Where to measure caster angle at? - JeepForum.com
 
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post #1 of 13 Old 06-17-2009, 08:54 PM Thread Starter
TJW909
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Where to measure caster angle at?

I wish I was not so picky about things. Where are you guys measuring the caster angle at for the front diff. I just installed a different axle assy and I have cam adjusters just wanted to get it dailed in.

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post #2 of 13 Old 06-18-2009, 03:33 AM Thread Starter
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bump to the morning crowd
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post #3 of 13 Old 06-18-2009, 03:45 AM
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Caster angle, or pinion angle? The way you're phrasing the question, I'm not sure which you want...

If you're working with pinion angle, the front driveshaft usually has a Double Cardan joint at the transfer case output. If so, the transfer case output shaft axis should be horizontal, and the pinion axis should point at the centre of the Double Cardan knuckle.

If you're actually talking about caster angle - the alignment spec - "caster" is the difference between a line drawn between the axes of the ball joint studs and a theoretical vertical line looking forward at the end of the axle.

There are three wheel alignment specifications:
"Toe" - "toe in" means that the front of the tyres are slightly closer together than the rear. "Toe out" means that the front of the tyres are slightly farther away than they are at the rear. This is typically measured in sixteenths or thirty-seconds of an inch.

"Caster" is the difference in angle between the axes of the ball joint studs (also called the "steering axis,") and a theoretical vertical line, viewed from the side (along the axis of the axle shaft.) Caster is usually the angle that makes steering self-correcting - if the lower ball joint is forward of the theoretical vertical line, you have "positive caster" - if the lower ball joint is aft of the theoretical vertical line, you have "negative caster."

"Camber" is similar, but you are now viewing from the front of the vehicle (you're still referring to the angular difference between a theoretical vertical line and a line through the axes of the ball joint studs.) Positive camber means that the wheel is tilted outwards, while negative camber means it's tilted inwards.

As a good demonstration of camber problems - think of a VolksWagen Baja Bug. They're usually lifted a few inches, but they use a "swing axle" design that can't readily be corrected for lifted geometry (or for lowered, in case it's been slammed.) Since the halfshafts don't change length, lifing the Bug will get you a heft positive camber problem, while lowering it gives you the same problem in reverse.

Chances are, you've seen a Bug somewhere down the line with either a fairly hefty lift or lowering job, so you should have no trouble picturing this once you recall. I know it can be corrected - I've seen it done - but I just don't know how.

When lifting or lowering any vehicle with a swing axle, and most vehicles using independent halfshafts, you're going to run into a camber problem (not so much using SLA suspensions, since both wheels are tied together anyhow on the opposite ends of an effectively solid beam.)

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post #4 of 13 Old 06-18-2009, 04:03 AM
Tom Hartz
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I think TJW909 is asking where is the best place to put the angle finder to check the caster. I too would like to know this.

Thanks.

Tom
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post #5 of 13 Old 06-18-2009, 04:36 AM
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Ah - then I'm not entirely sure. You have to make sure you get the correct steering axis - which would be difficult.

Getting the vertical is easy - a plumb bob and string will give you what you need there.

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post #6 of 13 Old 06-18-2009, 11:20 AM Thread Starter
TJW909
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Yep I am more worried about pinion angle. I have seen before that just going off the driveshaft and ujoint at the ft diff with an angle finder. And it sounds like 5-6 degrees with a little lift on the rig. Is this sounding correct? Both are changing anyway when you adjust the cam bolts caster and pinion angle?
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post #7 of 13 Old 06-18-2009, 11:28 AM
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Quote:
Originally Posted by TJW909 View Post
Yep I am more worried about pinion angle. I have seen before that just going off the driveshaft and ujoint at the ft diff with an angle finder. And it sounds like 5-6 degrees with a little lift on the rig. Is this sounding correct? Both are changing anyway when you adjust the cam bolts caster and pinion angle?
Pinion angle takes precedence over caster on a TJ. Yes, pinion angle and caster are directly joined together.

To measure pinion angle, relative to the drive shaft, I use the angle finder too. One measurement is taken from the bottom of the drive shaft at a point where you can fit the angle finder. The second measurement, I take from one of the two machined circles that are on either side of the front diff cover. These two circles are 90 degrees to the pinion. Your two measurements, when added together need to equal 90 (or 89 to 91). That will give a pinion angle of 0 degrees. Your pinion, once adjusted either with cam bolts or adjustable upper control arms should be +-1 degree.

http://www.jeepforum.com/forum/f9/diy-alignment-kit-steps-w-pics-2264465/
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post #8 of 13 Old 06-18-2009, 11:42 AM
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Quote:
Originally Posted by TJW909 View Post
I wish I was not so picky about things. Where are you guys measuring the caster angle at for the front diff. I just installed a different axle assy and I have cam adjusters just wanted to get it dailed in.

On the bottom of the inner "C" there is a straight flat rib. That is the best place I have found.

97 TJ Sport OPJ project (other peoples junk) I can't remember the last time I bought a new part.
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post #9 of 13 Old 06-19-2009, 01:08 PM Thread Starter
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Well finally got out to finish up. I can get nothing better than 5 degree's I am measuring at the middle of the front ds (on the tube) and also at the ear of the slip yoke with it bolted to the output yoke on the diff. I can see the rotation of the yoke but the magnetic angle finder is not moving much at all when turning the cam bolts? Time for adjustable arms???????
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post #10 of 13 Old 06-19-2009, 08:56 PM
spencerd76
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my 2cents...i just completed a homemade front long arm build and have been wondering all about the angles and making them exactly where they should be. after talking to my alignment guy he told me simply to put the ball joint at about 1 o'clock or 4 degrees. after that bring it to him and he would do the rest with the alignment.
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post #11 of 13 Old 06-20-2009, 07:56 AM
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Quote:
Originally Posted by TJW909 View Post
Well finally got out to finish up. I can get nothing better than 5 degree's I am measuring at the middle of the front ds (on the tube) and also at the ear of the slip yoke with it bolted to the output yoke on the diff. I can see the rotation of the yoke but the magnetic angle finder is not moving much at all when turning the cam bolts? Time for adjustable arms???????
I guess I don't know what you mean by "the ear of the slip yoke"?

Your middle of the DS sounds fine for the DS reading. The other (pinion end) measurement, if you are trying to get a yoke measurement, should be made using a socket on the u-joint that is attached to the pinion yoke, NOT a surface that is attached to the DS side of the pinion yoke.

When you are done setting pinion angle, the two measurements should be the same, plus or minus one degree.

I, as stated in your other post, use the two machined surfaces that are of each side of the diff cover that are parallel to the pinion. But, to each his own.

Here's a couple pics from Stu's website that illustrates what I'm trying to say...
Attached Thumbnails
pinion-1.jpg   pinion-2.jpg  

http://www.jeepforum.com/forum/f9/diy-alignment-kit-steps-w-pics-2264465/
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post #12 of 13 Old 06-20-2009, 02:22 PM
Jerry Bransford
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A more accurate way of measuring the pinion angle that does not depend on the yoke being perfectly vertical is to measure from one of the two flats on the rear of the axle located on either side of the diff cover.

These two illustrations from Tom Wood's website show what I mean...




Of course you don't need to use a digital angle tool, one like Rob has in his above post works fine too.

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post #13 of 13 Old 11-05-2010, 06:03 PM
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thanks for the pics I've been looking for something like that myself to check where mine is at thanks again guys
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