2000 STS Suspension with Scooter
 

My dad has a 2000 STS with the ride control suspension. He had a scooter and lift provided to him and installed on his Cadillac. This required the installer to weld a high quality hitch bar to the car.

Golden Technologies Luxury Scooter : Companion Series
Harmar Mobility - Lifts, Ramps and Hoists for Wheelchairs, Power Chairs and Scooters

The total added weight of the lift and scooter was about 270 pounds. The rear suspension seemed to manage, though it did lower quite a bit when the scooter was on. Then, after a few days or weeks (I can't be sure because I wasn't around at the time) the pump seemingly stopped working. Generally speaking, it wasn't an issue since the shocks were still good, except when someone was sitting in the back seat or when he filled the trunk up with groceries... then it would bottom out due to the additional weight and scrape the hitch attachment on the ground.

I checked all the fuses and replaced the relays for the pump. Nothing changed. Then, a couple of weeks ago I pulled out the EBCM to have it repaired by the folks at Module Masters. As soon as I received the repaired and improved module, I reinstalled it. When I turned the key, the pump immediately started working and the rear suspension rose up to adjust for the additional weight of the lift. The scooter was not on.

Now, my first thought was that the faulty EBCM was causing the pump to not work correctly, but the EBCM was faulty long before the scooter lift was installed and there were no problems with the automatic height adjustment. I don't like coincidences, but there isn't really an easy way to further test this.

Anyhow, the pump seemed to be working well again. With just the lift (about 100 pounds), the pump managed to keep the rear suspension up at a reasonable level. And even when the scooter (add about 170 pounds) was on, it still managed to avoid bottoming out.

But now, this week (about 2-3 weeks since the EBCM was reinstalled) the pump seems to have failed again. I checked all the fuses and swapped known good relays, but nothing. My dad is frustrated enough to have removed the scooter lift. He's convinced himself that towing around a 4 x 6 trailer is acceptable. I feel this is avoiding the issue. Not only is it more difficult for him to load and unload the scooter on the trailer, he'll have to fasten and unfasten it with adjustable straps every time he goes somewhere, and he goes somewhere all the time. Let's not even talk about his parking options at stores and restaurants now that he tows around a trailer. So, while the weight may be distributed in such as way as to relieve the rear suspension somewhat, it doesn't change the fact that something is not working properly.

I keep coming back to the pump. Even when it is working, it's not properly adjusting for the additional 270 pound of weight. Can it even do this? And if not, would the pump eventually fail? How can I narrow down the problem? The shocks are working fine and the ride is still relatively smooth, but it will bottom out often since the pump is not raising the neutral position to a reasonable level.

Lastly, assuming I can get the pump working again, what can be done to deal with the 270 pounds of scooter and lift so that the rear suspension doesn't give out again? I've been told by some that the system can be reprogrammed so that the neutral height counters the additional weight. But the local dealer says that isn't the case. I've read about people making custom brackets that raise the neutral height and can even be adjusted manually when needed. I've found custom air shocks made to interface with this model's ride stability system, but I would think those would stiffen the ride considerably - a trade off I'm not sure my dad would appreciate.

Any help or suggestions? How can I fix the problem and what can I do to help prevent it from happening again?

Thanks in advance.

there is a level ride sensor in the rear of the vehicle this tells the pump to turn off and on
check for line leaks by spraying soaping water and look for air bubbles
put straight power to the pump to make sure it works

I tested all the relays. Working. I checked the compressor by adding weight in the trunk (about 100 pounds). At this point, both the scooter and rack were removed. Working. I couldn't determine if there was a leak in the lines, but after a couple of days of driving it with the additional weight, there was no change in the suspension height. I removed the weight and the compressor adjusted again. Everything seemed fine. So, I set off to figure a way to adjust the neutral position of the ride height sensor so that the vehicle could accommodate the 270 pounds of scooter and rack.

I took a look at the sensor configuration.
http://i288.photobucket.com/albums/l...Oat/sensor.gif

A single rod connects between the ride height sensor and the suspension bar. It has a ball socket similar to the following picture, but the socket is permanently attached and non-adjustable.
http://i288.photobucket.com/albums/l...ballsocket.jpg

Both the ride sensor arm and the suspension bar have ball nuts that the rod snaps onto. They look similar to the following picture.
http://i288.photobucket.com/albums/l...at/ballnut.jpg

I'd read of other cadillac owners making brackets to extend the arms influence. But I opted for a simplier, more easily adjustable solution. I thought I'd share what I did for others who might have a similar issue. I am in no way recommending that anyone do what I've done. This may or may not be a good solution. I'm not sure what long term effects this will have on the shocks or the ride height sensors. So, follow along at your own risk.

I bought a simple, but high quality, stainless steel turnbuckle with closed eye loops on both ends.
http://i288.photobucket.com/albums/l...rnbuckle-1.jpg

Then I added rubber grommets that fit tightly inside the closed eye loops of the turnbuckle. They reduce the size of the eyelet on the turnbuckle as well as allow for a smooth pivot on the hardware.
http://i288.photobucket.com/albums/l.../grommet-1.jpg

I removed the ball socketed bolts from the sensor arm and the suspension bar, determined their thread (1/4" - 28 fine thread) and bought some stainless steel replacement bolts. Unfortunately, the factory bolts seemed tapered just enough to prevent the replacement bolts from threading in. Fortunately, both the sensor arm and the suspension bar had holes through and through, so I just used a long fine threaded screw that fit the holes relatively snug, added a washer on each side of the rubber grommet on the turnbuckle, then a nut. Tightened the nut just enough to give the turnbuckle some play to spin around as well as pivot perpendicularly. Added a lock washer and a second nut to keep the first nut in place.

I adjusted the turnbuckle to match the length of the factory rod, re-installed the wheels and measured the fender height from the floor at 28 1/4". The best part is that I can reach the turnbuckle without removing the wheels. And I can adjust it by hand. So, I adjusted the turnbuckles with several spins, turned the key on, let the compressor compensate, and after a couple attempts I was able to raise the neutral position of the ride height by 1 1/2" to 29 3/4".

The vehicle now has a slight forward rake, which makes it look pretty aggressive, but the ride is still very smooth and comfortable. Confident that the rig was working, I reinstalled the scooter rack. Drove it around today and everything is great. I'm going to give it a couple of days then I'll check the turnbuckle again to make sure the hardware is holding up and the nuts have not slipped. Once certain that the rig will withstand the elements and shock of day to day driving, I'll put the scooter on and adjust the turnbuckles to a more neutral position if necessary. Once I find a good neutral position with all the additional weight on the vehicle, I'll probably add some Locktite, or similar product, to make the rod non-adjustable and prevent the turnbuckle from spinning over time. Without the scooter on, it will undoubtedly ride a bit high in the rear, but it's still comfortable.

So far, so good though. The hardware cost me about 20 - 25 dollars and the installation took about 20 minutes, not including my trial and error with various nuts and bolts. No air shock replacements... no pressure adjustment kit... no vehicle modification. Simple, cost effective, and seemingly functional.

Should my dad ever decide to sell the vehicle, I can replace the turnbuckle with the factory rod and ball joint nuts.