Caster Update... Thoughts?

[Caver Dave]

OK, finally grabbed an angle finder, here's what I found as it relates to NT/WT (non-unit bearing model) D30s. The FSM calls what I'm measuring "kingpin inclination" (7.5* spec), but this is what I've been told is "caster" (the difference between the kingpin angle and plumb)...

*MY* SOA D30 w/ bottom of diff level = 14* of caster
Stock SUA D30 w/ bottom of diff level = 8* of caster (happen to have sitting on stands)
The 6* difference equals about 1" difference in the position of the steering arm or 1" more clearance between my draglink and the bottom of the spring.

The steering is tight, (one finger) on the highway at 65mph, but has never returned to center.

What's everyone's thoughts on this? Seems my theory is correct about too much caster (won't return to center), which rotates the steering arm too high and causes interference between DL & spring. I should be able to order up some 6* shims and prove the point, right?

 

[rattlecanpaint]

Shims might do the trick. You are correct in thinking the caster is why the steering won't return to center. Had a guy adjust the caster on a Dodge van at work and the steering wheel actually turned all the way to the lock on one side while sitting on the alignment rack 'cause he had it adjusted way wrong. It's amazing how hard alignments can be without the proper tool!

 

[Rich]

Wow.. 7.5* is a TON of caster, stock.. As an example, Toyota SA's have about 1*. My Dodge 3500 has only slightly more.

But anyway, I'd go somewhere between stock and what you have.. bigger tires like more caster than stock.

 

[zubz]

Wow.. 7.5* is a TON of caster, stock.. As an example, Toyota SA's have about 1*. My Dodge 3500 has only slightly more.

But anyway, I'd go somewhere between stock and what you have.. bigger tires like more caster than stock.

Are you positive on that Rich? Stock Jeeps(and Dodges from what I have seen in the past) are setup with 5-7 degrees of caster built into the housing.

Dave,
Where did you measure from on the housing? Check witht he angle finder on the front of the housing where the case spreader goes. That surface should be perpendicular to where the yolk comes out. Measure off that. Use shims to dial it in to 5-7 degrees. Do you have any shim at all in it now? If not, you are correct in trying the 6* shims, but you may need more in order to get it correct.

By the way.....Is your camber off as well? It should be if you have that much caster in the front end......

Give me a shout at the shop if anything I said was not clear.

Andy

 

[Caver Dave]

Dave,
Where did you measure from on the housing? Check witht he angle finder on the front of the housing where the case spreader goes. That surface should be perpendicular to where the yolk comes out. Measure off that.

Since the axle is still under the Jeep, I first measured a few places for reference. The underside of the housing was perfectly level, so I used it for reference between the two housings. With the bottom chunk level, the front face/spreader holes were about 3* shy of 90* (Sounds like the pinion is pointing down at 3*... ). I then measured off the bottom of the inner "C" (mainly because the D30 doesn't have much area on the knuckle and it didn't seem to be offset to get the 14* & 8* measurements...

Do you have any shim at all in it now? If not, you are correct in trying the 6* shims, but you may need more in order to get it correct.

No shims at this time... worn slap out OEM leafs w/ AAL & a little ducktape holding the backends together! Pretty sure the PO just eyeballed it when he welded the front perches back on... Luckily, 6* seems to be the starting point and about the most I've seen available. Do you have these in stock?

By the way.....Is your camber off as well? It should be if you have that much caster in the front end......

Give me a shout at the shop if anything I said was not clear.

Andy

With that much positive caster, I'm guessing the same thing. Can't say that it's hurt anything, but I have everything needed to go thru the POS (balljoints, spindle kits, etc. *IF* needed) when I drop the EZ-locker in. While it's not *that* big of job, I kinda wanted to put in the Waggy packs (ducktape won't last forever, but it has worked for several years) and a new set of perches (OEM are cast, only 1.75"w and too short to combat wrap... probably lost a 1/2" of height when they were torched off the bottom also!) while I have everything apart. Hopefully, I can adjust the new perches to eliminate any shims, but thought it may be prudent to try them on the current setup to make sure it does start driving like ass & will give me enough clearance for a beefier DL/TR combo.

 

[zubz]

Luckily, 6* seems to be the starting point and about the most I've seen available. Do you have these in stock?

Yup, no prob at all. We typically keep 2.5*, 4*, and 6* in stock and I have made other degrees when needed.

Yup, sounds like whoever did the SOA messed up putting the perches on.

Let me know what you decide to do, I have the offset perches for the DS one in stock as well.

Andy