I can feel (but not hear) a very slight bump in the rear-end when gentle acceleration is applied and released on the prop shaft (e.g. like driving stop- and-go in a parking lot or at a stop sign). At first I suspected a suspension or wheel bearing problem, but all these checked-out fine. The halfshaft U-joints are OK. Both prop shaft jurid couplings look brand new (have owned the car about 2 months now). The transmission and engine mounts look as though they have also been recently replaced. With the transmission in Park, I can wiggle the prop shaft slightly at the differential where the companion flange and pinion tail bearing enter the differential (red/orange oil seal area shown in photo). Is a small amount of "play" at this area normal? If not, am I correct to suspect the pinion tail bearing? It almost looks as if the companion flange kit and the pinion tail bearing can be replaced by dropping the prop shaft and working on the differential while it is still in place. Am I dreaming? Again, this is not a major problem, but one that feels as if it will gradually worsen. I should probably also mention that there is no play in either of the two differential bearings. Is there a relatively easy and inexpensive fix for this, or will I eventually have to bite the bullet on a differential rebuild or replacement? Is there another possible cause that I might be missing? Thanks in advance for your help!

 

Rotating the driveshaft back and fourth and having play is normal. Can you tell me what your feeling is worse if you were to go between reverse and drive? We had a customers car with similar concerns end up needing a driveshaft. The splines where the 2 piece driveshaft meets in the middle can also cause a noise.

 

Thanks! I'll check it out when I get a chance and get back to you.

 

Mine's been making a similar noise, going from off-throttle to on-throttle in parking lots, I believe when in Sport mode. I had the rear subframe out for other things recently and I checked my input flange and driveshaft for possible play. Didn't notice anything in the input flange/bearing but I did find a very very small amount of lash when rotating the rear driveshaft half and holding the forward half steady. Sounds like it's the same thing that Addicted2Boost is talking about.

 

Back in the mid to late 90's when I worked at a GM dealership, the suburbans, tahoes and full size pickups had the same thing concerning their 2 piece driveshaft. The fix was to separate the splines, clean it out, insert this foam spacer and lube both spline halves with this whipped cream like substance. It was light blue in color and came in a small tube like wheel bearing grease. That sure fixed the noise. Even wheel bearing grease don't work because I tried it. I don't know if this post surved any real purpose. Just wasting time I guess.

 

It does not seem to be worse going between reverse and drive. In fact, it does not seem to happen in reverse at all. I will have a chance to check the connection between the two halves of the prop shaft sometime in the next few days. I noticed from the parts diagram that there are two spacers at that point - one is "thick 0.58", and the other is "thin 0.41"
The center bearing mounting bracket also appears to be involved at that point, from looking at the diagram. I suspect it might have something to do with the 6 hexagon flange screws that are a part of that component. Here's hoping a little torquing down on the connection will solve the problem. If not, perhaps the spacers or the bracket are involved. I'll get back to you.

 

Hi CarGuy,

I've been hoping one of our differential experts would respond, but since they haven't I'll offer a few thoughts:

To answer your first question, yes, there should be a very small amount of play when you turn the driveshaft before one of the output shafts begins to turn. This represents the backlash between the pinion gear and the crown wheel/ring gear. I don't know the correct specification for the 14HU diff, but for the earlier GKN Salisbury and Dana diffs used in Jags the spec has been in the range of 0.004-0.007 in. If you sense that the backlash in your diff is greater than that, it probably is due to a worn pinion tail bearing or possibly worn gears (which have been reported).

The GKN/Dana 14HU diff in the X308/X100 is widely thought to be less robust than the older GKN 15HU Salisbury used in the XJ40/X300 and the similar Salisburys used in the Series cars. For some unknown reason, rebuild information and parts for the 14HU seem to be hard to find. I don't know for certain, but I suspect that as on the 15HU, the 14HU pinion tail bearing must be replaced from inside the case, so disassembly of the diff would be required.

In addition to excessive backlash in the diff, other possible contributors to the bump you are feeling could be the large rubber subframe bushings, which can allow excessive movement of the IRS when they deteriorate.

I haven't heard of problems with the driveshaft splines on Jaguars, but the rubber isolation bushing around the driveshaft center bearing deteriorates over time, so it would be worth checking for excessive movement of the driveshaft at the center bearing.

The rubber bushings in the differential mounting pendulum and wishbone tie are generally robust, but it would be worth checking them, along with the bushings in the monostrut that supports the rear of the IRS.

Cheers,

Don

 

Hey Don!

Thanks for the input. Those backlash tolerances seem awfully limited compared to what I am feeling, but I am not sure how to measure them more accurately than SWAG. I am going to take a closer look at the driveshaft center bearing.

The bushings you referenced all look OK to me, but I am finding it difficult to apply leverage to most of them (the old pry bar method) to determine how viable they are.

It is very difficult to reproduce the "bump" except in a level parking lot stop-and-go scenario. I am guessing that this is because the suspension component in question is already loaded or pre-loaded in up or downhill scenarios, and any kind of robust acceleration overcomes the subtlety of the motion. This would seem to make catastrophic failure unlikely (?), but no doubt the condition will worsen over time.

Will get back to the forum. Thanks again!

 

I think it would be possible to measure the backlash with the differential in situ if with a dial indicator and magnetic base. You could put the indicator tip against one of the bolts on the pinion flange as a reference point and get a rough idea of the backlash. Here's how it is measured during a diff rebuild. The blue coloration on the gears is from the engineer's dye paste used for checking the gear mesh pattern:





Cheers,

Don

 

Well, I think I found the problem, but it is so fundamental that I am a little embarrassed to report it. But, what are car forums for if not to embarrass oneself every now and then?

Today I greased the half-shaft U-joints which were so completely stuffed and covered with black crud that it took a lot of cleaning just to find the zerk fittings. It didn't look like the U-joints had been lubed since the car came off the assembly line. But, no, this was not my "bump" problem.

Having seen the crud around the U-joints, I determined to clean it up elsewhere on the rear suspension. The next glob of it I found was around the bottom mount of each rear shock. I gave it a good wipe, and Yikes! - the bushing in the bottom mount disintegrated along with the crud glob (highly technical term). Both shocks were in the same condition. See pics.

I had given the shocks a cursory glance before, but frankly did not suspect them because the ride is still quite smooth, and the handling is not bad at all.
I can't remember ever seeing a shock mount bushing deteriorate like this before the damping effect of the shock was bad.

I think (and hope!) that this is the problem. I had planned to replace all four shocks anyway, just not quite this soon. I always do all four at the same time, so I'll be saving for this for a few weeks, and then let you know if this was, in fact, the problem.

 

The rear shock bushings are actually spherical bushings instead of just rubber like the fronts. So, it's probably not quite as bad as it looks, but probably still time to replace them. OEM shocks, and most others, come with bushings pre-installed, as well as the upper shock bushings.