List,
Trust me...I prefer the airshift over a sprag any day. I, too, like the ability to engage the front axle before I need it. I agree with the posters who do not want to have to begin slipping before the front wheels engage. However, I think some are overstating the importance. I have two things to say:
(1) How many of you have actually seen how quickly the front wheels engage with a sprag when the rear wheels slip? It happens almost instantaneously. It is barely visible. How much slippage occurs before the front wheels engage? Not much, I'll guarantee you that.
(2) What about all of us M809 series or earlier 5 ton owners? None of the 5 tonners, until the M939 series trucks, had air shift front axles. I have never heard a 5 ton owner complain about it...probably because they (we) don't know any different in these trucks. Again, yes, I would prefer an airshift, but NO I do not think it is that big of a deal. I agree with David Doyle who said that a sprag is fine, as long as it is operated properly. One of the things this means is NEVER letting the truck roll backward in a forward gear and NEVER letting the truck roll forward in reverse. Doing so causes sprag windup. This is one of the leading causes of sprag failure. To avoid doing so, the "10" manual directs the operator to engage the parking brake when on a grade, only releasing the brake after the truck has started pulling. Yes, the manual suggests riding the parking brake for a moment.
My .02 cents,
Bruce
1957 M125 w/w
1968 M172A1
1972 M52A1
1972 M35A2C w/w
1982 M548A1 w/w
1984 M929
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