*CORRECT* method to measure caster angle?

Caver Dave

Caver Dave

Just holdin' it down here in BFV
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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
 
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...
 
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
 
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.
 
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:
 
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.
 
Caver Dave said:
Big Daddy's "ALL Beef" DL/TR set *WILL* be going in (extremely tired of this crap!) once the axle is back underneath.

TIA
Click to expand...


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....
 
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
 
Rich said:
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...
Click to expand...


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.
 
Aaron871 said:
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.
Click to expand...

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:
 
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
 
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:
 
foreman1063 said:
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
Click to expand...
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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