m818 transfer case engagement switches

[MT4222]

How do I add in the two switches in order to convert the m818 from sprag to air actuated? I know I will need 2 switches. One for forward and one for reverse. Thank you

 

[Jakelc15]

The search works.
You only need one switch (flipper valve), and it will still be a sprag transfer case.

 

[MT4222]

I cant find it so please direct me where to go

 

[augiedoggy]

Ok, the 809 series transfer case spragues are air actuated by the poppet valves on the transmission.
Reverse is one valve and Neutral and all forward gears are the other valve.
As designed it is one or the other. A field modification was to add a deuce front axle switch
to cut the air supply to the trans poppet valves, thus putting the sprague selector ( on the transfer case)
in neutral and disabling the front drive. It is spring loaded and with no air it, it's in neutral.
Personnally, I just put a ball valve on the air supply line (to the poppets) under the truck, and just flip it off for On road use.
Hope this helps.

 

[MT4222]

Thank you very much. What my problem is that I am unable to go into front whhel drive when I am going forward but the axle will engage when I am in reverse. If anyone has any ideas as to what is malfunctiining please let me know. By the way it is a bobbed m818 on 53's

 

[73m819]

Thank you very much. What my problem is that I am unable to go into front whhel drive when I am going forward but the axle will engage when I am in reverse. If anyone has any ideas as to what is malfunctiining please let me know. By the way it is a bobbed m818 on 53's

Try draining the transfer, fill with diesel, run the truck up and down the road bit (DO NOT PUT A LOAD ON THE TRANSFER), drain and see how much gunk comes out, keep flushing till no gunk, refill with oil, see if front engages, if not then we can go from there.

 

[Floridianson]

I have to disagree the 800 transfer case is not spring loaded. The Deuce is not 5 ton. There is no neutral pisition. The piston will in the last pisition the air was left in.

I have questioned this many times before and dont realy care for this mod. The answer is fix the piston seals and or check you poppet valve for correct working. If those are working then your looking at a new sprag unit.

 

[augiedoggy]

I have to disagree the 800 transfer case is not spring loaded. The Deuce is not 5 ton. There is no neutral pisition. The piston will in the last pisition the air was left in.

I have questioned this many times before and dont realy care for this mod. The answer is fix the piston seals and or check you poppet valve for correct working. If those are working then your looking at a new sprag unit.

Florida, you have far more experience than I do, and I totally agree about the piston seals being the problem.
After reading about the field modification to the 5tons (was it the Marines?), I did the mod and verified that the front drive was indeed in neutral. By the way, I tried to change the seal that allows air to leak into the transfer case from air actuator and could not find it, any pointers?

MT4222, check those transfer piston seals and, the poppet valves can be tested by disconnecting the air lines to the transfer case and with LOW air pressure in the truck (don't get hurt!), see if air comes out one hose in reverse and the other hose when the shifter in in neutral or 1st gear. Also the air must vent or release when shifting in and out of reverse.
That's the pssst you hear when shifting in and out of reverse.
Then, if all that works,like Ron said try to clean up the spragues. They get gummed up and lazy from inactivity.
Helpful tip on sprague piston service, take the 4 bolts and top cover off, then take the piston nut off down inside the piston, and take the cylinder and piston off together (very simple).
Test the spragues by jacking up one front wheel and with full air pressure, in reverse the tire should roll one direction only and in 1st gear it should only roll the other way.
Hope this helps,

 

[Floridianson]

No problem Dan. I thought there was a talk between me and Ron this mod was used for when we lift towed the truck. Like I said if you put the case in forward sprag then cut off the air just always go forward. By useing the air cut off then in theory we would before rolling backwards as the last time it was shut off the sprag was in forward now we have to turn on the air and put it in reverse sprag. This to me is just to much to think about and if we have a driver that does not understand this mod there could be problems. When all is working with the air sprag system that was first installed it works fine and dandy.

 

[Squirt-Truck]

Sorry guys, the 5-ton case for both the M-39 and 800 series is spring loaded to neutral. The towing and recovery manual also refers to this, if the front wheels are towed off the ground release the air to prevent engagement of the front axle. If your transfer does NOT go to neutral with the air OFF then you have a stuck piston or broken spring. Please note that some of the front axle disengagement mods were done WRONG and do not remove the air but try to balance the air pressure and that is a bad thing . (Just ask 73m819. . . )

 

[augiedoggy]

Florida, I see what you mean and that was a situation I had not considered. Even worse would be if a flat towed 5ton were aired up as designed for brakes, the forward sprague would be engaged. And when backed up.....not good, unless the front driveshaft were removed.
Any help on my air leaking into the transfer case?
Thanks,
Dan

 

[73m819]

Just so EVERYBODY knows, I DID NOT do the MOD on my 819, it was the way it is when I brought it, more likely done by the military because the dumping the air mod is not well known in the civi world, I learned of it though a old MV mag. many years ago. The why the mod was done worked fine TILL the rear poppet valve started to leak, hence NO neutral, found this the hard way on the way to Daves BBQ, had to drop the front drive shaft, as of NOW the military mod is DISCONNECTED, WILL do the CORRECT mod

 

[Squirt-Truck]

Ron, I did not mean that you had done it, but that you were a victim of it.
Seems like we had that discussion and you were as baffeled as to what had been done as any of us, but you figured it out.

So if anyone misunderstood, I apologize.

 

[73m819]

No, not you, there a few that would JUMP to conclusions, surprised that one of them has not posted yet.

 

[Floridianson]

Sorry guys, the 5-ton case for both the M-39 and 800 series is spring loaded to neutral. The towing and recovery manual also refers to this, if the front wheels are towed off the ground release the air to prevent engagement of the front axle. If your transfer does NOT go to neutral with the air OFF then you have a stuck piston or broken spring. Please note that some of the front axle disengagement mods were done WRONG and do not remove the air but try to balance the air pressure and that is a bad thing . (Just ask 73m819. . . )

No disrespect but are you going by what the TM says or have had one apart to change the piston seals. Last time I did two of them the sprag shaft moves free from forward sprag to reverse sprag with no spring pressure?

 

[Floridianson]

I'm going to take one apart today and see if I'm wrong.

 

[Jakelc15]

Just jack up a front tire and spin the front wheel. With air it will lock up, no air it will spin free forward and reverse.

 

[Floridianson]

Im going to take the transfer case air cyl. apart but thanks.

 

[Jakelc15]

TM 9-2320-260-34P-1 Section Il. Figure 148. Transfer Shift Mechanisms

Shows the clutch fork for forward and reverse. The piston has identical springs on both sides of it.

I sure hope when you take it apart it confirms that it is spring centered into neutral. I've put hundreds of miles on mine with the air dumped off. Thanks for taking the time Floridianson to take it apart so we know for sure.
The reason why I assumed it has a neutral is because in the Army they would plug off the forward air line on the transmission. That way the front axle would only engage when in reverse. Guys would drive the trucks into stuff they shouldn't have been in (imagine that) and instead of getting stuck they could always back right out.

 

[Floridianson]

[QUOTE=Jakelc1
The piston has identical springs on both sides of it.


I believe the spring you see in the TM are only there to stop the pistion from being slamed into the transfer case or the the end cap at 100psi. shock load on the sprag.