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Hello all. I have a 1990 jeep wrangler with a 2.5l 4cyl engine. The engine is young, only 4 or 5 thousand miles on it. However the rest of the drive train has 264,000 miles on it. Anyway the saga continues after adding new rear leaf springs. After the replacement on the way home this noise happens only when I let off the throttle. I think the ride hight is higher than what the stock was. But that should still not cause this noise Right? My question is what the stock springs should be just to verify I have the right springs and and what the awful sounds coming from the transfer case. Transfer cases are a bit of uncharted territory for me I'm unfamiliar with it. I have a video included. What shall I check first?

 

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SinisterWillys1940...If the rear springs now have more arch or the rear axle's location point has moved, you could have a rear driveline issue.  This is a slip yoke driveshaft, so moving the axle can cause the driveshaft to pull out from the transfer case splines.  The slip yoke could be ratcheting, or the U-joint angle could be too sharp.  Or the angles of the front and rear U-joints (at the rear driveshaft) could be wrong.  If the springs changed the pinion shaft angle, the rear driveshaft's U-joints could be at non-cancelling angles (not the same) or out of phase.

With the Jeep parked at curb height, wheels weighted, look at the rear driveshaft from the side view.  Compare the front and rear U-joint angles.  Note the position of the coupler/slip yoke to see whether it has retracted (moved outward) from its original position.  If the rear driveshaft is too short now, the slip coupler could be partially engaged in the transfer case's output splines.  Or the U-joints could be binding.  Check whether the rear driveshaft angle is too steep, causing the driveshaft to bang on the skid plate or bind the U-joint(s).

Moses

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If the driveshaft is too short now, it could be the rear springs and/or shackles dropping the axle too much.  Or the leaf springs' axle locating pins are in the wrong position (too far rearward).

In any case, if the only change you made was the rear leaf springs and/or shackles, that's enough to pull the splined slip yoke coupler rearward from the transfer case's output shaft splines.  Long shackles, since they're at the rear of the Wrangler's rear springs, will also do this.

Make sure that the springs are not installed backward (front and rear spring eyes reversed).  The spring axle perch locating pins are not at the middle of these springs.  They are offset in one direction.  If the springs were installed backward, the axle would set rearward, which would pull the slip yoke loose at the transfer case output splines.

Moses

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I never would've thought that the springs could be backwards. Now the shackles could do it too since they look nothing like the original ones. they had 2 different bolt holes one higher and lower. How do I figure out which oerientation the springs fo on? Suspension isn't really my cup of tea lol

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Normally, with stock springs, you could not reverse them readily; the front spring eye is larger than the rear spring eye.  With aftermarket springs, however, the eyes could be the same diameter and allow the spring to be reversed.  Compare the spring eye diameters...Also, measure from the center of each spring eye to the center bolt/locating pin of the spring where it aligns with the axle spring perch.

On the rear spring set, you want the short length of the springs to face forward.  If the springs are different lengths from the center bolt to the spring eye centers, and if you put the long end forward, the axle would set too far rearward.  This would pull the rear driveshaft outward from the transfer case output splines.

Also, if the shackles ("lift" shackles as you describe them) are too long, the axle could drop enough to pull the driveshaft rearward—especially if the springs have more arch than stock.

Overall, you want to maintain the Jeep's original wheelbase length.  The YJ Wrangler has a 93.4" wheelbase.  This is the measurement between the front and rear axle/wheel center lines with the front wheels pointed straight ahead.  If you're unclear about the rear axle position, measure your wheelbase length.

Keep in mind that any time you "lift" the vehicle with a chassis/spring lift, the axles drop lower, and the driveshafts become short.  Too short and you need longer driveshafts, and this is more likely at the rear of a Jeep YJ Wrangler.  With a chassis/suspension lift, it is very common to install a slip yoke eliminator kit*.  See details on the Advance Adapters SYE Kit:  http://www.advanceadapters.com/products/np231-sye--new-process-231j-fixed-yoke-kit-50-7906--50-7907/.  The page features a video on installing the AA SYE Kit in an NP/NV231 transfer case like yours.

*Note:  With a fixed yoke output at the NP231 transfer case, a longer CV-style rear driveshaft is also installed on the Jeep XJ Cherokee, YJ Wrangler or TJ Wrangler.  Here is my lifted XJ Cherokee with AA SYE and a CV rear driveline:  http://www.4wdmechanix.com/Moses-Ludel-How-to-Installing-a-Jeep-XJ-Cherokee-Long-Arm-Suspension-Lift?r=1.  See how this all goes together with aftermarket springs. 

Moses

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I Measured the lengths I got 23" from the front eyelet to the top of the axle, and 22" from the top of the axle to rear eyelet. Looking at the page I bought the springs they are 45" long in total length. But the eyelets defiantly are different sizes. One is noticeably bigger and is currently sitting in the front, and a smaller one in the back on the shackle. Maybe theres a shim that got left out? Heres the eyelets blob.thumb.png.6158dd13b52b7e3351ab4a3d1350cd04.pngblob.thumb.png.4b8d383ca0cb11f95eeb70490f8e9b35.png 

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This is the normal orientation of the springs, big eye facing the front.  The lower shackle bolt location is close to stock, this should not create much change in vehicle height.  Compare the spring center bolt location with the stock springs.  The bolt location determines where the axle sets.

These do look like aftermarket "lift springs" which would drop the axle position and raise the chassis height.  How much lift is this?  Arched springs pull the driveshaft rearward.  This is why the driveshaft length must change with anything beyond a very mild chassis lift.

 

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If you have lift springs, when you look at your Jeep from the side, the frame and body will look higher than stock.  Let us know what you find...

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Upon review of the fsm I found a test on how to check the yoke angles to see if I need some wedge shims.The vehicle needs a full tank of gas and nothing in the trunk space and on level ground. Then measure the angle from the yoke on the differential side, then the shaft side. The angles should be within 1.5 degrees of each other. If my angles are correct then my height is where it should be and the load change on the u joints.Then that means I need to look into diagnosing bad u joints. If the angles are out side of spec then I need some angle shims to angle the axle up or down a specified degree thus changing the load on the u joints to where it should be. The reason I think it looks higher in the back than the front is that the front has compressed the 4 years its been redone. I'll scan the fsm page on to here 

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This is helpful to others, Sinisterwillys1940...I discuss driveline angles and "cancelling" angles in each of my books.  An excellent guide is the Spicer driveshaft manual.  Your FSM pages are a reliable resource, too.  

I have the level/gauge in my tool box and have used it many times.  Worth noting, the vehicle should be at normal ride height when you measure the angles.  You can do this with the Wrangler parked on a flat surface or with both axles supported evenly on safety jack stands.

Sinisterwillys1940 has a stock YJ Wrangler with a single-Cardan joint at each end of the rear driveshaft...For those with a CV type rear driveline conversion, I like to rotate the pinion shaft at the rear axle to create a rear U-joint (single Cardan) angle of 1.5 to 2.0 degrees.  This will keep the cap bearings rotating and lubed evenly.  "0" degrees at the pinion does not work, the needle roller bearings cannot rotate and will fail quickly.  A double-Cardan (CV) joint has self-cancelling angles.

For a stock driveline with single-Cardan joints, the 1.5 degree maximum difference between the angles is reasonable...

Moses

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