Good point Joe. A sprag system is very sensitive to wheel diameter. If you
are running larger wheels in the front than in the back (even by a little
bit) you can bind the drive shafts, usually resulting in the busting loose
of the pillow block from the first rear axle. This is a real mess to clean
up. (note front wheels can be smaller than the rear but not larger.)
The problem with the sprag set up is that the adjustment must be spot on.
If it isn't it will slip and if it slips it will round out the teeth on the
sprag making it easier to slip again. This is where the problem gets messy.
Once messed up it's impossible to get it exactly right again. If you are
lucky enough to have a truck that was maintained well and not messed with
then you'll have little problems.
The key is the adjustment and wheel size.
----- Original Message -----
From: "Joe Foley" <redmenaced@yahoo.com>
To: "Military Vehicles List" <mil-veh@skylee.com>
Sent: Tuesday, July 25, 2000 16:46
Subject: Re: [MV] Sprag problem
>
> --- Buzz Szarek <buzz@toast.net> wrote:
> > Be careful who you listen to. This is a common
> > misconception about sprag
> > systems.
> +++++++
> What is?
>
>
> >
> > It is more precise to think of them as a one way
> > device. Like a ratchet.
> ++++++++++
> When I got my M-135 the back wheels had no power to
> them, one axle had a bad pinion, the other had a
> broken axle shaft. They had been running it on the
> front axle only. Because of the sprague clutch it had
> no "hold back" from the engine, it went down hills
> very fast. In consideration of your "one way device".
>
>
> > This is why it is critical to have the levers
> > between the trans and the
> > transfer case correctly adjusted (they select the
> > direction the ratchet will
> > free wheel). The most the rear wheels will slip
> > before the sprag locks is
> > just about a quarter turn.
> ++++++++
> Sure, if it locks up like it should.
>
>
> >
> > Nobody who has ever looked at a sprag assembly would
> > make the assertions you
> > have seen here.
> ++++++++++
> I've seen them, my M-135 has one, it doesn't always
> lock up the first time. It drops out and re-engages
> when shifting between forward and reverse. That's how
> it was designed, you can see that one the parts
> drawings, too.
>
>
> >
> > I'm basing this on my experience rebuilding the
> > transfer case in a 1954
> > M211. YMMV.
> >
> > Trust me, mine worked at all speeds and in all gears
> > (including reverse).
> +++++++++
> Yes, it does work at all speeds and in reverse, but if
> you shift between forward and reverse it WILL drop out
> and re-engage and if it doesn't catch the rear wheels
> will spin until it catches. They don't all work to
> spec.
>
> Still, I don't think his problem is the sprague
> clutch, it may just be that the rear wheels are
> binding together. I didn't want to see him tear his
> truck apart until he eliminated this possibility.
>
> Joe
>
>
>
>
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This archive was generated by hypermail 2b29 : Mon Aug 07 2000 - 22:16:04 PDT