Tested my 813 transfer case

[hvann]

OK guys here I go and I hope this all makes sense.
I have an 818 that is MO with my brother and he said the front wheels were not engaging in either forward or reverse. I have an 813 here in VA with me and I wanted to know if the front wheels would engage. I have just recently purchased both trucks. I don’t have tags on the 813 yet so I needed a way to test the functionality of the t-case without driving it somewhere.
I have been researching ways of testing the T-case on the site here and a lot of people talk about jacking up the wheel and checking that way but I was afraid that there may be enough resistance to keep me from turning the wheel but not enough resistance or engagement of the sprag to drive the truck forward. So I came up with the following way of testing the sprag for popper operation.
On my 813 I disconnected the drive shaft from the rear end and kept it in a rope sling so it could turn a little without causing any damage to it or anything else. (See the images) I wanted the shaft to rotate freely on the rope so it would not try to climb it or try to wrap in it, so I put some grease around the shaft where the rope would be in contact with it. I fired up the truck and put it in first and started easing out on the clutch. I could hear the clutch start to engage and almost immediately I heard the sprag engage and the truck started to move forward. I repeated the experiment in reverse and the front wheels would drive the truck backwards. There was an added benefit in adding the grease on the shaft. I could tell that the rear drive shaft only turned about a quarter turn in either direction before the front engaged.
I almost started putting the drive shaft back on when I started thinking about the questions about a neutral position on the T-case so I thought I would do some more experimentation.
I insured that I had air pressure and shut the truck off. I used a 2X4 between the clutch and the steering wheel to keep the clutch depressed. By depressing the clutch I was insuring the engine would not be keeping the drive shaft from turning.
When I talk about clock wise or counter clock wise you should envision looking from the rear of the truck to the front. So with the drive shaft disconnected from the rear end I was looking at the disconnected end of the shaft.
Here are my findings.
Air on system transmission in reverse, drive shaft will turn CCW but not CW
Air on system transmission in forward, drive shaft will turn CW but not CCW
Air on system transmission in neutral, drive shaft will turn CW but not CCW
No air on system, transmission in any position, the drive shaft will turn both CW and CCW
So this tells me that there is a neutral position on the T-case only when there is no air to it. So needless to say I will be putting the air selector valve in the cab so I can control air to the T-case.
I hope this makes sense and helps with the sprag T-case questions.
Van

 

[jwaller]

nice write up very helpful. I found out the hard way the other day that my front end isn't working in forward. not sure about reverse. I'm pretty sure mine works in reverse as it gives a good solid thunk and I can hear it come back to neutral when I come out of reverse. I just dont get any thunk when I put it in a forward gear.



I too will be adding the selector valve as was done by uncle same with an MWO on the 809's. the air line runs up the pass side and is the only air line on that side of the trans. it will be pretty easy as there is already a connection right there where it goes from frame to transmission.

one last question. could you determine if you get a forward sprag engagment in all forward gears or just 1st?

 

[hvann]

nice write up very helpful. I found out the hard way the other day that my front end isn't working in forward. not sure about reverse. I'm pretty sure mine works in reverse as it gives a good solid thunk and I can hear it come back to neutral when I come out of reverse. I just dont get any thunk when I put it in a forward gear.



I too will be adding the selector valve as was done by uncle same with an MWO on the 809's. the air line runs up the pass side and is the only air line on that side of the trans. it will be pretty easy as there is already a connection right there where it goes from frame to transmission.

one last question. could you determine if you get a forward sprag engagment in all forward gears or just 1st?

Thanks Jwaller
Yes I could tell that I was getting it in all forward gears. Basically the sprag has two positions it can be in when there is air on the truck. If in reverse the sprag is in the reverse position and when any other position on the transmission including neutral the sprag is in the forward position. With no air the sprag goes to the neutral position.
Van

 

[98hd]

It's been said that you must shift to 1st to get forward sprag engagement. Have you found this to be true? Just curious.

 

[hvann]

It's been said that you must shift to 1st to get forward sprag engagement. Have you found this to be true? Just curious.

Hey 98HD,

I found that just shifting from reverse to the neutral position would engage the sprag into the forward position. So, I can't say that you have to go into a forward gear in order to get it to go into a forward position. In fact, when I shift my truck from reverse to neutral, I can hear the air valves activate. No matter what I do after that point (unless I shift to reverse) I never hear the air valves again. So, this tells me that just pulling it out of reverse, sends the sprag into the forward position.

Hope this helps... Van

 

[emr]

My 813 's front axle did not engage on an snowy hill in my shop area a few years ago, so i waited a few months when i had time to try her again, and one day i took her out and started shifting around, i tried dumping the clutch once lightly, and than let her have it, well a large bang and the front wheels engage very nicely ever since......dug a very nice hole ...Randy

 

[jwaller]

I believe the first to reverse thing is ONLY for deuces with the sprag xcase. not the 5T versions.

thanks for your work. this helps clear the air.

 

[Chevytruck]

I believe the first to reverse thing is ONLY for deuces with the sprag xcase. not the 5T versions.

thanks for your work. this helps clear the air.

i thought the first to reverse thing was for airshift in deuces?? not sprag???


i could be wrong.. but i remember a thread about something of that