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Several upgrade kits are available for the GMC compressors.  If you have not upgraded yours, you are living on borrowed time.  The air systems are greatly improved with these modifications and the performance and reliability is excellent.  The following are some examples of the improvements to these systems.

Al Chernoff upgraded the system shown.  The fitting and upgrade components are available from Cinnabar Engineering, Inc.  (1-800-720-2227) Power level is $96.  Power level II is $86.  Electro-level II is $350.  Fitting kit $42.  Call them 1-800-720-2227 there are many different kits.

GMCer John Clement,951-737-0969, has any single part you will
 need to repair these compressors and he will also rebuild them for

and here is how to do it by Patrick

 the Ragusa piston tool.
 The order number is RV-14 ($5.00) from Ragusa Pattern Shop and R.
 V. Products, Inc. 714-261- 5898.


Stainless Air Tanks
Jim DeMaere  stainless steel air tanks 1st design $89 and 2nd design $59.
I have one and they are beautiful,warner
phone: 403-329-3091

The original plastic connectors on the air hoses have become brittle and leak.  They should be replaced with metal connectors (G).  The  kit can be ordered with all of the necessary connectors and fittings from Cinnabar Engr.   These fittings are air-brake fittings.  They are quite expensive from hydraulic hose suppliers.

The upgrade kit includes the pressure gauge (A).  This gauge shows the tank pressure.  The tank pressure should not leak down after the pump has stopped.  If the tank pressure will not hold, a leak should be fixed.  This gauge will also let you test the quality of your pump.  With the GMC stable at the normal running position, turn off the air system and put the height valves on hold. Drain the air from the tank using the  valve at the bottom of the tank.  Now turn on the pump.  The pump should bring the tank up to 125 pounds in one minute.  If your pressure cutoff stops the pump before the 125-pound level, you will still have an indication of the condition of your pump.  If the pressure never reaches this level or takes longer, it is time to rebuild the pump.  If you see a small red line below the cylinder head on your compressor (H) this shows that you have the old valves in your compressor.  An upgrade and rebuild kit is available for the compressor.

The pressure relief ( C ) and the stainless steel check valve   ,with a specific cracking pressure, (D ) are placed just before the tank.  These components protect the height control system and the air bags.

The water and sediment collector (E) is critical to the air system.  Without the sediment bulb, water, rust, dirt and so forth, collect in the air tank.   Most of the original systems have collected so much water and rust in the air tank, it is necessary to remove and replace the  valve in the bottom of the air tank to drain the tank.

Most experts recommend that a large copper loop (F) be placed between the pump and the water collector to cool the compressed air and condense out the water before the filter.  This improves the efficiencies of the water collection system.

Many GMC owners have added a second compressor to their system (B).  This provides a backup compressor and reduces the time to pump up the coach.  Two switching circuits are available on the pressure switch.  The unused one can be wired to turn on the second pump. The teed connection shown is the way my coach was connected, but, this is not a good installation.  The second compressor should have a separate filter and check valve to keep  failed compressors valves from venting the other pump.

The original design for rear mounted compressors, provided the power for the compressor from the front of the coach.  This long wire will drop about one volt of voltage to the running pump.  The reduced voltage is not good for the pump and results in a long pumping time.  It is a good idea to change the source power at the run relay to the coach batteries in the rear.

Schematics and discussion
Air Suspension Systems By Duane Simmons

Duane Simmons tells us that GMCs' with serial numbers (last four) from approximately ...0885 to ...1885 (about 1000 coaches) had two suspension compressors in 1978.  This is the Electrolevel II system;  it used electronic optical height sensors rather than pneumatic height controllers.  The Electrolevel I system had one compressor.
The GMC MH International newsletter issue #47 indicates that EL II was installed on some as early as s/n 742! Scott Shean
The Electrolevel II air system needs help in providing power to the two air compressors/motors.  They receive their power through a relay for each motor (GM installed).  A marginal design & age of connections creates low voltage for operation of the system.  A simple routing of a separate "stiff" power source w/10 AWG wire through a 30 amp circuit breaker to the power contacts of each relay does great things for the system. Don't rely upon color of wire to find the relay input power wire . . . probes to make sure before cutting the original power wire. Tape the cable wire up & attach the news power wire to the relay side wire.  Also add an additional 10 AWG ground wire for the return current path.  Do this for each relay & you will note the different in motor speed. Use the local House fuse bus to obtain the"Stiff" power for the compressor system.

Word of warning here, you should never use teflon tape on your air system threads. The tape can and will get into your air system and can cause the solenoids to leak and not seal right.  Only use a teflon type thread paste as a thread sealer.  John