10' Slick Under a Diplomat

Chassis, Suspension and wheels

  1. CM360

    CM360 Well-Known Member

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    Going to take my '80 Diplomat and ready it for 12.50 index racing. Anyone fit a 10" slick under one?
     
  2. BudW

    BudW Moderator Staff Member

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    Sounds like fun!

    Note: does your title says 10’ (10 foot) slick?
    I can’t comment about fitting a 10” slick (or tire) under one, yet.
    BudW
     
  3. CM360

    CM360 Well-Known Member

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    The 10' slick refers to the leaking trans in the Diplomat.
     
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  4. MiradaMegacab

    MiradaMegacab Well-Known Member

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    Obviously wheel BS is a factor, what axle too? B or a wider E body 8.75?
    The first clearance issue is between the inside of the tire and the front part of the wheel well, then the front of the tire to the leaf springs..
    Simply moving the rear axle back 1 to 1.5" usually overcomes the clearance issues.
    Tire height is a factor too.
    I ran a 30X10 tire by moving the axle back.....
    Section width is another factor..... lol
     
  5. CM360

    CM360 Well-Known Member

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    That's an additional 1-1 1/2" to the wheelbase on cars that have the boat anchor bumpers hanging out in the breeze. Its a solution that adds other issues.
     
  6. MiradaMegacab

    MiradaMegacab Well-Known Member

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    Yup, and mini tubbing does nothing as the front segment of the leaf spring is a problem.
    What's the intended use for your car? (Drag Race, AutoCross, ProStreet)
    Spring relocation kits only get you so far.
    Ladder Bar with coil overs or 4link might be the way to go, if you're doing a serious drag application.
     
  7. Locomotion

    Locomotion Well-Known Member

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    I agree that the wheel well tub is an issue for tire clearance at the front. I dented mine for clearance. But it's the leaf spring orientation that can cause a sidewall clearance issue at the back. It won't give a lot more room and backspace still has to be just right, but you can get a little bit more clearance with just E-body 3/4" offset shackles. The OEM leaf springs are actually toed-in, making clearance less at the back of the tire. The 3/4" shackle helps to straighten them out and there seems to be enough "slop" at the front to do it. But I confirmed that it's not legal for my racing application. I got 9x30 Hoosier radial slicks on 10" wheels to fit on my wagon, but I don't remember if the previous owner had already clearanced the front of the wheel well or not. It's best to do when switching to an 8 3/4 rear so the spring pads can be relocated. Yes, a lot of work for a little gain, but an option nonetheless. But the 8 3/4 and corresponding shock plates provides for a wide variety of race shocks. Front race shocks are another, bigger issue. Late '60's B-body 8 3/4 is suppose to be the closest width and the pads may line up as is with the offset shackles. (I read an article about it a while ago but don't recall where.)

    Axle dimensions: Dodge, Chrysler, Plymouth Rear Axle Dimensions

    (I believe the last 2 listings are suppose to be 9 3/4").
     
    Last edited: Nov 12, 2017
  8. Oldiron440

    Oldiron440 Well-Known Member

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    You don't need a 10-inch slick to go 1250s, in fact it will probably slow you down.
     
  9. BudW

    BudW Moderator Staff Member

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    That chart is helpful – but is not entirely correct.

    This chart is still under construction – but is a lot more correct.
    Note: I still need to add Jeep, Dakota’s and a lot of other Mopar's into the mix.
    Note: green cells - data not confirmed (or known), yet.
    Diff Excel 1.jpg

    Diff Excel 2.jpg
    BudW
     
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  10. M_Body_Coupe

    M_Body_Coupe Well-Known Member

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    I have a completely stock rear end setup as far as leaf-springs & hangers go anyways...the rims are aftermarket though (Centerline #175804545, Auto Drag III, Aluminum, Polished, 15 in. x 8 in., 5 x 4.5 in. Bolt Circle, 4 in. Backspace). I am running a Nitto NT555R street legal tire that is 275/60R15 in size. This is on 8-3/4" housing that has not been altered, so with the 4" backspacing on the rim and that tire width edge of the tire (sidewall) is literally vertically matching the fender lip. I've attached a photo of what that atually looks like

    Ideally I would love to "push" the wheels a tad back in, so go to a bigger backspace rim, I think I have about 1" free room, where with my tires I would not be contacting anything.

    I would be happy to measure this out for you.

    tire_leafspring_clearance_2.jpg
     
  11. BudW

    BudW Moderator Staff Member

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    There are three different B-body 8¾” differential widths that can direct bolt into FMJ vehicles.
    BBody Diff Excel.JPG
    Flange to flange: '65-67 54.250", '68-69 54.936" and '70 54.906".

    If you know which one of the three that you have – you might be able to find another year differential which is a tad narrower, that might work for you.

    By the way, things look very sharp and clean, from your picture!


    I spy an Iso-clamp system on an 8¾” housing.
    You might be the only one out there who didn’t toss the Iso-clamp system, in favor for the far better shock plate that originally came with that 8¾” housing.
    BudW
     
  12. M_Body_Coupe

    M_Body_Coupe Well-Known Member

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    LOL, yeah, you are probably right about that!

    I did that because I sourced some KONI adjustable shocks way back when...we are talking here specific F/M/J product, 5 way adjustable. Also, I thought I would make it a point to build a stock appearing suspension that performs well (including a HD rear sway bar).

    As-is that ISO setup actually worked quite nicely when I installed the machined angle shims to give the pinion the needed 'nose down' stance.

    If there is one thing I would change is to use the POLY biscuits instead of the NOS OEM pieces. I put the rear end through too much beating already!
     
  13. AJ/FormS

    AJ/FormS Well-Known Member

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    Just curious, what's a car like that weigh? like before and after
     
  14. Oldiron440

    Oldiron440 Well-Known Member

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    I will still say you don't need a 10in tire to run 12:50 s!
    The fact is a 10 inch slick will slow you down!
    Stock Class Cars are running below 10 seconds on 9 inch slicks!
     
  15. Oldiron440

    Oldiron440 Well-Known Member

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    I have a friend that runs an ES/A 62 Plymouth that can run almost a full second under the index @ 10:62 on nine inch slicks. Front end four foot in the air for sixty feet, so you cant tell me you need a 10" slick to run 12:50s. Im going to run up the BS flag!
     
  16. Oldiron440

    Oldiron440 Well-Known Member

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    E/SA
     
  17. Oldiron440

    Oldiron440 Well-Known Member

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    Come back and respond.
     
  18. Oldiron440

    Oldiron440 Well-Known Member

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    On my F Body I had to pull leafs in but I used SS springs and off set hangers. Every thing fit perfectly so I filled the holes on the lower spring plates to fit. I did have to clarence the front of iner wheel house. And to get the 30 ×10.5 s to fit. I had to trim the front of the wheel lip edge to work. But my Plymouth goes much much quicker than12:50.
     
  19. Oldiron440

    Oldiron440 Well-Known Member

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    That was over twenty years ago
     
  20. Locomotion

    Locomotion Well-Known Member

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    While a 10" slick isn't necessarily needed, the more rubber you can get under a car, the more "insurance" you have that it will hook, particularly at local tracks where prep may not be as good as it can be. It takes some work and can get expensive as well to properly sort out a suspension so it does hook when there are limits in the rules, like 9" slicks. People try different combinations of converters, gears, cams, etc. Same can apply to suspensions if you want to get it as efficient as possible.