My 67 is a peg leg, and i want to correct its handicap. In the procces of getting posi trac, i want to change the gear ratio. I would like to go with 3:73's. My question is since Im not too sure about switching out the ring and pinion set, would it be easier to just switch out the entire 3rd memeber? And, what years of GM 3rd member would fit into a stock 67 rear end? thakns,
james

Also, I have a 700r4 Tranny. Right now at 70mph the engine runs at 2000 rpm's. Would the 3:73's be ok for highway use, and if so, how about 4:11's? What im looking for is more speed off the line but still have the car driveable at highway speeds without redlining the tach. thanks agian.
James

3:73's would be good, along with an Eaton posi. Think this is a "don't do this at home" kinda deal for you. Find a good shop to do it, settin gears is tricky.

Or, swap the whole thing, to either a 12 bolt, or a later model 8.5" 10 bolt. Do some searching here for the info you need. Basically, a rear out of a nove/ventura/omega thru 74 will fit right in.

I think you are thinking GM's are like the 9" ford that has a changeable 3rd member. They are not like that. Remember, a 700r4 has a very low 1st gear and I believe 4.10's are too low. I have 4.11's (Italian gear) and a 700r4 and it is too low. I would go with 3.42's if I was to start over.

Setting up a ring & pinion set requires some precision work. The pinion depth and backlash must be set to within +/- .001 of nominal to get the correct contact pattern. The pinion bearing preload must be set to within 4 inch pounds. Installing a posi isn't quite as complicated, but still requires some precision work.