Advice on Buying a 5 Ton

[21lucian21]

I’m looking at buying a m813, the person selling says it’s full time 6x6? Is there anyway to change that?

 

[GopherHill]

I’m looking at buying a m813, the person selling says it’s full time 6x6? Is there anyway to change that?

Maybe download the -10 manual from this site. Will answer lots of questions. A good put you to sleep bedtime read.

 

[DeMilitarized]

I’m looking at buying a m813, the person selling says it’s full time 6x6? Is there anyway to change that?

not very familiar with the 809 series trucks but I believe you can change it between 6x4 and 6x6. if not you can always disconnect the front driveshaft.

 

[Floridianson]

Yes just by having an air switch or cutting off the air to the poppet valve. There is the rubber air line that goes from the passenger frame rail to the poppet valve on the Trans. If you do a switch valve you want to make sure the Transfer case air cylinder does not have any air held in forward or reverse sprag. After cutting off air switch between reverse and neutral a couple of times to drain air from sprag air cylinder. The you will have a neutral sprag.

 

[G744]

It is just fine the way it comes. The front drive is engaged automatically if needed.

The 800-series is the last 5-ton without the niggling electronic problems that affect operation of the later issues.

Buy it if the front drive operates as intended. A simple check is to let the truck build air pressure.

Then jack up one side of the front axle about an inch off the ground, and see if that wheel turns only one way. If so, it is healthy.

 

[Ajax MD]

It's "sort of" full time 6x6. The front axle does not engage unless the sprag is engaged by spinning the rear wheels faster than the front wheels.
You can buy a spare set of hubs and "de-spline" them but frankly, I'd just leave the whole thing alone.

Why would you buy a bull just to cut his nuts off?

 

[Floridianson]

I have owned plenty of 809 series trucks and never done the air cut off mod. Just said how it was done. Now you have to remember when off roading with the sprag working do not roll backwards while in any forward gear or neutral. Also do not roll forward while in reverse gear. This will lock up the sprag and become a problem. So as said do not push in the clutch and roll any direction if the sprag is not in the correct mode. Reverse gear puts it in reverse sprag and neutral or any forward gear puts it in froward sprag.

 

[G744]

^^This.

 

[msgjd]

I’m looking at buying a m813, the person selling says it’s full time 6x6?

1: "full time" is a common but incorrect misconception ...

2: 5-ton M39-series and M809-series trucks operate only as a 6x4 until there is rear wheel slip in either direction .. Rear wheel slip automatically engages the front axle. In slippery road conditions you can sometimes feel the front axle engage and disengage, especially at road speed, you can actually feel the front begin to pull you.. In off-road situations you rarely will feel anything at all .. I need not elaborate, everyone I see so far here has done a super job covering the bases involved

3: There have been occasions on blacktop long-hauls we have removed the front driveshaft, this saves on sprag wear .. But if you're not running long-distance and system is working as it should, a good rule is to leave it alone, it's not worth the extra time and work... But regardless of whether or not you alter the system, be sure the sprag gets enough exercise in both directions .. I get the occasional sticky sprag problem whenever any of the 5-tons sit idle for too many months