You may or may not have a leak. If your car drops after several days regardless of weather conditions, you have a leak. If it drops due to temperature or barometric pressure drops, you
may not have a leak. The owner's manual on the Mark VIII states that in cold weather, your suspension may drop due to temperature drops reducing the air pressure in the springs. My 1996 Mark VIII has brand new front air spring/shock absorber units and still has the original rear springs. I have had it tested at a Ford dealership service center and there are no leaks. However, it still drops on cold nights. This in perfectly normal. If it is a warm night, it doesn't drop an inch. Still, you should have it checked.
As far as installing new front air spring/shock units, it is easy as proverbal pie. I have it down to an exact science. I can change out my front air springs in less than 1 hour. If you have two people working on it, you can do it in 30 minutes. Here's how:
1. First, open the trunk and turn the air ride switch off. It is on the driver's side of the trund behind a small carpet panel. Next, jack up both sides of the front end. Both front wheels need to be completely off the ground. Remove the front wheels and put them aside (you will need them later).
2. Open the hood and remove the plastic covers on the shock towers. Then remove the three nuts that hold the top of the shock to the fender. Do this on both sides. It saves time. Put the nuts in a safe place.
3. Remove the nut that secures the air spring/shock assembly to the lower control arm. In order to remove the bolt from the lower control arm, you will need to turn the front brakes to get the steering tie rod end out of the way. Simple. Remove the bolt from the lower control arm and put the nut and bolt in a safe place.
4. At this time, the air spring/shock absorber assembly should move around pretty freely. However, you can't remove it yet. You have to let the air out of it first. The simplest way to do this is to remove the solonoid from the spring housing. It is located at the top of the air spring just below where the spring mounts to the shock tower. Removing the solonoid is pretty straightforward. Simply use a flathead screwdriver to remove the retainer clip and rotate, pull down, rotate, and pull out the solonoid. This will make sense when you see how the valve is inserted. The solonoid valve will still be connected to the air line. Let it hang down out of the way.
5. Now you are ready to remove the air spring/shock absorber assembly. Simply grab the shock at the bottom, pull out toward the spindle so it will clear the lower control arm, then pull it toward the rear of the car, and straight down through the upper A-arm, behind the lower control arm, and out of the car. Easiest thing in the world to do.
To install the new air spring/shock absorber units, simply reverse the process. The new air spring/shocks will come with new o-rings to put on the solonoid valve. Make sure you install these! If necessary, you may have to put a little petroleum jelly on the solonoid valves to make it easier to intall them in the new air springs.
I have done this three times on my car. It is so easy it should be against the law to actually charge money to do it.
I replaced my first set when the car had 100k miles on it and the front end started leaking down every night. I used Arnott spring/shock units that were brand new with a 1 year warranty. They sprung a leak at 14 months.
The next set I installed were used 1998 units that I got on Ebay. They worked fine for a while.
The last set I actually bought from FORD and they were ungodly expensive, but they are still holding air after 3 years. Never had any problems with the rear springs.
I hope this has helped you. And I hope I haven't rambled too much.
