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Customs Knowledge needed : 1959 GMC truck rear end options

Discussion in 'The Hokey Ass Message Board' started by Darin S Bernhardt, Apr 12, 2019.

  1. 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-
     
  2. Binkman
    Joined: Nov 4, 2017
    Posts: 378

    Binkman
    Member

    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.
     
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    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.
     
  4. 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
     

  5. 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.
     
  6. 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.
     
  7. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    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
     
  8. 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.
     
  9. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    it's a whole different thing....
     

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