Can't engage 6X6 on 5 Ton 1971 M813

[njm1578]

I recently purchased a 1971 5 ton, and after struggling on inclines I realized that the previous owner had the desplined hubs on it, so I swapped it over to the splined hubs he included assuming that would solve my problem. After installing the splined hubs today it was still struggling uphill and the front wheels were not engaging. I did realize I did not have the transfer case switched to low gear, but does it need to be in low gear to engage the front wheels as well? If not, is there something on the dash I need to engage that I'm missing? I keep hearing there is an air switch, but unless I'm not seeing the switch, I wasn't sure if this was standard on a 71 5 ton or not. I hear the air in the system when I put the truck in reverse and I assume the sprag is good, but please help with any advice on to why I'm not getting power to the front wheels.

Thanks

 

[marchplumber]

Sprag is engaged when different wheel spin rates are in play. Maybe search out Sprag operation....sprag operates independently of driver....air shift is driver engaged. Idk if five tons came with air shift then, i dont believe so.

 

[NDT]

The rear wheels have to be turning faster than the front wheels for the sprag to auto-engage. High or low range does not affect sprag engagement. Your issue could be with the air operated sprag engagement system, or, the sprag itself could be shot. Hope it’s the first.

 

[US6x4]

The kind of owner that puts de-splined hubs on his truck may also be the kind that adds an M35-type pneumatic toggle switch to the sprag plumbing that leaves the sprag in neutral. This add-on switch is usually quite visible and typically wouldn't be hidden. Something to check for. Removing the tranny cover from the floor gives you the best vantage point to check the sprag plumbing which is on the RH side of the transmission.

It's been advised to check the tightness of the 4 bolts that hold the sprag air valve to the transmission to avoid problems and that one is free. A long rachet extension can gain you access just above the battery box between the frame and cab. 7/16" socket, I think...

 

[glcaines]

Also, make sure you understand fully about the issues that can develop when backing up in reverse with the sprag. If not done properly, the internals can bind up and even break components.

 

[njm1578]

The kind of owner that puts de-splined hubs on his truck may also be the kind that adds an M35-type pneumatic toggle switch to the sprag plumbing that leaves the sprag in neutral. This add-on switch is usually quite visible and typically wouldn't be hidden. Something to check for. Removing the tranny cover from the floor gives you the best vantage point to check the sprag plumbing which is on the RH side of the transmission.

It's been advised to check the tightness of the 4 bolts that hold the sprag air valve to the transmission to avoid problems and that one is free. A long rachet extension can gain you access just above the battery box between the frame and cab. 7/16" socket, I think...

Thanks for this, this is something I'll be checking when I'm back at the property where I have the truck sitting. I do remember seeing some wiring and what looked like a relay near the passenger door, so perhaps this is related to the switch, but I'll get a better look and also remove the transmission cover to se if I can see anything and I can circle back with pics since I'm not familiar with what I'll be looking at in the transmisiosn.

 

[country]

You MUST always start in 1st gear ( hi or low range) in order to have the Sprague " ready"

also maybe bad poppet



5T-643 | Poppet Valve Actuator Rockwell Transfer Case T-138 M54A2 M809
Poppet Valve Actuator Rockwell Transfer Case T-138 M54A2 M809
NSN #: 4820-00-832-7013, 2520-01-164-9274
Part #: 8327013, 8327108, N-12934
$200.00

 

[njm1578]

You MUST always start in 1st gear ( hi or low range) in order to have the Sprague " ready"

also maybe bad poppet



5T-643 | Poppet Valve Actuator Rockwell Transfer Case T-138 M54A2 M809
Poppet Valve Actuator Rockwell Transfer Case T-138 M54A2 M809
NSN #: 4820-00-832-7013, 2520-01-164-9274
Part #: 8327013, 8327108, N-12934
$200.00

Thanks Country, to be honest this may be my problem. I believe I've been trying to engage low gear while in neutral as if it were a modern day 4X4 system and I'm not hearing anything, so that might be my issue if I need to have it in first/reverse before lowering the lever.

I've attached a onedrive video clip below where I was trying to engage it in neutral which has no sound/affect, but you can hear the air system sounds like it's working properly, so I'm hoping I just needed to be in first/reverse to engage it. My other concern was at 55 seconds where it appears that even one set of wheels on the axle doesn't seem to be spinning at one point on the driver's side, so I wasn't sure if this was normal as well. I didn't get a chance to see what was happening on the passenger side, but I'm hoping engaging it in gear fixes this.

On another note, when I bought this recently I had to drive it home on the highway for about an hour and a half, and I didn't notice any issues with it on the highway, so if the sprag was shot, would I still be able to drive it normally in high gear without noticing any issues, or would there be noticeable issues?

Microsoft OneDrive

1drv.ms

 

[country]

Thanks Country, to be honest this may be my problem. I believe I've been trying to engage low gear while in neutral as if it were a modern day 4X4 system and I'm not hearing anything, so that might be my issue if I need to have it in first/reverse before lowering the lever.

I've attached a onedrive video clip below where I was trying to engage it in neutral which has no sound/affect, but you can hear the air system sounds like it's working properly, so I'm hoping I just needed to be in first/reverse to engage it. My other concern was at 55 seconds where it appears that even one set of wheels on the axle doesn't seem to be spinning at one point on the driver's side, so I wasn't sure if this was normal as well. I didn't get a chance to see what was happening on the passenger side, but I'm hoping engaging it in gear fixes this.

Microsoft OneDrive

1drv.ms

definitely start in 1st or reverse - hi or low doesn't matter

with an open differential- you can see one wheel sin and one not - this is normal

Detroit /no spin lockers in the rear can help - but do not suggest in steering axle



5T-2218 | No Spin Detroit Locker Differential Top Loader Rockwell Axle M54A2 M809 M939A1 M939A2
No Spin Detroit Locker Differential Top Loader Rockwell Axle M54A2 M809 M939A1 M939A2
NSN #: 2520-00-734-6970
Part #: 7346970
Price: $2,175.00

Snow chains help too



ALL-5014-11 | Snow Chain 11.00 x 20 Tire Chain
Snow Tire Chain
NSN #: 2540-00-933-9022
Part #: MS500055-2
Price: $79.00

 

[njm1578]

Thanks Country, I'll give this a try. Just to confirm are you saying to put it in first gear and then lower the lever into low gear, or can I engage the lever in neutral, and you're just saying I need to make sure I start moving in 1st gear rather than 2nd? I assume the later since it does appear all axles are moving in reverse, but I do believe I may have been starting off in 2nd gear moving forward, so that could have been the issue. I assume once the sprag engages in 1st gear, it'll remain locked as I shift into 2nd gear on correct?

 

[country]

Thanks Country, I'll give this a try. Just to confirm are you saying to put it in first gear and then lower the lever into low gear, or can I engage the lever in neutral, and you're just saying I need to make sure I start moving in 1st gear rather than 2nd? I assume the later since it does appear all axles are moving in reverse, but I do believe I may have been starting off in 2nd gear moving forward, so that could have been the issue. I assume once the sprag engages in 1st gear, it'll remain locked as I shift into 2nd gear on correct?

no need to switch ranges

leave it in high or low - wherever you started

stay in shift order 1,2,3,4,5

always start in first - or reverse for 6x6

 

[US6x4]

You MUST always start in 1st gear ( hi or low range) in order to have the Sprague " ready"

also maybe bad poppet



5T-643 | Poppet Valve Actuator Rockwell Transfer Case T-138 M54A2 M809
Poppet Valve Actuator Rockwell Transfer Case T-138 M54A2 M809
NSN #: 4820-00-832-7013, 2520-01-164-9274
Part #: 8327013, 8327108, N-12934
$200.00

Country, are there rebuild kits available for the poppet valve?

 

[njm1578]

no need to switch ranges

leave it in high or low - wherever you started

stay in shift order 1,2,3,4,5

always start in first - or reverse for 6x6

Thanks Country, this could definitely be my problem since I tend to start out in 2nd gear more times than not, so I'll make sure I'm in first and pulling up the inclines before I start shifting through the gears, and hopefully that's been my issue the entire time. It sucks being a novice to these 5 tons, but I'm hoping once I get it figured out I'll be able to enjoy it since I hear these things can really crawl up inclines well, I was just surprised out how it struggled initially, but sounds like the sprag and 6x6 kicking in will make all the difference.

 

[njm1578]

@country , any thoughts on if this is Sprag related or not? I went over to the property today and I'm still getting plenty of power to the rear wheels in reverse and first gear, but it still won't pull with the front wheels. I'm not sure if the Sprag is just stuck or if it's not related at all, so let me know your thoughts and if there's any other solution like locking hubs, which sound like they're not easily available.

Below is a link to video of what I'm seeing as a reference.

iCloud Photos - Apple iCloud

View, organize, and share photos and videos with iCloud Photos on the web. Changes will sync across your devices with iCloud.

www.icloud.com

 

[njm1578]

@country, to add to this, it does appear that the front drivetrain is working in reverse, but doesn't seem to be in 1st/forward, unless I'm just not seeing it in the video I attached. If it is moving I was expecting more, although I purposely buried it into that mud and into that boulder to see if the wheels were spinning. Let me know if this looks like it's operating the way it should on the front axle, or if it appears weak/not moving how it should. Once I get it unburied I can try it uphill since it may be just too buried to get out of the mud, but I was expecting the front axle to pull me out and it just doesn't seem like it's moving like it should.

https://share.icloud.com/photos/0aaFafdTTchwu9z2q7nG9ZyfA

 

[country]

@country , any thoughts on if this is Sprag related or not? I went over to the property today and I'm still getting plenty of power to the rear wheels in reverse and first gear, but it still won't pull with the front wheels. I'm not sure if the Sprag is just stuck or if it's not related at all, so let me know your thoughts and if there's any other solution like locking hubs, which sound like they're not easily available.

Below is a link to video of what I'm seeing as a reference.

iCloud Photos - Apple iCloud

View, organize, and share photos and videos with iCloud Photos on the web. Changes will sync across your devices with iCloud.

www.icloud.com

send me an email

 

[njm1578]

Thanks Dave, email sent

 

[G744]

A simple test is get the air system up to pressure, Set the transmission in first. Shut down the engine and and jack up one front wheel. Rotate it both ways, it should go one way easily, not the other. Then shift the transmission into reverse, and do the test again. It should rotate the opposite way easily, not the other.

G744

 

[Superthermal]

Detroit /no spin lockers in the rear can help - but do not suggest in steering axle

Not to derail the great chat about the transfer case engagement here, but any particular reason not to have a Detroit in the front other than potential slipping out when traversing very slippery off camber terrain?
I very much like locked front axles for wheeling and understand the side hill slipping thing and that is why we all have chains. But any other thoughts? In the M813 I have this is the perfect setup, as the front axle is "decoupled" which keeps the front steerable with no noticeable change at all from stock open diff. But when it is needed the traction is there no issue.
Just curious, not looking to argue or debate, just want to know your specific concern since this is how my rig is and if there is something you feel I should look out for.
Thanks!