I want a 4.11 or 4.56 Ring and Pinion. It has 28" dia. tires on the back. Some of the lower ratios on this differential 4.11 and 4.56 ,says that it will only go in a 3.23 or higher case. My ration is 2.75 so does that mean I can't put these lower gear ratio in my car or should I be looking at other Ring and Pinion sets.Or am I misunderstanding the whole thing.

 

There's no such thing as a 2.75 rear gear ratio. You have either a 2.73 if it's a 10-bolt, or a 2.77 if it's a 9-bolt.

So let's start there... do you have a 9-bolt, or a 10-bolt? , You say 10-bolt; are your SURE? (No I'm not implying that you're too stupid to count, only, MAKE DOUBLE DAMN SURE) What kind of car is this? What year, what engine, what are the codes in your RPO list that start with G?

Given that info, maybe we can help.

 

I have a 87 Camaro with a 10 bolt differential It is 2.73, It has a transplanted 355 in it. The Differential is original.

 

Differentials (carriers) for almost all kinds of axles come in "series". For the 10-bolt, there are 2 series, and 3 series. The break is between 3.08 and 3.23. Some models of rear have more series than that.

The reason they exist is because the ratio is NOT ONLY between the tooth counts, BUT ALSO between the gear diameters. Which means, since the ring gear is always the same size regardless of ratio, that as the ratio goes UP, the pinion diameter goes DOWN. The 2.73 pinion is MUCH larger than, say, the 3.73. Therefore the ring has to be thicker, as the pinion teeth "move away" from the ring gear flange on the carrier. But it's EXPENSIVE to make thicker ring gears - they tend to warp during heat-treating, which scraps them - so what the factories do instead is to start out at the lowest ratios with the ring flange on the carrier as far away from the pinion centerline as it needs to be to accommodate the appropriate thickness of the ring; then as the ratio increases, the ring gets thicker; then at some point, they move the flange over toward the pinion CL, and start over with thin gears again.



2 series on the left, 3 series on the right. The 2 series happens to have a ring gear still mounted on it, the 3 series does not. Note how the flange is about .400" further toward the pinion on the 3 series. Observe how on the 2 series the flange is mostly flat on the back side, whereas on the 3 series, it's very much cone-shaped. Both of these are crappy Auburn carriers, but no matter whose you get for this model of rear, they will have that difference.

So, using stock gears, there's NO WAY to put a 3.23 or higher ratio (3 series) on a carrier that is for 3.08 and lower (2 series). There's NO WAY AT ALL to put 2 series gears onto a 3 series carrier, because the ring gear would have to have NEGATIVE thickness. (not in my universe!!) However there are plenty of aftermarket suppliers who make "extra thick" 3 series gears to fit on a 2 series carrier; they cost more than standard ones, because of the production yield problem. Imagine how much thicker a gear would have to be, to take up that .400" or whatever... for me to just say .400" is one thing, but the photo gives you an idea how thick such a gear really is. It's like TWICE as thick as a stock one, or more.

Butt: consider what I just said about you can't put 2 series gears on a 3 series carrier. Well, once you get those "thick" gears, you can't use them on a 3 series carrier either. Problem there is, there are ALMOST NO GOOD CARRIERS AT ALL available in 2 series, because no one in their right mind wants that. People want 3 series gears. So if you buy the "conversion" gears, you're stuck with your old carrier. No (or at least, far fewer) upgrades are possible, because the mfrs simply don't make them, due to lack of demand.

For some kinds of rear, they make a spacer or adapter, that you can put behind a regular 3 series gear to mount it on a 2 series carrier. Butt, in this particular model of rear, the carrier OD is so large compared to the ring ID, that there's no room to put a locating "step" on the adapter, to keep the ring perfectly centered. So for the 7½" 10-bolt, that's not really an option either.

Bottom line is, you need to be looking at both gears, and a carrier. Especially since your carrier almost certainly isn't a posi. Yet another thing NOBODY wants; a one-wheel-peel one-tire-fryer wonder.

 

That's fantastic information, Thank you, so I will be looking at Ring and pinion and carrier. I'm open for suggestions on parts, limited budget but understand the need for good parts. Again thank you for taking the time to advise.