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William Herren
William Herren, OWNER
Category: Medium and Heavy Trucks
Satisfied Customers: 26
Experience:  Mechanic at HERREN INDUSTRIAL GROUP
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I have a 2006 stetling A9513 single axle road tractor I am

Customer Question

I have a 2006 stetling A9513 single axle road tractor I am going to install a dump bed and I would like to keep the air trailer brakes and plumb them to my rear hitch plate the truck has wabco anti lock brakes what do I need to do to meet dot requirements to change this to a straight truck with trailer air brakes? Parts and part numbers too Thank you
Submitted: 6 months ago.
Category: Medium and Heavy Trucks
Expert:  William Herren replied 6 months ago.
Hello, my name is ***** ***** I will be assisting you.
Expert:  William Herren replied 6 months ago.
I believe your biggest issue is going to be your weight factor. Do you know the weight rating on the axle?
Customer: replied 6 months ago.
23000
Expert:  William Herren replied 6 months ago.
Are you planning on stretching the frame?
Customer: replied 6 months ago.
No I'm wondering what I need as far as braking because it will no longer be a tractor and will used as a straight truck with air plumbed to the rear for future air brake trailer ?
Expert:  William Herren replied 6 months ago.
The Tractor standards exceed straight truck standards. The only thing that you would need to do is plumb air and pig tail to your connection point which I'm guessing would be a pintle hook. The difference in tractor and straight truck air systems is there is no tractor protection valve on a strait truck.
Customer: replied 6 months ago.
What about inversion valve?
Expert:  William Herren replied 6 months ago.
Your truck currently has an inversion valve on it, these are better known as combination valves or anti-compounding valves. The function of these valves is to equalize pressure on the service side and parking brake side of the braking system. This is so in the event you have your parking brake set and hit the service brake it will not send air to both sides of the chamber, causing damage to your shoes and drums. It consist of a diaphragm with a spring that exhaust any pressure differences on the service and parking brake system.
Customer: replied 6 months ago.
I was told the inversion valve was in case you lost air in on tank i.e. Bro***** *****ne. It would give you the it from the other tank for braking? This is new to me my back ground does let me understand the reasoning I need to know what and where to use or does this system not need anything else or is it already equiped?
Expert:  William Herren replied 6 months ago.
What you are referring to is known as an Sr-7 spring brake modulating valve. It will only allow 107 psi into the parking chamber and holds it in the event you lose primary air.
Expert:  William Herren replied 6 months ago.
It will allow you to continue making braking applications but if you are going to have a trailer attached you would not want this because your secondary air tanks control your front brakes. This would cause a jack knife with a majority of braking from the front and little from the rear at the trailer.
Expert:  William Herren replied 6 months ago.
If you are going to continue to use a trailer then you need to leave it how it is, plumb air to the rear along with a pigtail. You always want your braking to begin at the very back.
Customer: replied 6 months ago.
what your saying is the difference from Tractor braking and straight dump truck braking is the ability to have trailer air brakes and when not hooked up the tractor brakes like a straight dump truck ?
Expert:  William Herren replied 6 months ago.
In your case, you do not want to install an Sr-7 valve because in the event of air loss to the primary air system which controls your rear brakes you will only be able to brake using your front brakes which will cause you to jack knife. If you leave it like it is now and have an air loss your parking brakes will begin to apply starting from the rear which will keep you from jack knifing. If you are going to have air brake trailer you can not add the Sr-7 valve used on strait trucks.
Expert:  William Herren replied 6 months ago.
What most people do is get a trailer with electric brakes, add a brake box.
Expert:  William Herren replied 6 months ago.
Then you can add your strait truck valve (Sr-7). And will not have to plumb anything in.

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