How to measure castor?

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Oct 24, 2006
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I just imported an HDJ 81 and it came with a mystery 5" lift (decided it was 5" from this baord with comparing center hub to bottom flare measuements) . It has camber bushings. The ride is a little sketchy at higher speeds and after reading all the info on castor, I believe mine is significanly off.
On a u-joint axle you can put an angle finder on the knuckle to find out your castor. I'm new to birfields, how would you do this?
I have castor plates from slee and will install these and replace the castor bushings with stock. After this I would like to measure the castor and lower the arms until the angle is back to stock. Any ideas/help would be appreciated.:)
 

landtank

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I personally would have pressed in the stock bushings then had an alignment reading done before buying anything. At least then you could formulate a solution.

Anyway, plates might do it or possible Slee's arms who knows?
 
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On top of the knuckle there are 2 large bolt heads. When my HDJ81 was bone stock I measured with a magnetic base angle finder on the tops of these 2 bolts and the caster was between 2 and 3 degrees so I think it seems like a suitable way to measure.

After adding J springs and a 30mm spacer to the front I had lost 6 degrees which I corrected with the "washer method" this weekend. Caster now measures 1.5 degrees (same on each side) and I'm lined up perfectly for a DC front shaft. Once I add my front ARB bumper and the springs settle a bit I expect to see the caster at 2 degrees or slightly better. It's very drivable right now so I'm happy and that's what really counts.
 
Joined
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Abbotsford BC
On top of the knuckle there are 2 large bolt heads. When my HDJ81 was bone stock I measured with a magnetic base angle finder on the tops of these 2 bolts and the caster was between 2 and 3 degrees so I think it seems like a suitable way to measure.

Thanks AdamB. That helps. As soon as I get my truck back from inspection I'll measure and see where I'm at. Right now at about 100km it feels a little spooky.
 
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Yeah, even with only 3" of lift from the J springs before adding the front spacer I found it to be a bit darty on the highway over 100km/h. Much worse on wet road with the 34" Trxus.

If you've got around 5" of lift and caster bushings you're probably still not even back to 0 degrees....
 

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