Swapping 2.56 rear axle to...?

Hi all,

Looking for some thoughts from you all regarding swapping out a 2.56 in my '96 RMW. I've read through the posts here and have a few questions before jumping into the swap. It seems a 3.23 posi is going to be the best compromise of highway cruising and driving around town. I'll be driving on the interstate most of the time, so any ratio lower than a 3.23, will likely result in running over 2,000 RPM on the interstate. The pinon seal on my 2.56 is already leaking, so I think now is the time to start digging into the work.

What I've already learned:
- The 2.56 uses a series 2 carrier; all other ratios use a series 3
- All rear ends from 91-96 should be compatible
- Rear ends for wagons are not compatible with rear ends for sedans
- The drivers side axle will likely be in great shape; there could be wear on the passenger side axle
- The PCM will need to be reprogrammed after the swap
- Since I'm removing the rear end, it'll probably make sense to swap all the trailing arm bushings at the same time (and maybe upgrade the lower arms)

Questions for the group:
- Given any rear-end from a junkyard will likely need at least a new pinion seal (and potentially new bearings and axles), does it still make sense to try and locate a 3.23 posi out of a junkyard, as opposed to finding any series 3 and building it from scratch? I'm guessing I'll need to be shipping a rear-end to MN regardless given the rust on anything up here.
- Are the axles for the series 2 the same? I'm guessing at 115k on my axles, they will be in very good shape.
- Does it matter if the donor rear-end has ABS?
- Some of the junkyard rear-ends are listed as a "round cover." Are these different from the later models? Does this matter for the swap?
- What else should I consider before jumping in?

I am also in Minnesota and just finished that exact change in my 96 RMW after coming to the same conclusions as you did on what gearing.

Any rear you find here is going to be pretty rusting, most likely so everything but the casting will probably need to be from yours. Shipping is pretty expensive for a complete axle. I had a 10.5" for our one ton Chevy single rear wheel van shipped from the east coast and it was like $300. It also was rusty so I had to use all of our existing parts on it, so been there. I don't think you will find a wagon complete axle with a 3.23 as they didn't make them AFAIK, at least on the LT1 wagons.

A full rebuild and gear change kit with an Eaton Tru-track was under $800 to the door, so I did that and put it in my axle. With a clutch posi it would be a couple of hundred less expensive, IIRC.

I am eliminating the ABS on the car, so that didn't apply, but you would need the right tone ring and gears designed or ABS. I think the 3.23 tone ring is a very hard one to find.

Where in Minnesota are you located?

Thanks for the reply, booster. That makes sense on the tone ring. I would think I’d be looking at a pre-‘94 rear-end if I’m looking for something stock with 3.23s. Not sure if anyone on here knows if the 3.23s from 91-93 could have come with ABS.

Am I correctly assuming that you swapped the 3.23s into a series 2 carrier?

I live about 30 miles south of the Twin Cities; the car will be spending lots of time on I-35, so glad to hear you’re happy with your 3.23s.

Roady182 wrote:

Thanks for the reply, booster. That makes sense on the tone ring. I would think I’d be looking at a pre-‘94 rear-end if I’m looking for something stock with 3.23s. Not sure if anyone on here knows if the 3.23s from 91-93 could have come with ABS.

Am I correctly assuming that you swapped the 3.23s into a series 2 carrier?

I live about 30 miles south of the Twin Cities; the car will be spending lots of time on I-35, so glad to hear you’re happy with your 3.23s.

Since I needed a carrier anyway because of the ratio split after 2.53, I just got the Tru-track limited slip which comes in it's own carrier. It worked out well because I wanted a Tru-track anyway as I don't care for the clutch type posi. Getting the whole kit as one also gave me the correct carrier bearings for the Tru-track as they are larger than the GM carriers use. All in one shipment to the door except for the whole works except the wheel bearings and seals.

Don't know for sure how happy I will be with the change as I just finished it, and the engine is still in process (block still at shop getting machined) and I will be assembling. It will be stock torque shape, but higher output I hope, built with much better parts and machining than it was stock. Trans will also be rebuilt and beefed up a bit by spring when we get a chance to try it out.

We are in Andover, about 30 miles north of downtown Minneapolis.

Ahh, that makes a lot more sense on the swap with the carrier. Thanks for the clarification. Not sure how I got to my assumption in the first place!

Continuing to read through more posts on the forum, and I don’t want to hijack someone else’s thread, so I hope you all don’t mind me continuing to ask questions here. Essentially it looks like I’ve got 2 options on the table:

1) Replace the entire rear axle with one from a salvage yard. To avoid needing to delete ABS, this would likely be a GW9, G80 w/2.93s. The risk here is that the salvage rear axle could be the reason the car is in the yard in the first place, not to mention ending up with 2.93s when the preferred ratio is 3.23.

2) Replace the rear differential, gears, and pinion with the desired 3.23 gear ratio. Going this route would require ABS delete, but would provide the opportunity to inspect axles, bearings, etc. and replace any other worn components.

Anything else I should be considering?

You would be able to keep the ABS with a gear change only in your axle if you can find a tone ring for the 3.23 gears as the replacement gears are OK with ABS if you get the right ones. I was removing the ABS anyway so it made it easy for me.

If you can find a 3.23 axle from a 91-93, it will bolt in. The only issue may be the mileage on the gears, and LSD. Get a southern axle, and build it. If you ship just the gutted rear, it may cost a little less. You are going to be replacing any and all possible wear surfaces. Mark your bearing caps before disassembly, to keep them in the same position. The tone ring will be right, but you will have to flash the computer. Make sure you get a set of gears that can accept the tone ring. For what it costs for axles, buy a pair of Moser axles. They are about the same price as the cheapy brands, and far superior, as well as made in the USA. Plan on buying a yoke wrench (JEGs 555-81656) to hold the yoke when removing the nut. When assembling the yoke, put some sealant on the splines, so it will not be an oil leak. You also need a dial gauge, magnetic stand, a micrometer, steel rod/tube to remove bearing races (long for the axle bearings), bearing race/seal installer (borrow from local parts store), 3-5 lb. hammer, in. lb. torque wrench, ft. lb. torque wrench, Socket to fit the yoke nut (new one will be larger than the OEM part), and probably a couple of other things I forgot to mention.

Use a 0.038-0.042 shim for the pinion, and you will be good without measuring it. Your lash is 0.005-0.009 in. You may have to buy some extra shims to get it right, and add .006 on each side for bearing preload. Mic all your shims before you start. I used my bearing caps to tap in the large shims for final assembly before tightening the caps.

I just did mine last summer, and it is nice and quiet, although it is a 3.42, and I deleted the ABS. Some of the early Caprice cop cars had 3.42s in them, and some of them had 3.23s. The tone rings are the same as the wagon tone rings on the Caprice 8.5 inch rears.

Fred Kiehl wrote:

If you can find a 3.23 axle from a 91-93, it will bolt in. The only issue may be the mileage on the gears, and LSD. Get a southern axle, and build it. If you ship just the gutted rear, it may cost a little less. You are going to be replacing any and all possible wear surfaces. Mark your bearing caps before disassembly, to keep them in the same position. The tone ring will be right, but you will have to flash the computer. Make sure you get a set of gears that can accept the tone ring. For what it costs for axles, buy a pair of Moser axles. They are about the same price as the cheapy brands, and far superior, as well as made in the USA. Plan on buying a yoke wrench (JEGs 555-81656) to hold the yoke when removing the nut. When assembling the yoke, put some sealant on the splines, so it will not be an oil leak. You also need a dial gauge, magnetic stand, a micrometer, steel rod/tube to remove bearing races (long for the axle bearings), bearing race/seal installer (borrow from local parts store), 3-5 lb. hammer, in. lb. torque wrench, ft. lb. torque wrench, Socket to fit the yoke nut (new one will be larger than the OEM part), and probably a couple of other things I forgot to mention.

Use a 0.038-0.042 shim for the pinion, and you will be good without measuring it. Your lash is 0.005-0.009 in. You may have to buy some extra shims to get it right, and add .006 on each side for bearing preload. Mic all your shims before you start.  I used my bearing caps to tap in the large shims for final assembly before tightening the caps.

I just did mine last summer, and it is nice and quiet, although it is a 3.42, and I deleted the ABS. Some of the early Caprice cop cars had 3.42s in them, and some of them had 3.23s. The tone rings are the same as the wagon tone rings on the Caprice 8.5 inch rears.

Thanks, Fred. Forgive my ignorance for a moment; we've been talking a lot in this thread about tone rings; most of the threads on the Impala SS forum reference an ABS reluctor. Are these the same thing? Does it matter if the 91-93 donor was equipped with ABS (it looks to be an option on the earlier cars) if I were to build from a southern axle as you suggested?

All of the cars had ABS. The tone ring and reluctor are the same thing. The tone ring is different for each gear ratio. I have not seen a 3.23 for a long time. There is a thread here, or on ISSF about swapping ratios, and it had some info about the tone rings/reluctors. There are a couple of wagons in the yards here, as amazing as that may sound. The rears are a PITA to remove, because of the weight. A friend of mine may have a rear with 2.73 gears in it available in a couple of months.

Regarding the computer flash, it looks like pcmforless is about the only place around that will be able to complete the change. Would you agree? Is it worth having any additional tuning done since the pcm is already there?

You might want to contact this guy.

LT1 tuning

He helped get my Jet tuner so it would do Buicks by getting me to the original creator of the product. Great person and seems very knowledgeable besides. He will be reviewing my program before I put it in and will fix it up if not happy with some part of it.

Fred Kiehl wrote:

All of the cars had ABS. The tone ring and reluctor are the same thing. The tone ring is different for each gear ratio. I have not seen a 3.23 for a long time. There is a thread here, or on ISSF about swapping ratios, and it had some info about the tone rings/reluctors. There are a couple of wagons in the yards here, as amazing as that may sound. The rears are a PITA to remove, because of the weight. A friend of mine may have a rear with 2.73 gears in it available in a couple of months.

I would be interested in your friends rear end if it becomes available.
Thanks

Thanks for all the replies; I've got some decisions to make. More to come in the future!

tip for breaking the pinion nut loose,.
big breaker bar, use a 2x4 and your power seat to push the brake pedal and hold it,.
or use a short breaker bar, brakes on, and whack it with a sledge,..

this advice only for experienced guys,. if you whack yourself or damage ****, you do so at your own risk,..