Shadetree Caster

[Bornindesert]

Today the '88 got treated to a radiator flush courtesy of my 16 y/o son, and is pretty much ready to roll after almost a year of rebuilding the truck. Last on the list, front end alignment. I set the tow in to an 1/8", and centered the steering wheel. The track bar is a JKS and has the axle pretty close to dead on center. Now comes the question... 

 

I set the UCA and LCA length up for a 4" lift, they are both adjustable. The ride height is closer to 5" of lift now that I've mearsured it. So, the visual eye ball castor seems like 6-8 degrees (maybe more) when I think stock is more like 2-3 degrees. The pinion angle is about horizontal to the ground, and I think it needs to be pointed at the TC.

 

The lower ball joint is fresh, and it set about 0.20" below flush. I think this is more a camber adjustment?

 

Before I push it out of the garage, wanted to set the castor or at least get it close. Three or four closing turns on the LCA's should raise the pinion and reduce the castor. Does anyone know how to properly mearure castor? I know it's the angle formed through the upper and lower ball joints looking from the side, but I can't seem to find a place to set up the angle gage. Have never done this adjustment before so any advice or experience would be great.

 

 

 

 

[HOrnbrod]

After lift to get in the ballpark, I roughed in the caster by setting a magnetic angle finder on the top flat of the upper ball joint on both sides. It read about 4*. Then added shims to the LCAs (non-adjustable) until I reached 7* (spec caster angle). Took an equal amount of shims on both sides. The next day I got an alignment at a shop and the caster was spot on at 7*. If you can't set the angle finder flush on the top of the upper ball joint because of the zerk fitting, you can use a socket between the angle finder and ball joint.

[Bornindesert]

Thanks Hornbord, I might be closer to where it should be set than I expected. Definitely makes sense to set up the magnetic angle finder on top of the knuckle. When you shimmed, you corrected the caster by moving the LCA's forward...so you started with less than 7* before adjusting, is that correct?

[HOrnbrod]

Correct, started w. a 4* reading, added 5mm of shims on both sides in the rear LCA bucket which moved the LCA forward.

[Bornindesert]

Well, I must have beginner's luck. After researching and reading some up on lift height vs. UCA and LCA lenghts...I picked what I though would be good starting lengths and it worked out pretty close. Got an angle finder and like Hornbrod suggested, put a socket on top of the upper ball joint and took readings. They were 7* and 6 1/2* caster. Close enough.

 

For the pinion angle, it's a fixed u-joint at the axle end and cardon at the XFR case. Stock MJ drive shaft. Is the correct pinion angle zero*. Does that occur when the pinion is pointing pretty much directly at the output yoke of the NP242?

[Eagle]

I set the tow in to an 1/8", and centered the steering wheel. The track bar is a JKS and has the axle pretty close to dead on center. Now comes the question..

 

The toe-in (not "tow" in) angle should zero, not 1/8". That's far too much toe-in and will destroy your tires quickly.

 

 

For the pinion angle, it's a fixed u-joint at the axle end and cardon at the XFR case. Stock MJ drive shaft. Is the correct pinion angle zero*. Does that occur when the pinion is pointing pretty much directly at the output yoke of the NP242?

Correct. More specifically, the pinion should be parallel to the driveshaft. Since the double cardan uses up some space, the pinion should actually point slightly above the transfer case output, but pointing at it is pretty close.

 

However, the pinion angle is changed any time you adjust caster, and the caster angle changes any time you muck with the pinion angle, so dialing in a lifted truck is always a compromise.

[Bornindesert]

Thanks Eagle. I'll take a turn off the tie-rod to back off the toe-in.

 

When you measure pinion angle, is it simply a matter of disconnecting the drive shaft, rotating the spline coupling to a vertical position and then placing the magnetic angle finder across the flats? Subtract 90* and that's the pinion angle?

 

Measure the drive shaft installed. Subtract one reading from the other should = zero.

 

What's an acceptable range in readings?

[Eagle]

I stand corrected. According to the 2000 XJ service manual, the "preferred" toe-in is 0.25 degrees (they no longer specify it in inches). I got curious and plotted that with my AutoCAD software. To my great surprise, that works out graphically to ... 1/8" for a 29" tire..

 

All I can say is that my 2001 XJ measured 1/8" toe-in after replacing some tie rod ends, and the steering was rather squirrelly. I set it as close to zero as I could (maybe 1/32 toed in -- you don't want toe-OUT), and things are much better. It's been like that for almost 10,000 miles and the tires are wearing evenly.

[Bounty Hunter]

Your adjustment should be a happy compromise between pinion angle and caster.   You may need to run slightly less caster than ideal to get a good pinion angle that doesn't vibe.

 

Since both your UCA and LCA are adjustable, keep an eye on wheelbase and where the tire is in the wheelwell.  You may need to change the length of the UCA's as well to get the wheelbase where it needs to be along with the proper alignment specs.

[HOrnbrod]

I stand corrected. According to the 2000 XJ service manual, the "preferred" toe-in is 0.25 degrees (they no longer specify it in inches). I got curious and plotted that with my AutoCAD software. To my great surprise, that works out graphically to ... 1/8" for a 29" tire..

 

What's it work out to with a 31" tire Eagle? I set my toe at 1/8".

[Eagle]

 

I stand corrected. According to the 2000 XJ service manual, the "preferred" toe-in is 0.25 degrees (they no longer specify it in inches). I got curious and plotted that with my AutoCAD software. To my great surprise, that works out graphically to ... 1/8" for a 29" tire..

 

What's it work out to with a 31" tire Eagle? I set my toe at 1/8".

 

9/64

[HOrnbrod]

Gracias. Considering parallax angle error while looking at a tape measure, ± 1/64" is in the ballpark.  :thumbsup:

[Eagle]

Gracias. Considering parallax angle error while looking at a tape measure, ± 1/64" is in the ballpark.  :thumbsup:

 

Oh, yeah. Definitely not worth losing sleep over.

 

I still maintain that zero toe-in is what we strive for. The least rolling resistance and the least tire wear will obviously occur when the tires roll straight when going down the road. So ... why do we set some initial toe-in?

 

Because of the "slop" in the steering components. Each tie rod and has a small bit of slop built into it, and that gets progressively worse as the miles add up. If the front end is aligned with all the tie rod ends at "mid-travel," once you start to drive down the road the rolling resistance of the tires on the pavement will tend to push against the TREs, taking out all that slop. If the setting was zero toe-in at rest, then the result will be toe-OUT under dynamic driving conditions.

 

In the "good old days," the better alignment shops used to put a spring-loaded spreader bar between the front tires when the vehicle was on the alignment rack, to force the fronts of the tires apart and take out all that slop. They could then adjust the toe-in to between zero and 1/16th, and you'd have a top shelf alignment job.

 

I don't have an alignment rack or turntables. I have a gravel driveway. I drive forward into my working position, measure, and make an initial adjustment. Doing so causes the sidewalls to bend while the tread contact patch wants to not move. To allow for that, I back up several car lengths, then pull forward to the same position again, which relieves the sidewall twist and (hopefully) gets the tie rod ends loaded as they would be when driving. Then I check my measurement, and adjust again if I don't have it right. Rinse and repeat as many times as necessary. My goal is zero, but I stop fussin' if I get to about 1/16 toe-IN. Toe-OUT is unacceptable, and I wouldn't be happy with 1/8 or more of toe-in.

 

But ... that's just me, I guess.