I've been trying to locate the cause of some rather unseemly vibration at any speeds over 30mph. Having replaced the shot juried coupling, central bearing, propshaft u-joints and re-aligning the the propshaft in accordance with the VSM, I improved things a bit but there is still a significant issue.

As I had to replace the diff output seals anyway (leaking like crazy) I just went ahead and dropped the rear end which aaas a relatively straightforward job. One thing that I noticed was that my differential 'dogbone' struts were different in both length and shape of the ends. Is this normal? All the pictures I've seen show the same part for each side and there is only one part number in the parts list?

Here are a couple of pics.

As you can see in this pic, the ends are round on one strut and oval on the other.


In this pic you can make out that the oval ended dogbone is about a 1/4" longer on the bushing centers.


I'm probably going to replace them with the later mono strut design but I'm wondering if they may be contributing to things being out of kilter?

I've also noticed that one of the upper pendulum bushings is completely shot, so will replace both upper bushings also.

My second question is about the rear springs. My car is an early 95 and I believe it has the shorter springs. There was a TSB about changing to the longer springs that became standard to improve ride. I was wondering how much difference there is in length and are any other parts needed? It appears not but I just want to be sure before I put the longer springs in

 

Can you elaborate a bit?

A year or two ago I had a pretty bad vibration. UJs and center bearing seemed to fix it...mostly. I still have "tingle" sensation at times.....it sorta wafts thru the floorboards. I've often wondered if I've just become over-sensitized. Passengers never notice it, even when I ask them.





Can't help, sorry.






This is new to me. Can you explain?


Cheers
DD

 

Hi Doug,

Yes, originally the rear of the diff carrier was bolted to the frame with the two individual dogbones. The XJR I believe had the monostrut design from the get go but Jag later made it standard on all XJ6, I think they may even have been a TSB recommending the change.

The mono strut looks like this. Also note all the bushes are round


My issue is very noticeable indeed, it starts with a fairly violent vibration felt through the whole body and continues at a higher frequency at higher speeds. I think I probably had a number of issues, the previous owners had obviously had troubles along the way.

The vibrations are felt most under load and you can particularly feel them through the center console armrest.

My first thoughts were driveline as the problem was worse when accelerating. Sure enough when I checked underneath, I found the center bearing bushing shot, the transmission mount on the way out, the propshaft u-joint at the gearbox loose and the jurid coupling had lots of cracks. So I went ahead and changed all those and did the u-joints as well. I then re-aligned the driveline using the plumb bob method. All this made a big improvement but the problem was still significant and unpleasant.

So I started a more thorough inspection from the front of the car to the back. First I wanted to rule out bad wheels or tires. I had just put on a new set of tires but I had them road force balanced just in case, no issues there. I also had the alignment checked.

Then I noticed some play in one of the front wheels, so I popped off the wheels and checked the bearings. The inner bearing had some cracked rollers so I went ahead and renewed both front wheels bearing sets. One of my lower control arm bushes had seen better days and also the boot on one of the lower ball joints was all but gone. As I inherited a ton of spares when I bought the car, including all of the bushes and ball joints, I went head and renewed all of them including the sway bar links and bushes and the tie rod ends. Phew! After that I got another alignment and road tested the car. Some improvement again but still a significant vibration.

So I headed to the rear of the car. On close inspection I noticed one of the upper bushes on the pendulum was completely shot, here is a pic.


So as the diff was leaking anyway, I decided to drop the rear end and inspect it and fix any issues. I'm wondering if the dogbone being a different length could have caused premature wear of the pendulum bush and thus caused the diff to change alignment with the propshaft? That's my current thinking but we'll see

 

My car is an early '95. The original owner took it into the dealership complaining of vibration over 50 mph a couple of times. At 18K mi. they replaced the original struts with the monostrut and no further problems were noted.

 

Thanks RJ, that is interesting. I have ordered one and will install it next week when I put the rear end back in. It should certainly locate the diff better. Hopefully that will be a piece of the puzzle

I still find the different length/shape dogbones a bit unusual though. Jag would most certainly have issued different part numbers for them but only show one? I've been looking to see if the design was used on an earlier car but no luck identifying it so far.

 

Where did you order it from?

 

Got it from a breaker on Ebay. It came from a late model XJ8 but it's the same part. Was told the car only had 60k on it and that the part was in perfect condition. Should get it Thursday and will see.