The nut should not be “solid” it should open, but it may be easier to take out the whole assembly by undoing the two smaller nuts that fir the assembly to the engine block.
There is not much room in there, when everything is in place. There should also be a a (brass?) cover. on the top of the assembly with a “zerk” housing with a grease nipple to allow putting 8and keeping) grease in the tach gear housing / cable adapter.
On mine the top had blown off when the oil pump shaft jumped last May. I found it and could put it back but the top of the housing is a bit cracked.
Yours looks a bit the same (cracked edges on top of the housing), I think it’s a good idea to check also if the lock ring is present on your oil pump (and tach drive) shaft. It could have saved a lot of trouble and a set of crank main bearings and gig end shells.
Ps. Yes, there is some “wobble” on the top of the housing, but not much, especially once it’s packed with grease and the cable is attached firmly.
There’s a trick to get a finger in there on a LHD car with the air cleaner in place.
On mine the black body and silver sleeve swivel together, but I suspect that is because I left the big nut loose, as I have not yet put in the tach cable.
Sounds like someone left yours untightened and it got crudded up. It shouldn’t wobble.
You should certainly remove yours and clean it up including the theads, as that big nut is supposed to stop it swiveling. Whether you can get or make a top cover disc, maybe there is something like a core plug, but it might be imperial size rather than metric. Or find another part, it’s not the kind of part that typically wears out, and there were a lot of Mark Vs that went to Australia so there must be someone with one in their stash.
Hello Frank, on my 3.5 Mark V the large brass nut is locked solidly onto its thread with no movement. The round metal section above the nut (silver in your photo with a small round indentation) is also locked on solidly without movement. The main body of the adapter with its right angled piece swivels around quite loosely in any direction horizontally. It also is loose vertically although only a little bit of give.
Thank you gents.
All of your replies have been very much appreciated and gives me a great reference in terms of how the adapter is fixed and functioning on your vehicles.
Thanks for the effort in replying.