Automatic Leveling Rear Shocks

[bocoogto]

Don't be eager to listen to people that tell you not to fix this system. If the shocks fail, you can buy replacements from Monroe and others with an adapter kit for the air lines. If the compressor motor fails, take the entire unit from under the car to an automotive electrical shop. They can rewind the motor for around $100.

The recent problem I had with the unit not working was a defective factory wire harness splice in the +12volt circuit near the leveling unit. The harness exits the body under the driver's side rear floor pan. The splice is adjacent to where the driver's side rear spring is mounted to the axle. You will find a 12 gage orange wire spliced to four 18 gage orange wires. I used a butt splice filled with silicone caulk and crimped it to fix the problem. Here in Wisconsin, salt and water aren't kind to anything under a car.

What a wonderful car these are!! If only GM would build an updated version with rear wheel drive and the new small block. My '93 gets 23-25 mpg on the highway. Imagine what they would do with the cylinder-on-demand technology!

[rnj]

when did the roadie wagon come with self leveling systems? If it is not raising the height, what can I look for? I have a 92 rm estate, and I looked at the shocks (rear), and they look like air shocks. They have a sort of rubber boot at the around 3/4 of the way down. The car sits noticably low in the rear, the wheel well sits lower than the top of the rim. If you can help me out I would appreciate it!!!

[bocoogto]

All years from '91 through '96 had this option. First, look in the fuse block on the left end of the dash between the dash and the driver's door. The option is on the car if the #4 fuse is in place or the fuse holder set up for #4 postion to have a fuse.

If your car has the option, there is an electric compressor under the car on the driver's side just in front of the rear axle. It is in a black sheet metal box that measures about 12"X12"X8" high. This pump will run whenever a load of more than about 200 lb. is placed in the rear of the car to push the suspension down. You can hear the pump run--the key does not have to be on.

I just had a problem with my '93 where the pump would not run. I found that the factory wire harness going to the compressor motor from the body had a corroded splice. There is an electrical plug on the back of the driver's side floor pan. If you trace this rearward toward the black box, you will see it splits into two bundles of wires as it goes to the box and up into the chassis to the level switch on the passenger side of the car. Look for a heavey orange wire (12 gage) spliced into four 16 gage orange wires. This corroded badly on my car until +12 volts did not get to the leveling system. Fixing it is easy. Use a waterproof splice (butt splice with silicone sealer or ?) and you should be back in business.

If you determine that the motor needs repair, the unit is easily removed from the car. Take the entire unit to an automotive electrical shop. They will rewind the motor for about $140. The compressor/motor/chassis assy. costs $750+ from GM.

This is the same unit used into the late 90's on other GM cars, such as '97 Bonneville.

Good Luck!!

[rnj]

Thanks for the help, I checked the fuse in the #4slot and there is a fuse there. But, I remember seeing a housing, like the one you described, and I'm almost positive that it was empty??? I'll check this weekend, but do you know th p/n for the compressor, tks.

[bocoogto]

Too bad if the housing is empty. The compressor assy. cost about $750 from GM several years ago. I do not have the part number, but your friendly GM dealer can look this up for you with price and availability.

If you are willing and able, one from another GM wagon like your Buick from a salvage yard would work--even if it needed repairs. The one I bought from eBay from a '97 Bonneville has the same compressor/motor/drier, but one of the plugs is different. I'm sure you could get one of these full-sized GM sedan units to work in the Roadmaster application if you can't find the exact one.

[rnj]

So, then a pump off of a 1992 CADILLAC SEDAN DEVILLE should work, as long as I connect it properly?

[HotZ28]

Originally Posted by rnj

when did the roadie wagon come with self leveling systems? If it is not raising the height, what can I look for? I have a 92 rm estate, and I looked at the shocks (rear), and they look like air shocks. They have a sort of rubber boot at the around 3/4 of the way down. The car sits noticably low in the rear, the wheel well sits lower than the top of the rim. If you can help me out I would appreciate it!!!

Check the compressor for operation first and if it is pumping, you have a leak in the air bladders on the struts and need to replace the air struts. Monroe Sensa Trac will work very well for a replacement.

Basically, this is how the system works;

System activates when ignition is turned on, and remains active until 6 min after switching ignition off.

Compressor head houses the dump valve. There is an 8-15 second delay in the sensor circuit, to prevent compressor/dump valve operation during normal driving.

Sensor also limits compressor run time/dump valve, cycle to 6 min incase of severe system leak - turning ignition on & off resets the run time. This is known to cause the fuse to blow, or the compressor to fail. (Too many cycles in a short period of time)

An air replenishment cycle is initiated when the ignition is turned on. If the vehicle is a the correct height, a timer starts and after 35-40 seconds, the compressor will run for about 4 seconds to ensure that the shocks are filled with adequate residual pressure.(8-14 psi)

If weight is added to the vehicle during the replenishment cycle, then replenishment is over ridden.

To reduce compressor starting current, the dump valve is opened for 1.5 sec. each time the compressor starts.

After turning on the ignition and allowing the replenishment cycle to complete add 300 pounds (1,2or3 friends depending on size) to the rear tailgate and observe the drop in ride height. After 8-15 seconds you should hear the compressor start (listen closely near the compressor and you will even hear the 1.5 second dump valve operation). Then with the 300 pounds still on the tailgate, observe the body trim moving up to the correct ride height. The compressor should then cut off, and your car will stay at the correct height.


Remove the load (car will rise too high) and listen again near the compressor, after 8-15 seconds, you should hear the air escaping through the dump valve.

The link below will give instructions on how to check the bladders for leaks;
ELC Strut Options for Bonnevilles

[rnj]

O.k, just as you described, corroded wire splice. I'm not sure how long it has been like this. But the non function of the pump overtime will degrade it right???

[rnj]

I'm making some progress on this corroded splice. I was able to repair the splice, and the pump starts, but there was no change in ride height. I started to loosen the hose from the struts, and air started to come out of them. So did the air coming from the hoses release some air already present in the strut, or did the pump fill it. How do I try to find out if the struts are not leaking? and how do I know for sure the pump is pumping the right amount of pressure???

[bocoogto]

Can you hear the pump run? The engine does not have to be running for this system to work. The fact that you were able to hear air escape from the shocks suggests they do hold air. If you sqeeze the rubber bladder around the shocks and can feel air inside, chances are they are OK.

Remember, there is a delay built into the system to prevent reacting to bumps in the road. It takes about 15 seconds for the system to turn on when you place a heavy weight--about 300 lb.---into the rear of the car.

[rnj]

Yes, the pump does run, for awhile, then shuts off. sound s normal. but I see no change in ride hieght. when the pump stops, I can lean on the rear bumper and the pump will start up, but I don't feel the car move. I did that for about a 1 min. and then took my knee off the bumper and the pump ran for about 5 sec. after I let go, and stopped. so the system sounds like it is reacting the way it should. but not 100% Do you know what normal ride height is and how do I check pump pressure?

[bocoogto]

If the pump starts and shuts off, the system is working properly. The rise in height is very subtle, so you probably did not see it. Measure the distance from the rear wheel well to the ground. Put at least 300 lb in the rear and recheck the dimension. I'll bet it stays the same after the system runs.

If you want to change the ride height, you can do it by changing the position of the ball that the sensor switch engages under the car. I don't think you will want to do this, however, as the ride height is fairly high with this system left stock.

Good luck.

[rnj]

You've been really, really helpful!!!Thanks alot, I appreciate it. But 1 well 2 more things. I was under the rm over the weekend, and had the rear of the car in the air on jack stands, and I noticed that one of the springs was lotally loose. and the other was just a bit snug, but not solid. Should'nt they have been really tight in there. for sure the one side I wouldn't even need a spring compressor to remove. when I lowred the car I had to make sure that the spring was in place. second, this would make the car sit low, if these are worn?

[bocoogto]

Yes, it would sit too low if it wasn't for the air shocks. With the leveling sensor, the height will always be the same if the system is working. I don't think anything is wrong with the springs or spring perches. The shocks are the only thing that keep the rear end from moving down any more than it does when you jack up the body. There are tolerances on these items in the area of a good fraction of an inch. Maybe this is why one spring is loose and one is tight.

Good luck.