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Thread: Front UCA relocation questions

  1. #1

    Front UCA relocation questions

    I think I'm going to move the front UCA mounts. No one currently has a set of adjustable units available for sale, plus I'd like to build in a little anti-dive. And I see pro's to keeping the GM units.
    Please offer any guidance you have for this mod. Should I match the C5 UCA angle for the anti-dive? I figured I'd just move the shock to the rear of the back tab, then move the front tab behind it? Thanks!
    Dave
    Pic shows new shock location, but no anti-dive yet..

    MK3.1 2004 Mach 1 donor.
    GTM #304

  2. #2
    Like this but less extreme angle of anti-dive.

    MK3.1 2004 Mach 1 donor.
    GTM #304

  3. #3
    So here's the vertical differences between the upper and lower UCA mounts (measured to center of bushings - some slight variations due to lower cam bolt orientation).
    For anti-dive, looks like moving the front UCA mount up is the way to go, rather than drop the rear mount? With regards to matching the C5 geometry at least.
    Did FFR ever explain why they modified the geometry?

    MK3.1 2004 Mach 1 donor.
    GTM #304

  4. #4
    Sawzall was getting dusty. So what's the verdict for anti-dive? Raise the front tab to better match the C5 geometry (favoring this) or drop the rear (I believe Crash essentially did this on the PDG GTM)?

    MK3.1 2004 Mach 1 donor.
    GTM #304

  5. #5
    I dropped mine for more camber gain. Would you happen to have the C5 lower control arm mounting heights relative to the GTM? I would not increase the distance between the upper and lower mounting points, less you loose camber gain.

  6. #6
    How much camber are you running? I really don't see myself going much higher than about 1.5.
    Wouldn't moving the upper suspension mounts up or down relative to the C5 setup negatively affect bump steer?
    Disclaimer: I'm no suspension guru!
    Last edited by beeman; 03-19-2017 at 05:12 PM.
    MK3.1 2004 Mach 1 donor.
    GTM #304

  7. #7
    I can only get about 1/2 degree negative camber if I keep a couple degrees caster. Maybe a little more if I lower the car. Yes, it will probably increase bump steer. I have the bump steer kit to try to improve that but I have not installed it yet.
    I used the alignment method suggested on an earlier post. It went something like "adjust the rear of the control arm all the way out to get maximum caster and then adjust the front of the arm out for camber". My car is only nearing go kart stage so I can't tell you how it drives.

  8. #8
    Surely guys are running a couple degrees of camber with some positive caster with FFR design. I thought the caster was about 2.5 degrees with some good camber. Other guys will chime in I'm sure.
    MK3.1 2004 Mach 1 donor.
    GTM #304

  9. #9
    Senior member Roger Reid's Avatar
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    I moved my upper front control mounts 1 inch rearward and 1/2 inch lower to get more caster and camber recovery. The bump steer was worse. I moved the mounts to the original height and found the best bump steer. I fabbed up a mount that I could move the up/down position and measure the bump steer. Yes I was using a bump steer kit and adjusted it during testing. What I remember from the experiments I made was that the bump steer went from toe in to toe out to toe in when the wheel traveled up over the full stroke of wheel travel. Changing the height of the mount changed the point of maximum toe out in relation to ride height. I decided to place the point of maximum toe out at ride height which wound up being the original upper control mount location. I did not try to change the steering rack location.
    Just an old man with a great hobby

  10. #10
    Roger -
    Did you keep the UCA level or did you angle it like the C5 setup?
    MK3.1 2004 Mach 1 donor.
    GTM #304

  11. #11
    Senior member Roger Reid's Avatar
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    Feb 2011
    Location
    Caldwell (near Boise) Idaho
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    level.
    Just an old man with a great hobby

  12. #12
    beeman,

    Maybe my question got lost. Do you have measurements to the lower control arm mounts on the GTM and C5 for comparison to the upper locations provided above? Thanks,

    Ken

  13. #13
    I wasn't sure what you were asking...
    Do you want the height from the ground of the lower control arm mounts with the car at ride height?
    The numbers I wrote out above are the DIFFERENCES between the lower and upper mounts, ie (upper UCA mount height) minus (lower control arm mount height) - these are independent of ride height. Maybe I didn't explain it very well.
    The numbers suggest that if you increase the distance between the front mounts by about 2.5" (ie raise the front UCA mount by about 2.5" and keep rear UCA mount location unchanged - ie tilt the UCA up) you would essentially match the C5 geometry - assuming same control arm angles /ride height relative to mount location.
    If you look at the C5 locations, the front UCA mount location is slightly aft of the lower control arm mount location. Moving the UCA aft about an inch or so - which most modifiers recommend - essentially corrects this - FFR setup has them about even.
    So basically we are all trying to undue the changes FFR made to the C5 geometry...
    Last edited by beeman; 03-23-2017 at 07:47 PM.
    MK3.1 2004 Mach 1 donor.
    GTM #304

  14. #14
    I have not measured the differences in location of the mounts in the frontal plane, which can affect camber obviously.
    MK3.1 2004 Mach 1 donor.
    GTM #304

  15. #15
    beeman,

    Thanks for the reply. Yes, I misunderstood. My mistake.
    So FFR basically reduced caster (maybe to make steering easier without power assist), helped camber gain (good for handling), and reduced anti-dive (I am not sure why you would do this unless just to make it more forgiving.).

    Thanks

    Ken

  16. #16
    I found this to be really interesting, he's also got some threads on aerodynamics and other cool stuff on there.

    http://www.lateral-g.net/forums/showthread.php4?t=42467
    MK3.1 2004 Mach 1 donor.
    GTM #304

  17. #17
    Started tacking in the new UCA mounts. 1 3/8" aft, a hair under 1 3/8" up (call it 1 5/16"). Moved them inboard slightly. Rearmost mounting tab at original vertical level, moved aft 1 3/8". So I basically have a little more than 1/2 the C5 upper/lower divergence which should help achieve some anti-dive. Quick and dirty (straight edge and digital angle gauge) - take this as a gross approximation - show caster at 8.2 degrees with camber 1.6 degree (at 4.5" front ride height). I'll include a pic of the orientation of my lower essentrics to show where they are (to show that there is some room for camber adjustment). The increased caster should help with camber in the turns. Thoughts?





    Last edited by beeman; 03-25-2017 at 05:53 PM.
    MK3.1 2004 Mach 1 donor.
    GTM #304

  18. #18
    New mounts coming off the line

    MK3.1 2004 Mach 1 donor.
    GTM #304

  19. #19
    Playing with the angle. Initial evaluation shows significantly increased bump steer compared to FFR mounts, without touching rack. Going to put the bump steer kit in and see how it goes.



    This setup gave me a basic idea of the bump steer trends, but I got screwed up by camber change - it rotates the construct. Need to use a laser at the centerline.

    Last edited by beeman; 03-27-2017 at 08:38 PM.
    MK3.1 2004 Mach 1 donor.
    GTM #304

  20. #20
    Bit the bullet and ordered a Longacre 79005 bump steer kit. Should be here Friday.
    MK3.1 2004 Mach 1 donor.
    GTM #304

  21. #21
    Jegs ships fast! Initial evaluation of passenger side (FFR) geometry- very decent bump steer out of the box (.030 or so through 2" compression).
    With my current modification ( moving UCA about 1.2" straight back, dropping rear mount about 1.25" to add anti-dive) shows a crappy .160" of toe out over 2" of compression. Makes sense, as the outer tie rod location rises as the hub is rotated back.
    Getting ready to add the bump steer kit and see what happens.



    EDIT: Here's my chart, with UCA moved, pre- and post- bump steer kit. Will start a new thread to discuss.

    Last edited by beeman; Today at 09:12 PM.
    MK3.1 2004 Mach 1 donor.
    GTM #304

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