Airpack modification for towing

[Stretch44875]

It's pretty simple to hook the brakes together on two deuces for towing. Take the J-pipe off the airpack on the towed deuce, insert male air nipple, then hook the service line on the back of the towing deuce to the airpack.

But, that darn J-pipe is a real pain to put back on sometimes. Flared fittings can be hard to start. And then, every time I wanted to tow, I had to crawl under the truck, hook the air nipple up, and then put everything back when I was done.

So I took the J-pipe off and modified it with a shut off valve, and an air chuck. Now I can hook the air line up, turn the valve, and have the brakes hooked together. The shut off valve prevents air from going into the airpack valve. Then, using a male to male air nipple, hook up the air line.

The reason for towing so much, is the M108 gets 5-6 miles per gallon on gasoline, and the deuce runs on free used oil.

Dennis

 

[gimpyrobb]

Looks good boss.

 

[DanMartin]

Interesting idea...hmm...make up a few of them and sell them man! I would buy one ready-made.

I'm assuming two of these tied together would need to be used for split-system trucks (mid 80s and up + all A3s).

 

[Recovry4x4]

I'd agree with your surmise Dan. Looks good Stretch, been meaning to do that, just lazy I guess. The 900 degree heat could be a factor as well.

 

[cbvet]

I assume what you're saying, is that this setup makes the brakes in the tow-ee vehicle work when the brakes in the tow-er are applied? (Boy, spellcheck doesn't like those words) Correct?
A great idea. But how does that work? How can brakes be applied without pushing fluid out of the master cylinder?
I know my M813 has the gladhands on the front for that same purpose, I just don't get how it actually works. Is there enough fluid in the airpack to work the brakes?
Eric
CBVET

 

[FormerNewMVGuy]

 

[CCATLETT1984]

i think i'd rather run an air line from the back of the truck to the front for towing, I'm lazy that way.

 

[Recovry4x4]

Checkvalves prevent it from being backfed through the system.

 

[Barrman]

I will take a stab at explaining the how.

Fluid is sitting in the master cylinder above the piston that moves when you push the pedal. When you do push the pedal, fluid already in that cylinder gets pushed or actually in a good system, pressurized. The next thing down the line from the master is the air pack. It has a bigger piston/cylinder inside the front of it. Fluid is just sitting there in that cylinder like it does in the lines and wheel cylinders throughout the brake system. This piston is connected by a rod to the back of the air pack where a huge piston lives.

When the front piston gets pushed back some by the pressurized fluid coming out of the master,(This is why M35 brakes feel springy with no air psi) some of that fluid goes to a plunger on the side of the air pack. This plunger then opens up an air valve that slams pressurized air into the huge rear cylinder. This pushed the huge piston forward. Since it is connected to the smaller front hydraulic piston, you now have pressure in the entire brake system which causes your brakes to stop the truck.

I over simplified the plunger on the side part, but you should get the idea. Putting air to the back of the air pack pushes that piston forward which pushes the hyraulic piston forward. In theory, it is the same as pushing the master cylinder itself.

That make sense?

 

[cbvet]

Thanks Barrman!
I figured it had to be something like that, but your explanation made it very clear!
Eric
CBVET

 

[Bill W]

Stretch
Is the shut off valve nessesary or precautionary.

 

[Stretch44875]

Shut off valve is needed. The line is vented without brakes being applied, so just blowing air in without the valve causes it to vent right out.

 

[cranetruck]

Kinda like the forward facing glad hand on the 5-tonners, note the Tee on the airpak.
Any failure in this connection and you'll be completely without brakes...this is where the tractor protection valve comes in.

 

[Rattlehead]

I am thinking of doing this on my deuce, but am considering a more permanent installation. If you install a double check valve where the ball valve is shown, wouldn't that work? One supply to the valve would be from the airpack valve assy, and the other supply would be from the air line to the front of the truck that is hooked to the tow vehicle. There are 2 outputs, so one would be plugged and the other would run to the airpack cylinder.

One other question to those that have hooked to the airpack when towing: Is there any delay in the release of the brakes of the vehicle being towed? Without a relay valve, when you release the brakes, all of the air in the towed vehicle's system has to be vented back through the tow vehicle's system.

 

[Stretch44875]

I've noticed a slight lag when releasing the brakes. But your only suppling air to one piston. Ball valve has to be open when braking normally, to vent the air.

 

[Sarge]

towing

What a great thread! Really useful stuff.
I wanted to add a quick blurb about how to make the lights work on the towed vehicle.
All of them!
Tracy (my old buddy in the military) taught me this trick.
You need a looong trailer cable. They are out there, they were made for towed loads like the M1022.
If you cannot find one, it's easy to make your own.
You take two old trailer cables, M105, M101 (whatever) and hook them together. Make them long enough to plug into the trailer receptacle on the towing vehicle, then all the way over (or down the side) of the towed vehicle. How do you make them long enough? Go to home depot and buy a couple of extension cords. Splice it all together, I don't have the pin-out handy, but it is on this website. Someone help me out here!
Okay, now your towed and tow vehicles are electrically connected.
The lights will not operate correctly.
So here is the big tip; disconnect the plug from the towed vehicle turn signal switch.
Ta-da! All lights operate (even the turn signals) on the towed vehicle from the tow vehicle cab. Kind of neat?
It's a good cable to carry with you when you are planning on rescueing me from BFE, Texas.
Thank you!
-Sarge

 

[Rattlehead]

Re: towing

The lights will not operate correctly.
So here is the big tip; disconnect the plug from the towed vehicle turn signal switch.
Ta-da! All lights operate (even the turn signals) on the towed vehicle from the tow vehicle cab. Kind of neat?

Sarge, where were you just yesterday!? I had to figure this out on my own. When I powered each turn or tail light, all of them would light up somewhat. I figured it must be backfeeding somewhere, and I knew there were no ground issues as trailer lights plugged into the truck worked fine. Then I thought about the turn switch and unplugged it, all worked well.

I have some temp lighting, but wanted to be able to activate the truck lights to save me from having to attach/detach the temp lights when hauling to a show. Plus for recoveries. I have a mil trailer connector that stubs out into a standard civvy 4-wire connector. Then I have a couple of different lengths of 4-wire cable with the 4 way civvy trailer connectors on each end. I even made up a "Y" so that I can tap into it for a LED yellow flashing magnetic light if needed.

I picked up a double check valve today, will try to get this plumbed into the truck. I am also thinking of making up a kit to bring along on a recovery of a truck that isn't prepped for brake activation. You would have to remove the J-pipe, but the kit would include the stuff needed to plug the valve side fitting and attach your air hose to the airpack can side fitting. If you remove the flare fittings, the size you need is 3/8" NPT.

 

[Stretch44875]

RE: Re: towing

Remember, you don't need anything other than a male 3/8 air nipple, in the back of the airpack, to hook brakes together. I just did the mod because I tow this truck often.

 

[Mark3395]

I'm going to try linking brake systems next week... maybe test the idea this weekend. I'm not up to speed on the systems so my quetions may seem odd, but I'm not clear from the links I followed.

A couple questions:

I understand tapping into the rear of the hydrovac after removing the j tube, but does the other hole have to be plugged?

I'd like to use an airhose to link the gladhands on the two vehicles. If I understand the text, that works too. Do hoses have to be linked to both sets of gladhands, or just the service brake?

Thanks much.

 

[Stretch44875]

You can use the glanhands only when towing a 5-ton that has the front gladhands.

Airline goes from service gladhand on towing truck-- airpack on towed truck. No need to plug other end of j-pipe.

Dennis