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Susp Geometry Tech Help

HiJinx

NAXJA Forum User
Location
Phoenix
Hi.
Ok, I have a 4.5" lift on my xj.
I was starting to get death wobble, so I got some longer LCAs and put those bad boys on. totally cured the DW, but I soon noticed a low speed dependant vibration. Suspecting a bad pinion angle, I removed the front drive shaft and viola! It went away. So, I put the shaft back on and sure enough it returned.
Sooooo
I picked up some adjustable UCAs to push the top of the axle forward, raising the pinion. The XJ is at the shop right now and they called wnated to make sure that I wanted to add negative caster to the ball joints.
I walked down there (a block from my office) and went over this whole thing with them.
So, in theory, with the longer lowers, adjustable uppers and lift, I should be able to have the caster and pinion correct by using the adjustables...correct?
I think the shop and I are all on the right page, but I just want to make sure.
Am I missing anything? Any advice? Any thing I should be aware of?
 
You can't independently adjust caster and pinion angle, if you raise your pinion, you are changing your caster negative.

Best you can do with out a knuckle rotation, is try to get a happy medium. Only raise the pinion a little at a time until your vibration goes away.

Then you'll have to evaluate your steering and decide if you can live with how it feels now.
 
Ya, after further thought I kind of suspected the same once I started using my fingers, a pen and a spoon to emulate the setup so I could visualize it a bit more (slow day at work).
On a good note, I discovered an almost completely ruined bushing in one of the stock UCAs when it was removed.
 
The spoon was the drive shaft 'cause it could rest easily on the table with the "axle"(pen) resting accros the bowl of the spoon. My fingers where the struts/knuckles
The little clippy part of the pen was a rough representation of the pinion.
I almost busted out the tape, but then I realized if someone saw me, I might have been removed from the building by the men in the white coats.
:laugh:
 
Sounds like a good way to get a visual. How bad was the vibration? And which adjustables did you end up going with?
 
The vibration is enough to make me not want to go above 60 or so. mostly noticable at 20-25, 40-44ish and near 65.
However, it's not horrible. My fiance has no idea what I'm talking about.
Oh, it also makes my antena do funny things at freeway speeds. so it's enough to cause a frequency to shake the antena.

I don't remember what kind of uppers they are. I got them from a member here who hooked me up on a good deal.
The chassis ends have greasable heim joints though if that helps.

edit: They are RE Adjustable Uppers (just read an email regarding the purchase of the ucas.
324.jpg
 
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