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Unread 11-19-2012, 05:06 PM   #1
freerider
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Possible to measure caster using front spring pad?

Im trying to see if my caster is correct after adding a front spacer on my LJ. Will an angle finder on the axle spring pad give a correct measurement? It seems as if it would.

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Unread 11-19-2012, 05:12 PM   #2
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Looking at a CAD drawing I have of an HP D30 (don't remember where I found it, but it has "Clayton" drawn into one of the pieces), the caster is shown at 7 degrees back from the vertical, and the spring pad is shown at 3 degrees up from the horizontal. If yours is the same as this setup, add 4 degrees to the spring pad angle (take the spring pad angle as negative if it points toward the front of the Jeep) to get your caster angle.

Edit: Found it - http://www.claytonoffroad.com/docume...231Drawing.PDF Go to the third page.
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Unread 11-19-2012, 05:34 PM   #3
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Quote:
Originally Posted by freerider View Post
Im trying to see if my caster is correct after adding a front spacer on my LJ. Will an angle finder on the axle spring pad give a correct measurement? It seems as if it would.
no.

FWIW, I've found no good spot on the housing to correctly measure caster repeatably and equal to a laser alignment rack. Tried the socket on the ball joint trick, lower C's, blah blah blah. Best I found was to get an alignment, after putting an angle finder either on the u-joint of the pinion, or on the housing spreader holes on the front and recording that number. Then you have a "calibration". Then when you change caster again later, you know 1° movement on your angle finder will linearly relate to the actual laser alignment rack by the same amount.
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Unread 11-19-2012, 08:15 PM   #4
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I use an angle finder with a straight edge. The angle finder is magnetic and has a place specifically to put a straight edge. There's a flat on the bottom of the "C" just inside of the lower ball joint, part of where the "C" is machine for the ball joint. It's as accurate as the angle finder itself. When measured on the alignment rack, the measurements were within a degree.
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Unread 11-19-2012, 08:33 PM   #5
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Originally Posted by Patrick H View Post
When measured on the alignment rack, the measurements were within a degree.
that is my point. +/- 1° can be a big difference when talking about caster...
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Unread 11-19-2012, 09:32 PM   #6
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Originally Posted by Unlimited04 View Post
that is my point. +/- 1° can be a big difference when talking about caster...
The discrepancy is in the angle finder itself I'm sure. I've run my caster (using this method) from 5° to 7.5°. I ended up setting it @6° and it handles great.
I guess if I can make it drive well, +/- 1° is good enough for me. The actual number is not as important as toe, as long as it handles properly.
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Unread 11-19-2012, 09:35 PM   #7
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Originally Posted by Patrick H View Post
The discrepancy is in the angle finder itself I'm sure. I've run my caster (using this method) from 5° to 7.5°. I ended up setting it @6° and it handles great.
I guess if I can make it drive well, +/- 1° is good enough for me. The actual number is not as important as toe, as long as it handles properly.
problem is you don't know if it's 6° tho, since your tolerance is +/- 1°. and it doesn't matter where the discrepancy is, the tolerance is 40% of your range, so the measurement system sucks.

FWIW, I do agree the actual number is not as important as the fact that you like the way it handles - but that also means you can not make a decision or recommendation based on your measurement method. You simply don't know what your caster is. All you know is it drives fine for you. It's qualitative vs quantitative.
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Unread 11-19-2012, 10:19 PM   #8
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Quote:
Originally Posted by Unlimited04 View Post
problem is you don't know if it's 6° tho, since your tolerance is +/- 1°. and it doesn't matter where the discrepancy is, the tolerance is 40% of your range, so the measurement system sucks.

FWIW, I do agree the actual number is not as important as the fact that you like the way it handles - but that also means you can not make a decision or recommendation based on your measurement method. You simply don't know what your caster is. All you know is it drives fine for you. It's qualitative vs quantitative.
Well, I know it's likely between 5.5° and 6.5°. If I really wanted to know for sure I could put it back on the rack.
My home- measurement system may not be good enough for you, but it gets me within a known parameter, and I know where it handles best within those.
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Unread 11-19-2012, 10:23 PM   #9
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For that matter, I could go buy a higher quality angle finder and get even closer.
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Unread 11-20-2012, 07:39 AM   #10
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Originally Posted by Patrick H View Post
Well, I know it's likely between 5.5° and 6.5°. If I really wanted to know for sure I could put it back on the rack.
That's exactly my point. If you want an accurate measure, you need to start on the rack.

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Originally Posted by Patrick H View Post
For that matter, I could go buy a higher quality angle finder and get even closer.
I've tried all the tricks I can think of with a digital angle finder that is about +/- 0.1°. What I've noticed on the two housings I've had is about what you're seeing...a good +/- 1° variation, and that it doesn't necessarily measure the same twice in row. For example, using the socket on the ball joint or lower-C tricks, today might show 6°, but next Tuesday may show 5° and the next Tuesday may show something totally different...and none of those necessarily equal what the rack says.

Like I mentioned above, the best I've found is getting it on the rack at least once, then relate that to pinion angle measured from a machined surface. Now, for future reference you know you can change the caster and watch pinion angle, and the delta will be the same.

The OP is looking for a way to get a correct caster measurement...and the only way to know that is start with the alignment rack to get a baseline measurement.
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Unread 11-21-2012, 09:13 AM   #11
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Im putting on a front G2 dana 44 and will have a shop check allignment after the swap.
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Unread 11-21-2012, 09:45 AM   #12
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A degree or 2 of caster is not going to make a noticeable difference in how the vehicle handles. If the spec for caster on the TJ is to be within 5-7 degrees then thats all that matters. Your not going to notice a difference between being at 5 degrees vs. 7 degrees.......FWIW what type of spacer is being put on exactly?
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Unread 11-21-2012, 09:59 AM   #13
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Originally Posted by GMBNT42 View Post
A degree or 2 of caster is not going to make a noticeable difference in how the vehicle handles. If the spec for caster on the TJ is to be within 5-7 degrees then thats all that matters. Your not going to notice a difference between being at 5 degrees vs. 7 degrees.......FWIW what type of spacer is being put on exactly?
I felt a very clear difference between 5° and 7° on my Jeep.
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Unread 11-21-2012, 10:02 AM   #14
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Quote:
Originally Posted by Unlimited04 View Post
I felt a very clear difference between 5° and 7° on my Jeep.
What differences did you feel? Trying to determine where I want to set mine with 37's. Was thinking 4-5 deg.
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Unread 11-21-2012, 10:26 AM   #15
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What differences did you feel? Trying to determine where I want to set mine with 37's. Was thinking 4-5 deg.
the road crown around here sucks and at 5° it followed every defect, return to center blew, and the steering felt very dartish with little resistance and no tendency to want to go straight with no hands on the wheel/little input. I also had a harmonic steering vibration feedback (not DW) at certain speeds, which could yield DW if hitting a big enough bump. As I dialed the caster up in 0.5° increments (with corresponding toe adjustments), the vibration incrementally moved into different speed ranges, incrementally decreased, and road crown became less and less an issue. Measured & aligned each time at Firestone, via my lifetime alignment. I finally settled at 6.5° caster and the drive-ability is pretty damn good, with no wobbles, and I can hold straight on uneven road surfaces & high winds. For reference, I had this conversation with -sean-, and IIRC, he ran 7° on 30s, 35s and 37s on his L-TJ. My neighbor has a very custom XJ, he runs 33s w/ 8° caster, after cutting the inner C's off and rotating them. So I don't drink this lower caster with bigger tires Kool-Aid. I say start someplace and dial it higher until you find something you like.
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