If you're lucky, then you'll never have the (mis)fortune of having to struggle to get your Jaguar sedan to ride correctly. There are, however, quite a few modifications, including

Unlike an XK or E-type, the sedan front ends ride on coil springs rather than adjustable torsion bars. Therefore, adjusting the ride height can only be done by installation and removal of shims, and in extreme cases, cutting the springs themselves. My hope here is to share some of the expensive experience I've gained by going through this exercise several times, to help you get it right the first time.

First a few tips on spring removal and installation. This can be done either in or out of the car with the aid of a spring compressor. I've made my own out of a long piece of threaded rod, a set of progressively larger washers, and a couple of big nuts. The final large washer which actually goes against the spring retaining plate is a 2.5lb weight I found at a local fitness store. The threaded rod passes up through the suspension tower, where the shock normally goes. The hole at the top of the tower needs to be enlarged to get the large threaded rod through. It is important to use a rod long enough so that you're able to completely relax the load on the spring before running out of threads. To do this in the car, you'll need to jack it up really high to be able to get the rod into the assembly from underneath.

Like most things, installation is much more difficult than removal. You must get the spring retaining plate to line up perfectly with the holes on the bottom of the lower A-arm... while simultaneously retaining around one ton of spring pre-load. The best trick I know of is to use old water pump bolts as guides. They're long, have the correct threads, and are smooth along the sides.

I'll probably never do it that way again. You can substitute threaded rods (about 1 foot long) for the spring plate retaining bolts, with nuts snugged up against the plate one at a time. Then to remove the spring, just back the nuts off evenly. To install, just spin the rods into the A-arm, slide the plate on, start the nuts, and then evenly draw the plate up with the 6 nuts. When it's tight, substitute the retaining bolts back in-place of the threaded rods one at a time. Sounds a lot easier than using a compressor to me; and by all accounts it works very well.

OK, so now you've installed the springs. How do you tell if they need to be adjusted?

First of all: DRIVE THE CAR. every time you lower it onto the front wheels, the tires will get pinched in, artificially raising the front end. Just driving around the block will be enough to let them find their natural position. Secondly, never trust a single measurement. If they aren't already, take the shocks and sway bar out of the car (they just add friction for this exercise). Go drive the car for a short distance, stopping everywhere you see that looks level and repeat the measurements. Throw out any that are way off the others, and use an average of the rest. You'll be surprised how much they vary, and will be glad you didn't do anything drastic based on a bad measurement.

I measure from the ground to the highest, outermost point on the fender lip. How and where you measure isn't really important- so long as you find a way that can be consistently repeated.

On a Mk1/Mk2 the easiest way to tell if you've got a sagging front spring is actually to park the car on a level surface, and check the rear (yes rear) bumper for level. If you have a bad front spring, it's like having a table with one leg too short. The table will either sit perfectly level, or will teeter over onto the short leg- depending on the weight distribution. With a bad front spring, because of all the weight (motor) up front in the car, it will definitely fall onto this short front corner- raising the opposite rear corner. The result is that it makes the rear spring on the same side as the bad front spring look bad. If you've got a 'sagging' right rear corner, first suspect the right front spring.

If you suspect this might be the case, there is a test to verify. Support the car with a big floor jack centered under the front cross member. Take off both front wheels and lower the front end to about where it normally rides. Now, re-measure the rear; if it's level (and wasn't before) then you've got front spring problems. If it's still crooked, then you get to play with your rear springs... I put brand new rear springs in my car, and the rear still sagged to one side. Swapped them side to side, and the same rear corner sagged. It turned out to be a bad front spring all along.

The first, and most important thing to remember about front spring changes is that any adjustments you make to a front springs length will have approximately double the effect on ride height. This is because the lower A-arm is a lever, with the spring mid-way between the wheel (ball-joints) and the fulcrum. After a lot of experimenting, I can say with some confidence that the multiplication factor on these cars is a little less than 2; say 1.8 or 1.9.

If your aim is to raise a front corner, then all you need do is add shims under the ends of the spring. There are washer-type shims that go at the top of the spring (your car almost certainly has these in it) and flexible C-shaped shims which go under the pig-tail end. In addition to the 1.9 rule, expect that the opposite side will follow the one your adjusting a little bit. If you raise the left side an inch, by adding a 1/2" shim to it, expect the right side to come up... maybe 1/8".

The real challenge comes if you need to lower a front corner. First of all, see if you have shims that can be removed, or replaced with thinner ones. If so, this is definitely the easiest way to make adjustments.

But what if you've taken out all the shims, and are still too high... If the required adjustment is small (less than 1/2" or so) then there's another trick you can use: simply shim between the spring retaining plate and the lower A-arm. My final 1/4" adjustment on one side (1/8" shims) was done this way. For shims, you can just use washers. To play it safe, longer bolts are also recommended. Actually the stock bolts have non-threaded points on them; I'm using bolts the same length but with threads running all the way to the end and feel perfectly safe with them. If you over-lower a car with this method, you can simply take the shims out... you can't undo a spring cut.

Which brings us to cutting springs. The actual cutting is a piece of cake, I've used a hack-saw, a sawzall, and a rotary air-powered cutting wheel; all with success. The challenge is determining where to cut them. What you need to do is cut the desired adjustment (divided by 1.9) from the compressed (loaded) coil; not from the free coil. So, what you do is: with the car on its wheels, measure the distance between adjacent coils on the spring. Measure along the axis of the spring; not perpendicular to the coils. This measurement, and your desired adjustment is about all you need.

Example:

Say your measured distance between coils is 1.625" <- it will vary a lot from one car to another, depending on springs used. Don't worry if your number is a lot different.

And, suppose you want to lower that corner 0.75".

0.75" * (1 compressed coil / 1.625") / 1.9 => 0.243 compressed coils.

You want to cut 0.243 coils off the spring. The point of this is to find a unit (coils) that is constant in or out of the car.

But there's more. If you look at your spring, and it hasn't been cut before, you'll probably see a flattened end on the pig-tail. (it is the pig-tail end that you need to cut). So, get out the calipers again, and measure the distance (in the middle of the spring, along the axis) between 2 uncompressed coils. Now find the point on the spring which is that same distance down from the end of the flattened pig-tail. It will probably be about 1.25 - 1.5 coils down. It's a bit of an eye-ball measurement... so mark both springs at the same time and be as consistent as possible with it. Mark that point (felt tip); which will be the reference point for any cuts: denoted as 1 coil from the end.

Back to our example:

What we want to cut is 0.243 coils, or 0.757 coils short of the mark we just made. Start at the 1 coil mark, and go 272 (0.757*360) degrees towards the tip and that's your cutting mark.

Alternate calculation:
Another way to theoretically get to the exact same cutting point is to use the following equation:

distance between compressed coils		desired adjustment / 1.9
	=
distance between free coils		X
You want to cut X off the free spring, which can be measured off of the end of the pig-tail.

My car (with S-type/420) uprights has got cut down springs from a MKX in it. I had to install them as is to get a reference (talk about a spring pre-load), and then: using the above (first) method, lowered the car to almost the perfect height in one shot. I cut over 2 coils on one side, about 1.5 coils on the other. (my towers have quite uneven heights for some reason).

If you get the sides within 1/8" of each other, you've done a great job. In the US, if anything, you might want the right side to be a hair higher than the left to help compensate for road crown. If you want to be very accurate, then be sure to load the car as it will be when driven (you might toss 150lbs of sand-bags into the drivers seat for instance).