park brake

[heavyhaulerss]

NEED SOME HELP HERE. WHEN I DO MY BRAKE CHECK, MY PARK BRAKE (RED & YELLOW BUTTONS ) DO NOT POP OUT UNTIL AIR GAUGE'S BOTTOMS OUT. I HAVE REPLACED THE PARK BRAKE WITH A NEW ONE. THERE IS NO DIFFERENCE, IT WILL NOT POP OUT BETWEEN 15 & 40 LBS LIKE SUPPOSED TO. ANY IDEAS ? THANK YOU. TROY

[Jackrabbit379]

Well,they are supposed to. When that air pressure drops to that point,the breaks set. They do that so that there is enough air to set the breaks for safety reasons. I'm not a diesel monkeynick,but that is the best that I can come up with. :P

....::EDITED::... :shock: :?

Sorry,I totally misread that. I am sorry,I thought that you wrote that your red,and yeller knobs DO pop out. Maybe a senser that tells them to pop out,isnt working? I'm sorry,not much help. :? Hope ya get r fixed.

[bob h]

NEED SOME HELP HERE. WHEN I DO MY BRAKE CHECK, MY PARK BRAKE (RED & YELLOW BUTTONS ) DO NOT POP OUT UNTIL AIR GAUGE'S BOTTOMS OUT. I HAVE REPLACED THE PARK BRAKE WITH A NEW ONE. THERE IS NO DIFFERENCE, IT WILL NOT POP OUT BETWEEN 15 & 40 LBS LIKE SUPPOSED TO. ANY IDEAS ? THANK YOU. TROY

if your pressure gauges are correct..., install a new dash (push-pull) valve

[heavyhaulerss]

THE NEW DASH PUSH PULL BRAKE IS WHAT I WAS REFERING TO AS PARK BRAKE. I DID INSTALL NEW ONE. SAME RESULTS. HOWEVER I HAVE NOT REPLACED THE AIR GAUGES. THEY SEEM TO WORK?? IS IT POSSIBLE THEY CAN LOSE ACCURACY ?

[bob h]

THE NEW DASH PUSH PULL BRAKE IS WHAT I WAS REFERING TO AS PARK BRAKE. I DID INSTALL NEW ONE. SAME RESULTS. HOWEVER I HAVE NOT REPLACED THE AIR GAUGES. THEY SEEM TO WORK?? IS IT POSSIBLE THEY CAN LOSE ACCURACY ?

yes, but surely not simultaneously

[bob h]

THE NEW DASH PUSH PULL BRAKE IS WHAT I WAS REFERING TO AS PARK BRAKE. I DID INSTALL NEW ONE. SAME RESULTS. HOWEVER I HAVE NOT REPLACED THE AIR GAUGES. THEY SEEM TO WORK?? IS IT POSSIBLE THEY CAN LOSE ACCURACY ?

on your keyboard; look to the far left, above the "shift" key and below the "Tab" key, the button is labelled "Caps Lock". press that key once

thank you,

p.s. - when you type with all caps it indiCATES THAT YOU ARE YELLING AT ME!!!

and......... my last nerve is already hanging on by a thin thread ;0)

[heavyhaulerss]

thanks for the response bob. didnt mean to yell. i must have caught that from my wife . lol

[bob h]

thanks for the response bob. didnt mean to yell. i must have caught that from my wife . lol

L O L !

[JoeyB]

I've seen that happen in other trucks as well. I think the forces (air pressure vs spring pressure) balancing that valve are so low by the time you're down to 45 psi, any O ring that has a little too much drag is enough to hang it up. The only thing I could suggest is to try to dribble a little air-tool oil into the valve to lube the o ring that seals the knob shaft.

[heavyhaulerss]

hey now get this.. ready?.. here goes... when i do my brake check engine off & key on the buzzer & light work just like supposed to. the brake valves do not pop out until the air gauge bottoms out. maybe 2-5 lbs at most.. but... but... if i do brake check with engine running the valves pop out between 25- 40. tried 12 times. pops out every time. i just pump brakes faster than my ole won out compressor can replenish & out they pop. let it build back up & pump down again & pops out just like it supposed to.. one more thing.. is this type a problem a shut down offense if a had to do a full insp at scale with the d.o.t ? thank you. i know bob will have imput here..

[Birken Vogt]

As far as I know the yellow valve does not really have to pop until basically 0 psi and many trucks are set up this way. The reason being you want to have manual control of your tractor brakes as long as possible in an emergency situation and not have a "dynamiter" where the spring brakes all set up simultaneously. Which could definitely cause loss of control if you are still trying to get the thing under control while moving at a pretty good clip. This is not loss of a safety feature as the spring brakes will still come on gradually as the pressure drops below 40 psi or so anyway but you want them to stay off as long as possible to give you every chance you've got to fix whatever is wrong yourself.

Now the red valve on the other hand, is supposed to pop somewhere between 45 and 60 IIRC, too lazy to look it up right now, but always well before the yellow knob does to close the tractor protection valve and stop catastrophic air loss through the trailer.

And of course many yellow knobs will pop at pressures substantially higher than zero, there are 10psi, 20 psi, 40 psi, and even higher available, it all depends what you buy and install.

Birken

[JoeyB]

No, they must BOTH pop at 45-20, although not necessarily at the same time. As far as their poping with the engine running, that gets back to what I said earlier. Just a hair too much internal drag in the valve and no dice. But add the slightest vibration to the equation and presto!

Don't know for sure, but I'd guess that as long as you can get them both to pop, even if it's near zero, you're good to go with the DOT. The only reason I say that is because if it were any other way, half the trucks in the country would be O/S.

[bob h]

i agree with birken here; the tractor protection valve (breakaway valve) shuts off air supply to the trailer in the event of trailer air system failure, and stops it from depleting the tractor air tanks

red button should pop well before the yellow

[Birken Vogt]

No, they must BOTH pop at 45-20, although not necessarily at the same time.

State your source

Birken

[heavyhaulerss]

bob & all the rest.. i really appreciate all your time & input here. i over a short time i put in a new dash valve. then i got a used one. then last week another new one. all have performed the same. somehwere around 5 lbs before poping out. they both pop out at same time every time. i guess this is one of those things that keeps ya scratching your head..

[JoeyB]

No, they must BOTH pop at 45-20, although not necessarily at the same time.

State your source

Birken

Federal Motor Carrier Safety Regulations 393.43 (b) ..."One of these means shall operate automatically in the event of reduction of the towing vehicle air supply to a fixed pressure which shall not be lower than 20 pounds per square inch nor higher than 45 pounds per square inch"...

Trailers will usually pop before the red knob does; that's the trailer's relay emergency valve response to the lowered supply pressure from the red gladhand. The trailer does this on it's own. If you keep fanning off air, usually the trailer supply knob will pop next, and then the yellow one.

[heavyhaulerss]

thank you joey...

[Birken Vogt]

Not trying to be a lawyer here, but 393.43(b) applies to trailer brakes only. There is no reference to the tractor emergency/park system at all.

Right or wrong, the trend for the yellow knob on newer trucks has been for it to pop just above zero PSI, or not at all due to o-ring drag, in order to give the driver the most chance possible to control the vehicle manually. In the event of catastrophic loss of air the spring brakes will come on anyway so what's the difference.

393.43(b) Emergency brake requirements, air brakes. Every truck or truck tractor equipped with air brakes, when used for towing other vehicles equipped with air brakes, shall be equipped with two means of activating the emergency features of the trailer brakes. One of these means shall operate automatically in the event of reduction of the towing vehicle air supply to a fixed pressure which shall not be lower than 20 pounds per square inch nor higher than 45 pounds per square inch. The other means shall be a manually controlled device readily operable by a person seated in the driving seat. Its emergency position or method of operation shall be clearly indicated. In no instance may the manual means be so arranged as to permit its use to prevent operation of the automatic means. The automatic and manual means required by this section may be, but are not required to be, separate.

[heavyhaulerss]

thank you birken

[bob h]

quote="JoeyB"]

No, they must BOTH pop at 45-20, although not necessarily at the same time.

State your source

Birken

Federal Motor Carrier Safety Regulations 393.43 (b) ..."One of these means shall operate automatically in the event of reduction of the towing vehicle air supply to a fixed pressure which shall not be lower than 20 pounds per square inch nor higher than 45 pounds per square inch"...

Trailers will usually pop before the red knob does; that's the trailer's relay emergency valve response to the lowered supply pressure from the red gladhand.

there is no trailer valve that causes the red button to pop off. the valve pops off based on line pressure ; when pressure over the piston of the red pp valve is reduced to 20psi (20 to 45) the spring force under the piston pushes it out. that dumps emergency line pressure and then closes the tractor protection valve to isolate the trailer air system from the tractor

The trailer does this on it's own.

the tractor controls the air supply and service function to the trailer, the trailer only reacts to what it is told by the tractor

If you keep fanning off air, usually the trailer supply knob will pop next, and then the yellow one.[/quote

agreed