XM816 Wrecker - Only Took Ten Years

[msgjd]

1: Yeah, those black marks are telling the world your sprag isn't shifting between fwd and reverse position as it
should and the transfer case is getting bound up

2: Another situation is this: Did the truck get rolled forward while in reverse, or likewise got rolled backwards
while in neutral or a forward gear? Either of these scenarios will bind it up , even if it's just 10 feet

2: There's nothing that physically keeps you from putting the transmission/transfer in gear when self-recovering
with the front winch , but it's clearly not a good idea.. The winch doesn't spool at the same rate as truck
travel, thus it's possible to bind up the transmission/transfer if the tires grab some traction

 

[Flyboy207]

1: Yeah, those black marks are telling the world your sprag isn't shifting between fwd and reverse as it should and the transfer case is getting bound up

2: There's nothing that physically keeps you from putting the transmission/transfer in gear when self-recovering with the front winch , but it's clearly not a good idea.. The winch doesn't spool at the same rate as truck travel, thus it's possible to bind up the transmission/transfer if the tires grab some traction

What should I do to test/free the sprag? Those marks were only there after backing the truck off of the lowbed, I dont think I saw any when I backed up and turned into the driveway.

UNRELATED UPDATE:
Tried to run the crane a few days ago (still dealing with the bees), and couldn't figure out what I was doing wrong... Until I got underneath and found part of the driveshaft for the crane hydraulic pump was missing. Ordered a new stub shaft, boot and bearing, should be good to go (with some gentle breaking loose of the upper boot bearing) sometime next week.

 

[msgjd]

What should I do to test/free the sprag? Those marks were only there after backing the truck off of the lowbed, I dont think I saw any when I backed up and turned into the driveway

how exactly was it backed off? .. Rolling it down the ramps backwards in neutral (or a fwd gear) will bind it up if the air is up

When anyone is in a situation where they must freewheel an aired-up M39-series or M809-series backwards , the cheat is to put the tranny in reverse and put the transfer case in neutral.. That way the front output shaft is turning in the same direction as the rear output shaft while it freewheels (no power to the axles)

 

[Flyboy207]

how exactly was it backed off? .. Rolling it down the ramps backwards in neutral (or a fwd gear) will bind it up if the air is up

Exactly as you said. Rolled backward in neutral until the rear tires touched the ground, then into reverse and backed it all the way to where I took the picture. I didn't realize the rules yet.

 

[msgjd]

Exactly as you said. Rolled backward in neutral until the rear tires touched the ground, then into reverse and backed it all the way to where I took the picture. I didn't realize the rules yet.

If it didn't leave black marks after you drove it back and forth a ways, then you are good to go.. It apparently released the tension on its own .. Sometimes they do, sometimes they don't. When they don't, you can try shutting the truck off, drain the air, leave the drain open, start the truck and drive it forward or backwards until it feels like it's rolling freely .. If you push in the clutch and it stops like the brakes are on, it's still bound .. Basically, you have to go in the opposite direction that bound it up , unwind the clock... You can also jack up one front tire, but be careful, it might spin .. (PS: you should also jack one front tire up before removing any of the driveshafts)

If something in the system isn't working right, it can continue to bind up and feel like the brakes are on until you hear a big "bang!" and the truck jumps and pops you right outa the seat .. That's not a good thing but most of the time it won't break anything, but there have been times on blacktop where the "bang!" has damaged a sprag

You have to have good ears with standard-tranny 5-tons.. When shifting between reverse and neutral, listen for the poppet hiss.. And when you shift to change direction, or just as you let out the clutch, listen/feel for the "clunk" of the sprag .. The clunk means it has moved into position for the chosen direction of travel ..

The sprag is activated by the tranny poppet valve in two positions, being neutral and reverse.. Neutral on the tranny activates the default position of all forward travel for the transfer case sprag .. Clear as mud