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Discussion Starter #1
I've been quite convinced that my setup was allright, however...

I recently installed the RE 4,5" longarm on my JK, along with 37" tires. Got it to the alignment shop to get the whole setup properly. Never been totally satisfied with the overall handling of the Jeep since the lift (bouncing/vibrations). Today, when checking the protocol from the shop it says "Jeep Wrangler *TJ* 2003"...:what?: Makes me think something isn't like it should be. Tried search and found many different explanations, so I'd like to know the perfect numbers for the following on my JK, front respective rear:

1. Camber

2. Caster

3. Toe-in

4. Tire pressure (37"x13,5"x18")

5. Anything else to check/think about?

Any help appreciated!:)
 

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I am not an expert- but.

toe does not change when you lift a JK
camber is not adjustable
I ended up adjusting in more positive caster until we were at about 8 degrees.

I have about the same lift and tires you do.

Its possible you have some driveline vibration from too much angle--- especially if you have a 2 dr. My 4 dr does not need drivelines changed.

Some 37s are difficult to balance- mine were. I ended up with "balancing sand" in mine. Got it pretty good now- still not perfect. I have TruXus MTs. But I have seen some 37s take almost no weight also (Scrogg's 37" Toyos have next to nothing on them)
 

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Discussion Starter #3
Thanks, just checked the rear driveshaft angle - it was way out of angle, and I now had it adjusted, hopefully this will help someway as well.

8 degrees positive caster have I heard before, so I guess that's were I wanna go...:)
 

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if you have aftermarket double-cardan driveshafts, 8 degrees will be way too high.

if you don't have aftermarket driveshafts, and have a 2-door, you'd better get some soon, because your stock shafts aren't going to last long.

with 37's, you should have a slight toe-out - about 6 degrees.

make sure to have front and rear aligned so that both axles are running perfectly parallel to each other.
 

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Discussion Starter #5
Yes, I have J.E. Reel 1350 driveshafts front + rear. So, what caster do you recommend then, since you say 8 degrees is way too high?
 

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Yes, I have J.E. Reel 1350 driveshafts front + rear. So, what caster do you recommend then, since you say 8 degrees is way too high?
8 will most likely make the front shaft vibrate. You really have to play with it until you find out how much caster you can run and not have a drive line vibration. I run about 3.5-4 (best I can measure with crappy gauge), that's the most I could run without vibrations.
 

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This may help regarding pinion angle and caster

http://www.jkowners.com/forum/showthread.php?t=2357


Here's the factory spec:

FRONT

CASTER
+4.2° ±0.5°
Max Lt/Rt 0.65°

CAMBER
-0.25° (fixed angle) ±0.37°
Max Lt/Rt ±0.5°

TOE
+0.20° ±0.03° (0.10° each front wheel)
Max Lt/Rt 0.04°


REAR

CAMBER
-0.25° ±0.25°

TOE
+0.25° Range 0.0° - 5.0°

THRUST ANGLE
0° ±0.25°
 

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Discussion Starter #8
Ok, however the front shaft is only used when 4wheelin' so I guess that's not the big issue. But I take what you said in consideration - all inputs are higly appreciated!

And I'm a lazy guy, so I guess the alignment shop will have to play with this!:Then they can start with your numbers and work their way up...
 

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Discussion Starter #9
Thanks Phil!:)

That's very helpful.

So, you can actually apply the original numbers to a lifted vehicle as well?
 

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Ok, however the front shaft is only used when 4wheelin'
It spins all the time, so it is an issue on the highway. Too much caster will result in too large a pinion angle, which will cause vibration and potential failure of parts at worst, or premature wear at best.
 

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So, you can actually apply the original numbers to a lifted vehicle as well?
For toe yes, caster with JE Reel shafts is going to be driven by pinion angle.

http://www.trailduty.com/temp/pinion_angle.pdf

There really isn't a pinion angle that will work for everyone, lift height, tire size, gear ratio, etc, will have an effect on what is the correct pinion angle for your set up. So the best way to get the pinion angle right is with a little experimentation. Start low and increase it until the point you feel vibration then go back to the previous setting. This will give you the best compromise between pinion angle and caster.

Before setting pinion angle you should make sure that the track is correct and the axles are in the right position.
 

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Discussion Starter #12 (Edited)
Yet useful information! Thanks again, Phil!:)

So, perhaps the gears also matters... I'm still waiting for my 5.13's to the rear to arrive (got the front on the bench), then we'll see what happens.

Any more suggestions on the tire pressure?

And, btw: in the RE instructions http://www.rubiconexpress.com/Img/Products/Pn/5/3545/PDF/Instructions/0.pdf they show on the last page the proper geometry for the rear driveshaft, anyone knows if the same apply to the front?


...........................................

Compared Phil's spec's above, with the ones I have from the protocol:

FRONT

CASTER
+4.2° ±0.5° LEFT: +3°19' RIGHT: +3°30'
Max Lt/Rt 0.65°

CAMBER
-0.25° (fixed angle) ±0.37° LEFT: -0°40' RIGHT: -0°37'
Max Lt/Rt ±0.5°

TOE
+0.20° ±0.03° (0.10° each front wheel) LEFT: +0°02' RIGHT: +0°02' TOTAL TOE: +0°04'
Max Lt/Rt 0.04°


REAR

CAMBER
-0.25° ±0.25° LEFT: -0°30' RIGHT: -0°03'

TOE
+0.25° Range 0.0° - 5.0° LEFT: +0°09' RIGHT: +0°18'

THRUST ANGLE (IN THE PROTOCOL CALLED " ANGLE TO CENTERLINE") +0°05'
0° ±0.25°
 

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So, perhaps the gears also matters...
Yes gears matter, the faster a shaft spins the less pinion angle it can handle before vibrating. Higher numerical gears = faster spinning shaft = less pinion angle.


Any more suggestions on the tire pressure?
I've found that about 32 works best for me. The best way to find your (correct) tire pressure is with a chalk test. Draw a chalk line across the tread on each tire. Drive down the street (try not to turn) and then look at the chalk line, comparing the center of the tread to the outer part.

You want the lines to wear evenly at the center of the tread and on the edges. If the chalk is worn off the center but not the edges, your tire pressure is too high. If the chalk is worn off the edges, the pressure is too low.


anyone knows if the same apply to the front?
The front is going to be driven by getting the best compromise between pinion angle and caster. If you set it up like the rear, ie: based on pinion angle only, then you would have an horrible caster angle and it would be very dangerous to drive.

Start with a low pinion angle, 3°, then start increasing it in small increments, with a quick test drive between each adjustment. When you feel vibration from the front driveshaft, go back to the previous setting, and that is about as good as you are going to get it. No vibration with highest caster angle.
 

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Discussion Starter #14
Thanks - again - Phil!

So, according to my numbers from the protocol above, I should probably go back to the shop and have them re-do the whole thing, right?
 

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Compared Phil's spec's above, with the ones I have from the protocol:
I presume these are the actual numbers after alignment?


FRONT

CASTER
+4.2° ±0.5° LEFT: +3°19' RIGHT: +3°30'
That would be close to being right, I certainly wouldn't expect to see caster any higher with 4.5" lift and JE Reel shafts. The question is, is there any vibration from the front driveshaft? If not then you are good to go, if so then you are going to have to reduce pinion angle, which will also reduce caster.

You can usually feel front driveshaft vibration through the floor, commonly around 50-55 mph. Slowly accelerate from 40 - 65 mph and feel for a vibration coming in at a certain speed and then going, there should not be any.



CAMBER
-0.25° (fixed angle) ±0.37° LEFT: -0°40' RIGHT: -0°37'
Max Lt/Rt ±0.5°
Nothing you can do about this and it is within spec anyway.


TOE
+0.20° ±0.03° (0.10° each front wheel) LEFT: +0°02' RIGHT: +0°02' TOTAL TOE: +0°04'
Max Lt/Rt 0.04°
This is a little off, but nothing that is going to really cause any issues.


REAR

CAMBER
-0.25° ±0.25° LEFT: -0°30' RIGHT: -0°03'

TOE
+0.25° Range 0.0° - 5.0° LEFT: +0°09' RIGHT: +0°18'

THRUST ANGLE (IN THE PROTOCOL CALLED " ANGLE TO CENTERLINE") +0°05'
0° ±0.25°
All within spec.

The only thing that is very slightly out is toe. You could go back and get it adjusted, but I'm betting you'd never tell the difference or notice if you didn't.

If you are going to go back and get the toe corrected, make sure you have your pinion angle correct first (ie: vibration free), and tell them that you do not want caster changed, although they could correct for cross caster if it is too high.
 

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Discussion Starter #16
You can usually feel front driveshaft vibration through the floor, commonly around 50-55 mph. Slowly accelerate from 40 - 65 mph and feel for a vibration coming in at a certain speed and then going, there should not be any.
Yup, that's what I feel! Right on the spot - vibrations through the floor! I don't recall exactly at what speed, but it comes and goes... I'll check it out, thanx a lot!:)
 

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Discussion Starter #17
Back from today's testdrive. The rear vibrations are now close to completely gone, which makes me :). The front still behaves a bit spooky. It have a flighty feeling and you have to compensate movements by the steeringwheel all the time, and vibrations are still there. I think I'd better try to reduce the pinion angle and try again...
 

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The front still behaves a bit spooky. It have a flighty feeling and you have to compensate movements by the steeringwheel all the time, and vibrations are still there. I think I'd better try to reduce the pinion angle and try again...
The more you reduce the pinion angle the lighter the steering will become. For my setup 5° is the magic number for front pinion angle, any more and I get drive shaft vibration, any less and the steering gets way too light.

A good steering dampener will help with the light feel, and going down to the bottom of the tire pressure range (still within chalk line specs) will also help. I found the Poly Performance high steer setup also helped with the steering feel, and bump steer disappeared too.

My steering is still on the light side, but it is manageable and not too bad. After a while I got used to it and now it feels fine to me.

The real solution is to cut the knuckles off and rotate them. This will allow you to have a perfect pinion angle and set the caster to 5° which would be ideal. I don't trust my welding to do this, and there is no one local that I know of that can do it, so I won't be rushing out to get it done anytime soon, but it would be the best solution.

Likewise on the rear axle, cutting the spring mounts off and rotating them would allow the springs to be perfectly straight and prevent any bulging/leaning of the springs. I'll do this one day when I have the time.
 

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Discussion Starter #19
Seems like good ideas! Winter project...:)

Is there an easy write-up somewhere on how to measure pinion angle? This is how my front looks right now, hard to tell from a photo of course, but how does it seem?

 
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