QUESTION- I've heard that the 3.54:1 ring and pinion gears are stronger than the 4.7:1 ring and pinion gears and switching will make my differential stronger.
ANSWER - This reply comes from Bill Davis in the mendorecce Land Rover e-mail list:
One of the common misconceptions about Rover ring and pinion gears gears is that 3.54 gears are substantially stronger than 4.70. This is not correct. The inaccurate information that propagates this myth is that the size of the pinion gear is the major determining factor of the overall durability of the gear set. In reality the most crucial factor is the size of the ring gear teeth. A 3.54 gear set has 46 teeth. A 4.7 has 47 teeth so there is very little difference in ring gear tooth size and hence not much difference in overall durability.
Why are the ring gear tooth size more important? Think of it this way, the pinion gear teeth are always larger than the ring gear teeth. It doesn't matter whether you have a 3.54 or 4.7 ratio's. Whether you have a hypoid or non-hypoid design. It just doesn't matter because the pinion gear teeth are always larger. So assume you shock load a differential gear set hard enough to break a tooth. Which tooth is going to break? The larger tooth (pinion) or the smaller tooth (ring). If you answered - the smaller tooth, you are correct. The cross section diameter of the pinion gear is not really much of a factor.
Along these same lines, all aftermarket gear ratios are actually more durable that both stock ratios. Here are some examples with ring gear tooth counts - 3.9 (39 teeth), 4.1 (41 teeth) 4.11 (37 teeth) 4.14 (29 teeth), 4.43 (31 teeth), 4.71 (33 teeth) and 4.75 (38 teeth)
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