Rear Axle Gears
I recently purchased a set of 3.70:1 ring and pinion gears for the 9" rear axle in my 69 Mach 1.  I chose U.S. Gear because they are made here and have mostly good reviews.  Anyway, they come with a few teeth with gear marking compound on them showing the contact pattern from lapping at the mfg.  The drive side looks nice, centered on the tooth, the coast side is not very good at all, it is near the toe (inside edge) of the tooth.  I haven't built many rear axles, but I encountered this once in the past and I returned the gears for another set and all was fine.  My question is, are these gears going to make noise when coasting because the coast side contact pattern is not very good?  I'd rather exchange them now before trying to install them.

Man Mike, boy you are working the old brain to hard. I think you'll be ok, with the coast side being being closer to the center. It seems to me they whine when the coast side, is out at the outer edge. The pull side is the most critical as you know. I'm trying to remember for sure. but I think it should be ok. When you get the pattern out toward the outer portion of the ring gear is where you get your whine. I'd be dang sure to check the play, and back lash once installed. I know they come with a crush sleeve now a days. but that wasn't the case back in 69". So I'd probably check and set every thing just like we did years ago, with shims if necessary. Good Luck.

I'm getting older, but vaguely recall from a class on differentials back in the 1980's that a pattern close to the inside of the ring gear is stronger but has a tendency to cause noise.  And when you coast the ring gear tries to pull the pinion gear closer to it and walk the pattern to the inside.  I haven't done enough of these to go by experience.  So when things don't look textbook perfect I don't know what to do.  I got them from Summit Racing, I think I'll have them exchanged.  If the next set is the same, I'll use them.

I've researched reviews on different brands of ring and pinion gears and the consensus is basically avoid the value lines regardless of brand.  For every bad experience of a brand, there is always a good experience.  But, from people that do this for a living, they always seem to say, use OEM if possible, for aftermarket it's a gamble whether or not you get a good set.  From what I understand, there are only a few ring and pinion gear mfgs in the world, U.S. gear being about the only U.S. mfg.  All brands buy from these mfgs. then inspect them and determine which sets go into their value line boxes and which set goes into their upper end boxes.

I know MustangMike has had good luck with Yukon gears.  But, those are usually at least $100 more than other brands.  Plus, Yukon buys from the same mfgs. as the others.  Motive's performance line of gears, made in Italy, I've had good luck with.  Just thought I'd try a U.S. made gear this time around.

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