Hey,
I was wondering if a set of 4.10's can be put on a 12 bolt 2 series posi using a spacer. Would it be better to use the 4.10's designed to be used on a 3 series carrier?? Have a chance to pick up a 2 series fresh for little money and was just curious.
Caleb

Not sure, but 4.10s for a 3-series "might" work with a spacer...

I have run the spacers before, and never had a problem (even when reusing the 20+year old bolts and beating the car with a four-speed...

All said though, why not just buy a new 3 or 4-series carrier??? You should be able to find a new Eaton unit for under $300 (check Tom's Differentials in So Cal...

Otherwise, you have to buy the spacer, and the used posi unit, and hope it is in good shape... Plus the added expense of bearings and installation... Might as wel invest the money in doing it the right way...

Well the reason I was looking at this 2 series is that a friend of mine is selling it and it is freshly rebuilt with new bearings for 100.00. I was just curious if this could be used with 4 series or the thick 4 series gears made for a 3 series carrier.
Caleb

what do the series mean. also why is it that it says u can only use certain gear ratios please explain

jocww the castings are different for the gear ratios used because of the pinion diameter. My neighbor has a new 12 bolt posi for sale and I believe it is a 4 series. It was in a GM box first time I saw it, but now the box and the part number are gone. These are the casting numbers I found on it. EDB-30174 8J 21 and on the other end where the gear bolts on 174. I can get a price if anyone is interested.

what do the series mean. also why is it that it says u can only use certain gear ratios please explainjocww,
as Phillip was saying, the castings are different between the 2, 3 and 4-series carriers...

Since the pinion gear diameter changes with the number of teeth (and the overall gear ratio), the teeth of the ring gear must keep the same clearance with the pinion. Therefore, either the ring gear thickness (from the mounting surface to the teeth)or the mounting flange on the carrier (where the ring gear bolts) or both, must change...

For the Chevy 12-bolt, its both... The carrier mounting flange, where the ring gear attaches, is moved slightly between the different series carriers (about 1/4 to 3/8 inch...).

For a 12-bolt: The4-series use "factory gears" from 4.10/4.56/4.88. The 3-series is used with 3.08/3.31/3.55/3.73s. the 2-series is used with 2.29/2.56/2.73s gears... So the "#-series" is not really an official term, but just that that carrier is generally used with gears in the # range...

Since the pinion for three series gears is generally larger than a 4-series. If you tried to put 4.10s on a 3-series carrier, the ring gear would not be close enough to the pinion... You would need to use a spacer behind the ring gear to get it close enough to use... Same thing with the 2-series with 3-series gear...

The aftermarket has stepped up with some hybrid gears, like 4.10s specifically for 3-series carriers, but GM never did...

For Chevy, 3-series and 4-series positraction carriers are available brand new, but the 2-series is not... Not too much call for 2-series, and not even any "new" gear available...

All rear ends are different... For example, Ford 9-inch rears use the same carrier for all ratios...

ok thanks. but what if i wanted to use 3.55s but at the race way 3.73s or 4.11s

Changing ratios is not easy. If you want to change for racing and then back to street it would be best to have 2 complete rear ends and change back and forth or install an over drive unit.

I would add that this is the wrong forum for differentials to be discussed.

Realized after I posted that it was in the wrong forum. Oooops.

2 rear ends thats alot more money though. my dads friend said that he use to be able to change rear gears in 25 min when he was young but now he's like 60 or so and can barley bend down to see his frame