Posted by Brian in Oregon on September 19, 2000 at 12:22:40:
In Reply to: hey ray suiter-- i saw something you might be interested posted by mannyc on September 19, 2000 at 11:06:01:
I thought about this, and am familiar with the Ford 9". I'm not familiar with the M37 axle assembly itself to know whether this would work or not.
Ford 9"'er are the rear end of choice for many racing applications.
They are reasonably simple to work on, swap out easily as a unit, and particularly with the double ribbed nodular iron case are bulletproof.
There are also aftermarket aluminum cases for weight savings (not that it amounts to a hill of beans for an M37).
The factory Traction-Lok differential (ie - "posi") works very well. I beat hell outta one for several years of drag racing and daily driving. It would be the best solution for the those not happy with an open differential for the front axle, being much more friendly than a locker. And the Detroit Locker is a bulletproof combo for the rear. I believe an ARB Air Locker is available.
A differential swap, if you've had some practice, can be done in under 30 minutes. This made the 9" very nice for running 3.25 or 3.50 on the street and swapping in 4.57's for the drags and Saturday night cruising. Obviously that time line wouldn't apply to the M37 front axle. But, imagine this - you could cruise to a military vehicle rally a couple of states away with your 3.91 or 4.11 gears in the rear (not needing four wheel drive) and within a few minutes pull the pumkin and swap in the 4.88, 5.13 or perhaps they have 5.83's (I'll have to check on that one).
Gear availability is virtually unlimited. Back when I was racing, 5.13's were the lowest available at that time, but I'm sure with these being popular for rockclimbing that lower rations are available now. Performance gears were 3.50, 3.70, 3.91, 4.10, 4.11, 4.30(!), 4.57, 4.88 and 5.13. All but the last three were available factory installed, and the 4.57 and 4.88's were available over the dealer counter. The 5.13's were aftermarket. (Now most are aftermarket.)
My partner and I managed to blow up some single rib cases. But never a double rib, even the non-nodular double rib.
Keep in mind that there are three spline sizes used in Ford 9" differentials. The spline itself is not weak, rather it is the axle itself that counts. The 28 spline is the most common, and the weakest axle. The 31 spline was Ford's performance axle. I never ruined one. My partner used a 33 spline setup from Strange Engineering. Bulletproof.
If it was up to me, I'd go with 31 or 33 splines with a heavy custom axle shaft. I would also put a reduction in diameter just before the axle flange as a break point. This would make fishing out a broken axle shaft easier. Given my experience with Ford 31 spline 9 inchers, most likely something else would break, like the u-joints.
I'd be REAL interested in a conversion that used a Ford 9".