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Suspension Adjustments

Discussion in '308/328' started by PDB, Apr 8, 2017.

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  1. PDB

    PDB Formula Junior

    Feb 1, 2011
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    Leicestershire, UK
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    Paul
    Does anyone know what affect the different thickness shims make to camber, toe etc?

    On the rear suspension of my GT4, three of the shim packs are either 6 or 7mm, but one of them is 11mm, is that normal? I realise that the chassis isn't exactly precision engineering, but that seems like a big difference.

    Paul
     
  2. waymar

    waymar Formula 3

    Sep 2, 2008
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    Wayne Martin
    My '82 308i - The rear shims adjust camber and toe. So the difference may be toe related. Also are you certain the alignment is spot on? Just saying.
     
  3. PDB

    PDB Formula Junior

    Feb 1, 2011
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    Hi Waymar,

    My apologies, I wasn't clear enough with my question. I realise that the shins are to adjust the toe and camber, but what I wanted to know was by how much e.g. what affect does a single 2mm shim have on toe and what would a pair of them (one on each lower mount) do to the camber?

    I haven't yet checked the alignment, but there was nothing about the handling to suggest it was out. In fact, it drives beautifully. The rear suspension is off the car at the moment while I replace all of the bushes etc.

    Paul
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #4 Steve Magnusson, Apr 8, 2017
    Last edited: Apr 8, 2017
    The 308GT4 WSM suspension section has some good figures that you can trig out such things, but if it's handling well and the tire wear behavior isn't poor = nothing to fix ;)
     
  5. 328GTB

    328GTB Formula Junior
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    Do the 308GT4 WSM suspension diagrams apply to an early 328GTB?
     
  6. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Don't have any specific information on that, but can't see how they could be much different. Sadly, my pdf copy of the "328 tech specs" (which I believe F put together for FNA):
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    seems to have a place for such figures on page 28, but the figures themselves are not shown:
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    Maybe, if someone has an original copy this document, they can confirm/deny if such figures were just never added, or if they were on different pages, or something else...
     
  7. 328GTB

    328GTB Formula Junior
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    One of the issues I'm dealing with is point B is higher than point A at static full load when suspension bushings are not tighten.

    Is my understanding correct that point B height controlled by the spring?

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  8. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Don't have any information on whether points A & B should also be at the same height on a 328 at the rear. Are you sure nothing else has been modified? Do you have stock shocks and lower spring perches? Stock rear tire size? Are both sides the same?

    It's actually the height of point A that is determined by the spring (and its mounts). The height of point B is effectively set by the tire size.
     
  9. 328GTB

    328GTB Formula Junior
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    Everything is stock. Nothing's been modified. I just got done replacing front/rear OEM suspension rubber bushings and I'm trying to do final checks before everything is torqued down.
     
  10. thorn

    thorn F1 Rookie
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    Aug 7, 2012
    3,322
    Tallahassee, FL
    If you have the car on the alignment rack, you can determine the angle change for thickness by removing two shims, recheck the number, subtract the difference, and there is your mm formula.
     
  11. 328GTB

    328GTB Formula Junior
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    Given the same load, and A=B, if the tire height is changed, wouldn't A and B change by the same amount?
     
  12. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Yes, but that doesn't change that the height of point B is only set by the (new) tire size. The spring sets the height of point A relative to point B.

    Are things radically different now with the new bushings vs the old bushings?
     
  13. 328GTB

    328GTB Formula Junior
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    I'm not 100% sure yet. The rear suspension is the first thing that appears to stand out thus far. I will be doing more checking to confirm and will report what I find.
     
  14. 328GTB

    328GTB Formula Junior
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    I'm 100% sure of one thing. The springs are swapped. The fronts are in the back, and the back springs ended up in the front. How you say? the paint shop swapped the color codes:
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  15. 328GTB

    328GTB Formula Junior
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    #15 328GTB, Jan 27, 2019
    Last edited: Jan 27, 2019
    Steve,

    Do you think this spring swap would have distorted the spring compression on the taller spring fitted in the front?
     
  16. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    I wouldn't be too concerned -- true that the longer rear spring was compressed an extra ~22mm to be mounted on the front shock, but it probably wasn't then further compressed from there (i.e, the amount of compression to mount the rear spring on the front shock might be about the same amount of compression a rear spring would see in normal operation when the rear suspension is deflected down on the bump stops). How does the free length compare to the 344mm spec in the 308GT4 WSM?
     
  17. 328GTB

    328GTB Formula Junior
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    I'll post the free length once I take them apart. Thanks.
     
  18. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Now I'm not so sure that the 308GT4 WSM spring specs are that similar to a 328 -- on the 308GT4, the front spring has a longer free length than the rear spring even though it is compressed to a shorter length in the nominal working position (and this makes sense because the front spring is tipped at about a 45 deg angle in the geometry; whereas, the rear spring is more directly upright). Maybe one of the F parts suppliers could confirm/deny if the 328 front spring is the longer one in the free state, or if it's the rear spring that's has the longer free length.

    Still not too concerned that a spring would be damaged installing them onto the shocks if you got them reversed, but have to say I have no sure idea which end the longer spring goes on. Small instrument coil springs can be compressed to their solid height without damage, but these suspension springs are a little bit different in that the (coil diameter)/(wire diameter) ratio is so much smaller (i.e., it's very thick wire for the size of the coils) -- but, even if reversed, it wouldn't be compressed to it's solid height just to get it onto the shock.
     
  19. 328GTB

    328GTB Formula Junior
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    It looks like the rear spring for the 328 has the longer free length from one parts supplier:

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    The red numbers are my measurements and puzzled on the free length large discrepancy for the rear spring. I'm also concerned that the rear spring was compressed an additional 57mm (384 to 251 vs 384 to 308).
     
  20. 328GTB

    328GTB Formula Junior
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    An original document scan from a local Ferrari dealer shows the same missing figures on page 28. :(
     
  21. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Oh, that's a disappointment. Looks like they planned a place for the figures, but just never created/added them. IIRC, Rifledriver had previously indicated that that document was something FNA had pressured F to create to support US version 328 maintenance. While those 328 suspension figures would be a great reference to have, they really aren't needed for maintenance so maybe that's why the F engineers were allowed to wiggle out of making them ;)..
     
  22. 328GTB

    328GTB Formula Junior
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    Circulating back... Adding or removing shims to the lower A-arms only changes the camber angle?

    Here's some preliminary measurements (in red) vs spec (in black):
     

    Attached Files:

  23. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Generally, yes, but a very large change in the camber shims will also change height A a small amount -- adding shims reduces height A; removing shims increase height A.
     
  24. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Forgot to add - your 2+ degrees of negative camber at the rear is a bunch. I found I could only run about -1 deg camber at the rear (with the 8x16 wheels) without have excessive wear on the inboard tread.
     
  25. 328GTB

    328GTB Formula Junior
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    Looks like I have plenty of shims to work with. Is there a simple way to estimate mm to deg of camber?
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