Hi, I have 66 GMC 3/4 ton with a 305E V6 and a SM420 transmission. It currently has 4.10 gears. I am planning on getting 235/85R16 tires for it. I think it has a Dana 60 in it. It has a 10 bolt cover and is approx. 12 inches long from the top of the cover to the bottom of it. Is this a Dana 60?? Can I get new gears for it? The reason I am asking is I have read in some various forums that say you can't and some say you can. Some say to get an entirely different axle from a 67 to 72 truck. Is this necessary? Now my question is which gears should I get (if I can) the 3.73 or 3.54? How fast can I go with either of these two without destroying my engine? I would like to be able to go 70 or 75mph, but is the 3.54 to high for this setup?? I don't know if I will change the engine or transmission later or not. Has anyone ever put rims from a 2001 GMC on their truck?? Mine seem to fit fine. I actually have an extra half inch of backspace. The rear center caps are a half inch too shallow though. Any suggestions to remedy this?? All responses will appreciated! Thank you!
The problem with the rear end is the carrier. To go smaller than 3:73 you need to change out the carrier. As far as trannys go I would recommend the 700R4 swap if you want to cruise at 70-75 MHP. And yes I tried to put 2001 rims on my 66. They didn't work. Not enough back spacing. You can install spacers but I don't trust them.
To Drabo: May I ask was yours a Chevy or GMC and a 1/2 ton or 3/4 ton? Why do mine appear to fit fine? Mine are steel rims and not the aluminum ones, I don't know if that matters. I measured with the rim on the back from the edge of the leaf spring to edge of the rim and I came up with an extra 1/2 inch and then I put it on the front and it did not hit the tie rod end or anything else. Why would yours be different?? Am I missing something? So you are saying that I can get new gears for my old carrier, but nothing smaller than 3.73? Can a 700R4 be fitted to my 305E v6? Thank you for responding!
