Hey guys- newer to the Buick family. I picked up a 1972 Skylark that has a transplant 1971 455 stage 1 +TH400 Auto in it. The rear is original and 2.56 gears. I want to get some more kick out of it but from what I am reading this rear end is a "peg leg". I still want to cruise the highway without to high of RPM. what are you suggestions and how easy is it to swap in higher gears? I have read 3.42's are the go to? Suggestions on size, where to buy, how to do it would be great!
With 2.56 gears, 60 MPH will be about 2000 RPM. With 3.42 gears, 2700 RPM. Your 1972 Skylark should have the original 8.5 10 bolt rear. You should confirm that before ordering parts. The car is 46 years old. If you have not owned it since new, the rear could have been changed, not likely, but could have. You can order parts for the 8.5 right out of the Sumitt or Jegs catalogs. Here's the posi, https://www.summitracing.com/parts/etn-19557-010 Gears, https://www.summitracing.com/parts/...MIlJ_f3feU2wIVzQOGCh38GA_WEAQYAyABEgK9z_D_BwE Setting up the gears requires specialized tools and knowledge. There are guys here who can help you if you want to try it.
Thanks Larry! I was watching some videos and it looks like a press is needed that I don't have. However I wonder if I could get Napa to press on a new bearing for me prior to install. I'd prefer to not remove the rear. I guess I could find a shop that could do it. Trying to save money Do you suggest no matter what putting in the posi when doing the gears? or do I need to because the housing I have won't fit 3.42s
The carrier you have for the 2.56 gears is a 2 series carrier. If you just wanted to run the 3.42 gears, you would need a ring gear spacer for the 2 series carrier. There are a few guys who could answer your questions better than I. Monzaz and BrianTrick come to mind.
Hmm- Probably need the posi, the rear tire is always letting loose with slow turns because of the torque this thing has.
3.08 gears aren't bad for a stock motor and decent cruise. What do you intend to do with the car? That should be the question you answer before you pick a gear ratio although a posi unit is never a bad idea. If you are going to go on long trips, 3.42 would be the highest gear I'd consider unless you are using 30" tall tires. If you want to win stop light battles, I'd go at least 3.73. Answer these questions and we'll help you make an informed decision: 1) Desired cruise speed 2) Desired rear tire size 3) Desired cruise RPM From there it is s simple formula to figure the gear range that will satisfy your desires.
I like a 3.23 for your combination with a 27-29 inch tire. Your best bet is contact Everyday Performance, JD Race or Brian Trick, have them build you an axle with the correct posi and send them back your core. You or your shop then just bolt it in, no worries or mess.
Thanks guys. right now it has 28" tall tires (cooper cobras 275/60R-15) on the rear. The mods are listed in my signature. Im not sure I'll do much else other then rear gears and maybe headers someday. I'd say I don't want to be limited to town driving but highway driving is likely 50% and town 50%.
I went from 2.56 open to 3.08 posi in my 350 car. I do a lot of highway running. I am very happy with the results, feels a little bit spunkier but still can run 75-80 mph down the interstate.
I have 2.93s in my ‘68; they’re great for the highway and the torque will light the tires at will. I’ve had several cars with different rear gears and feel that, without overdrive, 3.08, 3.23, maybe 3.42 are the good numbers for cars that get any interstate running. Patrick
