Can a 5 ton cargo convert to tractor?

[mdog]

I see a 5 ton cargo truck up for sale but want a 5th wheel tractor. I can do the conversion of cargo bed to 5th wheel but don't know how to supply air brakes to the trailer. Is this an easy add on or more trouble than its worth? My hunch is that I should just wait for a tractor.

 

[m.walker]

Buy a tractor , they're fairly easy to find .

 

[rosco]

A heavy truck parts store will have diagrams for the air systems. There is a lot to converting them & mounting the fifth wheel, etc. I did it on a M211, but always drooled when I saw a standard built Tractor. I recommend as above.

Lee in Alaska

 

[bulldog_mack13]

Yeah , just buy a 3,000 drivable good M818 from GL. Id rather have the cargo , hmmm

 

[mdog]

The 5 ton cargo is coming up soon at Ft Bragg. I sat in it and it cranked right up. I beleive it was a cummings engine.

 

[timntrucks]

haft tract in new orleans is want to swap a tractor for a cargo. give him a shout he is in new olreans but his is a nice running one

 

[poppop]

My cargo trucks have glad hand connections at the rear of the bed. Am I wrong in thinking all you have to do is cut the air lines behind the cab and install fittings and coiled lines with the glad hands on them??? They were set up to pull the 105 trailers with air over hydralic brakes. You would also have to relocate the electrical plug behind the cab but that is simple also.

 

[mdog]

What you say makes sense but in my quick walk around I did not notice the rear glad hands. I did notice that the axles had hydraulic brake lines instead of the air brakes I had hoped to see. I am more comfortable with civilian style brakes and have decided I don't want to do a home made brake system.

 

[ida34]

The tractors have a manual control for the trailer brakes also. I think the lines for the fifth wheel trailer is run separate from the pintle trailer lines.

 

[vinny-socom1]

mdog pm me I'm selling one of my 5tons maybe we can trade??or quick sale? I just drove mine back from Fort Bragg they run great!

Vinny

 

[houdel]

Re: RE: Can a 5 ton cargo convert to tractor?

Am I wrong in thinking all you have to do is cut the air lines behind the cab and install fittings and coiled lines with the glad hands on them???

Yes you are incorrect in that line of thought. The air plumbing for a cargo truck pulling a straight trailer is much different that for a road tractor pulling a semi trailer. The straight trailer behind the cargo truck weighs generally a very small fraction of the weight of the cargo truck, whereas a fully loaded semi trailer could gross at 4-5 times the weight of the tractor towing it. This requires a much different brake design so that the trailer does not significantly overbrake or underbrake relative to the tractor.

First off, as ida34 pointed out, the tractor has a separate trolley brake lever (like a directional signal lever) mounted on the right side of the steering column to allow independent control of the trailer's brakes as needed. My M125 10 ton truck also has a trolley brake, but because it was designed to haul towed artillery in the 30,000-50,000 pound range.

Also it is important that the trailer and tractor brakes apply at the same time. Since the trailer's brake cylinders may be 30' or more aft of the tractor, and it does take a significantly measurable time for air to travel that distance, specific plumbing and additional air valving is required to speed the flow of air to the trailer's brakes. Were the trailer's brakes actuated simply from the tractor's service brake line, the tractor's brakes could be fully applied before the trailer's brakes begin to apply, meaning the trailer with it's not yet applied brakes and high GVW is trying to push the lighter tractor with it's brakes already applied down the road. Ever hear of "Jackknifing"?

Finally, another valve, known as a "Tractor Protection Valve", is mounted in the tractor's instrument panel to protect the tractor in the event of an air system failure in the trailer or the uncoupling of the air lines to the trailer. In the event of a sudden air loss from the trailer, the tractor protection valve shuts off the air flow to the trailer so the tractor's braking system is not compromised and the tractor driver still has a fully functional braking system in his tractor.

I hope this explains some of the differences in the semi braking system..

 

[rosco]

RE: Re: RE: Can a 5 ton cargo convert to tractor?

A couple of small points: Semi trailer brakes are always actuated via the treadle valve. Most, but not all tractors are equipped with the squaw handle/trolly valve. In fact, some truck companies don't have the trolly valve, to insure that the brakes are uniformly applied, and the driver doesn't just apply the trailer brakes. Owner operators notoriously use only the "Company" brakes on the trailers, saving their own!

The Tractor Protection Valve, per se, is usually mounted at the rear of the cab or even outside. There is a push/pull valve on the dash - it actuates the TPV via air pressure. The brakes are
balanced between the tractor & trailer/trailers with differential air pressure. For instance the trailers Relay Valve/Relay Emergency Valve will be actuated with say 2 PSI less the the tractors brakes (You want the trailers brakes to come on slightly before the tractors).

The Trailers brakes are actuated/applied with air from a storage tank on the trailer. It is filled & supply maintained with the "Emergency" (left side usually) air line. ***Here is the Punch line*** It is the Service Air that actuates/controls the various air valves! It opens the Relay valves that charge the brake pots, that apply the brakes, with air from the various storage tanks. That short circuits the long distance between the tractor & trailer and gives an immediate response. That is the short story!

Then you have other valves, like quick release valves, & the valves related to MVSS121 which mandates a dual air brake system
after a certain year. It refers to the "spring brake pots" that hold the brakes "OFF" with air pressure. But that is another story & I already have gangrene from typing too much!

Lee in Alaska

 

[DaveP]

Looks as if there is a lot to be learned here about brakes. the first thing to remember is the 900's have straight air brakes. the rest of the 5 tonners do not. the 818's do not have tractor protection valves. the trailer air lines have manual valves that have to be turned on in order for the service and emergency lines to flow. brakes are one thing that a person should be sure the information is correct before telling someone else how they work or how to use them. lives and equipment could be at risk.

 

[Recovry4x4]

The deuce tractor does have a tractor protection valve. It also has a shuttle valve. The TPV on the deuce is automatic in the sense that it is always on and providing air to the trailer. It's principle purpose is to insure that in the event of a air line failure on the trailer, the tractor still has air. I'n not quite clear on the roll of the shuttle valve.

 

[cranetruck]

Looks as if there is a lot to be learned here about brakes. the first thing to remember is the 900's have straight air brakes. the rest of the 5 tonners do not.....

Good write-ups Lee and Lee.

FWIW, the m656/757 (5-tonners) also feature 100% air brakes....

 

[oifvet]

This was informative.

Now I'm concerned about my 2 1/2 ton cargo-to-tractor conversion being an issue for the installation of the Johnny-bar and associated trailer-braking hardware.

Can it be done? What is the PITA factor?

 

[rosco]

Sure it can be done - you just have to learn the system, but right now, need to get to work. Later Lee

 

[Recovry4x4]

Oifvet, check with Boyce Equipment. For a while they were selling kits to add the trolley brake assy. Had the handle, plumbing and shittle valve for around $60 IIRC.

 

[ida34]

I think I have a shuttle valve but not the hand control. I will try to find it and post a pic.

 

[oifvet]

Thanks Kenny!!! I called them, and they can hook me up. Awesome!