Mac
I have only been next to one V12 XJS with the intermediate silencers removed. It was DEAFENINGLY loud. I actually have the silencer replacement pipes in my parts stash (I was young and inexperienced when I bought them!), but gave up on using them when I heard a car without them!

 

I appreciate you saying that, as I am on the fence. I'd like a little more exhaust note, but don't want to go overboard. Having read numerous threads on exhaust modifications, my understanding is that there is a huge difference in how loud the system is when all four cats are in place as opposed to what it sounds like with straight no cat downpipes or gutted cats.

I saw this video from the Living With a Classic guy, and he was really pleased with the silencer delete:


I don't know if he has cats or not, but he said in the video he only made the delete modification to the exhaust and went to K&L filter inlets.

 

@Grant Francis @Greg in France @Jagboi64 and all you transmission gurus out there. I successfully replaced the u-joints (without spilling needle bearings everywhere!), and reinstalled the prop shaft.

Unfortunately, and frustratingly, the forward u-joint is not the source of the mystery noise. Of course I didn't discover this until after putting the reinforcing plates/shields back in place. I think it is coming from the tail of the transmission. If I rotate a rear wheel with the transmission in neutral, it's a 'clicking' sound every 1/2 turn of the prop shaft. If I turn the prop shaft in the reverse direction, it will make the sound at about the same spot. Sounds a little like a ball bearing contacting another ball bearing.

See the original post of the thread with the video file attached where you can hear the sound.

Anyone tell what it is? Is this something that can be addressed with the trans in place before I put the trans mount back in place?

 

Has to be one of
driveshaft ujs
hub bearings
Diff output bearings, or
Diff/pinion bearings

If someone turns the wheel for you, you might be able to feel the click by touching various places

 

Great suggestion Greg for determining where the noise is located. I was able to clearly pinpoint the clicking, and looked up what that part of the transmission might be. Turns out that part is the cover for the governor, and after a bit of online research, it appears the clicking is the weights in the governor rising and falling and is supposed to be perfectly normal on the TH400.

 

That click sounds to me like the weights in the governor. That's behind the squarish cover on the right side of the transmission with 4 bolts. Normally it would be balancing speed with oil pressure, so the weights will be biased outward, but just turning the governor on it's own the weights might flop over and contact the stop and make that noise. There are 2 weights, so makes sense that you hear it twice per revolution. If that's what it is, I think it's a perfectly normal noise and don't worry about it. I think it's only occurring when the engine isn't running.

Might be hard to test, but it might go away with the rear wheels jacked off the ground and the car in gear and the wheels turning.

A photo of a governor, the two weights are at the top end. The geared end is on the tailshaft of the transmission.

 

We have a winner (see my last post). Thanks