A Tail of Two Flanges - The Tailshaft saga

Reading back over the blog when I first installed the tail shaft I kind of skipped over some of the messing around I had to do to get it fitted.
One of the reasons I didn't blog all of it was that it seemed like a criticism of the guys that made the coupler and tailshaft and the problems were sorted out pretty quickly - but maybe they weren't after all.

Here is the whole story.
The first ever time I installed the tailshaft, it took me a longer time than I would have thought possible to realise that the four bolts that hold the front tailshaft flange to the motor coupler didn't actually line up. The holes in the motor coupler, while being the correct Pitch Circle Diameter (PCD), were arranged equidistantly around the circle. The universal joint flange on the front of the tailshaft was arranged as a rectangle. This is pretty standard for universal joint (UJ) flanges - at least with cars that I have played with.

This picture isn't of mine but shows what I mean. The two holes on the right are closer than the two holes across the top.

That being the case, the first drive of the Vogue had the front of the tailshaft being held to the coupler with two M8 bolts 180 degrees from each other as all four bolts could not be fitted.

Obviously I wasn't going to leave it that way, so before the second drive I removed the coupler and tailshaft and took them back to the guys that made them and they added some holes and tapped them out to M10. (The original M8 tapped holes were left alone).
When I got it all back and managed to find some fine thread M10 bolts of the correct length, I took another huge period of time under the car before I decoded that there was no way I could get these standard hex bolts in past the universal joint ears (the bits jutting out that hold the cups). So a day or two later I bought some M10 Allen head machine screws.

Again I messed around for an hour or so trying to get these in with no success. They fitted through the tailshaft (UJ) front flange OK but would not all thread into the motor coupler when I offered it up. At some point I realised that the tailshaft flange holes were imperial 3/8 inch - that's 9.525mm.
So I pulled the tailshaft out completely, held the tailshaft as best I could in my workmate, and hand drilled the holes out to 10mm - the biggest drill I had. I cleaned up the facing side of the flange with a 1/2 inch drill bit and ensured there were no burrs.

Once the holes were drilled out, I could almost get all the bolts in by hand. Importantly I could now place the tailshaft flange on the coupler flange, mate the spigots up (the 60mm diameter sections used to correctly locate the flanges) and insert and tighten the bolts up. There was always one or two bolts that I had to pull in with the Allen key the last 6mm or so but it all looked correct.

I explained this to the guys that made ther tailshaft and coupler but they weren't too concerned and have had the tailshaft back twice since then.

So now we are up to this week.
When I picked up the tailshaft on Monday night, it was explained that the balance was fine and they hadn't changed much. It fitted it Tuesday night and it behaved pretty much the same way as before. However, this time I had arranged a system were I could control the motor speed while lying under the car so could have a "play" without having to ask someone else for help controlling the speed. What I found was, even though earlier tests showed the front of the tailshaft rotating without excessive runout, that was not the case on the slip yoke. The UJ flange rotated true but the inner part of the slip yoke did not.
I whittled a chunk of wood and tried moving the UJ centers in their housings (in the direction that would remove the runout) - no give at all (they were properly installed and very good).

For some reason I decided to remove the four M10 bolts and track down the two M8 bolts and washers that I had used on the first drive.
Once I had the tailshaft bolted to the coupler with only two M8 bolts, there was an immediate and substantial improvement. I made a further slight improvement by loosening the bolts and using the tiny bit of play in the spigot to move the mating flanges in a direction that would help.

That's how I drove it today - a lot better. Not perfect yet, but better.

It appears that there is a concentricity problem in the front slip-yoke and UJ combination at the front.
If the tailshaft is being held by the front flange during balancing I would think it would be balanced out.
So we know what it is, the front end of the tailshaft involving the slip-yolk and universal joint - now to fix it completely.

A note here. I measured runout months ago and concluded that the tailshaft was fine. The closest I can normally get to the front of the tailshaft is about 300mm from the front, and it's a lot better at that point. I've got a lot braver with rotating machinery (while still being careful) over the time. A whole lot of factors have conspired to create this problem and make it hard to track down. My inexperience hasn't helped.

Edit: Some changes made for clarity thanks to comments from AEVA forum member weber.