Re: AMC Model 20 rear end parts swap discussion part 99

[farna@xxxxxxx]

I'm not so sure the aftermarket carriers have the ring gear mount flange in a different position than the factory. Otherwise the gears wouldn't fit a factory carrier. I've only seen one or two manufactuers note that certain ratios they carry (usually the real low ones, 5.xx for Jeeps) won't fit factory carriers, but I don't mess with many gear changes like Randy has. 

One point Randy made really stands out: there's more than one way to make the same ratio, and that explains an aftermarket company having a different "break point" than the factory, like the example he gave. 

On January 16, 2005 Randy Guynn wrote (and I edited down further):

> If you already ''know it all;''  on Model 20 rear ends,then don't bother
> reading this as you could not possibly learn anything from it. If you
> are teachable you might just learn why there is so much confusion over
> model 20 gear/carrier swaps.
> 
> Tom Bunsey, you are right. But also the Aftermarket is right Where the
> problem comes from is Factory parts and Aftermarket parts. Just because
> a certain gar ratio in Factory gears fits in Factory carriers does not
> mean that every aftermarket gear, or carrier will affect the same swaps.
> 
> You have to understand that the aftermarket carriers that are advertised
> as 3.08 and up gears really do fit the gears advertised.Just because a
> gear ratio is say, 3.08 does not mean that every manufacturer arrives at
> the 3.08 in the same way.
> 
> Example a 3.08 AMC Factory gear is a 13/40 count but a Precision
> aftermarket 3.08 gear is 14/43 count.
> 
> One thing that is 100% constant in all rear end applications is that the
> Pinion gear is always located in the exact same place in the housing.
> So, with that in mind, you can easily see that when the number of teeth
> on a Pinion gear increases, the gear gets bigger in diameter. Since the
> centerline of the pinion never changes, then it stands to reason that
> the Ring gear gets Thinner as the Pinion gear gets bigger. The reason
> there is more than one carrier is because they moved the Ring Gear
> Mounting Flange on the 2.73 and 2.56 model carriers because the pinion
> had grown so large that the ring gear was too thin for strength needed.
> So, they move the flange.and the ring gear can then gain more width and
> be strong enough to not easily break.

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