1995 Jeep YJ Wrangler New Suspension Lift Creates Driveshaft Issues

[topher]

I'm in a pickle.  

Had to install new shocks (both tore away from rear upper shock mounts..due to weak springs(?)..lower rear shock mounts also damaged) and leaf springs (which say a 2-2.5" lift).

Upon installing the springs, the output shaft from the rear pumpkin (I'm not a mechanic) pulled-out approx 1.5 inches (shiny..no dirt) and the shaft entering the front pumpkin, also pulled-out some. I drove yesterday and all kind of God-awful noises...not good.

I'm told the rear axle has to rotate towards the front of the jeep to push the shaft back into place. This can be done with shims? Any idea what degree shim would bring all into original alignment? I was told a couple options by a past professional rock climber....Manager of a NAPA Parts store locally:  One, lower transmission crossmember (skid plate) by no more than 1" and insert spacers if fixes problem.  The second option:  remove axle mounting perch, rotate axle towards front to re-seat shafts to original stock position and then re-weld perches in place.  I didn't think of asking about shims which might be the easy fix if lowering the crossmember doesn't work.  Yikes!  Thank you!

Vehicle Information: 1995 Jeep Wrangler YJ, 2.5 engine, 4x4

[Moses Ludel]

topher...Welcome to the forums...Understand that you've installed a 2"-2.5" spring/suspension lift on your '95 Jeep YJ Wrangler.  The distance between the transfer case input and output and the front and rear axle joints has now increased, and this did stretch the drivelines.  The rear driveshaft has a slip yoke at the transfer case end, that's the piece with the shiny new surface exposed.  The front driveline has a slip collar with male/female splines, and the collar has been stretched from the chassis/spring lift.  Here is a diagram of the stock front and rear driveshaft designs:  http://www.quadratec.com/jeep-replacement-parts/wrangler-yj/yj-drive-shafts.php.

Rotating the rear axle pinion shaft upward is often a remedy for chassis lifts but only if you install a double-Cardan (CV-type) joint at the transfer case end.  In this method, the rear axle single U-joint is normally set to a pinion-to-driveshaft angle of 1.5-2.0 degrees and not straight up or "O" degrees.  You need this slight angle to keep the bearings in the U-joint caps rotating and lubricating.  

Here is a typical example of a CV rear driveshaft which also requires a slip yoke eliminator kit (SYE) in the transfer case.  Note that the shaft shown is for a 4"-5" chassis lift: http://www.roughcountry.com/rear-cv-drive-shaft-jeep-yj-5087.html?gclid=CjwKEAiAkuLDBRCRguCgvITww0YSJAAHrpf-y5EWNinN_7rIu08YC6Msnl8OljHgBAqJStO-0bjRghoCGtPw_wcB.  Advance Adapters makes a popular SYE Kit for your NP231 transfer case if you do install a CV-type rear driveshaft like this one.  There is parts cost and labor involved with the SYE installation and the new CV-type rear driveshaft.

The front driveshaft already has a CV-type joint at the transfer case.  As for joint angles, you are limited at the front axle by the need to set the correct axle caster angle for proper steering and handling.  A 2"-2.5" chassis lift is seldom enough to create a front driveline length issue, especially if you lower the transfer case with spacers.  If the front axle caster setting is correct, and if the driveshaft has not been separated at the slip collar and installed with the splines not matched properly, you should be okay with the front driveshaft.  Did you separate the front driveshaft pieces during this chassis work?

The rear driveshaft is a judgment call based upon whether the slip yoke is safely onto the splines of the transfer case output shaft.  With the vehicle suspension at full drop, the yoke splines must be sufficiently engaged to be safe and not put a bind on the splines.  The yoke must not bind nor slip out completely!  Slip yoke splines must engage a safe distance onto the transfer case output shaft at full suspension and axle drop.  Also, the slip yoke cannot travel too far forward or bottom out when the suspension and axle rises.     

Whether you keep the original slip yoke driveshaft at the rear or not, rotating the pinion shaft/axle upward will reduce the rear U-joint angle and shorten the driveshaft.  Dropping the transfer case skid plate will also reduce the slip yoke joint angle and shorten the driveshaft.  Overall, what you really need is: 1) proper slip yoke spline engagement, 2) virtually canceling U-joint angles at the slip yoke and the rear axle pinion U-joint (angles must cancel each other as necessary) and 3) enough unobstructed travel of the rear driveline's slip yoke and the front axle's driveshaft coupler.

Summing up, I would try the skid plate drop first, which is a very common quick-fix remedy, many suspension kit manufacturers include these spacers and longer, graded fasteners with a mild lift kit. With the skid plate dropped no more than an inch, check the slip yoke spline engagement, front axle driveline length and the front driveline coupler travel.  Also, and importantly, check the U-joint angles at the rear driveshaft.  Make sure the rear U-joint angles cancel each other, or come very close, with the vehicle at a static (flat on the ground, normally curb weighted) height.

Again, the front driveshaft must accept the front U-joint angle that results from proper axle/steering caster adjustment.  With its CV-type joint at the transfer case and its longer length, the front driveline seldom creates a problem.  The dropped skid plate can help restore the front and rear driveshaft lengths.  Start here if the goal is to retain your original driveshafts and not have to install an SYE and CV-type rear driveshaft.  See whether you come close enough for a 2"-2.5" chassis/spring lift.

Let us know how the joint angles turn out if you do lower the skid plate...Be aware that lowering the skid plate will alter your transmission and transfer case shifter positions.  Check for adequate transmission tower and transfer case clearance, proper shifter movement and complete gear engagement.

Moses

[topher]

Wonderful response Moses, thank you!  Dropping the skid plate 1" had no effect on the driveshaft at the rear, unfortunately.  I prefer to keep the original slip yoke driveshaft.  What are your thoughts on spacers?  Someone said start with a 2" and see if that works, might need up to 4."  Also, in my original lamentation, I referenced the NAPA fellows last resort of  removing the axle mounting perch, rotate axle towards front to re-seat rear driveshaft to original stock position and then re-weld perches in place.  What are your thoughts on this approach?

Many thanks Moses,

Chris

[Moses Ludel]

topher...The problem with spacers beyond 1"-2" is that you're dropping the rear mount of the powertrain while leaving the engine's front mounts in their normal position.  This cocks the angle of the engine/transmission/transfer case.  Both the front and rear driveshaft angles change because the transfer case vertical angle has changed.  The angles do not change in the same way:  The front driveshaft's transfer case joint angle becomes steeper while the rear slip yoke U-joint angle decreases.  Shift linkage and console fit will suffer from the shift, too.  This is a good reason to minimize the skid plate drop.  I've seen chassis lifts with longer skid plate spacers, which doesn't make sense.  The OE front driveshaft can become too short and bottom.

Again, rotating the rear pinion shaft angle upward will reduce the rear joint angle but does not change the slip yoke joint angle.  You wind up with angles at each end of the rear driveshaft that do not cancel each other properly.  You do shorten the distance between the transfer case output and the rear axle's pinion flange.

If you want to stick with the slip yoke rear driveshaft, I would first create canceling angles at the two U-joints.  This can be accomplished with the mild (perhaps one inch) skid plate drop, then rotate the rear axle in whichever direction necessary to achieve canceling U-joint angles.  You can rotate the rear pinion with wedge shaped shims placed between the axle perches and the springs.  I use hard steel shims and not aluminum wedges.

Once the joints are canceling each other's angle, measured with the vehicle parked on the ground and loaded normally, you can take accurate length measurements for a new rear driveshaft.  Have a local driveshaft shop build the new shaft to length, using a slip-yoke at the transfer case end.  This can be as simple as installing a new tube section or could involve rebuilding the entire shaft at the same time if there is wear at the flanges, slip yoke and U-joints.

Overall, you do not want a steep rear driveshaft angle/slope, and the stock Jeep YJ Wrangler with a slip yoke has a short rear driveshaft.  A short shaft plus steeper joint angles will decrease the torque capacity of a driveshaft.  If your lift were any more than the 2"-2.5", I would strongly suggest the use of a CV rear driveshaft and an Advance Adapters' SYE kit.  The SYE kit actually shortens the transfer case's output shaft and tailhousing.  This allows for a longer driveshaft, which reduces joint angles and increases the torque capacity of the driveshaft.

Moses

 

[topher]

Thank you Moses for your time, thoughts and guidance.

Chris

[topher]

Hi Moses,

Hope I'm not being too much of a pain-in-the neck.  Much of this fix is "above my pay grade" as they say.  I've read reviews of people installing the SYE kit themselves and watched your presentation and the video from Advance.  My Rancho springs say the lift is 2.5" and shackles I put on the front and rear of the jeep years ago lift it 1.25".  So, the jeep currently is at a 3.75" lift, a lift heighth that you, "would strongly recommend the CV rear driveshaft and the SYE kit."  I'm inclined to do this myself.  The folks saying they installed these kits themselves (reading the reviews), suggests to me it was performed at their "homes" on jackstands.....no lift to raise the vehicle as in a garage?  You strongly suggest the use of a transmission lift when removing the transfer case...if I read you correctly.  I imagine this type of lift is only useable with the vehicle raised.  If folks are removing the transfer case themselves (home), I presume they are using jacks and stands to keep the transmission in place?  I live (rural-Sonoita, Az) at least 40 miles from any place that I would trust to do this work and moreover, the jeep would have to be towed there given its' condition mentioned in my original lamentation.  Also, why pay to have this done IF I can do it myself?  I do like the way the Rancho 5000 leaf springs have raised the jeep and I believe they are more hefty than new stock leaf springs (which I could order if returning the ranchos were possible, and bring the jeep back to its' original position), but I also pull a trailer at times and the ranchos contend their springs are good for this.  Additionally, I like the idea of a more stout driveshaft as you have recommended.  Do you think the removal/installation of your recommendations is dooable in a garage without a lift?

Thanks again Moses,

Chris

[Moses Ludel]

Chris...I'm not clear how your tools stack up, but if you have the necessary tools, you can work off your shop floor with the use of a transmission/transfer case floor jack.  Add safety jack stands if you prefer a bit more ground clearance, this makes it easier to get the transfer case out from beneath your Jeep.  Get yourself a nice creeper while you're at it!

Look at the transmission jacks available from Harbor Freight.  You're not doing this job day in and out, so this caliber of lift would be plenty.  There's another alternative that I purchased from Summit Racing, it's also available elsewhere:  a transmission jack head that fits into the common floor jack cup socket.  With the adapter, the only caveat is stability:  a floor jack has a narrower footprint than the wider based transmission jacks.  If you use the adapter with a floor jack, be careful not to side load the adapter and tip it over.

As for level of difficulty, if you use my steps and a factory shop manual or equivalent, you can rebuild the NP231.  Following the step sequences carefully, this is not a complicated assembly to rebuild.  You're doing the equivalent of an overhaul when installing the Advance Adapters SYE Kit.  Look for wear and other needs while you have the 231 unit apart, there are rebuild kits available for the NP231...The net result is a sturdier rear driveline that is longer than stock.  Despite the cost, you'll have a "permanent" fix for an otherwise common problem area.

With a CV-driveline, the CV double Cardan joint has "self-cancelling" angles.  You will rotate the rear axle with shims and set the pinion shaft to achieve a 1.5-2.0 degrees rear U-joint angle (a mild but necessary angle for U-joint life).  Set/measure this angle with the vehicle on the ground and normally weighted...SYE flange yoke in place and the pinion rotated, you can take an accurate measurement of the length for your new CV rear driveline.

Moses

[topher]

Thanks again Moses.  This is good information and I'll certainly check-out these two sites.

Chris