Where to measure caster angle at? - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Wrangler Forums > TJ Wrangler Technical Forum > Where to measure caster angle at?

HELLA FF75 12V 55W H7 Fog Lamps - SPECIAL OVERSTOCK SALE FBaseline 4x4 Lifetime Warranty 4340 Chromoly Axle Shaft KiJeep Gear & Install Packages!

Reply
Unread 06-17-2009, 09:54 PM   #1
TJW909
Registered User
1998 TJ Wrangler 
 
Join Date: Apr 2007
Location: Maple Park, IL
Posts: 152
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.

TJW909 is offline   Reply With Quote Quick reply to this message
Unread 06-18-2009, 04:33 AM   #2
TJW909
Registered User
1998 TJ Wrangler 
 
Join Date: Apr 2007
Location: Maple Park, IL
Posts: 152
bump to the morning crowd
TJW909 is offline   Reply With Quote Quick reply to this message
Unread 06-18-2009, 04:45 AM   #3
5-90
Registered User
1988 XJ Cherokee 
 
Join Date: Sep 2006
Location: San Jose, CA, Hammerspace
Posts: 5,344
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.)
__________________
"recon" (sic - reckon)(tm) "hihgly"(tm) "seceed"(tm)
"Outback AIDS - Alcohol-Induced Dizzy Spells"
5-90 is offline   Reply With Quote Quick reply to this message
Unread 06-18-2009, 05:03 AM   #4
Tom Hartz
Registered User
1997 TJ Wrangler 
 
Join Date: Oct 2005
Location: Santa Clarita, Ca.
Posts: 433
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
Tom Hartz is offline   Reply With Quote Quick reply to this message
Unread 06-18-2009, 05:36 AM   #5
5-90
Registered User
1988 XJ Cherokee 
 
Join Date: Sep 2006
Location: San Jose, CA, Hammerspace
Posts: 5,344
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.
__________________
"recon" (sic - reckon)(tm) "hihgly"(tm) "seceed"(tm)
"Outback AIDS - Alcohol-Induced Dizzy Spells"
5-90 is offline   Reply With Quote Quick reply to this message
Unread 06-18-2009, 12:20 PM   #6
TJW909
Registered User
1998 TJ Wrangler 
 
Join Date: Apr 2007
Location: Maple Park, IL
Posts: 152
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?
TJW909 is offline   Reply With Quote Quick reply to this message
Unread 06-18-2009, 12:28 PM   #7
robncar
Registered User
2005 TJ Wrangler 
 
Join Date: Nov 2005
Location: La Verne, CA
Posts: 8,423
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.
robncar is offline   Reply With Quote Quick reply to this message
Unread 06-18-2009, 12:42 PM   #8
cj847
Registered User
1997 TJ Wrangler 
 
Join Date: Oct 2006
Location: AR
Posts: 1,189
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.
cj847 is offline   Reply With Quote Quick reply to this message
Unread 06-19-2009, 02:08 PM   #9
TJW909
Registered User
1998 TJ Wrangler 
 
Join Date: Apr 2007
Location: Maple Park, IL
Posts: 152
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???????
TJW909 is offline   Reply With Quote Quick reply to this message
Unread 06-19-2009, 09:56 PM   #10
spencerd76
Registered User
2001 TJ Wrangler 
 
Join Date: Feb 2007
Location: New Castle, IN
Posts: 52
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.
spencerd76 is offline   Reply With Quote Quick reply to this message
Unread 06-20-2009, 08:56 AM   #11
robncar
Registered User
2005 TJ Wrangler 
 
Join Date: Nov 2005
Location: La Verne, CA
Posts: 8,423
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...
pinion-1.jpg   pinion-2.jpg  
robncar is offline   Reply With Quote Quick reply to this message
Unread 06-20-2009, 03:22 PM   #12
Jerry Bransford
Administrator
 
Jerry Bransford's Avatar
2004 TJ Wrangler 
 
Join Date: Jan 2003
Location: Escondido, California, California
Posts: 60,726
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.
__________________
Getting Savvy...

Coolest offroad magazine ever! CRAWL Magazine

When you have a choice, buy American.
Jerry Bransford is offline   Reply With Quote Quick reply to this message
Unread 11-05-2010, 07:03 PM   #13
Eskimo
Registered User
2004 TJ Wrangler 
 
Join Date: Apr 2008
Location: Denver, Colorado
Posts: 9
thanks for the pics I've been looking for something like that myself to check where mine is at thanks again guys
Eskimo is offline   Reply With Quote Quick reply to this message
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.
Note: All free e-mails have been banned due to mis-use. (Yahoo, Gmail, Hotmail, etc.)
Don't have a non-free e-mail address? Click here for a solution: Manual Account Creation
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.


Thread Tools


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.