with no vacuum to the booster.   

good luck
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« Reply #23 on: December 07, 2008, 02:13:04 PM »

Jim,

Just additional data for you -- I have dual application gauges (one for each half of the redundant system) and a normal "service" application rarely runs above 20psi, a "hard stop" runs about 30psi.  If I put 60 psi to the brakes, I'd probably lock 'em up.

Also, make sure you use a "protection valve" ahead of your coupler (and I'm with Dallas on this: use a glad-hand).

Without such a valve, a tear-away of the toad (or road debris severing the air lines, whatever) will empty your service line on application, resulting in either 50% reduction of coach braking power, or full emergency application, depending on how your system is plumbed.  Neither is good, which is why federal law mandates the protection valve for truck tractors.  FWIW.

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« Reply #24 on: December 08, 2008, 09:35:14 AM »

Clifford, I think I will pass on the vacuum pump.  Want to keep the system as simple as possible.

Sean, no sure what you mean by protection valve.  The valve that comes to mind is the one that shuts off at, say 60 psi, and is used on one of the supply tanks to feed the aux. tank.  If that is the case, I can't quite see how that would work.  If I would put in in the line that runs between the relay valve and the toad, it would never allow pressure to get to  the toad, except for the panic stop (pressure would be below the opening pressure).

I want to make sure that I am clear about how I plumbed this system.  I simply plumbed into a port on the bogie relay valve and when the brakes are applied, the toad air line is pressurized.  If a line brakes in this system, there is no air loss until the brakes are applied.  I use a 1/4 inch line, so the loss is minimized (but would be a problem with extended brake pedal application). 

It seems to me that a glad hand would not help if the air line between the glad hand and the toad broke (most likely scenario).

A good friend who read this board, but will not post, called to strongly remind folks that have this type of system to use a pedal return spring.  He had a friend who had a battery go down because the brake pedal did not return sufficiently to turn off the brake lights.  He also had a friend who lost a toad to a fire that could have been caused by the brakes not releasing fully (they are not sure).  I use a bungee cord and that seems to do a good job.  I check it at each stop and the brake pedal is retracted and the brake lights are not on (on most cars, the first key position will unlock the steering, and allow the brake lights to work, but nothing else).
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« Reply #25 on: December 08, 2008, 03:51:49 PM »

Jim,

A protection valve allows air to flow only at a certain rate, above which the valve closes.  Note that this has to do with flow rate, not pressure.

The idea is that, under normal service brake application, the pressure builds smoothly and the flow rate in the lines, which terminate in slave cylinders, is actually very low, remaining below some threshold.  The valve is pre-set above this threshold.  If a line is open to atmosphere, air under pressure will try to leave the line at a much higher rate, and the protection valve will close, preventing further air loss.

The (possibly deadly) danger of not using such a valve is that, under normal but prolonged braking, an open line caused by the toad air line being severed would ultimately result in loss of service pressure, as the compressor could not keep up with the loss.  Now this is not likely to be a problem in normal stops on normal roads, but let's say you're coming down from Monarch Pass and you're on the brakes pretty steady, when you lose your toad (or the line comes apart, for whatever reason).  Now you're going to run out of air before you get to the bottom of the hill -- or your spring brakes (if equipped) will engage, completely outside of your control.  At that speed, on that hill, I would figure a spring brake application to be a sure way to catch the bearings on fire, and then you'll get to do a live test of your Cold Fire extinguishers Wink

The glad hand comment, BTW, was unrelated to the protection issue.

-Sean
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« Reply #26 on: December 09, 2008, 09:35:59 AM »

Tom,  I looked-up the  Air Force One and could not find out how they do what they claim.  A regulator can help to limit the maximum force, but the cylinder diameter sets-up the proportional braking.  All things considered, you would like your toad to brake at the same deceleration rate as your coach.

Optimally, if you are stopping your coach alone at a medium decel and there is x psi air pressure to the rear bus brakes, your would like the x psi, operating the cylinder in your toad, to give you the same braking decel - proportional.    I think the 2" is too large.  When I went through the numbers a few years ago, I think the cylinder diameter was to be ABOUT  1 1/4"  to 1 1/2" - as I remember (my paperwork is at home and I am in Florida).  You will not be able to slide the toad tires on pavement under no power, below 150# pedal effort.

Jim, you are on the right track with some testing - light bus braking, ? decel, ? air pressure.  Repeat med bus braking, heavy bus braking.  Now go repeat in toad - light toad braking, ? pedal effort ...  Then it is just sizing of cylinder so a given bus braking/air pressure applies toad pedal force to give equal/proportional decel.

The difficulty in all this for us, is we just don't have decel meters and pedal force transducers readily available.

The difficulty for toad brake manufacturers is the multitude of combinations of coaches and toads.   So, the manufacturers have to design to assumptions.   When I asked them about their designs, they admitted that proportioning meant more toad braking when there was more coach braking - NOT equal proportioning.   

I support having toad braking.  Someone may have a true proportional toad brake system, I just have not seen an effective system available.

Ed Roelle

i'm trying to talk smi or a local dealer into making a presentation and/or exhibiting at the Bussin rally in Arcadia.  They explained to me tha their system is not really that complex.  air line from relay valve on bus, to air force one system on toad, with special disconnects at the bus bumper.  Their system manipulates the brake pedal while systems such as m&g manipulate the brake cylinder fluid.  The proportional part comes from the amount of air pressure being applied to the air brakes on the bus being applied to the pedal on the toad.

that's my extremely limited, quick explanation, or interpretation, of what they said.  like i said, i'm trying to get them to come to the rally.
sounds like what Jim is doing himself.
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« Reply #27 on: December 09, 2008, 03:04:05 PM »

Tom,
   I would love to have them do a seminar at our rally.

Jim,
   Not sure how they figgered their cylinder size, but the M&G unit uses air pressure from the tag axle brakes to move an air cylinder that pushes the plunger in the toad brake master cylinder. More air pressure in tag axle air line= stronger toad brake application.  Jack
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« Reply #28 on: December 10, 2008, 07:02:54 PM »

Hi Sean.  I went all through my Bendix Air Brake Handbook and looked at all the various components and none work based on flow limitation that I could find.  I did find the pressure protection valves (PR-2, PR-3, and PR-4) but they are pressure operated.

I really like the idea of the valve you suggest, but I can't find anything that works on flow.  I did a general google search and found Haldex and Midland pressure protection valves, but they also operated on pressure.

If you have a source, let me know.  It is a great idea and I would guess someone has them, but not the major suppliers in the air brake market that I can find.

Jim
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« Reply #29 on: December 10, 2008, 09:55:49 PM »

Jim,

I don't think you'll find such a valve in an air brake catalog, for a simple reason: DOT air brake systems forbid single service-line connections to trailers.  In a commercial hauler such as a truck tractor, you will have a "supply line" to the trailer, also known as the trailer emergency line, as well as a "control line" also known as the trailer service line.

With this arrangement, full breakaway protection, as well as protection from failure of either line, can, indeed, be detected and prevented by means of pressure alone, and this is normally done with a pair of pressure-operated control valves such as a PP-7 and TP-3 (which ought to be well described in your Bendix catalog).

So, I think, to get the required protection in your non-DOT arrangement of only carrying the service line back to the trailer, you will need to get a valve from another application.  I don't have a specific part # for you, since I haven't had to solve this particular problem.  But in gas lines (in the strict sense of the word, e.g. air, helium, etc.), the type of valve is known as an "excess flow valve," and you should be able to find one that meets your needs by Googling around a bit.  Incidentally, in fluid lines, such a valve is known as a "hydraulic fuse."

BTW, any one out there who has an LP cylinder aboard already has an excess flow valve -- there is one built into the cylinder to protect against a rupture in the high-pressure line leading to the regulator.

HTH.

-Sean
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« Reply #30 on: December 10, 2008, 10:15:48 PM »

Jim,

After I just posted my last reply (wherein I discussed two-line, breakaway-protected systems as found on trucks), it now occurs to me to ask:

How are you implementing automatic application of the toad brakes in the event of a break-away, as required by many states?

-Sean
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« Reply #31 on: December 11, 2008, 06:13:41 AM »

I have read this thread with interest and am wondering why not use a system similar to trailer brakes such as used on car trailers/tow dollies.  They have a kind of spring loaded torque rod and as the towing vehicle slows the brakes are applied on the trailer.  Using this technique in conjunction with air (or other) assisted braking would seem to be the best way to keep the load off the front vehicle.  This would also reduce stress on the tow/hitch set up if properly adjusted.  I mention this as the brake air line pressure is going to vary so much it would seem wiser to have a separate system based solely on deceleration.
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« Reply #32 on: December 11, 2008, 08:02:04 AM »

Sean, I have not had time to look for the "excess flow" valve, but I will do that in the next few days.

I have not yet implemented a breakaway system yet.  Jack Conrad and another person have been giving me guidance on how to do that. 

Basically, Jack uses a system the mimics the M&G system.  That is to use a typical trailer breakaway switch that operates a solenoid valve.  I have been looking for a suitable pressure reservoir.  One person suggested using PVC.  Not sure I feel comfortable with that material.  I do have a copper tubing accumulator that I built for another application that I will probably use.

The system seems pretty simple.  Air in to a pressure chamber via a one way valve, air out the the brake cylinder via a solenoid activated by the breakaway switch.  I have to think my way through how to deal with stopping the flow back out the broken application line.  I think that can be done with another check valve.  Jack has given me that information, but I have not studied it in detail.

Jack charges his pressure cylinder via the air from the brake supply line.  He hits the brakes with full application and that charges the cylinder.  I am a bit concerned about that process on my application, as you need to bleed the vacuum out of the toad brakes before you make the full pressure application.  Otherwise, you could overload the the master cylinder.  That is not an issue with the M&G system since it is between the vacuum chamber and the master cylinder. 

When we get ready to depart, I have my wife apply the brakes a few times while I check the toad.  When I get the breakaway plumbed in, I will have her do several light applications while I do my checking (to bleed the vacuum) and then I will do a couple of full applications before I depart.

At least that is the plan

Jack, my apologies to you.  I probably butchered you "system", but I know you will straighten me out Smiley.  I think there is a thread on this specific subject, but I did not do a search.

zubzub, what you are describing is what is typically called a surge brake system.  It is used on tag type trailers (and I think one dolly manufacturer uses it).  The tongue is free to float and activate a master cylinder if the towing vehicle slows down.  The only ones I have seen are a "closed" hydraulic system contained withing the trailer.  I am not sure how you could make that concept work with a air system or withing the hydraulic system of the toad.  You would definitely not want to try to plumb it into the toad hydraulic system!!!

Many folks do not like trailers with surge brakes because they activate when you are trying to back the trailer.  That would probably not be an issue with a bus/toad, since you really should not try to back them up (exception very slow short distances).

Jim
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« Reply #33 on: December 11, 2008, 03:07:20 PM »

I think the over-riding issue with surge brakes is that there is no way for the driver to confirm that the brakes on the trailer are actually working, and to what degree.

In other words, how do I test them during the pre-flight?

happy coaching!
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« Reply #34 on: December 11, 2008, 03:59:22 PM »

Jim,
    I will try to explain my break away system. I installed a small aluminum pressiure tank on the toad. It is fed through a one way check valve from the tag axle brake line. (same line that activates the M&G toad brake). Whyen doing our pre-trip, I make a hard service brake applicatio (at least 60 PSI). This fills the pressure tank and a one way check valve prevnts the air from leaving the tank.  A tee is installed between the check valve and the tank.  This goes to a 12 volt solenoid controlled valve. When the breakaway switch is activated it supplies power to the solenoid which opens the valve between the pressure tank and the M&G, and simultaneously closes the valve between the M&G and the airline from the bus.  Jack
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« Reply #35 on: December 11, 2008, 07:17:36 PM »

Hi Jack...what control the air leaking from the bus's brake service air during brake application after the line break away from bus?

Thank you. Gerald
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« Reply #36 on: December 12, 2008, 05:15:42 AM »

Only leaks when service brakes are applied. I did a test drive with an open male quick connect couping installed in bus fittng. I had plenty of air to stop (both normal and "emerency" hard stop). Once stopped, I set the park brake and released the service brake (no more leak). Dash air pressure gauge never showed less than 80 PSI.  Normal stopping uses about 10-15 PSI, hard stop used about 40 PSI, so in either stop, you are not pushing air out the leak at anywhere near the tank pressure of 125 PSI.  If toad should break loose, only bus brake application will be to stop the bus as quickly as possible and set parking brake. This should not be a problem.
   Now if I was coming down a mountain at 60 MPH, I migh have a problem, but first, we don't travel in big mountains and if we did, I don't expect to come down at much faster than 30-40 MPH.  Just our way, YMMV  Jack
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