Question on caster alignment

[Eagle]

Here ya go.

http://go.jeep-xj.info/HowtoAlignment.htm

The toe in procedure works good, I am still tying to figure out the caster measurement.

Refer to the diagram Langer1 posted above.

Your understanding of positive and negative caster is backwards. Caster is what used to be catted "kingpin angle" when front suspensions had a single kingpin that ran from the upper yoke to the lower yoke. Now we have an upper ball joint and a lower ball joint. The caster angle is the angle of the imaginary line that connects them. Caster is positive if the upper ball joint is farther back than the lower (as pictured in Langer1's illustration), and negative if the upper ball joint is farther forward than the lower.

What GoJeep has done is document the fixed relationship between the differential housing and the steering knuckle. Once you know the difference between the two, by measuring the angle of the differential housing you can calculate the caster angle directly. Remember, the knuckles are welded to the axle tubes, and the exle tubes are pressed and welded into the differential, so if you change the caster angle you simultaneously change Dke angle of the`lifferential hodqing (a>a phnion%shaft)@dy the same amount.

 

[jcnoble]

Yes, I understand caster angle. What i don't know is where to measure the angle of the diff. cover or axle. And where does the 9 degrees come from, is that the offset of the ball joints from the axle? If i measure from the flat spot on the bottom of the diff cover i get 1 degree from vertical. If I subtract from 9 thats 8 degrees. The shop says I am at 6.5. It seems I am not measuring the axle rotation correctly.

 

[langer1]

I had pictured caster angle backwards also, untill you look a the front wheel of a Motorcycle or bike.

 

[langer1]

Yes, I understand caster angle. What i don't know is where to measure the angle of the diff. cover or axle. And where does the 9 degrees come from, is that the offset of the ball joints from the axle? If i measure from the flat spot on the bottom of the diff cover i get 1 degree from vertical. If I subtract from 9 thats 8 degrees. The shop says I am at 6.5. It seems I am not measuring the axle rotation correctly.

He is measuring the flat surface on the back of the diff housing, where the cover is bolted on.

If that cover surface was straight up and down (90 deg) the caster would be (9 deg) because the knuckles are welded on at (81)deg. I don’t by the whole thing though because your floor would have to be perfectly level to start and most concrete is sloped for drainage.

 

[ang31-0f-d347h]

wow guys...

I think im getting it slowly.

may I ask what is the point in have 9 degree caster in a direction? why not make it 0 ?

 

[ang31-0f-d347h]

well... I have to admit this is kind of embarassing.
I love my Jeep but im having serious trouble understanding this stuff. Im really a more hands on kind of guy. I wish I knew some jeep people in tampa. I do computer networking , body piercing, and goto college. so you figure I would be able to figure something like this out really easy. but I guess not.
sigh

 

[langer1]

The caster causes the wheels to return to straight ahead. Without caster you have to steer all the time as the wheels will not want to stay straight ahead. To much caster and you can't turn easily.

 

[jcnoble]

I saw a good post on caster. I wish I could remember where. Actually most vehicles used to have negative caster before radial tires, this makes low speed handling easier, positive caster became more prevalent after radial tires for better high speed handling. So the post said.

 

[ang31-0f-d347h]

hmm.
I have the same issue with wobble

I dont know if I trust the mechanics that worked on my car. I wish i knew a good one in tampa... or way to check if my control arms are adjusted correctly. They tried to tell me the couldnt adjust them more (rustys control arms) something about them not being adjustable enough.

 

[techno1154]

On two of Eagles post, he seem to contradict himself. One post said that no caster should positiov and on the other he said that the caster should be positive. Which one is it? :dunno: My XJ has about 3* of positive caster with Rusty's LCA that meaures 16.25". Of couce the drive shafr vibrates above 45 MPH so that is riding in the back if the XJ and the wheel is lazy to return to straight after a turn. I need to get it done properly once and for all.
:doh:

 

[ang31-0f-d347h]

On two of Eagles post, he seem to contradict himself. One post said that no caster should positiov and on the other he said that the caster should be positive. Which one is it? :dunno: My XJ has about 3* of positive caster with Rusty's LCA that meaures 16.25". Of couce the drive shafr vibrates above 45 MPH so that is riding in the back if the XJ and the wheel is lazy to return to straight after a turn. I need to get it done properly once and for all.
:doh:

I know how you feel dude.
I feel the same way.
(im sorry I dont have your answer)

 

[Dirk Pitt]

On two of Eagles post, he seem to contradict himself. One post said that no caster should positiov and on the other he said that the caster should be positive. Which one is it? :dunno: My XJ has about 3* of positive caster with Rusty's LCA that meaures 16.25". Of couce the drive shafr vibrates above 45 MPH so that is riding in the back if the XJ and the wheel is lazy to return to straight after a turn. I need to get it done properly once and for all.
:doh:

How much lift do you have?

XJ's should have 5-7 deg of POSITIVE caster.

 

[Danno]

you also need to check the track bar mounts on both ends. I've worked on half dozen XJs with DW and they ALL had trackbar looseness to some degree. Have somebody start the vehicle and rotate the steering wheel back and forth without actually turning the wheels. Check both ends of the bar for looseness. You'll be surprised at how loose these things can get. It's a common XJ problem. Also the axle end of the TB bolt wallows out the hole it's mounted in. HTH, Danno

 

[langer1]

There was no contradiction, Eagle's post was in reply to a post the said he had -5 deg, Eagle's post was NO (as in wrong) caster should be + not-

 

[jcnoble]

I think I'm gonna get rid of my flimsy tie rod and go with some kind of inverted y or o.t.k. setup. Right now Ive got my eye on the bulletproof stuff. Looks pretty beefy. They have a track bar with Heim joints on both ends. They claim its quiet on the street. Price is right also.

 

[Dirk Pitt]

I think I'm gonna get rid of my flimsy tie rod and go with some kind of inverted y or o.t.k. setup. Right now Ive got my eye on the bulletproof stuff. Looks pretty beefy. They have a track bar with Heim joints on both ends. They claim its quiet on the street. Price is right also.

What's the steering configuration now?

 

[jcnoble]

Stock junk right now. I think the flimsy tie rod may be adding to my dw problem. Oh by the way, I am going to try to videotape my dw today. I have never seen it visually. I will post it if successful, I got a volunteer to ride in passenger seat with camcorder.

 

[techno1154]

There was no contradiction, Eagle's post was in reply to a post the said he had -5 deg, Eagle's post was NO (as in wrong) caster should be + not-

The '+' means the pinion looks up or down? My Home Depot angle finder goes from 0 - 90*. With the angle finder on the bolts on the diff, it reads 87*. That means the pinion looks down 3*; 3* down from a 90* vertical. I am having a bit of problem understanding how one arrive at the 9* and 81* mentioned in earlier posts. What do these numbers represent?

 

[RCP Phx]

From GoJeep's page.

I check caster by using a bevel square ( adjustable square ) with a level on it against the diff cover bolt heads that are above and below the axle or use the flat round area next to this. Then use a protractor the read the degrees. I have checked many XJ's including one that was still on the showroom floor and providing you are on level ground then it should read 87.5 degrees if done as shown. This is not the true caster angle as the steering knuckles are at a different angle but they will always be relative to this angle so it is used as a reference point. But with these Dana 30 hi pinion's, you can work out the caster by the formula; 9 - diff angle = caster which Max Johnson from feels he worked out first. This was very easy to work out as once you know what the true caster read from a print out you only have to work out what to add to the diff cover angle ( in this case -2.5 degrees ) to get to +6.5 degrees ( -2.5 + 9 = 6.5 degrees of caster ). You always start with 9 degrees and subtract the amount off vertical read on your protractor, ( -2.5 degrees ) = a caster of 6.5 degrees.

If you have a standard pinion like that come on '00-'02 XJ's then the rule does not apply as Angus from found out. He took the measurements and compared them to a stock late model XJ and found that they run 7 degrees of caster and after having an alignment done I was able to work out that on the standard pinion ( the front uni is near the bottom of the diff ) they have a 12 degree start value instead of the 9 degrees as used above. i.e.. if you measure 5 degrees off the vertical your have 7 degrees of caster ( 12 - 5 = 7). It makes sense that the start value is higher as the pinion still has to point at the transfer case yoke ( 3 degrees below it usually ) but with a low pinion it starts off quite a bit lower to start with so needs more angle to start with

 

[Gojeep]

The '+' means the pinion looks up or down? My Home Depot angle finder goes from 0 - 90*. With the angle finder on the bolts on the diff, it reads 87*. That means the pinion looks down 3*; 3* down from a 90* vertical. I am having a bit of problem understanding how one arrive at the 9* and 81* mentioned in earlier posts. What do these numbers represent?

You have 87* which = 3* off vertical. 9-3 = 6* of caster. The 81*= 9* off true vertical ( 90* ) so is the same thing. This angle is what the knuckles ( hence caster ) are welded at compared to the pinion or diff cover angle.
Hope that helps.