I have a 1959 gmc 150 8 lug build that I am looking for options. I would like to keep the frame in tact as much as possible. It is currently a .456 gearing or similar as they are common. I am looking to lower the gear ratio to be able to cruise at some higher speeds near 70 at 3000rpm. What options do i realistically have other than changing out axles to a 5-6 lug? I am hoping there is at least a rear end that will be able to be swapped and welded that will allow gearing to near low .310-330 ratios, but i understand 8 lug is an issue. Thank you-
I did a lot of them back in the 80's. Mainly 9 inch fords and a lot of 12 Bolt Chevy's. Easy swap with minimal welding to the housing for the spring perches. If you want to stay with the 8 lug look for a 3/4 ton Chevy GMC rear from the late 80's.into the 90's. Good ratios and lots of parts still available. They are god awful heavy and should work for you.
I had a 1980 Chevy 3/4 ton pickup with a 3.21 rear gear ratio.. I also had a 1957 Chevy 3/4 ton truck that I swapped in a 3.73 ratio rear from a 1986 3/4 ton Suburban. Without knowing about the rest of the truck you have, it's hard to make a recommendation as to what gear ratio would work best. The engine and transmission you have will make a difference. And driving one of those old trucks at 70 mph can be an adventure in itself. also what you have for front suspensions and brakes will kind of make a difference, as to whether you want to keep an 8 lug rear. What you plan to do with the truck, should determine what changes you might want to make. btw that 57 I had got a lot of highway use at 70 mpg, it had a 454 and the original SM420 4 speed, and stock front brakes.
I have a Cameo, and for years ran a 55 3/4 ton rear end with the 4.57 gears. There is a 3.90 gear set available, but I bet they are as rare as hen's teeth. I also ran a 3.73 (if I remember correctly) Dana 60 for a time, and that worked great. I had some 8x15, 8 stud rims made up to mount a tire that would get me better traction. I used these rims with both the 3/4 ton rear ends. I would imagine that the easiest and cheapest way to get the better mileage, would be to find a 55 or later 3 speed O/D transmission. I wouldn't run this against a wild engine, but the o/d was made by Borg/Warner, and they also supplied the same o/d for many other makes, making it possible to find the parts. I run a Hone-O-Drive O/D, which is a separate planetary transmission, behind a TH 400, and found that worked great to keep the rpm down and get better mileage. I don't know what engine/transmission combination you are running, but if you are running an automatic, you could install a 4L60, 4L80, or a 700R4 transmission. I am not sure, but there might be an adapter to make the swap easier. That would set you up with the overdrive, all in one case. My son is running a B&M 700 R4 behind his small block, and that is a nice setup. The B&M built unit would withstand a lot of horsepower, (my son is running a wicked 400 small block), but would cost about $2000. However, no computer to worry about. I am sure there are more options out there, but this is a good start. Bob
I had a '65 C30 with the SM420 and a mild 283. I believe it was a 5.14 or 5.38 rear and I had 17.5" tires on 8-lug wheels. It was wound up by 50-55 even with the tall tires. I never even looked, is the ham on those a drop-out like the Ford 9"? That was a full floater rear, plenty heavy duty.
I am planning on converting to disc all around with a GM 14 bolt similar to what you have done. I also want to keep the sm420. I will be using a beefy 283 motor. I would like to drop the truck an inch or two! There is a few more details for you hopefully.
I wouldn't bother with disc brakes on the rear, unless that's what you find available. Might want to find a 3.73 rearend, too....that's a lot of weight for a little motor to move around
I'm not sure if you could put the 1/2 ton gears in the 8 lug rear but I just listed a 57 rear for sale in the classifieds.