Posted by Brian in Oregon on September 19, 2000 at 16:09:29:
In Reply to: Re: Better than 9" Ford axles (long, sorry) posted by Charlie on September 19, 2000 at 14:47:10:
Bigger is always better.
There are other variables besides pure diameter of the ring gear at play here.
I don't know how you are arriving at your match, but there is no way a Ford 9" ring gear is 23% weaker than the M37 ring gear. 23% is a huge number when you are talking about the forces these parts take. Are you saying the M37 ring gear and indeed entire differential will withstand the forces beyond what an 1800+ HP top fuel or altered dragster will put out or how about a Pro-Stocker or NASCAR? The 9" has been proven beyond the shadow of a doubt in these applications.
The real difference is in tooth contact area. This is not only controlled by the diameter, but also by the depth of the teeth. One would have to measure the actual contact area and the thickness of the tooth at that point. Also, angles or curves of the contact area play a major part as well. That is, does the design provide for total support of the tooth and speads that support over at least X many teeth?
Another factor is metallurgy. Is the metal in the gears and case of the M37 differential better than that of the 9 inch? Given that the M37 differential is circa 1950, and Ford constantly improved the 9 inch right up to circa 1970, says that this may well be a factor too.
Few are running anything but a stock flathead or a 318, 350 or 360 or a small diesel at best in their M37. The 9 inch has taken the torque from Ford big blocks in 4x4's with low ratio. There is no reason I can see why a 9" should not be capable of taking what an M37 can dish out.
I'm not saying the Ford 9" is THE most suitable for this application, but I don't think it can be dismissed as unsuitable so easy either.