brmurph Posted September 11, 2004 Report Share Posted September 11, 2004 My98 Concours has a sagging rear end when it is loaded (4 people with luggage) after driving for a long period of time, usually a 1/2 hour or more. I would say it drops about 4-5 inches. Even when the rear is low it still rides OK, does not bottoming out, it just looks like a low rider. If I stop the car and restart the rear pumps back up where it should be until I drive down the highway again. I have let it sit over night in the garage with about 300 pounds of sand in the trunk and it only drops about 1/4''. If I drive around town with the sand in the trunk for 10 or 15 minutes the car stays level drive down the freeway for over 30 minutes and it droppes down again. Is the automatic leveling suppose to continuously adjust the level even during highway speeds? The only thing I can thing of is that the leveling control only adjust at startup and the air must be leaking out as I drive down the road. Any thoughts? Link to comment Share on other sites More sharing options...
Ranger Posted September 11, 2004 Report Share Posted September 11, 2004 I don't think it adjusts only at start up. That would mean if you unload the 300# of sand while the car is running, it would be high in the rear. I am pretty sure it would level out as you unload it with the engine running. The question now is, is it speed related (Drive around town vs highway) or time related (:10-:15 min vs :30 min). My guess is it is time related and there is a slow leak somewhere but since it doesn't happen when shut down it must be powered for this to happen.That would isolate it to the compressor. If memory serves me correctly I think there is an exhaust valve or solenoid on the top of the compressor. It may be sticking open slightly when energized. Just a thought FWIW. Link to comment Share on other sites More sharing options...
KHE Posted September 12, 2004 Report Share Posted September 12, 2004 Check the air lines from the compressor to each rear shock. You may have a line that is chafed through and is leaking. Follow every inch of the lines and pay close attention where they are near moving suspension parts. If you do find a leak, a splice kit is available from the GM parts counter. It is only about $2.00. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
brmurph Posted September 13, 2004 Author Report Share Posted September 13, 2004 Thanks guys. I think you must be right, has to be a leak. I will start the car, let it run for about 10 minutes in my driveway, add the sand back in my trunk see if it levels out, if it does then I will let it run for about 40 minutes while it just sits there (with the sand in the trunk) and see if it drops any or if the compressor comes on during that time. This will hopefull tell me if it a timming thing or not. Will post my results. Thanks again. Link to comment Share on other sites More sharing options...
Garlicdude Posted September 14, 2004 Report Share Posted September 14, 2004 HOw about spraying some soapy water on the air lines. Make a real strong solution of dishwashing liquid in a spray bottle and spay it alon the lines to help find the leak Link to comment Share on other sites More sharing options...
brmurph Posted October 4, 2004 Author Report Share Posted October 4, 2004 I don't think it adjusts only at start up. That would mean if you unload the 300# of sand while the car is running, it would be high in the rear. I am pretty sure it would level out as you unload it with the engine running. The question now is, is it speed related (Drive around town vs highway) or time related (:10-:15 min vs :30 min). My guess is it is time related and there is a slow leak somewhere but since it doesn't happen when shut down it must be powered for this to happen.That would isolate it to the compressor. If memory serves me correctly I think there is an exhaust valve or solenoid on the top of the compressor. It may be sticking open slightly when energized. Just a thought FWIW. I have come to the conclusion that you are right on with your exhaust solenoid theory, that is the only explanation of why it would be intermittent. My guess is that about 1 in 10 times the solenoid will not seal completely (hence the intermittent problem). I checked the lines with soapy water, no leaks. I also had the dealer look at it and they found 0 leaks. It is now leaking down just sitting in the garage (again about 1 in 10 times and with a 300 lbs load). Has anyone replaced the compressor head (includes the exhaust solenoid) and if so how hard is it to replace? Is there an easy way to remove the compressor? Is it worth replacing just the compressor head or should I replace the whole compressor? Anyone else have this problem? The dealer doesn't think there is a problem, they said it is designed to drop in the rear, I could understand an inch or so but not 3 to 4 inches. Thanks for the help. Link to comment Share on other sites More sharing options...
KHE Posted October 5, 2004 Report Share Posted October 5, 2004 The compressor head assembly is easy to replace but you want to make sure that it is bad. You will need to remove the compressor from the car to gain access to all of the bolts. The new head must be sealed to the compressor using RTV along with the mounting bolts. There are specific tests outlined in the service manual to test the exhaust solenoid as well as all components of the level control system. Did you check the connections at the rear struts? Are the rear air struts leaking? Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
brmurph Posted October 5, 2004 Author Report Share Posted October 5, 2004 The compressor head assembly is easy to replace but you want to make sure that it is bad. You will need to remove the compressor from the car to gain access to all of the bolts. The new head must be sealed to the compressor using RTV along with the mounting bolts. There are specific tests outlined in the service manual to test the exhaust solenoid as well as all components of the level control system. Did you check the connections at the rear struts? Are the rear air struts leaking? I do have the service manuals, it suggest to check using soapy water which I did but I am guessing I would have to remove the compressor to really be able to check the head assembly (although I really don't know where to check). Is the compressor easy to remove? I did not check the connections to the rear struts, I probably should have but since it is an intermittent problem I guess I have rulled them out (could be a mistake). Thanks Link to comment Share on other sites More sharing options...
KHE Posted October 5, 2004 Report Share Posted October 5, 2004 The compressor isn't difficult to remove. You will need to leave it hooked up in order to test for leaks at the head assembly. Check the area where the head assembly meets the body of the compressor as well as the head mounting bolts. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
brmurph Posted October 5, 2004 Author Report Share Posted October 5, 2004 So I should be able to remove the compressor from the car but leave all the lines connected and virtually bench test (check for leaks) the compressor and head unit under the car? Link to comment Share on other sites More sharing options...
KHE Posted October 5, 2004 Report Share Posted October 5, 2004 Yes. I did that very same test on my Dad's '94 Fleetwood two years ago. The problem was a chafed air line near the rear suspension. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
brmurph Posted October 5, 2004 Author Report Share Posted October 5, 2004 Yes. I did that very same test on my Dad's '94 Fleetwood two years ago. The problem was a chafed air line near the rear suspension. OK I wll give that a try. Thanks for your help. Link to comment Share on other sites More sharing options...
Maximln Posted October 6, 2004 Report Share Posted October 6, 2004 I would definately double check the shocks themselves. I had a similar problem with my 98 STS. My car would attempt to level when it was just me in the car and seemed to do OK but when I had additional passengers, it never would. I took it in and the tech told me that the shocks needed to be replaced as the air boots were rather worn (my 93 STS had 180,000 miles on it when I sold it and the shocks were perfect--didn't leak and no "SERVICE SUSPENSION" message). As I'm sure you know, they were rather expensive so I opted to only replace 1. The other one didn't look that bad. After that, the car would always level fine with passengers but then as I was driving, the rear would always leak down. So I sucked it up and replaced the other shock and now the system works perfect. It is very sensitive. When I get out of the car, I can always hear the system exhaust air to level (quit laughing, I'm 6'1" and 190 lbs). Max Link to comment Share on other sites More sharing options...
bigfoo Posted October 6, 2004 Report Share Posted October 6, 2004 heh.. i've never heard mine do anything.. on my 99 sts.. i don't even know if it works after reading this.. is there an easy way to Test it?? I have no codes that refer to it but i've never heard it level or exhaust air.. Link to comment Share on other sites More sharing options...
KHE Posted October 6, 2004 Report Share Posted October 6, 2004 heh.. i've never heard mine do anything.. on my 99 sts.. i don't even know if it works after reading this.. is there an easy way to Test it?? I have no codes that refer to it but i've never heard it level or exhaust air.. Yes - turn the key to ON and sit on the rear bumper for 30 seconds or so and you should hear the compressor run. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
brmurph Posted December 30, 2004 Author Report Share Posted December 30, 2004 Just wanted to post the fix on this problem for the next guy that runs into it. Turned out to be the compressor like Ranger suggested. Got a free pair of rear shocks ($1600.00) out of the deal though, the dealer first thought it was the shocks and replaced them (covered by extended warranty), still had the problem though so next time they replaced the compressor, that took care of it. I have to wonder why it was so hard for the dealer to diagnose this problem? By the time they replaced the shocks it would leak down (with 300 pounds of sand in the trunk) in about 1.5 hours. After the shock replacement they said it was all fixed, I took the car home and sure enough the car still dropped in about an hour. Why couldn't the dealer check that before they gave the thumbs up on the repair? So to recap, first dealer said there was no problem, then they said it was the shocks, finally they said it was the compressor, all of this took about 5 months of time of which I had to ride around with a bunch of sand in my trunk. The factory service manual explains how to diagnose the problem and how to isolate the shocks from the compressor why is it so hard to fix a fairly simple repair? Link to comment Share on other sites More sharing options...
fubar0715 Posted December 30, 2004 Report Share Posted December 30, 2004 I have just the opposite problem....My STS is high in the rear...... Any ideas???? Link to comment Share on other sites More sharing options...
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