Longer shackle and Driveline angles

I heard/read somewhere that a longer rear shackle can actually help improve rear DS angles by angling the differential up. Would this be true? I am thinking about adding a longer shackle to my RE pack but am worried about vibes.

The rumors are true. Anything that points the pinion more towards the output shaft of the transfer case is better than not. A tapered shim is also a way but the shackle is easier on the leaf spring center pin.

Okie Terry said:

The rumors are true. Anything that points the pinion more towards the output shaft of the transfer case is better than not. A tapered shim is also a way but the shackle is easier on the leaf spring center pin.

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That's a pretty broad statement. What if your pinion is already just right, or up too high. What if he doesn't have a SYE. Would the advise still be the same. Tossing out a general statement like that is irresponsible.

MaXJohnson said:

That's a pretty broad statement. What if your pinion is already just right, or up too high. What if he doesn't have a SYE. Would the advise still be the same. Tossing out a general statement like that is irresponsible.

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I thought I said it's better to have alignment than not. Are you saying that there is a case when it's better to not have the pinion pointed toward the output shaft? If there is, please tell so I won't make the mistake of aligning my pinion.

Or are you addressing the fact that shims are harder on the centering pins? Because I thought it was common knowledge that a flatter perch is best.

Okie Terry said:

I thought I said it's better to have alignment than not. Are you saying that there is a case when it's better to not have the pinion pointed toward the output shaft? If there is, please tell so I won't make the mistake of aligning my pinion.

Or are you addressing the fact that shims are harder on the centering pins? Because I thought it was common knowledge that a flatter perch is best.

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Depends on your u-joint configuration. Check out "Geometry 101" in Tom Wood's Tech Info section.

http://www.4xshaft.com/

Compare the conventional two joint shaft with the double cardan or CV style shaft. With the double cardan style joint at the transfercase output, you want to point the pinion at the output or slightly down (~1°). With the conventional (factory) style you want the output shaft and the pinion shaft to be at the same angle (parallel) or slightly down (~1°). The 1° is to compensate for leaf spring wrap-up under power. With any configuration, 1/2° of misalignment at the joint is a good idea to exercise the needle bearings.

I do not have a SYE. I have been extremely lucky thus far and only have a tiny bit of vibes at 30 - 35 mph. I wouldn't even call them vibes just enough to rattle the plastic pieces around my shifter. I think my 242 is part of the reason for lucking out even though it is a 96. Go Figure. :dunno:

MaXJohnson said:

Depends on your u-joint configuration. Check out "Geometry 101" in Tom Wood's Tech Info section.

http://www.4xshaft.com/

Compare the conventional two joint shaft with the double cardan or CV style shaft. With the double cardan style joint at the transfercase output, you want to point the pinion at the output or slightly down (~1°). With the conventional (factory) style you want the output shaft and the pinion shaft to be at the same angle (parallel) or slightly down (~1°). The 1° is to compensate for leaf spring wrap-up under power. With any configuration, 1/2° of misalignment at the joint is a good idea to exercise the needle bearings.

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Oh.

Well in the future, I won't post on anything that has worked for me just because I don't know the math behind it. I guess it's a good thing the forum system lets more than one person post. That way a person can get different opinions from several people instead of just the first misguided soul to come along.

Now that I think about it, I remember the problem with spring wrap and pinion angle. Oh well, I guess I must've gotten lucky thus far.

Disclaimer: All info gained is just in my humble opinion and not to be mistaken for anyone else's opinion or the truth for that matter.

I have also experienced pointing the pinion up reducing some vibes, and there is sound reason for why this works (sometimes). Max is correct in his alignment for the single cardan shaft, but problems arise when you start running high angles. Spicer recommends that single cardan shafts be run at 0 to 3.5 degrees. Most Jeeps including the Cherokee are already running outside this design recommendation at stock height. The higher angles produce greater variations in velocities in the shaft that can't be cancelled by two 180 degree out of phase cardan joints. Pointing the pinion up reduces both angles, and even though they are not opposite and of equal magnitudes ---they are less-- I don't recommend this as a fix--just trying to explain why it helps--sometimes!!

96, my XJ is very similar to yours. I added an RE lift shackle and opened up pandora's box. After an RE hack'n'tap, RE CV d-shaft, 4* shim, and a D44 my XJ rides smoother than stock. Be careful, its alot of trial and error.

--Matt