So I am looking for recommendations on what to do, what to buy and I've never had to spec or work on a differential before. History: At some point, the previous owner blew the original rear and installed a junk yard rear end. This is all from memory from 20 years ago. By the numbers on the axle, I have a 12 bolt 2.73 non posi with from a 70 Chevelle installed in my 70 Buick GS 455. All I know is a drive shaft shop replaced the U joints for me and referenced a 3R to 1310 for the rear one. So I am looking for recommendations on what needs to be done to change gears to around 3:31 with a Posi rear end. I want to be knowledgeable once and if I find a rear end shop around me to do the work. I don't want to be hustled and I'm not sure if I can do this swap myself in the garage. never done it before I was looking for your recommendation on what I would need to buy/do? Not sure what's needed. Do I need a new pinon? or can it be done with just a ring gear? or is it just something that comes out and new module going in? I'm assuming I'd leave the rear axles and seals alone since I don't think they are leaking. Thanks, Nick
You should go to a reputable shop and have everything done , new carrier, ring, pinion, bearing, seals…the works. $$1200-1500 will be your target.
Gears come in matched sets. Ring and pinion are made together. 3:31 gears are available new and original used GM. You will need a 3-series posi not of some type. The new helical units,like the Tru Trac,are a nice unit. This is also the time to check the axle shafts to see if they are good. The axle bearings ride right on the shafts itself,and they are known for cutting into the shaft after all these years of use. If they are,you will want to get a new pair of shafts. There are pre-made replacement c-clip shafts available,so they are rather inexpensive,compared to custom shafts.
I would have either Brian or Jim do the complete rear for you. It’s a simple principle but set up is critical for a noise free rear end, plus you need a few special tools and know how to use them.
