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  #1  
Old July 18th, 2006, 11:44
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87xjco 87xjco is offline
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Check my figures on knuckle rotation please

O/K

I am installing a low pinion, waggy D44 in my 87 XJ (Xota). I could use some help checking my figures to make sure I am doing this right. Im hoping some people who have done this will respond and answer questions.

From my measurements it appears that in order to get a good drive shaft angle, I am going to need a 20 degree pinion angle.

I basically made a jig that set the housing at the same height that it will be, with my 35 tires, and then a point on the jig, that is the same distance and height from the housing, at the transfer case yoke center, as it is on my vehicle. Then I rotated the housing until a straight line off of the pinion yoke, pointed about 2 degrees below the transfer case yoke center point.


But, looking at it, that angle seems kind of excessive.


Q; Does that angle seem excessive to you?
Q: Would there be pinion oiling problems with that angle?


Next I measured the angle at the lower ball joint surface and it was 6 degrees



Q: By looking at the chart above, am I correct, that is a 6 degree, negative caster angle?

Q; Am I correct that if I want a 5 degree, positive caster angle, I need to rotate the knuckle 11 degrees clockwise?

Your answers are appreciated!!!

Terry
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Old July 18th, 2006, 13:08
fatwreck fatwreck is offline
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Re: Check my figures on knuckle rotation please

I think your little diagram is showing a positive caster angle. I put my knuckles at negative 7 degrees, welded the coil buckets on level, and let the pinion angle fall where it did. I knew that I had manual hubs and it didn't matter a whole lot.

Here are some pics for reference (5.5" lift, 35s, waggy44 front):




Last edited by fatwreck; July 18th, 2006 at 13:16.
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Old July 18th, 2006, 13:12
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87xjco 87xjco is offline
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Re: Check my figures on knuckle rotation please

I was hoping you would chime in FATWRECK. The lower ball joint now, is rearward of the centerline. I was pretty sure that is negative caster.

I was thinking the spec. is 4 to 7 degrees positive caster.

Am I wrong on both counts?
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Old July 18th, 2006, 13:13
fatwreck fatwreck is offline
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Re: Check my figures on knuckle rotation please

Yeah, I guess I'm not sure which is positive and which is negative, but I know that I rotated the top of the knuckle towards the rear of the vehicle until it showed 7 degrees. I remember because I was worried that my pinion angle would only get worse the more I rotated it. It ended up being fine though.....even without cutting and turning the knuckles.
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Old July 18th, 2006, 13:18
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Re: Check my figures on knuckle rotation please

Quote:
Q: By looking at the chart above, am I correct, that is a 6 degree, negative caster angle?

Q; Am I correct that if I want a 5 degree, positive caster angle, I need to rotate the knuckle 11 degrees clockwise?
Yup, that looks correct.

If you're running manual hubs though, it's not as crucial to get that "perfect pinion angle", unless you want to run on the street with the hubs locked all the time (or are going to run on the street all the time using drive flanges...basically the same thing). I would sacrifice some pinion angle to improve pinion oiling if you have manual locking hubs
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Old July 18th, 2006, 13:33
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Re: Check my figures on knuckle rotation please

Quote:
Originally Posted by bobnoxious
Yup, that looks correct.

If you're running manual hubs though, it's not as crucial to get that "perfect pinion angle", unless you want to run on the street with the hubs locked all the time (or are going to run on the street all the time using drive flanges...basically the same thing). I would sacrifice some pinion angle to improve pinion oiling if you have manual locking hubs
Thanks bobnoxious, good point that with locking hubs that i'll be running, pinion angle is not that crucial.

I am thinking of setting the pinoin angle to 16 degrees and the caster at 5 degrees positive. Then I have a couple degrees either way to play with
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Old July 18th, 2006, 14:02
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Re: Check my figures on knuckle rotation please

On RS Ford diffs, I set the caster at 5-7, and the pinion at 13. So a total difference of 18-20. That is perfect for 6-8 inches of lift. You'll need a little more because of the LP.
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Old July 18th, 2006, 14:10
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Re: Check my figures on knuckle rotation please

Quote:
Originally Posted by CRASH
On RS Ford diffs, I set the caster at 5-7, and the pinion at 13. So a total difference of 18-20. That is perfect for 6-8 inches of lift. You'll need a little more because of the LP.
Thanks CRASH, i've read your many of your tech. posts, and you've probably covered all this already and I just wasn't able to find it.

A little more research and I found this diagram for caster. I wasn't sure if I remembered correctly that pos. caster equals the upper ball joint back from vertical centerline. This diagram helps show that is correct.
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Old July 18th, 2006, 14:38
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87xjco 87xjco is offline
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Re: Check my figures on knuckle rotation please

Thanks everyone.
I was starting to feel like I was over my head on this one. I've rebuilt many axles but i've never done the knuckle rotate on any of them.

I feel alot more confident about rotating those knuckles correctly now.

Terry
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Old July 18th, 2006, 16:07
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Re: Check my figures on knuckle rotation please

Quote:
Originally Posted by 87xjco
Thanks everyone.
I was starting to feel like I was over my head on this one. I've rebuilt many axles but i've never done the knuckle rotate on any of them.

I feel alot more confident about rotating those knuckles correctly now.

Terry

One last thing, make sure you get your camber angles set correctly once you've rotated the knuckles. It's very easy to screw this up, measure the angle between the upper and lower ball joint mounting ears before you cut, and duplicate the angle after rotating. Believe it or not, they can get cattywhompus on the tube even though it's a tight press fit.
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Old July 18th, 2006, 16:30
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87xjco 87xjco is offline
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Re: Check my figures on knuckle rotation please

Quote:
Originally Posted by CRASH
One last thing, make sure you get your camber angles set correctly once you've rotated the knuckles. It's very easy to screw this up, measure the angle between the upper and lower ball joint mounting ears before you cut, and duplicate the angle after rotating. Believe it or not, they can get cattywhompus on the tube even though it's a tight press fit.
Ah, I wondered anout that, thanks i'll check that.
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