This is by far not a complete write-up, it's just some big points. If you need more detail or have any questions, feel free to ask!
I apologize that there a no pictures from the car, I was in a hurry, but I'll provide visuals with the help of stock images.

Disassembly:
Remove the Transmission Control Module fuses from the engine compartment fuse boxes for a while and then put them back in. This resets the learning of the transmission and allows it to adapt to the new pressure valve.

The drain and fill plugs are the same size. They're both 8mm hex. The fill plug is on the right hand side of the transmission just above the pan and near the rear end (See photo).

The transmission pan bolts are T-27 torx and are all the same size (don't worry about getting them mixed up). The heads are very easy to strip. I recommend replacing them all with simple M6-1.0 x 20mm hex headed bolts of at least grade 10.9. These can be found at auto parts corner stores and hardware stores. You can also buy new wave lock washers for them.
The wave lock washers can also be transferred over from the old bolts by cutting off the heads and drilling out the washers to a slightly larger size.
If you don't plan on replacing the bolts, use lots of upward pressure while cracking them loose and torquing them to spec to avoid stripping.
If you happen to strip one, use a T-30 torx and give it some good smacks with a hammer to get it to seat. Then wrench it out normally.

The filter bolts and all further bolts referred to in the valve body are T-27.
After the filter is removed, the lower valve body can be removed. The wire on it can just be pulled out of the clip and the other retainer unbolted. All of the bolts on it must be removed, there are large and small ones, but they're not easy to confuse (either fit or they don't), so don't worry about mixing them up.
The valve body may put up a fight to get down even after the bolt are out. Wiggle, don't pry because there's a dowel pin (see picture).
The plate holding in the pressure regulator valve is under spring tension, hold it with your free hand to avoid it flinging parts all over the place. You can use a c clamp too (don't clamp very hard or you'll bend the soft aluminum). When removing the old valve, it may be a little stuck. Use a small flat head screwdriver to push it out. Just don't scrape the sealing surfaces on the valve body. Keep the new transgo part frozen for 24 hours beforehand and install it with a bit of transmission oil to let it slide in well. Don't force it, freeze it for longer if need be.

Re-installation:
When reinstalling the valve body parts, alignment is key.
The bracket for the wire that screws into the lower valve body has a small nub that aligns with a hole; ensure that it is aligned (see picture).
*VERY IMPORTANT* Ensure that the shift linkage is slotted in the rod coming off the valve body (see picture). Go ahead and run through the gears once it's in (without the engine on of course) just to make sure it's together properly. You don't want to have to take it all apart again.

Put the pan gasket in a large heavy book a day before hand to flatten it (or use something else heavy and flat). If the gasket is rubber, it can be held in place by placing it on the pan and running the bolts up a few threads (see photo).
When tightening the pan bolts, work in a criss-cross pattern to allow for even compression of the gasket (a pattern is attached).

Filling:
The exhaust is very close to the fill hole, I recommend covering it with aluminum foil.
I don't have a scanner capable of measuring transmission temperature, so I just used an IR thermometer to see when the transmission pan was at 30c.
You'll need some sort of hand transfer pump to get the fluid up there.
After you're finished following the fill procedure, be sure to put the fill plug in before the car is turned off.
I drained about 7 quarts in total and the filled it with a little under 9 (2 quarts low, that's not good). So, you may need up 9 quarts of fluid, not more than 10.5 (the full capacity of the transmission).
When buying fluid, just get something that meets the LT 71141 specification. I used Valvoline maxlife full synthetic ATF.

Get a good torque wrench, especially for the valve body bolts. I tested a harbor freight torque wrench and it was hilariously out of spec for low torque bolts. I prefer the deflection beam type torque wrenches, they're far more accurate.
Torque specs:
Fill plug: 24-28 ft-lbs (32-38 nm)
Drain plug: 20-24 ft-lbs (27-33 nm)
Pan bolts: 6.5-8 ft-lbs (9-11 nm)

Note that the following specs are in in-lbs
Filter bolts: 40-48 in-lbs (4.5-5.5 nm)
lower valve body bolts (large head, long): 70 in-lbs (8 nm)
lower valve body bolts (small head, short): 53 in-lbs (6 nm)

I couldn't find documentation on this torque spec but I assumed it was the same as small headed bolts.
pressure regulator valve plate bolts: 53 in-lbs (6 nm)

Can someone verify these conversions as well? I was a fool and made a mistake, accidentally torquing the pan bolts to 11 ft-lbs instead of nm. So my math might not be super reliable.


Fill plug located on the back right of the transmission


lower valve body bolts


Light red: there is a nub on the bracket that must be placed in the circled hole.
Dark red: this is the pressure regulator valve plate that is removed after the lower valve body is removed.
Green: pay attention to the routing of the wire and how it is in the circled clip
Purple: the arrow points to the dowel that aligns the lower valve body. The dark purple visualizes it.
Blue: the arrow points to the groove in which the shift linkage must be slotted into during assembly.


thread the pan bolts partially into the gasket like this to keep the gasket in place


torque sequence for pan gasket

 

I take back my statement about transmission fluid. Most multi-vehicle ATFs are not suitable because they have a different viscosity. Use something to specifically replace the lt 71141 spec.
Mobil lt71141
Lifeguard 5 (not 6, 8, or 9, just 5)
Febi bilstein 14738 or 29738

 

I also just wrote a DIY guide for the ATF full flush and filter change:
https://www.jaguarforums.com/forum/x...-flush-265900/

I don't really understand why you remove the valve body?

 

A common failure on these cars is the A-drum breakage. 9 times out of 10, when a ZF5hp24 is bricked, it's due to this failure. This usually occurs around 100-150,000 because of pressure spikes when due to leakage around the pressure regulator valve in the valve body. The pressure regulator valve wears down it's bore and allows fluid to get past its sealing surfaces. A Transgo pressure regulator upgrade kit replaces the all metal valve with one that has o-rings in order to expand to the size of the worn out bore.
My car was shifting hard from park to drive and it was also getting hard, banging downshifts. So I figured the valve was bad. The Transgo kit fixed it.

Attached is a file about the failure.

 

I understand. Actually, since my last post a few hours ago I found some youtube videos about this new replacement pressure regulator (it is also differently shaped).
My transmission still shifts alright.

However, I am still trying to find the reason (now after timing chain kit replacement) for 5-10 seconds of rattling noise at cold startup only. Since you had a transmission problem: Was there any rattling coming from your transmission at cold startup?

 

No rattling whatsoever.
When I first put in transmission fluid (before the complete fill procedure) the pump was making groaning and chirping sounds because the fluid level was low. But this is very much not a rattle sound.

Unfortunately it sounds like you'll have to take off the cam covers again. 5-10 seconds it a lot of rattling. I'd check it out in the next 100 miles. I believe there were some old threads on checking if tensioners are working properly.
And, I don't want to make you out to be a fool, but you took out the holding pins on the tensioners right? Just making sure because it's rare that tensioners are bad right out of the box.

 

The Duchess never had a rattle,from the PS pump but she did a little whine which I determined
by using the "broomstick method". I decided to get a rebuilt pump for the lady and once done,
wouldn't you know the new pump was producing more whine than the old one. When I questioned
the provider, he was fairly flippant such that there "was no guarantee on noise levels" I suspect
my only recourse is trying to find a new one.

 

@ asdf: Yes, I understood the "pulling the pin" thing on the hand-grenades, aka tensioners. Definitely on the secondary tensioners (that was obvious), and on the primary tensioners it was not that obvious, thus I asked here in the forum before I closed the timing cover (I also pulled the pins out of those).

Since there are only a few seconds per day where I could locate the source of the noise, I am not too sure yet, where it comes from, but I am fairly sure the noise for not come from the timing chains. Presently I am undecided, if the noise comes from the bellhousing or the pistons. I'll start a new thread about it...

 

Try putting the car into gear and seeing if that alters the noise.

One of these is invaluable, I have a friend's dad that let me borrow it once. It'll set you back a pretty penny though.

Could be an exhaust rattle, I had a 300 with a similar sound only when cold at certain rpms from an exhaust leak. You could see if raising the rpms to what they are at cold start ('round 1200 I think) will induce the rattle.

 

Thanks, asdf, I will try that with the gear tomorrow.
Good idea with the exhaust rattle. I remember that a very long time ago I also had that on some other car...

PS: I remembered now: No, it was not a car with an exhaust rattle, which I had, it was 30 years ago my 200cc Honda motorbike with a rattle in the flute (=exhaust).