Rear End Vibes.

:wantyou: to review some numbers.

There is a consistent noise and vibe coming from the D44 out back at speeds starting about 50 MPH and get worst the faster the XJ go. I know the leafs back there are as old as the XJ but I added a main leaf from a Dakota under the XJ main leaf which netted about 1" lift. Some shackles were added to get a total lift of 4" to match the 4" on the front from some CE9131Fcoils I bought from DPG some years back. I expected only 3" from these coils but ended up at 4" and have not sagged in more than 5 years. My XJ is a Country edition and had an inch of lift over the regular XJ's since I bought it in 2003.

Here are the numbers.

Differential angle is 13*.
Drive shaft angle is 12*

There is a 2* or is it 3* shim under the springs to point the pinion up.

I do experience some axle wrap when the tires loose grip offroad. Would that axle wrap show itself on the highway at speeds?

techno1154 said:

:wantyou: to review some numbers.

There is a consistent noise and vibe coming from the D44 out back at speeds starting about 50 MPH and get worst the faster the XJ go. I know the leafs back there are as old as the XJ but I added a main leaf from a Dakota under the XJ main leaf which netted about 1" lift. Some shackles were added to get a total lift of 4" to match the 4" on the front from some CE9131Fcoils I bought from DPG some years back. I expected only 3" from these coils but ended up at 4" and have not sagged in more than 5 years. My XJ is a Country edition and had an inch of lift over the regular XJ's since I bought it in 2003.

Here are the numbers.

Differential angle is 13*.
Drive shaft angle is 12*

There is a 2* or is it 3* shim under the springs to point the pinion up.

I do experience some axle wrap when the tires loose grip offroad. Would that axle wrap show itself on the highway at speeds?

Click to expand...

Ive been playing this game for a month or more.....your angle sounds fine.....

1st make sure its not the tires....

driveshaft balance....
u-joint at pinion, play, worn out, no grease in the caps....
double cardan cv joint has play or is toast.....
pinion bearing is toast has play...
sye output is toast or has play....
Only other driveshaft component is the slip joint could be trashed....

not sure how old your stuff is etc.... but thats what I would look at....

generally vibe associated with speed are fixed by dealing with worn parts...how old is your driveshaft? did you change anything recently?

I had a chance to look closely at this today and the results were disappointing. You see, I have been chasing this problem since 2007. Everything I do seem to make little difference. All the while I keep convincing myself that it is something I did and kept looking for a resolution in the wrong direction.

In early 2007 I change the tail section of the TC so I could have an SYE. Everything there went well and still is. I need a double cardan drive shaft to complete the new SYE install. A good front drive shaft from a Pic Your Part did the job for some months without a hiccup. I drove the XJ with this front shaft while I continued to perform other upgrades and although there were some vibes I paid it no attention blaming it on the set of worn tires on the XJ at that time. Later that same year I was working in Iowa and bought a set of tires there and had them balanced and installed. That same day I also received a new drive shaft from Tom Woods. Both these things should have solved the vibes that were present at speeds above 60 MPH (that same speed we normally experience tire vibes). I seldom drive my XJ above 65 MPH where the vibes were bearable. In addition, I was out of the country for several years and the XJ was not driven while I was away. In the three years I am back in the US it must have done about 3,000 miles 90% of which was in stop and go traffic.

Fast forward to 2 weeks ago. I went to Daytona beach for the Jeep Beach meet down I95. Trying to keep up with traffic at 75 MPH the vibes were unbearable. I did make it to Jeep Beach and back with no more problem than a broken speedo drive sending unit. :repair: Today I went under the XJ to check the drive shaft and found the slip yoke had excessive play in it that was felt when I held one section and tried to turn the other. I removed the shaft and set it down on the work bench so I could take a close look at it while I plan my next move. What I saw there on the bench both angered and disappointed me. The main shaft and the slip yoke end were out of phase. Yes, the front and rear 'U' joints were between 10 and 15 degrees out of alignment. I had to pull out the old OEM front shaft that was still in the Tom Woods shipping box and lay them side by side to be sure I was seeing things that were not true and sure enough the OEM 'U' joints are in perfect alignment.

I will ponder my next move.















.

Too bad you are so far away. From experience, you learn the frequency of the vibes. They are different if they are at the rotational speed of the axle, or the higher frequency of the driveshaft.

Are you sure you don't have a busted belt in one of the tires?

I would pull the diff cover and look at the gears. You might have a bad bearing, either in the diff or even a wheel bearing.

I had a D44 that had the bearings put on backwards on the axle shafts. The backing plate didn't keep the bearings together that well and the axles were walking back and forth.

Do the vibes vary under load vs. coast vs. deceleration? Do they vary if you are doing a sweeping turn at speed?

If you hit a dip, do they change?

Does rotating the tires change anything?

Techno: you sure the shaft isn't one spline off at the slip joint?

old_man said:

Too bad you are so far away. From experience, you learn the frequency of the vibes. They are different if they are at the rotational speed of the axle, or the higher frequency of the driveshaft.

Are you sure you don't have a busted belt in one of the tires?

I would pull the diff cover and look at the gears. You might have a bad bearing, either in the diff or even a wheel bearing.

I had a D44 that had the bearings put on backwards on the axle shafts. The backing plate didn't keep the bearings together that well and the axles were walking back and forth.

Do the vibes vary under load vs. coast vs. deceleration? Do they vary if you are doing a sweeping turn at speed?

If you hit a dip, do they change?

Does rotating the tires change anything?

Click to expand...

I knew all along that the vibes were timed to speed i.e. the faster I go the faster and more pronounced the vibes were. I tried three different sets of tires over the years with no change. In less than 6 months and 3 thousand miles I had the diff completely rebuilt a second time by a reputable 4 wheel and offroad shop in Miami. Nothing changed. I changed the oil several times to allow me to look inside. Everything in there look perfect. Driving around town at a maximum of 45 MPH there is no vibe at least nothing noticeable. The vibes are from say 60 MPH when I am on the gas although now I think of it there was a little on deceleration. I do not know if the vibes were there while coasting because I did not take the AW4 out of gear to do that check. Long highway turns do not make a difference.

markw said:

Techno: you sure the shaft isn't one spline off at the slip joint?

Click to expand...

I am sure something is off or should I say different on that drive shaft. Of the three double cardan shafts I have, that one is the only one where the rear single 'U' joint is not in line with the two in the front double cardan assembly. I have not disassembled the shaft so I cannot say for sure how many splines it is off. If there are a few large splines it could be just one spline. If the splines are fine then who knows by how much it is off. The two other shafts I have are the XJ OEM un-modified skinny front shaft. One shaft is for the front axle and the other was sitting in the back of the XJ since 2007 in the Tom Woods shipping box.

OK! Here is the low down.....

I laid both the OEM shaft and the one from Tom Woods on a work bench and took an angle finder to each of them measuring first on the double cardan side then the opposite end,...the slip yoke end.

The angle finder was placed on the flat area where the 'U' joint goes. The OEM shaft was dead on at 0 degrees at both ends. The Tom Woods shaft was 0 degrees on the cardan end and 23 degrees at the slip yoke end. If one was to look at the shaft from the cardan joint end, the 'U' joint on the other (slip yoke end) is rotated 23 degrees in a clockwise direction.

I am happy now that I finally realize that I was not chasing ghosts all these years. :yelclap: I could now move forward with confidence to the next item to be repaired/modified,...the ball joins and steering linkages.

Thanks to all who contributed to this thread. Just having someone to bounce a couple of ideas or grievances off is worth 10,000 bucks.

So I removed the Tom Woods drive shaft and re-installed the OEM front shaft on the rear of the XJ. Since then I have driven about 300 miles sometimes at speeds of 80 MPH with no vibrations what so ever. I do not know why I did not do this long ago,.... but then again I made many changes to the XJ including lifting it and a full set of tires at the same time I installed the Tom Woods drive shaft so I looked elsewhere for the problems. I will get the drive shaft re-made and close that long chapter on rear end vibrations.