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Discussion Starter #1
Help!

Looking for feedback if my 2 door JK might have too much caster. What symptoms might I notice?

Recently installed:
Rancho 2 inch progressive sport lift,
Rancho 9000xl shocks
Rancho Geometry Correction Brackets.
Net 2.75 inches in front and 2.5 inches in back; with winch, steel bumpers and tire carrier already installed!
Tires are 255/80/17 (33's), approx 34 PSI (not sure if this is even relevant).

Attached pic has the alignment poop-sheet provided by shop.



Prior to lift, the Jeep drove flighty at highway speeds - which is why the geo brackets were added.

After lift, the Jeep handles very solid, not flighty. However, I swear there is a slight vibe running 4th gear around 2500 rpm...but it might be my imagination.

If there is too much caster, does that mean my pinion angle is outta whack and possibly causing vibe?

How/what would I check?

And why can't this be easy!?:pullinghair:
 

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If it’s driving good don’t mess with it anymore. Caster looks good for the lift and is needed but if there is a vibe probably need adjustable control arms in front instead of geo brackets to adjust pinion. Hopefully others chime in cause I’m still trying to figure all this out for myself!😁
 

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Too much castor will not cause a speed related vibration. And if it is driving great you don't have too much castor.
Speed related vibrations can be drive line induced, an easy test would be to remove the front drive shaft and see if it goes away. You clearly would not be able to use 4 wheel drive with the front drive shaft removed, but you can drive it in 2 wheel drive until the cows come home. If the vibration goes away with the front DS removed it may be a failing front drive shaft. You could either replace the DS or replace the Rzeppa joint. Most replace the DS.
That said, most speed related vibrations are tire balance issues. That is likely your issue.
There are a few other options, like brakes, bearings, etc.. But most are tire balance issues, with DS issues probably being next on the list but a distant second.
 

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JKU for me vs JK but rancho 2" lift and geo's. Left was 6.0 right 5.9 so you are in the ball park.. for the vib in 4th, is it there in 3rd or 5th same speed etc? I would try to confirm you have it, maybe have someone else drive the Jeep. try adjusting the shocks firmer or softer see if that helps.. and maybe rotate the tires. again start with the simple stuff.
 

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Which holes were used on the geo brackets?
 

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You should be in the top hole on the Geo bracket for 2” lift.
If the pinion angle is too high you will get driveline vibe but with only a 2” lift and the Geo brackets set in the top hole that shouldn’t be an issue.


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Discussion Starter #9
Too much castor will not cause a speed related vibration. And if it is driving great you don't have too much castor.
Speed related vibrations can be drive line induced, an easy test would be to remove the front drive shaft and see if it goes away. You clearly would not be able to use 4 wheel drive with the front drive shaft removed, but you can drive it in 2 wheel drive until the cows come home. If the vibration goes away with the front DS removed it may be a failing front drive shaft. You could either replace the DS or replace the Rzeppa joint. Most replace the DS.
That said, most speed related vibrations are tire balance issues. That is likely your issue.
There are a few other options, like brakes, bearings, etc.. But most are tire balance issues, with DS issues probably being next on the list but a distant second.
Thx for the reply. I'll remove the front DS and see what happens, but it'll be a bit before I try...after vacation.
 

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Discussion Starter #10
JKU for me vs JK but rancho 2" lift and geo's. Left was 6.0 right 5.9 so you are in the ball park.. for the vib in 4th, is it there in 3rd or 5th same speed etc? I would try to confirm you have it, maybe have someone else drive the Jeep. try adjusting the shocks firmer or softer see if that helps.. and maybe rotate the tires. again start with the simple stuff.
Thx for the reply. I'll have a buddy drive the Jeep and get his opinion. At this point, I think my perspective on vibe while driving is a bit tainted...
 

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Discussion Starter #11
How would I verify/check pinion angle...besides taking Jeep to shop? Sorry for a stooopid question, but drive line mechanics is out of my skill set.
 

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. Hi, jadmt. Top holes are used.
one easy way to decrease your caster is add some 1/2" spacers to increase your lift a bit. Stock DS are pretty forgiving. Something seems a little off if you got that much caster if you are running stock lower control arms. I would be shooting for around 5*. One thing with only 2" you really don't reap the benefits of the geo brackets like you do on taller lifts simply because your control arms are not at steep angles. You might be better going with a set of adjustable lower control arms up front.. One thing if your ds is vibrating it can cause your TC to crack altho that is more of an issue with big tires and higher numerical gearing.
 

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. Hi, jadmt. Top holes are used.
one easy way to decrease your caster is add some 1/2" spacers to increase your lift a bit. Stock DS are pretty forgiving. Something seems a little off if you got that much caster if you are running stock lower control arms. I would be shooting for around 5*. One thing with only 2" you really don't reap the benefits of the geo brackets like you do on taller lifts simply because your control arms are not at steep angles. You might be better going with a set of adjustable lower control arms up front.. One thing if your ds is vibrating it can cause your TC to crack altho that is more of an issue with big tires and higher numerical gearing.
Thanks for input! When I get back home, I will try a couple suggestions from the forum members. Although, I'm leaning heavily toward swapping out the geo brackets for adjustable LCAs (Synergy seems to be a favorite?). The geo brackets were installed to solve the low caster (pre lift) which was around 3.5/3.7....the Jeep handled squirrelly at highway speeds....and I expected to gain more than 2" of lift, which I did. However, now I sorta question the pre lift caster numbers as a local tire shop (not an off road shop) did the alignment when I bought new tires.
 

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It sounds like you like the way it drives, so unless you have an issue you are fixing I am not sure why you would replace the geometry brackets with adjustable / longer front lower control arms. There are more than a few people with that same lift running the brackets and they seem happy. But every Jeep seems to be different.
If it drives well as is, I would figure out where the vibration is coming from and fix that.
 

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You can check pinion with an angle finder. Some phones have them in measurements section or get an app. It’s a rough easy way just to see.
 
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