1979 5-ton - on demand 4-wheel drive

[javedev]

I have a 1979 AM General 5-ton with air-engaged transfer case and I want to re-plumb the air to select 4-wheel drive on demand - in all gears. Am told that it is usually just available in first and reverse. Any suggestions? Thanks

 

[doghead]

You do have all wheel drive in all gears now. Look in the resources section for the tech manuals, read up. If you don't shift it correctly you will cause damage to the transfer case.

 

[ida34]

The front axle will engage when the rear is slipping while in all the forward gears. When you put it in reverse the air shifting mechanism engages the rear traveling sprag. When you shift back into neutral the airshift mechanism puts the transfer case back to the forward traveling sprag. You still get all wheel drive whether in 1st or 5th. The sprag is an overrunning clutch that engages when the rear axles start going faster than the front axle. When the clutch engages power is sent to the front axle. You still have all wheel drive all the time. The airshifter only tells the transfer case to look for forward or backward slip. If you had manual switches and accidentally engaged the front sprag while you were traveling backward the drivetrain would bind up and something expensive would break. My suggestion is to make sure your system is working properly then leave it alone. You have been misinformed about the lack of 6x6 in higher forward gears.

 

[ida34]

I almost forgot. Welcome to the forum and where in Michigan are you?

 

[javedev]

I am in just south of Traverse city. Thanks for the information, however, still a bit confused. Could I call you to discuss this (would you give me your number)? I have two 5-tons and an am using one for parts but neither seem to be working correctly. Thanks again. Jose

 

[ida34]

I could try to help you but I am new to the five ton system and someone else straightened me out a month or so ago. I am still waiting for my EUC to clear on my five ton. Some of the other guys who have taken the system apart can probably help you better.

To get the ball rolling, what are your symptoms and are both of your trucks 800 series?

 

[javedev]

I have no front wheel assist in any forward gears, high or low range. The only time I hear air activate or engage is going in and out of reverse. I have no front wheel assist in any forward geras.

I am headed out to work on it some more now - will check back later. Thanks for any help.

If anyone can help me out I can be reached at 231-409-6567.

 

[javedev]

Oops. My trucks are a 1975 Kaiser Jeep 817 and a 1979 AM General 813.

Thanks again!

 

[area52]

How do you know that you don't have "front wheel assist"? The air hiss is normal and there also should be a "clunk" which indicates the air valves are working to "tell" the transfer case if you in forward or reverse.

 

[javedev]

What tech manual addresses 800 series forward gear engagement?

 

[doghead]

Look on the dash tags on the right side of your truck for the manual numbers. For starters

 

[m139h2otruck]

The M51/52/54 trucks and the 800 series use more or less the same transfer case and air shifting system. With the air system charged (at least 75 psi or higher), and the engine off, just jack up the front end (both sides) and try to rotate the wheels with the transmission in a forward gear. If the sprag is OK, the wheels should rotate in one direction but not the other, and with the transmission in reverse, the wheel rotation should be reversed. With no air in the system, the front end will free-wheel like a normal part-time 4 wheel drive pickup. The Army really did a good job on this system, and if everything is tight and working right, it is almost dummy proof (notice I said almost).

 

[ida34]

I have heard that the air system can get gummed up. You may want to take the shifter out and clean it. If that does not help then you should clean the engagement cylinder in the T-case. Either way you need the manuals from the Tech section so you don't accidentally mess something up. Again, I have not done it so I can't help past the stuff I have already posted.

 

[houdel]

Re: RE: 1979 5-ton - on demand 4-wheel drive

I have no front wheel assist in any forward gears, high or low range. The only time I hear air activate or engage is going in and out of reverse.

With the sprag setup you will NOT have front wheel assist unless the sprage senses a speed differential (i.e., wheel slippage) between the front and rear axles. You should hear the air activation every time you shift between FIRST and reverse, all that is doing is selecting the front or reverse sprage, but the sprage will not engage unless there is wheel slippage.

 

[wdbtchr]

RE: Re: RE: 1979 5-ton - on demand 4-wheel drive

I had the same problem with both my 5 tonners,'65 m51a2 and '67 m54a2. In both cases it was the air valves on the shifter. My sprags engaged only in reverse, the seat in the forward valve was worn too deep to allow air to pass. I got kits from Memphis Equipment and rebuilt both, work fine now.