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need help with Front and Rear wheel Back space 1968 GTO.

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  • need help with Front and Rear wheel Back space 1968 GTO.

    Hi all I am wondering if 15x10 with a 3 3/8" back space would fit under a 68 GTO?
    If not could I shorten the diff enough to get them to sit inside the guards.
    I hear that a 5" back space is ok with the 68 and 69 GTO's I just like the amount of dish you get with the 3 3/8" back space.
    And 15x7 with a 3 3/8" back space on the front will these fit?
    Regards Dane.

  • #2
    Won't sit under the fenders. It'll look 70's-80's style sticking out, and need air shocks, or a higher lift.
    -Mike

    This is not something you buy. It's Something you Build!

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    • #3
      Re: need help with Front and Rear wheel Back space 1968 GTO.

      I think you need 4.5" backspacing...

      From a Remote Destination....
      - Christopher - They call me Devil Beard

      Hoarder of various 2nd gen Trans Ams and Firebirds/ 73-77

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      • #4
        need help with Front and Rear wheel Back space 1968 GTO.

        U can fit a 9.5 wide with 4.5 back spacing no problem. That's what I run on my 72. I tried 10" and they seemed they would rub. The 9.5 are tight

        1972 LeMans W/Endura Front End & 461 CID

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        • #5
          Hi all,
          Thank you for your response.
          It's bloody hard to get parts in OZ for these cars I am looking into welding up my own 9" diff for this rig I am putting an "All Pontiac street engine" package in her and she will be about 505 ci with 700ish hp at the flex plate through a manual TH400 reverse pattern shift and this is why I am changing the diffs over and was planning on shortening it to suit,
          So my next question would be how much to reduce the diff down over all.
          Sorry to keep pestering you but this car doesn't have to be kept original as it was RHD converted in the late 60's early 70's and ran out of Rego in 1982 so it's been sitting for 31 years.
          I have a million other questions to ask i.e where to get a RHD steering Rack etc etc, I will try and find or start other threads for this.
          Once again thanks for your help,
          Cheers Dane.

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          • #6
            need help with Front and Rear wheel Back space 1968 GTO.

            Do you mean narrowing the rear end? Only if your going to tub it for bigger rims an tires

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            • #7
              I think thats what he's saying Scruff.

              As to answering your question on how much to narrow it, thats purely up to you and the GTO. If you're staying with stock frame rail locations, then you're limited by that as to how narrow you can or should go. If those are or can be replaced, its cut it to what ever width you desire, depends at that point on rim/tire combo and how far in or out you want the tires to be.
              I'm the Rick in prick.

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              • #8
                They make 2 different 9" Ford housings as for as the center section goes. The lighter duty has the center housing and the axle tubed go into it and it welded. If you look at the tube where it goes into the housing it is a round joint. Usually like a truck rearend. The heaver duty housing has a couple of finger like reinforcements that go out onto the axle tubes.That housing has more meat to weld up upper control arm bracket too.I need to take a picture of the housing under my '77 LTD II.
                '65 Goat

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                • #9
                  The center section (hogs head as some call it) they have regular and the Nolanger (Can't spell it right but it's a better cast material) housing with a big N above the front snout. Usually find then in trucks.
                  '65 Goat

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                  • #10
                    Re: need help with Front and Rear wheel Back space 1968 GTO.

                    Nodular iron.

                    posted with love,
                    Lord of Hardcore
                    -Mike

                    This is not something you buy. It's Something you Build!

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                    • #11
                      He was close. His began with N and ended with R. LOL
                      I'm the Rick in prick.

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                      • #12
                        You figured out what I was talking about! They always say if the first and last letter is correct the letters inbetween can be in almost right position and you can read it alright. That is if your in your right mind.
                        '65 Goat

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                        • #13
                          Hell, if we can read Gordonese, anything else is a piece of cake.
                          I'm the Rick in prick.

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                          • #14
                            Hi All, well I have spoken to J&S Gear Co Huntington Beach as a mate of mine here in OZ put me on to them, I will run 15x8.5 convos on the back with a 275 tyre so it all fits nice on a new 12 bolt diff (Disc Brake) that J&S will make up and ship to Brisbane, Once again thanks for all your help as there are hardly any resources available here in OZ and people can't believe we are not putting this car back to original,
                            Engine ordered as well through All Pontiac hmmm sweet 505,
                            Cheers Dane.

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                            • #15
                              need help with Front and Rear wheel Back space 1968 GTO.

                              Oh ya Convo Pros. I'm loving it. That's what I ran on my 72 for years

                              1972 LeMans W/Endura Front End & 461 CID

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