A 3.73 gearset usually has a 41 tooth ring and an 11 tooth pinion. 41/11 = 3.727 or "3.73"

A 3.23 is generally a 42/13 = 3.230.

The 11 tooth pinion is probably almost the same diameter as the 13 tooth one, and the teeth may be a little thicker. Relative strength should be very similar.

"2-series" gearsets have larger pinions (2.73 = 41/15) so the carriers are thinner so the ring can be about the same thickness.

There are 9 inch Ford gearsets in the 6's. Pinion tooth count gets down to 7! A 6.14 is 43/7, and takes torque quite well.

My $.02

 

oldSS, in your opinion would how well the gears where aligned on setup be almost as large of a factor as the slight differences in size/strength?

-brent

 

Absolutely! If the contact pattern is wrong they will wear faster or break sooner...or both. IMO, that may be the second most important factor in failure after gross overload due to great traction from slicks and chassis.

Hypoid gears, or "spiral bevel gears with non-intersecting axes" are very strong, but also have lots of sliding motion between the teeth. Each ratio combination has a specific tooth size and angle. For example, you can't just take a 11 tooth pinion from a 39/11 = 3.55 set and run it with the 41 tooth ring gear from a 41/12 = 3.42 set to get a 3.73. Many production gears are lapped as a matched set after heat treatment.

If a stock F-body on production tires cuts a 2.2 60 ft time, for example, reducing that to 1.8 - 1.7 or so puts a great deal more stress on the ring and pinion. Production tires are the safety valve in OEM driveline breakage. Dropping the clutch (or "unfooting" it as a Brit friend says) at high rpm with slicks generates impact loads a stock 7.5/7.6 R&P was never designed for. Going to 9310 high-impact or strip-only gears can help in the tooth breakage, but they wear out VERY quickly due to the high rubbing loads described above and the softer surface of the teeth. Impact strength and long wear are mutually exclusive.

Sometimes an automatic, even with much higher torque going into the rear end than a stick, is easier on the gears than a bonzai start with the stick due to less impact.

My $.02