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Modifying Airpack Plumbing to Lock Brakes or be Towed.

M37M35

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I was searching for info on rebuilding the airpack and came across this thread.

And that got the gears turning... I've been wanting to add a brake line lock to my deuce for winching operations, as the parking brake just doesn't cut it for that.
It seems the majority of the ones on the market now are called 'launch control valves' and use electric solenoid valves. They say they are only for momentary use because the electric solenoids will burn up. I did find a few old-school mechanical ones, which is what I'd go with. But some of the info for both kinds said not for use with silicone brake fluid, which I found odd.

Anyway, the above thread got me thinking... What if a simple 3 port-2 postion air valve was plumbed into the J-pipe on the airpack?
The common port goes to the large air chamber.
Port 'A' goes to the front of the airpack.
Port 'B' goes to the air tanks.
When the valve is in position 'A', the front of the airpack is plumbed to the air chamber, port 'B' is blocked, and everything functions normally.
When the valve is in position 'B', system air is plumbed to the air chamber on the airpack and port 'A' is blocked. The brakes are now applied.

This valve could be located under the drivers seat close to the airpack so the air lines are short. That would eliminate two connections and an extra device on the hydraulic side that would result in total loss of brakes if they failed. Failure of this air valve or the lines to it would only result in loss of brake boosting, not total brake failure. It would also be easier to install as air line is easier to work with than the brake lines, and the brake system won't have to be bled afterwards.

Another benefit would be to use a 3 position valve instead of the 2 position, then plumb port 'C' to a gladhand on the front of the truck. If the truck needs to be towed, simply put the valve in position 'C' and the towing truck controls the brakes on the towed truck like with the mod in the above link.

The biggest downside I see to this is possible damage or premature wear to the airpack from applying full system pressure to it for longer than normal during winching operations or what have you. But that could possibly be eliminated by regulating the applied air down to the minimum pressure needed to hold the truck stationary.


For those of you with more knowledge about this system than I have, did I miss something obvious, or could this work?
 

M37M35

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Well my searches only turned up this idea in one other thread, and nothing ever came of it.

So............
Brilliant idea?
Awful idea?

Unless someone tells me why this won't work, I might just give it a try.

Thoughts?
 

cattlerepairman

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M37M35

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Thanks for the links, but I found those during my initial search and they aren't really relevant. They talk about line locks on the hydraulic side of the brakes, which I already know about. And it's asked about applying air to the master cylinder cap to apply the brakes, which I know won't work.
They don't discuss applying air to the airpack to apply the brakes.

I guess I'll just have to be the first test case and see if it works like I think it should...
 

cattlerepairman

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There is a subtile suggestion in these links that locking brakes based on air pressure is unsafe.

I find your proposal interesting and notice that the military went for hydraulic line locks instead. Just for discussion, I was also wondering what specific problem this setup would solve on a Deuce. In order to operate the winch the operator needs to sit inside the cab. All that is required to lock up all six brakes is to keep the foot on the brake when winching. The wreckers have line locks because they have a drag winch operated from outside of the cab - makes sense. Otherwise, is this going down a complicated path for a solution in search of a problem? No judgement. Just asking.
 

M37M35

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Gotcha. Well I've never been good with subtle.

A big part of this post was thinking out loud, and trying to find out if anyone else had tried this before. Apparently nobody has.

No specific problem, just thinking it might have some benefits over a line lock. It would be cheaper and easier to install. It's easier to run plastic DOT air line to a convenient place than metal brake line. If the line lock or one of the hydraulic lines to it failed while driving, it would result in total loss of brakes. Failure of an air valve or air lines going to it would only result in loss of brake boosting, not total brake failure. Also, keeping constant air pressure to the airpack would maintain more consistent pressure on the brakes than a line lock would.

For operating the front winch, yes. But you saw my other thread asking about PTO horsepower and adding a rear drag winch. If I power the rear winch hydraulically, I'll set it up so I can operate it from outside the truck or with a remote, and I'll need all the brakes locked.

I'm always up for discussion and ideas, and that's what this thread is about.
 

Jakelc15

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I like this idea and think it will be very useful while winching.
Need to use a double check valve like a M809 to supply the chamber with air from 2 sources. A transfercase air shift valve would then work perfect to supply air and vent when turned off.
 

clinto

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M37M35

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So I got curious and tapped a pressure gauge into the J-pipe on my airpack. Applying the brakes normally, as if coming up to a stoplight, the airpack receives about 60-70 PSI. When pushing the brake pedal hard, like during an emergency stop, the pressure is over 100 PSI. (That's as high as my gauge went) So applying the full 120 PSI system pressure shouldn't be an issue.

When I get a chance I'll temporarily hook system pressure to the airpack for 30-60 minutes and see how it reacts. If that works okay, I'll order an air valve and plumb it in.
 
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