I am in the process of installing new propshaft flex couplings (genuine Jaguar, CBC8996). With the flex couplings mounted first to the propshaft, the coupling sits fine at the diff side when the propshaft is engaged onto the diff flange centre pin but at the gearbox side (MB 5G-Tronic), the centre pin of the gearbox flange bottoms out inside the propshaft bush about 2 mm before the flex coupling touches the three "fingers" of the gearbox flange. If I just tighten the bolts, they will pull the flex coupling towards the gearbox flange and the flex coupling will assume a mild "zig-zag" shape. This will also keep axial pressure onto the bottomed-out centre pin.

Has anyone noticed similar problem with the front flex coupling on supercharged (or NA) cars? The flex coupling is 35 mm thick but it looks like it should be 37-38 mm if to be installed without undue stress.

 

I don't think I ran into this issue when I did mine (only replaced the trans side coupling) though I think I used the Uro flex coupling. I'll look around to see if I still have the old coupling lying around to measure but I think it's been thrown out by now...

Couple dumb things to check: is the flex coupling oriented the correct way? There's indicator marks on the outside that show which direction the flanges should be if I remember right. Also, any debris in the center pin, corresponding receiving socket, or around there? Do you still have the original bushing that was in there, either to measure or dry-fit to see if it also warps under tighening?

 

Any oblong distortion of the disc would seemingly almost assuredly cause an imbalance. Here's the application for the S-Type from Jagrepair.com starting on page 244 ... http://www.jagrepair.com/images/Auto...M-Workshop.pdf ...just for review. It didn't come up for the x308.

Here's my post on the center bearing, but in post 3 I show the flex discs. I'd review them and see if they match yours.
https://www.jaguarforums.com/forum/x...g-info-188400/

 

Thanks for the suggestions.

I do not have the original flex discs as the PO replaced them with aftermarket ones (which are still very good) but I decided to replace these with genuine ones together with replacement of all bolts, nuts and washers. The existing front coupling and the new coupling both show the same about 2 mm gap towards the gearbox flange fingers. I first suspected that there was something lodged inside the propshaft socket but found nothing.

"Highhorse", interesting picture you attached to your post that you provided a link to:



It appears that the coupling was under constant axial pull causing the embedded bushes to move and the washers to sink into the rubber. Exact same thing would happen, after some time, to my front coupling if I just force-bolt it up. Do you remember whether this was your front coupling? Perhaps it is meant to be pre-stressed in this way (although it does not make much sense); or maybe just a Jaguar's design fault? I am considering inserting three 2-3 mm thick washers between the coupling and the three gearbox flange fingers to fill the gap so that the coupling is not under any axial pull.

 

My theories about the front flex coupling are all out. After some thinking (this morning, better than last night), I realised that I had not raised the transmission up enough (it was supported by a scissor jack) while I was connecting the propshaft and the flex coupling. Due to an angle between the transmission and the propshaft, of course I had a gap looking at the two transmission flange fingers that I had positioned at the bottom because the third finger on top, which I could not see, was hitting the bush in the flex coupling. What confused me was the fact that, as I pushed on the propshaft engaging the centre pin, the stop was hard with a metallic sound and I felt the impact on the propshaft - felt very much as if the centre pin was bottoming out. But, it was just the top flange finger hitting the bush in the flex coupling. Even though the bush is in rubber, it still produced a hard stop with a metallic sound as the rubber of these massive flex couplings is not really soft. When I raised the transmission to its normal position, there were no more gaps, i.e. the flex coupling sat well against the flange fingers.

I apologise for mentioning a possibility of faulty design by Jaguar (not possible, is it?). I had a fault in my brain last evening, aka "brain fart".

 

Sorry for not getting back sooner, I had a friend unexpectedly come into town and we were out and about. Glad you figured out the scenario, better a simple brain fart fix than an actual issue, brain farts are usually cheaper.