Register now to get rid of these ads!

Understanding Scrub line.

Discussion in 'The Hokey Ass Message Board' started by PurdueSD, Aug 29, 2012.

  1. Looking for a little help looking over my shoulder on this one.

    51 chevy p/u

    Ordered up a tci leaf spring kit to drop the rear of my truck. Really nice product, they claim its nets 4" drop.

    I would like to go a little lower so i mocked up some three inch blocks. I plan to run 15" steel wheels which measure out to 16-1/4" overall diameter (as it would relate to scrub line)

    [​IMG]

    As i see it, with the 3" block that i have mocked up, My scrub line is right at zero.. . Correct?

    Seeing that drop springs below the axle shouldn't have any effect on axle scrub line. Just seems odd to me after seeing so many of these AD trucks around with 3" blocks.

    Looking at this, it seems the most block i can safely run is 2". Can someone confirm my math? Thanks in advance!
     
  2. junk yard kid
    Joined: Nov 11, 2007
    Posts: 2,718

    junk yard kid
    Member

    why dont you cut some of them threads off?
     
  3. Doctor Detroit
    Joined: Aug 12, 2010
    Posts: 1,051

    Doctor Detroit
    ALLIANCE MEMBER

    I believe I am correct is saying that on the tape measure you are showing in the picture, at 8.125" is the bottom of your wheel. (16.25" diameter divided by 2 equals a 8.125" radius) Really nothing should be below 8.125" except tire. If your tire was completely flat, you'd still have some rubber lower than 8.125", so any metal wouldn't contact the ground.
     
  4. Gearhead Graphics
    Joined: Oct 4, 2008
    Posts: 3,890

    Gearhead Graphics
    Member
    from Denver Co

    Easier to tell with a wheel on it. But yes cut the threads and it will help, or even a 2 inch block will make a difference.
    As for understanding scrub line. Imagine the car going down the road and getting a flat tire, when that tire is flat and on the rim anything on the ground is at or below scrub. So yes, springs under the axle could violate that line.
     

  5. i don't think you and me have the same definition of scrub line, are you taking in consideration the diameter of the rim?
     
  6. Exactly Doctor Detroit. There is a shock mount tab hanging off the bottom of the u-bolt plate on the front left of the picture right around 8-1/8th" Half of the 15" steel wheel overall diameter measures out to 8-1/8th as well.

    Please ignore the threads hanging lower, they will get cut to the right length once the wood blocks and green slime are replaced with steel solid blocks and a ford 8.8. :)
     

  7. Ok you need to have 8 1/8 from the axle center minimum 8 3/8 would give you a little wiggle room. I think that you would be alrght with the 3" blocks but those are some numbers for you to work with.

    By the way only amatures neglect to trim the bolts once everything is pulled up tight. If you don't use long nuts you can actually end up with about 3/4" below the axle plate, maybe as little as 5/8".

    Ok I said that wrong, 8 1/8 would be your maximum length from axle center to longest hanging down part. I hate it when that happens.

    You are less than 7" to the plate so with nuts and washers I think you would still have an inch of clearance.
     
  8. 383 240z
    Joined: Oct 28, 2007
    Posts: 429

    383 240z
    Member

  9. Yeah you are a little dicey. As mentioned normally you would have the tire to add a bit of height if it was flat but if it comes apart and you are left with just the rim it is going to be close.

    Guys that thing that looks like a bolt at the left side of the plate is the shock mount so he isn't going to be trimming that down.
     
  10. Doctor Detroit
    Joined: Aug 12, 2010
    Posts: 1,051

    Doctor Detroit
    ALLIANCE MEMBER

    Here are some pictures for reference. I like that website link in the previous post.
     

    Attached Files:

  11. Thanks for the help guys! I think i am pretty solid on the theory, just wanted to make sure i wasn't overlooking or over-thinking.
     
  12. 28TUDOR
    Joined: Jan 25, 2007
    Posts: 419

    28TUDOR
    Member

    If I'm reading the tape right. If you can keep the nut and washer at 3/4 thick you will be 3/4 from scrubing (the u-bolts) with no tire.
     
  13. ^Shock tab hangs down at 8.125" it looks like a u-bolt (left hand side).
     
  14. 28TUDOR
    Joined: Jan 25, 2007
    Posts: 419

    28TUDOR
    Member

    Can you flip it to the top? shorter shock mabey?
     
  15. Oh hell ya, if i swap it with the one from the other side the orientation is the exact same with the tab being up. Hah no fab, and i might possibly be able to run the shocks that came in the kit.

    This would give me 3/4" scrub line buffer with 3" blocks... I think i'm cool with that.

    Thanks man!
     
    Last edited: Aug 29, 2012
  16. what is the diameter of the rim? not the tire size , but the actual OD. i just measured some 15" Americans and the OD is a hair over 16"
     
  17. 117harv
    Joined: Nov 12, 2009
    Posts: 6,589

    117harv
    Member

    It seems that you have it figured out and what you have will work. I have seen u-bolts used the other way, they fit in a small grooved plate that fits against the spring and the nuts are on top with a axle tube sadel.

    Also if one tire were to come off and you were running on the wheel, the rear end travels up toward the otherside. If you were right on the scrub line, you may gain say 1/2 or so depending on how close the spring is to the axle.
     
  18. could also have the eyes on the spring reversed (if they aren't already) and that will give you another inch lower without affecting scrub line. Also if spring hangers face down, you could flip them up, again not affecting scrub line. And like was already mentioned, flip the lower shock mounting plate from left side to right side, then upside down - or cut it off and re-weld it where it needs to be.
     
  19. Checkerwagon
    Joined: Jul 30, 2007
    Posts: 449

    Checkerwagon
    Member

    I like the way you think!
     
  20. the-rodster
    Joined: Jul 2, 2003
    Posts: 6,945

    the-rodster
    Member

    Give some thought about moving the axle back about an inch and a half farther back than stock. It will then look centered in the wheel well.

    Rich
     
  21. Yep, thats where the 8.125" i got came from.

    Pretty sure the spring kit was supposed to move the centerline, but its on my list of items to check. Thanks!

    Thanks for all the other advice too guys! This is my first build to this extent and i appreciate you all looking over my shoulder!
     
  22. One last question for anybody looking...

    Do you think this will require a small c-notch? Ive got 4" clearance to the frame with obviously no weight on it.

    [​IMG]
     
  23. walls
    Joined: Oct 6, 2005
    Posts: 635

    walls
    Member

    I would call the company who made the springs and ask them first.
    It looks like you may need one once there's weight on it.
    Don't forget to put a tiny bump stop on it or when it does bottom out it'll rattle your teeth.
     
  24. Lone Star Mopar
    Joined: Nov 2, 2005
    Posts: 3,811

    Lone Star Mopar
    Member

    A notch wouldnt hurt either way, I'd rather do it now while it's easier to access.
     
  25. Atwater Mike
    Joined: May 31, 2002
    Posts: 11,625

    Atwater Mike
    Member

    Funny 'legal' story about scrub line, California 1959:
    I had a full-fendered '26 T tudor sedan, on a '30 Model A frame...looow in front, 8.20 X 15 rears, 5.50 X15 fronts.
    Cop stops me, says I'm too low, he's gonna have to measure it. He measures my front apron below radiator, it's about 5"...then he goes to the REAR, and measures the ground to the bottom of the wheel. (7" or so)
    I ask him how the front's gonna drop if the back goes flat.
    He opens a code book, (freshly printed) and reads:
    "No part of the vehicle shall be lower than the highest rim."
    Scrubbed my plans for the night...I was adding leaves! (just to get it checked off)
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.