*CORRECT* method to measure caster angle?

Discussion in 'Axles / Suspension / Tires' started by Caver Dave, Jul 16, 2005.

  1. Caver Dave

    Caver Dave Just holdin' it down here in BFV Moderator

    Joined:
    Mar 10, 2005
    Location:
    Hooterville (24171)
    For over 5 years, I've fought the draglink contacting the Pass.front spring (D30 NT, SOA, stock leafs, 4" drop pitman arm). Usually, it puts just a scrape on it and puts a slight bend in it. Only at places like Tellico & Windrocks when getting everything crossed up good or tires bound (usually in BFE) does the DL pretzel (3 & counting :mad: ).

    Anyways, I've looked at it numerous times and it *appears* the PO put too much caster in (pinion pointed more towards ground than TC... steering arm on knuckle parallel/even with spring...IOW, rotated back too far). I'm getting ready to go thru the axle (balljoints, spindle bearings, LOCKER... all setting here since May), install some Waggy offset front leafs (the ducktape on my OEM leafs is starting to fray :flipoff2: ), and new "anti-wrap" perches (OEMs are like 3" long :rolleyes: )

    How do I correctly measure the caster? Some say the flat of the chunk, some the perches once the chunk is 90* to flat surface, & other "less credible sounding" methods :confused: SCREW "eyeballing it"... that doesn't tell me anything! :D

    This should confirm my theory and allow me to correct it with new perches. If I can gain enough between the DL & spring... Big Daddy's "ALL Beef" DL/TR set *WILL* be going in (extremely tired of this crap!) once the axle is back underneath.

    TIA
     
  2. Lee

    Lee ECGS

    Joined:
    Mar 20, 2005
    Location:
    Rougemont NC
    The way I have always done it is to put an angle finder on a flat part on top of the knuckle. Not saying it is the "correct" way, but it has never let me down
     
  3. Rich

    Rich Asshole at large

    Joined:
    Mar 17, 2005
    Location:
    Central PA
    The true way to measure it requires tearing down the knuckle... Caster is the line though the upper and lower balljoints, being forward or backwards of a vertical line through the center.

    When we do a cut & turn, I run a large bar through the upper and lower, and take measurements from that...

    Could you maybe lay a flat edge across the front of the inner C and get the angle from that? Not terribly familiar with D30's..

    Oh, and you should thank the PO for adding caster, it's helping the front end track straight/avoid death wobble...
     
  4. Tradarcher

    Tradarcher Well-Known Member

    Joined:
    Mar 20, 2005
    Location:
    Creedmoor, NC
    Hope I don't convolute this thread, but does caster matter much on a trail only rig?
     
  5. Rich

    Rich Asshole at large

    Joined:
    Mar 17, 2005
    Location:
    Central PA
    If you ever get to ~35mph, it'll matter.

    My junk is "trail-only", but there are times when it does see street time, limited as it may be.

    A nice side benefit of the cut & turn to get caster, is the 6" of additional ground clearance I gained at the pinion.. :D
     
  6. Down&Dirty

    Down&Dirty Well-Known Member

    Joined:
    Jun 26, 2005
    Location:
    Greenville SC
    Alignment machine will do it no problem. Other than that you can put a little spacer on the axle where the ball joints tie in. Then place a piece of steel between the spacers. Make sure the spacers are the same size. This will kill the measurement if they aren't. Then put the angle finder on it and run. If the pinion is pointed towards the ground, and you don't have enough caster then you will have to break the knuckles loose and redo the caster. I shot for 6-8 degrees when I set mine up, but I don't know what you should aim for. All I know is that I run 35s with no stabilizer at speeds up to and exceding 70 mph. So it isn't the best thing to do, but I am trying to slow down.
     
  7. uglyjeepoffroad

    uglyjeepoffroad Registered Loser

    Joined:
    Mar 20, 2005
    Location:
    Hickory, NC
    I think I know where one of those 3 draglinks came from. :flipoff2:
    I was always told that, if you wanted to keep stock caster on a SOA, make sure the new perches are exactly parallel to the OEM.

    Hurry up, so you can send me my spare DL back... :beer:
     
  8. grapehead

    grapehead Well-Known Member

    Joined:
    Mar 21, 2005
    Location:
    Raleigh
    yeah, id second throwing it on an alignment machine, many places will do a free check.

    then you will have an exact number for current situation, and know exactly how many degrees of correction you need.
     
  9. Aaron871

    Aaron871 Member

    Joined:
    May 11, 2005
    Location:
    Charlotte, NC

    BTW:
    On my old CJ (you know the one) my DL never rubbed until I installed the Big Daddy drag link. The diameter is bigger. So make sure you take that into account when you set it up. :)

    I used a straight pitman arm to get it off of the springs....
     
  10. OBX Fisherman

    OBX Fisherman Well-Known Member

    Joined:
    Mar 21, 2005
    Location:
    Winston-Salem
    I'd also like to be able to measure the castor on my axle. With the long arms everything is adjustable and my only source of info was from the installation instructions which said to set the UCA to 16 3/4" in length. It seems to drive fine the way it's set, but I would like to know if its correct. I'm not sure an alignment shop would want to unbolt the UCA to adjust them either.

    Gary
     
  11. braxton357

    braxton357 Robot

    Joined:
    Apr 6, 2005
    Location:
    Morganton

    Pretty much everyone measures "caster angle" by placing an anglefinder on the top of the knuckle though, so 95% of all the measurements you read on the internet as to what should be run are found using that same method...therefor, if you were going to set your own caster...it would be a good choice to use that method to measure it.
     
  12. Caver Dave

    Caver Dave Just holdin' it down here in BFV Moderator

    Joined:
    Mar 10, 2005
    Location:
    Hooterville (24171)
    I'd thought of that... hopefully the angle finder method will tell me something good (eyeballing says the there's too much caster & the pinions pointed down). I may have to hunt down a pitman arm with more drop to get farther under the leafs (I'm SOA & your CJ was SUA)... hell, the pitman arm may be the whole problem anyway!

    :beer:
     
  13. foreman1063

    foreman1063 Well-Known Member

    Joined:
    Jul 11, 2005
    Location:
    Raleigh
    Check out this link. Seems like a logical method. I put the angle finder on my front diff today and got a reading of -8 degrees. According to this method my caster would be 4 degrees which is probably right since I just installed a 3.5 inch lift and have not had the caster checked and adjusted at a shop yet. When I take it into the shop I'll see what the caster is before the adjustment and see if it matches my findings. I'll post the results if anyone is interested.
    John

    http://go.jeep-xj.info/HowtoAlignment.htm
     
  14. just-fabricate-it

    just-fabricate-it New Member

    Joined:
    Mar 21, 2005
    Location:
    Raleigh
    Do you know anybody that races oval track cars locally?

    Gauges like this
    http://circletrack.com/howto/138_0306_meas_caster_camber/
    are pretty common to those guys. It needs a flat spot on the hub to magnetically mount. A lot of the oval track guys also have a jig that mounts on the outside of the wheel rim and then the gauge mounts to it.
     
  15. Lizooki

    Lizooki Well-Known Member

    Joined:
    Mar 21, 2005
    Location:
    Stokes Co. NC
    Yeah...why not just use a castor/camber guage. It's good enuff fer 200 mph racecars. We used it on our shorttrack car. Only thing better or more accurate would be the alignment machine. You just stick it on with the wheels straight, that tells one, full lock right then full lock left tells the other.


    Matt :huggy:
     
  16. foreman1063

    foreman1063 Well-Known Member

    Joined:
    Jul 11, 2005
    Location:
    Raleigh
    I took the Jeep in today to have the alignment checked and this caster adjusting method seems to be fairy accurate. I was off less than one degree from the alignment computer. Just thought I'd let you know.
    John
     

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