pinion angles

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8)Ok guys and gals, I have a '74 fj-40 that I put 2" longer than stock shackels on the rear to level it. Since then its developed a rumble, on acceleration, and backing off, and I can only assume it's because of the change in the pinion angle. Does anyone have a  formula for the correct angles, as I've researched the files and there dosn't seem to be any answers other than front axel fixes, and those are for caster correction. Please help! And does anyone know where I can get steel shims, I've heard aluminum ones are BADDD.          Earl :beer:
 
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The formula is: inverse sine (increase shackle length) / (spring length)

for your example and stock 42 inch springs it is: invsin (2/42) = 2.7 degrees.  

This is an approximation that assumes that the shackle is 90 degrees, but it is good to less than a degree.

HTH
 
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Pin head,    So I guess you'r saying I need 2 1/2 degree shims to correct the change in the pinion angle! Am I the only one that has had the problem on the rear axle? I have a hard time believing a 1" lift would give me that kind of a rumble?    I sure saw a lot of your wisdom on the SOR forum, so I can trust what you write! By the way, when you say the shackle is 90 degrees, 90 degrees to what, the spring or the frame?Thanks,   Earl :beer:
 
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Chances are that you have a slightly wore out u-joint and or a worn slip yoke. Check those before you try and figure out what 2.7 degrees is. After you fix the loose stuff keep it greased up real nice and you probably wont ever notice those 2.7 degrees ever again. Just my not so humble opinion. :beer:
P.S. If you put the 2" shackles in just to level off the sagging springs I doubt you changed the pinion angles much. If anything you probably brought the angle back to where it should be. This aint rocket science remember :beer: :beer: :G
 
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If it didn't vibrate before and it does after the longer shackle, chances are that it is a pinion angle problem. You can also check the angles with a magnetic angle finder with the drive shaft off.

the calculation is with the shackle 90 degrees to the frame, but it wouldn't change much if it was 90 degress to the spring. If you know the shackle angle you can calculate it more precisely.


This aint rocket science remember :beer: :beer: :G

Actually, it is rocket science. You need to know trigonometry to put men on the moon.
 
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Actually, it is rocket science.  You need to know trigonometry to put men on the moon.  

:bow:I agree. If it was'nt fpr guys like we you we would not have all these nifty computers to play with. If it was up to me we'd still be milking goats by hand, sleeping in bear skin rugs and grunting alot. :G :beer:
Heck its almost rocket science to make good beer.
Ooops I'm sorry for getting off topic.
 
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aZ..fj-40) Is it possible that the slip-yoke reinstallation misaligned u-joints? ... big vibration!!
Whoa whats this about misaligned slip yoke reinstallation? When I had my front springs on backwards, and tried to set the axle down, the slip yoke seperated, I didn't think much of it, just reversed the springs, slipped the yoke back together and forgot about it. Should i check for some kind of u-joint alignment? This is the front driveshaft, so its not in use that much, didn't have any vibration when I had it in 4wd last, so I guess all is fine? ???
How come a 1" shackle lift caused pinion angle problems when my 4" spring lift didn't?
 
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:dunno: Thanks for all the insight, but I've checked all the u-joints, slip joints, and the u-joint allignment. The cruiser only has 66,000 mi. and was towed in it's priveous life, I had no shudder, or vibration before I put the longer shackels on, so i'll have to try a set of shims, 2 1/2 degree, and see what happens. Does SOR sell steel shims? Earl :beer: :beer:
 
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:p Hi again all,    I'm tired but happy, I found a pair of 2 degree shims at Desert Rat here in Tucson, and put them in today,PROBLEM SOLVED, runs smooth, no shudder..... By the way Cruisen Ga. the SOR instructions on the page you said to look at are wrong for the rear. The thick end always goes to the shackel end!!!!!!!!!!!!!!! You would increase the problem on the rear if you put the thick end to the front!!!!! Also a spring lift kit is designed and engineered with the correct caster, and driveline angles. Thanks again PIN HEAD       Earl
 
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I thought the thick end would go shackle end to help driveline angle? I can understand it being the other way to correct steering stuff, but doesn't it worsen your already worsened driveline angles to put the thick end shackle side? ???
 
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:stupid:No, Crusin Ga. , the reason the angle is off when you add length to the shakle, is because that rotates the pinion up, and to bring it back down you put the thick end of the shim twards the shackle, that applies to the front or rear, except if you have reversed the shackle in front, ( put the shakle at the rear of the spring)
I hope that makes sence to you, if not, put it on paper and look at it! Earl :beer: :beer:
 
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That only works in a stock set up with the springs under the axle. It took me a minute to calculate, too, because I am so stuck on springs being on top of the axle.
 
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That only works in a stock set up with the springs under the axle. It took me a minute to calculate, too, because I am so stuck on springs being on top of the axle.
 
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It makes sense, but being one with a lift, driveline angle is a concern of mine, and I would hate to after I improved it with longer shackles to worsen it again with shims. Guess thats why I stick with stock length shackles. :dunno:
 

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