Drive Shaft Angles

I am a noobie to the XJ and need some help on my drive shaft vibrations. I get vibration in the 25 to 35 MPH range during acceleration and a vibration similar to driving over a section of road where a bulldozer has cut tracks in the pavement when de-accelerating (this is intermittent). I have searched the forum for the answer but have found only bits and pieces of the information I need.

OK here is the setup: a 1993 with Automatic, 4.0 L HO, 8.25" Rear, RE 5.5 Lift with drop brackets, fixed UCA,s & LCA's, 231 transfer case, RE long travel yoke, stock driveshaft. Currently have 235 tires (but not for long).

I know that the best solution to my vibration problem is an SYE and I am saving up for one now but I was wondering if I could reduce the vibrations as much as possible until then. I have a 4 degree down angle on the transfer case, a pinion up angle of 6 degrees and it appears that the driveshaft angle is around 15 degrees. I have a set of 4 degree shims from RE and a set of 2 degree shims (no shims installed at present). My question is: Do I use the 4 degree or 2 degree or neither? I will need to get a 1 degree difference (pinion less than transfer case) from the info I have got from the forum searches. This means the pinion needs to be at 3 degrees up? I will need to install the shims with the thick end towards the front of the XJ to lower the pinion angle?
I really appreciate any help or advice I can get!
Thanks

Take a look at the yokes (especially the TC end) and see if there is very little clearance between the yoke and the u-joint. When braking, it pushes the front end down and allows the rear to come up a little, making the angle a little worse and sometimes causing binding between the u-joint and yoke.

There seems to be plenty of room. I installed the RE long slip yoke which has a larger opening than the stock yoke. I can also feel a slight pop when I barely touch the gas and let off. Almost seems like the ujoint may be bad? Oh and I forgot to mention in the original post that I have the RE Transfer Case drop installed.

First of all, chock the front tires and put the jeep in neutral to take any pressure off the rear driveline. Then get under there and wiggle everything to see if you have a loose yoke, pinion or u-joint. If that is all OK, then get yourself an angle finder and a level piece of pavement. Take the rear shaft off. Put the angle finder across the yoke of the t-case and the pinion yoke. The angle down of the t-case yoke should be one degree more than the angle up of the pinion yoke. If that is not the case, shim the rear axle or add longer shackles to make it so. That is about as good as it is going to get short of doing it right and getting a SYE.
mattk

Check for how much of the slip yoke is actually engaged at the transfer case. The put a jack under the pinion snout and jack it up to simulate diff rotation under acceleration and check again.

As I wrote in a post to someone else, you are right "on the bubble." I know of people at 5" or so of lift who can run the stock driveshaft. But I also have a friend who went from 3" to 5" in a '95 and had the driveshaft fall out 1/8 of a mile down the road when he went for a test drive.

If the slip yoke doesn't have enough engagement with the output shaft, under load it can wobble around and start running eccentrically. You'll definitely feel that.

I have about 2 inches of yoke shaft visiable from the seal to the back of the yoke. This is a longer yoke than stock and there seems to be enough engagement. I have already measured the angles with an angle finder and have 4* down on transfer case end and 6* up at the pinion end (driveshaft angle about 15* down). I have already checked for play in the driveline and ujoints by doing what you suggested. There seems very little movement in the shaft with the XJ in neutral. I am not sure about the shims I should use. I know that based on my measurements I need to lower the pinion to about 3* (this will provide 1* less than the transfer case end which is at 4*). What I do not know is the relationship of the shims to the pinion angle. If I install a 2* shim to rotate the pinion down is this a direct relationship to the pinion angle? i.e. will I get 2* down on the pinion with a 2* shim? (I have 2 sets of shims 2* and 4*).
Thanks for the help guys!

First off Im curious what you are using to measure the angles because a "Stock XJ" (without a TC drop kit)has an output shaft angle of 4-5*.Second,yes with a single joint driveshaft you will get an angle change equal to the shim.On a DC shaft you get about 1.5X as much as the shim since the driveshaft angle counts then also!

Maybe I did not measure correctly. I am using a magnetic angle finder found in a hardware store. I placed the angle finder on the tailshaft housing of the transfer case. I have since found out to use the engine valve cover and I will try that when I get back to the house (currently at work). Thanks for the help! I will get the angles again and get back to you.

Angles

I could never understand the long travel yoke. It seems to me it only adds to the problems. Getting the correct angle is done with the shims. Getting less DS angle is done with a shorter slip yoke.
I cut the output shaft so I had only 1 inch of spline. Center drill and tap it, like you would do when installing a RE slip yoke eliminator. Take your yoke, cut it to fit the shortened output shaft, drill a hole in the end to bolt it to the output shaft. I also drilled and tapped for 3 set screws around the yoke to further keep it in place. Measure for a new drive shaft. With that measure, have your original drive shaft made to that dimension with a slip yoke installed. The longer DS gives you less working angles and no wobble of the yoke at the T-case.
My 2 cents. Walt

That's good to know Walt. I hadn't thought of that but what you said makes sense about the yoke length. I installed the longer yoke because I feared not having enough spline engagement with the stock shaft. I ulitimately will go with an SYE when the funds allow but am trying to get by until then. My vibes just seem to severe to me to run as is. I am going to try lowering the pinion angle to get my joints closer in phase and see what happens. Thanks again for the advice.

Ok I re-measured my angles and here are the numbers:
measuring from the valve cover 6* down on transfer case. measuring on top of the pinion 8* up. Will 4* shim be too much to lower the pinion or should I use 2*?

Thanks for the help

The ideal is to have the pinion 1* down from the transfer case. The 4* shim will put you 2* down. Can you find 3* shims? That should put you right on the money.

This may be of some assistance:

http://www.pirate4x4.com/tech/billavista/PR-shaft/index.html

It does appear that 3* would be what I need and I wish I had some but I thought I might be able to get away with a 2* difference rather than 1* but after reading the link from BillaVista I discovered that 2* difference is OK. I have never seen the dirveshaft angles explained as well as this link does it. This is a great source of information!
Based on what I have read so far from BillaVista's link it seems 4* shim is what I need to provide a matched angle under load. Thanks BillaVista!

Well I installed the 4* shims thick end towards transfer case to lower the pinion angle. It did reduce the vibrations but they are still there. I guess that means time to invest in an SYE and DC shaft! Thanks for the all the help on this guys!

Two other things you didnt mention.Try a new set of u-joints and have the driveshaft balanced(about 15-25$).

I did not consider that! What is the process used to balance the driveshaft? It is done independant of the vehicle and if so would installing the lift change the geomtry such that it would require balancing? I guess I assumed (I know the saying about assumtions) that since it was fine pre-lift it would be fine post lift. Thanks for the help RCP Phx

Odd vibrations at coast speeds

I think I got my acceleration vibration tamed down somewhat after changing pinion angle but I have a question about a coast vibration that I am experincing. The acelaration vibration only occurs at the 35 to 40 mph range. But no matter what speed I am running when I let off the gas (Coast) I get a vibration that is intermittant with no particular speed that lasts only for about a second or two. The vibration can be felt in the driver side floor board and sounds similar to driving over the small speed breaks at some stop signs but not as severe. Almost like driving over a spot in the pavement where a bulldozer cut tracks across the highway.

I would have thought that if this was driveline realted it would occur at certain speeds even when coasting but this occurs at random speeds. Has anyone ever experienced this type of vibration and have any clues as to how to remedy it?

Anybody out there that has knowledge of these coast vibrations?

Well you could check your motor/trans mount(s).After that you "can " have vibes on deceleration as your pinion rotates down!That could be from soft springs or what youve been avoiding,a need for a SYE kit!