Special thanks to XJRJR for his original question, then answering his own question for everyone's benefit.

I'm doing a number of preventive maintenance items and this transmission mount replacement was inexpensive and easy. His instructions made it simple. After 16 years and 106K miles it was due. The original one is much more sloppy than the new EuroSpares brand I used.

There was a thick oil visible in mine after removal. Car is smoother running now too.

Did you have to remove the transmission cross member to access/remove the transmission mount or can it be accomplished with leaving the cross member in place?

Dropped the crossmember. Replacing it connected may be possible. But access to the mount is limited by the crossmember.
Support the tail shaft well and drop it to give your self room to work.
Doing off Rhino Ramps is tough. If you have access to a lift it is a 30 minute job.
I am too thick to work well on the middle of the car using a sloped driveway and ramps. Ramps work fine for me getting to engine, rear end, and wheels. Bought a low profile racing jack to get under the cars when clearance is tight.
I maintain a small fleet of family cars.

Luckily I have a ramp that gives me about 42" clearance under the car. I'll remove the cross member. Thanks for the tip about the drive axle. Didn't think of that!

@XJ8JR Can you please tell me what was the milage of your XJ when you replaced the trans mount?

@Panelhead Can you please tell me if you got rid of your vibrations between 40 to 60 mph after replacing your trans mount.

Thank you guys!

I believe the X350 was around 125-130k miles when I first created this thread and performed this repair.

I have since done it twice on my X351, once in 2018 at 85k (turns out the mount was ok), and again earlier this year at 122k miles (ripped by all the supercharged hard pulls).

Thanks for your quick reply @XJ8JR . You described one of your symptoms before replacing the trans mount as „vibrations at initial acceleration which would disappear until around 30 mph and then again just before 70mph.“

I got exactly the same vibration problems with my 05 XJ8. Besides from rough shifts of my automatic gearbox my car has no other issues. I am wondering if trans mount replacement might solve my vibrations as well although I only have 50k miles on my clock so far. OEM trans mount is currently at almost 200 Euro. It‘s a little bit expensive for just try and error.

The symptoms sound about right. There are several less expensive aftermarket options now that weren't available back then.

I had similar issues. Swapped mine out at 105K miles with OEM equivalent - issues went away; 2004 XJR on 20" Sepangs

Thank you guys. I‘m also riding on beautiful Sepangs.

You guys raise my hopes on finally getting rid of these annoying vibrations.

In Germany there is only the OEM part available. In UK you can also get a „direct replacement“ part but without any manufacturer listed. OEM should be produced by Lemförder I guess. But I cannot find any part number. As long as I don‘t know the manufacturer and quality of the non-OEM part I will go for OEM.

My XJR broke a motor mount at around 95K. The transmission mount never failed, but was leaking and loose. I think 100,000 miles is about right for these.
Not sure our Lemforder parts are better than aftermarket. These mounts should last a lot longer than they are.

Thanks for your response @Panelhead . I guess leaking and loose is the paragon of a failed trans mount.

Did you get rid of your vibrations between 40 and 60 mph by replacing your leaking and loose trans mount?

Changing the mount made it run smoother. It seems like a maintenance item. At least with the SC engines. Don said he has never changed one. So these must not be on people’s radar.
I doubt you can tell if they have failed visually without removing. This is not a large part and the mount is in the way.
There is a 94.00 replacement on eBay. Fits x351 also. May last as long as OEM.
Not a big fan of OEM. Some parts not drivetrain related seem to be short lived.

I've changed a couple of them since this thread started in 2015. The first one I got from the local Jaguar dealer and it was in a Jaguar box, so it may have been a Lemförder. When I did one on another car a year or so ago, the owner didn't want to spend the $200 on one from the dealer and the only other option I could find was the Eurospare, which I think I got from PartsGeek. As far as I know they've both held up.

Cheers,

Don

Don,
since you have replaced two were there visual indications with mount in place? Also were there signs of failure once Mount was removed?
I suspect many have failed mount. Just either ignore the symptoms or figure it is engine, transmission, driveshaft, or other expensive repair. Would be great if failure could be identified prior to dropping the cross member. It is awfully tight in there.
Did not realize how small this mount was until the Eurospare part came in. Mostly steel and only weighs a couple pounds.

It's difficult to see the condition of the rubber with the mount in situ because of the way the rubber is formed on the outer ends. Even with my inspection endoscope I couldn't tell much. But prying on the transmission with a long pry bar I could tell the mounts were loose and sagging. Neither of the mounts I removed was visibly cracked or torn, but the rubber was distorted and it was obvious that the bridle was sagging.

If you aren't doing this job at the same time as the transmission pan and connector sleeve, while you have the crossmember and mount off, disconnect the connector and inspect it for oil contamination. It will never be easier to disconnect the harness connector from the sleeve or to get a mirror up for a good view of the inside of the connector.

Cheers,

Don

Hey guys,

I want to give you an update on my work. Changed my trans mount against a brandnew OEM one. As I marked the trans mount frame before removing I put it back in exactly as before. Vibration didn‘t change at all. Now there is also a slight droan in addition to the vibrations.

My 2005 XJ8 with 50k miles on the clock feels a bit rough from initial acceleration. At 30 mph you can feel this slight roughness again. At around 50 mph a vibration comes in with peak at 50 and stays till 70-75 mph. You can feel it in the steering wheel, in the floor pan and the seats. Checked with a vibration app: Vibration frequence is at the same speed the propshaft turns. According to the app it’s either a 1st order propshaft vibration or a 3rd order wheel vibration.

The vibration and roughness is unaffected by throttle load or gear. When between 50 and 70 mph the vibration stays exactly the same even when I shift to neutral.

When car and/or temperatur is cold vibration ist distinctly more intensense. It gets better after driving for a while but never goes off.

So far I have replaced brake discs at the rear and all brake front and rear, replaced front lower arms, changed differential oil, did wheel/suspension alignment, replaced all 4 tires, get tires balanced. No change at all!

When inspecting the propshaft it seems an balancing weight at the rear half of the shaft might have fell off. At least there is a rusty mark in size and shape of a postage stamp. Could a missing weight lead to the symptoms which my cat has?

The vibration absolutely drives me crazy. Unfortunately, there is no Jag specialist around me which I could take my car to.

Yesterday I called a dealer which is specialiced on X308, X100 as well as X350. Before I sketched my vibration problems at all he already stated it must absolutely be transmission related as X350 are known for such problems. He suggested to do a ATF flush and reprogramming the transmission first. I‘m a bit confused as I don‘t have any evident problems with my transmission at all.

Any thoughts on my vibration? What do you think on the statement the vibration must be transmission related? @Don B @XJ8JR

I highly esteem you support, guys. Thank you!

New noise. First thought is driveshaft related. Worn U-joints drone, seems worse when light load. I think my prop shaft looks like yours, I assumed they balanced it by grinding on that.
Bearing noise is a drone. Those front wheel bearings wear quickly. IF it this is that bad you should be able to hear by Hand spinning the tires. Good thing is new front hubs are under 100.00 and come with fresh studs and wheel speed sensors. Rear wheel bearings seem to hold up. Big and beefy.
Those beautiful wheels can be an intensive upkeep item. Have someone good check for out of round. Not Discount Tire. This is normal with those rims. Usually miles not age, but road condition related too. Low profile tires (20”) are hard on rims.
I have bent my 19’s.

Some of the weights on the propshaft are postage-stamp size, so you could be right about a weight falling off.

I like panelhead's suggestion of a bent rim, though I would hope the tire shop would have noticed that while installing and balancing the new tires. It would definitely be worth having the rims checked. I have also had a couple of sets of tires that were difficult to balance and could only be successfully balanced on a Hunter Road Force machine.

Does the vibration change at all when you are going around a sweeping curve to the right or to the left? Just curious as to whether a change in weight-loading of the suspension has any effect.