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 About a year ago my friend had his engine replaced with one I got him from my favorite scrap yard.  I have spent a year fixing problems such as engine mounts, starter, AC actuators, coolant leaks, and now the rear shocks.

He bought this car with a blown head gasket, at the time, his level compressor would run without stopping because the air shocks were leaking, so I pulled the ELC fuse out to stop it from running and burning itself out.

This is a base Eldorado and does not have the RSS Ride Control system.

I purchased the following:

ACDELCO 504579 {#19241356} [Shock Absorber] Specialty; Air Lift; Load Assist  rear air shocks from RockAuto

MOOG K200174; Spindle/Knuckle Bushing; Rear Upper, I installed the upper rear knuckle bushing about a month ago, it went smoothly, but it could have gone better, I need to find a proper sized socket/pipe to press the knuckle bushing in the next time, I called NAPA and they suggested I have a machine shop turn one for me.  A typical socket hugs the rubber part of the bushing too much. 

Here is a photo of the new rear air shock,  Rockauto sent me a second pair, the first pair was leaking and looked like someone tried to installed them :blink:.  Just sent back the first pair to them today.

DSCN9886_zpsdgcsllaz.jpg

The shock installation went smoothly, very easy install.   I figured that I would just reinstall the ELC fuse and when I looked someone had reinstalled the fuse...  Hmm, not good, the motor was not running. (whoever installed the fuse is still under investigation)

OldCadTech was kind enough to send me the 98 ALC schematic for the 98 Eldorado, and I discovered that the compressor's green wire provides 12 volts when the ALC relay is energized.  Here is the schematic (thanks OldCadTech):

ALC%20SYSTEM%2098%20ELDORADO_zpsoyunbuyc

So to determine whether I was getting power, I detached the ALC level compressor's connector, I connected a volt meter (DC) with alligator clips on the black ground (D) and the green 12v relay power (B) contacts.   I detached the rod at the level control height sensor that is located in front of the left rear wheel and pushed the sensor all the way down.

I turned the key to the ON position and crawled under the car and slowly moved the level sensor arm through its range and suddenly got 12 volts, backed the arm down the other way and the power turned off.  I repeated this a few times to verify that the level control sensor was good, slowly sweeping the arm getting 12 volts, and then sweeping it the other way and the power went off. 

To test the exhaust solenoid, I connected my voltmeter to pin (C) at the compressor (hot all the time) and back probed the automatic level control height sensor at terminal (E) to test power to the exhaust solenoid and I got 12 volts as I swept the level control height sensor arm.  So I determined that the ALC compressor was getting both compressor motor and exhaust solenoid power properly so I had a bad ALC level compressor.   I confirmed it was bad, by connecting an ohm meter to the motor green (B) and black ground (D) terminals and showed no resistance unless I banged the motor, so the motor appears bad.  

Removing the ALC level compressor was difficult, there was very little room to get it out.  The compressor has 2 air hoses attached to it (see hose #10 below), a compressor intake, and a compressor exhaust.  The intake hose was detached because the hose was brittle and deteriorated.  This is not good because the compressor ingests water.  After about an hour of jockeying it around, I finally got it out from the bottom around the parking brake cable. 

Here is a typical photo of the level compressor

970131GM07-104_zpsujtybfwz.jpg

I removed the bracket that covers the compressor piston and wow, the motor definitely burned out as the smell from the burned motor windings was really bad and it was obvious that the motor had ingested water, see photo below

DSCN9882_zps3c2d8dwr.jpg

Water ingestion corroded the compressor and piston

DSCN9885_zpsn68ysqfy.jpg

Off to the scrap yard.  They had about 100 level controls sitting on a shelf and I went through every one, and I found 2 that might work, one for a 95 and one for a 99.  I took the 99, it was in terrific condition as it was housed in a protective box in 99 and it was clean.  However, the electrical connectors were different, see below, the connector on the left was for 98 and the connector on the right was for 99 in addition the brackets looked different so I would need to swap the brackets over.    Each of these connectors had their leads marked A,B,C and D, so I assumed that all I would need to do was swap the connector from the 98 on to the 99 compressor.   The 99 compressor cost me $50 from the scrap yard, I was pretty sure the units were identical except for the electrical connector and brackets but I was warned by the scrap yard that they would not accept a return if I cut the plug off. 

DSCN9880_zpsqiymsyge.jpg

This is the 98, below, notice the straight connector and the bracket orientation, look to the right that is the 99 compressor, see the different bracket?

DSCN9876_zpsu2idwteo.jpg

This is the 99, compare it to the above photo for brackets.  The 99's plug is up in the dirt, but its a square plug marked A,B, C and D.

DSCN9877_zps12dozlft.jpg

My friend from the scrap yard told me that if I cut the plug off he would not accept a return, so I used alligator jumpers for all four connections (A,B,C,D) and the new 99 motor ran and I was able to energize the exhaust relay all by sweeping the level control sensor arm.   So I cut the plug off the 99, and soldered on the 98 plug, paying attention that I put A to A, B to B, and so on.    I heat shrink wrapped and taped the 4 wires to keep moisture out.

Here is the inside of the 99 ALC compressor!, nice an clean, you can see how much water the 98 sucked up above.   Word of advice, if you have level compressor get under there and inspect the intake and exhaust hoses replace them if they are deteriorated (you can see it in the above photo), if that hose deteriorates and comes off, you can suck up road dirt and water destroying the compressor.  I replaced ALL 7/32" vacuum hose used for compressor intake and exhaust. 

DSCN9881_zpsvic6tuxr.jpg

I installed the new 99 compressor, plugged everything in, I left the leveling rod off the level control sensor and BAM, the Eldorado, leveled beautifully, and even better exhausted beautifully.   I was able to raise and lower the car simply by manually moving the level control arm up and down, slowly.  The ride was 1000% better and took bumps and curb cuts beautifully.

I hope this helps someone.

A tip, these units are very difficult to get out as the brackets get in the way, if I were to do this again, I probably would remove the compressor retaining screws (3 screws), and them remove the two brackets from the compressor (after taking a photo so I know their orientation), that makes the compressor much smaller and easier to get out.  On installation, I would put the compressor up, then install the brackets. 

 

 

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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thanks for posting this.

A few tips.

I remove the compressors from above the right muffler. I have done enough to get them down to a science. Not a great placement.

The Vent hoses are horrible, I use fuel hose to replace them.

As for the bushings, buy one dorman set. It comes with the sleeves to install them.

You should always replace both the upper and lower knuckle bushings.

Note it is very important to not tighten the center bolt (the one on the back side of the knuckle that keeps the knuckle straight)

If it is tightened while jacked up it will put excess strain on the bushings when at ride height.

Also FYI pontiac had the square plug on the compressor, I think olds did too

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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14 minutes ago, rockfangd said:

thanks for posting this.

A few tips.

I remove the compressors from above the right muffler. I have done enough to get them down to a science. Not a great placement.

The Vent hoses are horrible, I use fuel hose to replace them.

As for the bushings, buy one dorman set. It comes with the sleeves to install them.

You should always replace both the upper and lower knuckle bushings.

Note it is very important to not tighten the center bolt (the one on the back side of the knuckle that keeps the knuckle straight)

If it is tightened while jacked up it will put excess strain on the bushings when at ride height.

Also FYI pontiac had the square plug on the compressor, I think olds did too

I did try to come over the muffler and came close to dropping the muffler system to do it, but it was tight, I ended up going out the bottom, but thanks for that tip

THAT is GREAT info about the dorman set, I need those sleeves!!

Good tip on the center bolt, I knew that from my 96, but this is a good place to mention it.

Yes, I saw that square connector a few times in the 100 compressors I went through.  I tried to stay with Cadillac compressors.

I am going to order a Dorman set tonight, I have to install the upper bushing on the other side!  Thanks

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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  • 2 weeks later...

Rock!, I bought a DORMAN knuckle bushing set with the tools, THANK YOU!!!!

You know, I called MOOG's tech support and specifically asked them what tool was used to install them.  They actually sell the bushings WITH a tool and the TECH did not tell me about it!   I got off the phone thinking I would need to have a machine shop turn a piece of pipe to fit, and he suggested that was the best thing to do, wow.   Uninformed tech support, very disappointed.  He had the bushing up on his screen and all... aggravating

That said, thank you for the heads up on these installation tools.  Without the tool and trying to use a socket the bushing gets damaged thanks

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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no problem. i have done tons of them. i used to use dorman to get sleeves. now i use mevotech or moog. they work wonderful.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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