I could have called this thread 'The solution to a non-existent problem, which has created a new problem'..!
this is a bit of a grumble, but it is no-one's fault, just a result of beaurocracy and Health-and-Safety-gone-mad.
three months ago my XJR failed its Warrant of Fitness (WOF), the NZ version of Britain's MOT. The fail was a surprise as I maintain the car well and it usually passes.
The problem was the inspector spotted the small manual brake pedal had 2 drill holes in it where the previous owner had screwed on some aluminium treadplate.
the drill holes constituted a 'modified pedal' which is a no-no.
I explained to the inspector the car had originally been an automatic, but was converted to factory-spec manual (correct Getrag 290, pedals, bracket, etc)
This got the inspectors in a tizz, and I went around in circles for 2 weeks between the inspectors and the Low Volume Vehicle Certifier, who had to OK the modification. The WOF inspectors couldn't tell me what needed correction to make my car road legal again, and in the end their Boss said 'We can't be held responsible if the pedal snaps and you die'. I never wanted them to take responsibility for my occasional desire to exceed 100mph. That is my decision.
Ironically when the previous owner (who also frequents this Forum) did the manual conversion, he contacted the appropriate authorities who were happy verbally that it was done to factory specs. All very common sense...
It turns out the H&S people have changed the laws 3 times in a year and the poor vehicle inspectors are all sh###ing themselves , so the knee-jerk response is to fail any car that is slightly altered.

So to solve my problem I had to track down a new manual brake pedal for an X300. Good luck with that...
initially I seemed in luck as UK Jag parts suppliers listed the part number so I ordered one, but when talking long-distance to the parts man in the Midlands in turns out with parts number successions, what should have been the small manual pedal had morphed into a large automatic-spec brake pedal.
So the correct pedal is in fact unavailable.
I tried for a secondhand one, none in NZ or anywhere else for that matter.
Luckily the previous owner dug out an old XJ40 manual pedal box and I bought the pedal and box from him. problem solved, I thought.
But my mechanic went to fit the new pedal and found the top two holes (pivot point and master cylinder attachment point) were different by 10mm.
So I went round in circles a few more times, and the guy that needed to certify the mods was happy if I presented him a car with a new flat pedal of the correct size welded over the offending original with the two holes in it, then covered in a correct factory pedal rubber. This was duly done, and I took the car for it's certification.
unfortunately I had forgotten that the car had a custom driveshaft professionally made and fitted at the time of it's manual conversion. This is also a no-no, and the certification law states any non-factory driveshaft needs a yoke to stop it dropping on the road if it breaks. I have tried pretty hard to break this driveshaft at times with no success so far, and the previous owner tried even harder, I think - he tells me he did a timed 0-60mph in 5 seconds at Manfeild race track in NZ once (the car has Andy's reprogrammed EPROMs and should have about 340bhp).

So the front seats came out and a custom yoke fabricated and fitted around the front end of the driveshaft, as per pics.
The car is finally certified and legit again.
But they had to cut the exhaust to fit the yoke and re-fit the shaft, and also cut away some of the original heatshielding. The new sections of exhaust (pics) are not mandrel-bent and are somewhat flattened on their bends, which is making a small dent in power I think. Hmm.

And now, when I floor the little right-side pedal in 1st or 2nd gear, there is an unholy noise from beneath the floorboards as the drive shaft rubs on the (unnecessary) yoke, and a small groove is now on the circumference of the shaft where it rubs on the yoke on full throttle, presumably as the engine/gearbox shift a bit on their mounts. Ironically, this could ultimately lead to driveshaft failure.

So it will have to go back to have this rectified, but at the moment I want to use my car for a while. So I am not using full power in the first two gears for the time being.

 

Al,
Nothing worthwhile is ever simple, although I guess you are only too aware of that at this point!
I saw your photos of the yoke before I read your post, and I did wonder how it was going to perform. On the odd occasion in the past when I came across yokes on propshafts, they tended to have a much larger circumference, and have a flexible rubber center, which didnt seem to contact the propshaft at all, at least not in the stationary position. I never had a problem with them, so didnt interfere, or spend too much time wondering what they were for. Your thread has prompted me to conclude that they were primarily for limiting or damping propshaft flex, and ,in extremis, catching the propshaft once it broke.
As you have now discovered, the trick seems to be leaving a bit of clearance to allow for normal propshaft movement....

 

Interesting to see how the authorities sometimes over-manage with the ultimate aim of protecting themselves for tolerating vehicle modifications. In contrast, the U.S. seems to be a haven of vehicle modifications where it is not uncommon to see Jaguars running with Toyota or GM engines. This issue aside, I agree with countyjag's observation. If your driveshaft is not original maybe it needs to be calibrated or aligned to reduce the vibration that may occur during high speed. Here is an earlier thread in this forum that talked about driveshaft alignment. Wonder if it helps.
https://www.jaguarforums.com/forum/x...gnment-138118/

 

there is no issue with driveshaft alignment or balance. No vibrations at all, right up to 125mph.
the problem is occasional rubbing of the shaft on this new yoke - not enough clearance, and some torque movement of the engine/gearbox on the rubber mounts under full load in low gears.
The car had new engine mounts recently.

 

I just had my car back to the mechanic who did the driveshaft yoke.
I have done 10-12000km since this yoke was fitted.
I have had two problems with it - (1) shaft rubbing in yoke, (2) thumping under car under hard acceleration in 1st, 2nd, 3rd gears. I had thought problem (2) was from exhaust hitting floor with engine twisting on mounts.

Today the original mechanic bent the yoke so it doesn't rub any more. he couldn't work out where the exhaust was bumping.
On the way home I tested it out a bit in first and second gears - no more thump. I think the drive shaft was hammering against the yoke. So that is two issues solved

I still don't like the narrower sections of exhaust as shown in the original post pictures.
However I want to get some extractors/headers made up to Andy's secret specs, and no point doing exhaust work twice...

 

This may be too simple, but now that you have the WOF, why not remove the yoke and all the unnecessary parts?