I'm getting a grunt noise from the back of the car with hard acceleration. It began with a few months ago accelerating through a corner, but now it is whenever i speed up quickly. It's worse once the car warms up and even worse -louder and lasting longer-going uphill and accelerating. My mechanic thinks it might be the LSD going but i thought I would post here to pick the brains of the forum experts. (I did not see anything in the FAQ section)
Thanks, Alfred

 

I had something similar. Upon changing the fluid I no longer had the grunting noise on hard accelerations. I had 100K on 7 y.o. car when I changed it. I used the below fluid which meets the Jaguar/ Ford differential spec. I found this fluid cheapest by ordering through amazon. I recall that you need the "wobbler" extensions to get the fill plug out due to the angle. Also, buy a variety of fluid pumps on amazon. I ordered 3 or 4 different attachments that totaled about $10 which made both the differential fluid change and transmission fluid change very easy.

Dear Sir or Ms.: The SL2495 -- Syn-Go(r) OEM Grade/Extended Interval, Synthetic Gear Oil, 32 Fl Oz and SL2496 -- Syn-Go(r) OEM Grade/Extended Interval, Synthetic Gear Oil, 64 Fl Oz meet Ford Specification m2c192a. Christine Richie Technical Information Specialist CRC Industries, Inc. crichie@crcindustries.com Ph: 800-521-3168 Fx: 215-674-5147

 

Thanks, fluid change sounds like the next step.

 

Unless you added it yourself, you don't have an LSD. XK8/Rs do not come with an LSD. Too much competition for for big brother Aston Martin.

Mark

 

Ok, I assumed the clutches inside te LSD were the cause of the grunting sound. Would there be something else that could do that inside the differential?

 

Now, if you're sure that you don't have a LSD, then I had the exact same problem with the exact same noise. Since you mentioned mechanic and LSD, I thought there was a chance you had one added (or a previous owner). I had the same grunt as you: hard accelerations, longer up hills, worse when warmed up. Your oil has simply lost its protective and sticky properties.

 

got the diff. fluid changed this week. Now it "grunts" when the tranny shifts up to a higher gear. Could this noise be comming from somewhere else, or does it take some time for new diff. fluid to work in?
Alfred

 

You may be hearing the infamous "ZF bark". It occurs when the ZF clutch packs briefly grab during upshifts. The noise is sometimes described as a bark, a grunt, a chirp, a whirr, etc. The six-speed ZF transmissions from 2003 and newer can all be struck by this annoyance as the friction modifiers in the Lifeguard 6 ATF degrade and lose their effectiveness. There are a number of threads covering this issue in the S-Type section as well as here in the XK8 section. The current recommended fix is to drain-and-fill your ATF with fresh fluid....

Our S-Type developed this sporadic bad habit in late August 2010. As we got deeper into autumn and the weather cooled off, the annoying bark went away and has not returned. Still running the factory Lifeguard 6 ATF at about 71,700 miles....

ZF tech support told me by phone that this "ZF bark" is simply an audible annoyance and will not damage the clutch packs or any other component of the ZF transmission. I have no idea how accurate that statement is, however....

 

When I changed the tranny filter and fluid, it took care of the transmission bark noise I also had. It is funny the choice of words we use, but my rear differential was a loud grunt only when I was hard on it; whereas the transmission had a low volume bark, which would happen somewhat often while driving normally. For whatever reason "grunt" was the appropriate word for the rear differential noise and "bark" was the right word for the transmission noise I had. Doing all the major fluid changes at 100K made my XKR quiet again other than the rear shock / bushing noise which I have grown accustom to. When I had both these noises, they did sound like them came from their respective areas....grunt from rear and bark from underneath.

 

I was wondering if it was time to put the girl up on jacks and do the tranny fluid next. Too hot right now to drive top down anyway, so into the shop she goes.

 

Red1BW Curious how you got access to the Diff Plug. I built an extension to fit the plug and tried using a ratcheting box end. There is no way to access the plug on my 2000 XKR lying on your back using jack stands.

 

Very easy. Use a wobble extension (google it and look at images). They are socket extensions that purposely have a significant amount of play in them. This gets you the angle you need. I forget what size, so buy the 3 or 4 pack that covers the standard socket square drive sizes...1/4, 3/8, 1/2 (it definitely wasn't 1/4"). Use them in conjunction with regular extensions (1", 2", whatever) to get you the right depth so you can turn your ratchet. Easy to find them at any decent tool store such as a Sears, and can also be found easily online.

 

Maybe the problem is that there may be a difference in access. There is no room top, bottom, sideways or rear to access the plug that I can feel or see. No way a wobbler would fit in that space. Would like to see a pic of someone using one.

 

I originally typed wobbler, but meant wobble extension (those images are much more accurate of what I'm talking about). You will actually use the smaller, square 1/2" drive (or 3/8" drive) to go into the fill plug. Mine fit very easily. I have many different sized / length extensions, so it was very easy for me to also get the correct distance / depth to a spot where I could put two hands on the ratchet to turn it. I recall, the total of wobble and straight extensions was approximately 10" from the fill plug to where the ratchet was. I may have even used a universal joint in there as well.
The first time I attempted to do it, I did not have a wobble extension set; so put off that fluid change until after acquiring a wobble extension set.

 

I was thinking the same as Excalibur. I work on these all the time, and getting that fill plug out is darned near impossible without a special tool. So, what do the dealer techs use? On other Jags I have had success using a particular adapter that comes with the serpentine belt tensioner tool kit. It has a 1/2" drive on one side, and a 16mm or 5/8" drive in the backside for the long handled tool to fit onto it. If you just use the 1/2" square in the plug, you can attach a 16mm or 5/8" ratcheting box end wrench to the other side and work the fill plug loose.Works well in confined spaces.

 

Some of them have mentioned using wobble extensions just like Red1bw.

 

There must be something all of us are missing. From my time under the car, it appears that the only thing that will fit might be a 3/4" long 1/2" square with one end in the plug and the other ground to fit a ratcheting box end. Red1bw, if you show me your able to get a setup made of wobbler extensions and a universal 10" long snaked into the plug on an XKR, I'll send you a bottle of your of your favorite booze.

 

Maybe there is something different between the pre 2003 XKR's and the post 2003 XKR's in that final drive / rear differential area. I'm not aware of any. Unfortunately, I do all my XKR work outside as I do not have a garage yet; and now that the weather is cold, I doubt I'll be under it until next spring. Otherwise, I would be glad to take a picture. I definitely used a wobble extension and a regular ratchet. I believe I may have used some other short extensions and / or universal joints in there as well. I recall being able to put both hands on the ratchet and pushing with all my strength grateful that the fill plug twisted off rather than strip.
Do you have the stock dampers and springs? or is yours a convertible where the whole trunk area, fuel tank, convertible storage area are different (I suppose)?
Based on what you describe, perhaps one of those generic fan-belt tool kits will work. They generally have a 1/2" square drive mounted on a metal bar whose total width is no wider than 3/4".

 

Never thought of it! It is a drophead. We may have found our difference.

 

Trust me, if those clutches start to go, you will not hear them, unless you have a microphone next to them or they break.
If you are hearing gear whine, chances are the fluid is really low and when you here the whine, you are already overheating your ring and pinion gears and that is not good.
A u-joint starting to go bad can make all different types of sound, from a thumping sound when going into or changing gears, to a loud whine and grinding sound from the roller bearings.