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Need Rear Diff Help!! Bonneville is coming Quick!

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  • Need Rear Diff Help!! Bonneville is coming Quick!

    Been a while since I posted but here it is. I have decided to remove the 1UZ lexus motor from my Road Race 240 and install a built LS backed with a Tremec 5 speed. It will be running around 450 to 500 hp to the wheels hopefully. The car is not going to race in budget endurance racing anymore! I am going to begin racing with NASA Southeast in ST1/ST2 Class. Anyways. We have a once in a lifetime chance to go to Bonneville in 6 weeks and I cant resist taking the car. We are going to run in the 150mph club that is for street cars. The car should have no problem getting there but I would like to ensure that. I am wanting to run a taller gear set. I would like to run a 3.13, 3.54 or 3.69 all out of Q45s. My questions is I have several VLSD laying around from J30s can I use the Q45 gears in the J30 diff. I don't want to have to the axle swaps and so forth if not necessary to run these gears.

    FYI with these gears at 7k rpm the car should run between 213 and 180 mph with my current tires.
    91' S13 Endurance Racecar
    Sponsored by Pallets and Crates LLC Gainesville Ga
    04' Chevrolet 3500 Tow Vehicle, 02' Dodge Ram 1500 Truck, 87' Toyota 4 Runner "Top Less",
    15' Toyota 4Runner, 07' Honda Fit

  • #2
    The Q45 gears should be a direct swap as they're R200 diffs. It doesn't matter if its VLSD or non VLSD if you're just changing Rings and pinions.

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    • #3
      FWIW, you might as well just use an early Q45 diff directly. I think it's a 3.69. No point in getting the gears out of one and installing it in another case. Use the Q45 case as it'll be setup for proper pinion height already. Toss in a diff, check backlash and tooth contact then rock and roll. 9/10 you won't need to adjust anything from factory shims.
      '18 Chevrolet Volt - Electric fun hatch for DD duty!


      DefSport Koni Sleeve and Spring Perch Buy!!!
      http://www.nissanroadracing.com/showthread.php?t=5902

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      • #4
        Def, If I do that, don't I need to change the axles, hubs and such to make it work? If not please let me know!! That is the reason I was going to swap it into one of my J30 diffs to keep the other stuff the same.
        91' S13 Endurance Racecar
        Sponsored by Pallets and Crates LLC Gainesville Ga
        04' Chevrolet 3500 Tow Vehicle, 02' Dodge Ram 1500 Truck, 87' Toyota 4 Runner "Top Less",
        15' Toyota 4Runner, 07' Honda Fit

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        • #5
          If your LSD (the actual differential, not the housing + gears + output shafts etc.) has unique output shafts, just swap it all into the Q45 case with the Q45 ring gear on the LSD/differential (itself). They're both R200 differentials of the same vintage, so everything internal should swap right over.

          If you just get the gears to put into a new case you'll have to setup the pinion height + pinion bearing preload, get new bearings everywhere (they rarely go bad due to how oversized everything is in an R200, so just added expense IMO), and then redo your ring gear backlash and differential bearing preload setup via shims.

          Swapping your LSD into the Q45 case will mean you should only have to worry about ring gear backlash and differential bearing preload. But like I said, 9 times out of 10, you can toss your LSD in there with the factory shim arrangement and everything will be in spec, this saves a load of time and expense. Essentially check tooth pattern and ensure differential bearing preload is good by testing the break away force on a ring gear bolt. The FSM details all this, but knowing how to shortcut the work by swapping the LSD makes it a pretty easy ~1-2 hr job vs. an 8-12 hr job setting a diff up if you're not used to doing the work.
          '18 Chevrolet Volt - Electric fun hatch for DD duty!


          DefSport Koni Sleeve and Spring Perch Buy!!!
          http://www.nissanroadracing.com/showthread.php?t=5902

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