5 ton Sprag Switch

kubotaman

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I am looking for actual photos of the installation of the Sprag cut off switch that goes on the lines between the transmission and transfer case on an M39/M809 series 5 ton. I have read through almost all of the threads and have not seen any photos of how it is plumbed or seen the MWO that everyone references but no one has posted.

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Floridianson

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Sorry I don't have any pictures. The cut of switch / valve is not between the transmission and transfer case. The line you put the valve in line with is the rubber air line that comes off passenger side frame rail and supplies air to the poppett valve.
 
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simp5782

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I can take some when I get back to Memphis after the 29th if noone else posts any
 

73m819

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The MWO was not a total unit (all 39/809 series) but a user unit mwo meaning a unit using a 39/809 had a choice of installing the mwo or not. I got the mwo info from "Military Vehicle Magazine" about 2000, the reason given for this mwo was that soldiers were getting injured and trucks were getting tore up during front end lift tows due to the sprag operation (lazy recovery crew by not pulling cap or drive line as called for), the MVM article said that as a side effect of the mwo was the being able to put the sprag in NEUTRAL while on road use, the mwo was aimed at the 39 series but also pertains to the 809 series because the same sprag setup is used. The mwo called for a deuce front wheel drive air switch/light, fittings, hoses cut to fit to go from the air supply to the dash air switch then to the trans. air sprig control switches, there never was a "kit", just a parts list.
 

Floridianson

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I have not done the valve on any of my 5 tons. Thinking about it I might remove the rubber line from both frame and poppet valve. Then run Synflex line from frame to new valve where ever you want to mount it. Then Synflex from shut off valve to poppet. The only problem I see is if the line from the frame to valve then the poppet hold enough air to keep the sprag in gaged in the last shift. That's if you shut it off with an aired up truck. Seems like if the system had no pressure like before starting the truck then it would not be a problem. Guess if one was to be aired up and then shut off the air supply just work the shifter from reverse to neutral would dump the air pressure and the sprag would not be in gaged.
 
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73m819

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The deuce air switch has a built in air release when in out/off position.
 

Scar59

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Ron,
You list "air spring control switches" in the parts list. Is this a different switch than the M35 dash air control switch?
I have the dash air control switch and plumbing, trying to ensure I have the correct components before I start the mod.
thanks
JC
 

Floridianson

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Know you asked Ron yes the Deuce air control for the transfer case on the dash is perfect as it will dump any held air pressure. One would think if using the Deuce air switch and you wanted it on the dash then one could cap the old frame rail air line and just pick up air supply closer to the dash and then just run from switch to poppet. Lot less Synflex used.
 
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Scar59

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Know you asked Ron yes the Deuce air control for the transfer case on the dash would be perfect as it will dump any held air pressure.
I have the M35 front axle engage switch; the question is there an additional air spring control switch required? See Ron's last sentence where he list parts required.
 

Floridianson

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No think it's the poppets valves and that might be what the TMs calls the transmission sprag air controls.
Guess the Deuce switch has the light if you wire it up for those of us that are a little forgetful.
 
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Scar59

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OK, so the poppet valve remains in the system once the M35 front axle engage switch is installed. Ron's parts list is confusing. Hence, the MWO or schematic would be helpful.
 

kubotaman

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OK, so the poppet valve remains in the system once the M35 front axle engage switch is installed. Ron's parts list is confusing. Hence, the MWO or schematic would be helpful.
Yes, the poppet remains. The switch simply cuts off air to the poppet.
 

73m819

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The MWO was not a total unit (all 39/809 series) but a user unit mwo meaning a unit using a 39/809 had a choice of installing the mwo or not. I got the mwo info from "Military Vehicle Magazine" about 2000, the reason given for this mwo was that soldiers were getting injured and trucks were getting tore up during front end lift tows due to the sprag operation (lazy recovery crew by not pulling cap or drive line as called for), the MVM article said that as a side effect of the mwo was the being able to put the sprag in NEUTRAL while on road use, the mwo was aimed at the 39 series but also pertains to the 809 series because the same sprag setup is used. The mwo called for a deuce front wheel drive air switch/light, fittings, hoses cut to fit to go from the air supply to the dash air switch then to the trans. air sprig control switches, there never was a "kit", just a parts list.
Ron,
You list "air spring control switches" in the parts list. Is this a different switch than the M35 dash air control switch?
I have the dash air control switch and plumbing, trying to ensure I have the correct components before I start the mod.
thanks
JC
You read my fist post WRONG, I did NOT say "air spring control switches", I DID say "trans. air sprig control switches"

This mod is so simple, all it is turning on/off the air supply to the transmission poppet valves, How you do it is up to you, this could be anything from vice grips on the supply line to a supper duper trick valve and very custom install with a lot of bells and whistles, this is NOT rocket science and there is NO NEED to make it so. The military gave standard part numbers so parts could be sourced though the supply system for the mwo install and needed fixes.
 
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Scar59

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Thanks Ron,
I thought you may have misspelled "spring" w/ sprig. I'm clear now.
Kubotaman,
thank you too. I'll need to measure up some airline and get w/ the install.
JC
 

simp5782

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I found these on my phone. I will try to crawl under the 818 when I get back home


Basically you need a 4/3 way valve. Basically an On/Off/On switch. You plumb the reverse feed line to one side of the switch that comes from the transfer case. And a do the same for the forward feed line to the case. So basically you flip either way for going forward or reverse and when you flip back to center it puts the sprag in the neutral position. You can get your supply air for the valve from other places on the firewall and cap the frame rail line.

Sometimes that flipper valve can be hard to find. Easiest way is to add two TW1 switches that are one way on/off. Add one for forward and one for reverse and plumb it accordingly


KN20001 is a Haldex valve number for the on/off single valve
 

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Floridianson

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I found these on my phone. I will try to crawl under the 818 when I get back home
Basically you need a 4/3 way valve. Basically an On/Off/On switch. You plumb the reverse feed line to one side of the switch that comes from the transfer case. And a do the same for the forward feed line to the case. So basically you flip either way for going forward or reverse and when you flip back to center it puts the sprag in the neutral position. You can get your supply air for the valve from other places on the firewall and cap the frame rail line.
Sometimes that flipper valve can be hard to find. Easiest way is to add two TW1 switches that are one way on/off. Add one for forward and one for reverse and plumb it accordingly
KN20001 is a Haldex valve number for the on/off single valve
Why would you need two valves to control forward and reverse that's the poppet valve job. Just one Deuce air switch plumed into the air supply line. You could also use a air switch from a lift axle. Just as long as the switch relieves the pressure when off.

The question I have is why do this? Unless one plans on towing a truck with the front end lifted a lot, why?
Correct all you have to do is air down the truck and relieve any pressure in the sprag system if you tow it.
 
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kubotaman

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The question I have is why do this? Unless one plans on towing a truck with the front end lifted a lot, why?
Allows you to run locking front hubs/desplined front hubs, more control over the Sprag, and other reasons
 
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