2x4 to 4x4 conversion

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by kd4pbs, Jul 30, 2009.

  1. kd4pbs

    kd4pbs New Member

    I know it's been asked a million times before, and I'm a glutton for punishment, so I'll ask again. Which way would be best to convert my '87 Suburban; to swap the crossmembers, suspension, and powertrain components, or swap the whole frame? Here's what I have...
    A 1987 3/4 ton 454/THM400 2x4 GMC Silverado classic Suburban with FF rear axle that is in relatively good shape. This is the vehicle that I will be driving. The body is nice, no rust, has the barn doors that I want to keep, etc.
    A 1987 3/4 ton (heavy half) 350/THM 4x4 with SF rear axle. Drivetrain components are all there and are in decent shape. The body is crap, it's rusting out behind the rear wheels, it's got a plastic bench seat, and is generally in bad shape. The engine will probably be marinized, built up, and put in my boat. The 454 will be in the final vehicle, as well as the THM400 from the 4x2 (with needed swappage of the 4x4 particular parts), unless a 4L80 can be found cheap.
    I do know I'm gonna have to wail on the transmission tunnel some unless I put in a body lift.
    I don't have access to a lift, so I'm leaning towards swapping cross members and suspension instead of a full frame swap.
    Has anyone done both and have an opinion of which is better?
    Thanks, and sorry for my ignorance for my first post!
  2. L0sts0ul

    L0sts0ul Rockstar 100 Posts

    I personally would grab the frame with drivetrain and move all the pieces you need because the fram is already rigged for the tcase and so on.
  3. Joeairforce

    Joeairforce Epic Member 5+ Years 100 Posts

    It'll be alot easier to just swap all the good stuff to the 4x4 frame..... (engine, body, rear axle, etc)
  4. 2COR517

    2COR517 Epic Member 5+ Years 1000 Posts

    I would agree to put your good body on the 4x4 frame. Is it a 3/4 or heavy half? How many lugs on the wheels? 8-3/4 ton; 6-1/2 ton. If it's an 8 lug, you're golden. It will already have a TH400. Just need to drop your 454 in and you're ready to roll. If it's six lug, it probably has a 700R4. Maybe not the best trans behind a big block. Depends on who you listen to. As for the 4L80e, it would be nice, but it's big money. Trans alone will probably run you a grand, stand alone controller is even more. If you decide to swap the 700R4 for the TH400, you might need to do some mods to the crossmember (or get the correct one), and get the correct adapter for your transfer case. A TH350 might be a much easier swap.

    As for getting the body off, that's going to be a challenge. Might be best to rent / hire an earth moving machine. If the transmission tunnels are grossly different, you could cut the tunnel from the 4x4 and weld it in the 4x2. All this will still be less work than putting the 4x4 suspension under your truck. Plus, when the body is off, it's all topside work.
  5. kd4pbs

    kd4pbs New Member

    The 4x4 is a 3/4 ton (heavy half) with 8-lug semi-floating rear end. It's the 14-bolt SF, not the 14-bolt FF the 4x2 has. Different carrier all together. I'll probably hold on to the FF rear end and save it for whenever I get 40" tires on the truck :)
    Attached to the 4x4 frame is a THM400 (sorry, I forgot to write "400" in the original post). This THM400 is in poor shape, so I'll be putting the THM400 from the 4x2 on the 4x4 frame. Also, the 454 from the 4x2 will be going into the 4x4.
    I did not know the 4L80 needed a TCM. I thought only a 4L80E needed a TCM.
    So, all this being said, the general consensus is that it's best to just swap the whole frame rather than just the front suspension and crossmembers? Have any of you guys done this and know for sure it's the easier way out?
  6. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    If you want to swap in the 400 out of the 2WD into the 4WD you will have to tear down both trannies and swap the output shafts. :(
  7. Joeairforce

    Joeairforce Epic Member 5+ Years 100 Posts

    There is no non-electronic version of the 4L80, they only came electronic...... Unless you swap in a completely manual valve body.....
    Last edited: Aug 4, 2009
  8. kd4pbs

    kd4pbs New Member

    Yep. And your point? ;)

  9. kd4pbs

    kd4pbs New Member

    Dangit. I see that now. I was mistakenly told there was a 4L80 (non E) with hydraulic automatic functions. Oh well. Perhaps an overdrive for the THM 400. Or perhaps put that part on hold for a while until I can afford a standalone TCM for the 4L80E. Or, the easiest would probably be to adapt a PCM from a 4L80E vehicle for use in this Suburban. Whichever way I go, i just would love to hear from someone who has done a 4x4 conversion both ways so that I could get some input as to the best way to approach.

    Thanks to all so far!
  10. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Having done a couple SAS's over the years I'd say swapping to the 4x4 frame might be the easiest route. You'll still need to do some welding on the body mounts but it wont be as much as trying to mount in new spirngs, T-case, and Trans mounts, also keeping the front suspension steering and geometry straight.

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