Ok so I have a 72 skylark daily driver with a poston intake, 4 bbl edelbrock carb, doug's headers, pertronix points eliminator kit, and flowmaster dual exhaust. I wanted to know if I were to change the gears to 3.08 what will I need to replace? I don't know much about cars but I'm learning as I go. I am on a budget so I would like the most reasonable option. Any help would be appreciated. Thanks Manny
The first thing you need to verify is exactly what rear is in the car. The stock rear would be an 8.5 10 bolt, which is a great rear, but the car is 43 years old, and unless you have owned it since new, the rear may have been changed at some point. This isn't likely, but you do need to verify what you have. The easiest way to tell is to look at the cover from the rear. There should be 2 corners, one on either side of the cover on the bottom. They are circled in yellow in this photo, http://jdrace.com/diff_id/10b85/10b85_1.jpg Then look at the rear u joint. It should be retained to the yoke with 2 brackets and 4 cap screws. That would be an 8.5 10 bolt. You likely have 2.56 gears in it now. It probably isn't a posi. To go to a 3.08, I believe you will need to go with a 3 series carrier. The carrier bolts in to the rear end case and holds the ring gear. You can buy the right posi carrier from Jegs, Sumitt, or even from our member Monzaz here. It takes some specialized knowledge and procedures to set everything up right, so you may want to look to a rear end or transmission shop to install everything.
In the rears and gears section there is a guy that can answer that for you he is known by the handle monzaz, he sell parts as well very reasonably priced as well. GL Derek
I believe 3.08 is the break on the stock 2 series carrier. With the higher rpm needed for the series you might want a different carb like mentioned. There was a 3.23 gm gear and carrier on eBay recently. Would be a good option vs the 3.08. Might still be there. Do a 8.5 gear search. 72 is bolt in axle not cclip. Carriers still swap up to 87 after which the axle spline are not 28. A 2200 stall torque convertor would be a decent add to this combo
Thanks for all the input guys! Now I have a better idea of where to start and what to look for. Hopefully soon I will be letting you know how everything worked out and how I like it. Thanks again. Manny
Keep in mind the speeds you drive in your area vs. other parts of the country, as well as the overall usage of your car. Do you have a cruise rpm in mind as well as mileage goals?
The 'break' for the GM 8.5 is 2.73 for 3 series. Anything that or numerically higher on the 3 series; 2.56 and 2.41 for the 2 series. Available in 30 spline or 28 spline. The 'break' for the GM 7.5 is 3.23 for 3 series. Anything that or numerically higher on the 3 series; 3.08 or numerically lower down to 2.14 (not a typo--it's 2.14 not 2.41, though there is a 2.41 too) I believe on 2 series. Maybe you were thinking of the GM 7.5? The 'break' on the 2 series is 3.08 for the 7.5. Available in 28 spline or 26 spline. Just an FYI. Did a lot of research on this at one point. Someone correct me if I'm wrong, as I am not infallible. Gary
