GMC Western States

 Tech Center Number 9 - October 1994



The original type fan clutch can be replaced with a heavy duty type. A popular replacement is a Hoyden #2749 which is rated 'severe duty", and costs leas than half of the OEM part. The cooling performance resulting from this change can be significant. You can hear the fan clutch engage during cold engine starts when it is noticeably engaged for a block or two (normal} and then free-wheeling as noted by the sound subsiding. If and when the temperature goes up above the 1/4 gauge point you will also hear it engage. It sounds like the transmission is slipping with the engine RPM significantly increased. So, if you have never heard your fan clutch engaged, have it checked and make sure it's working properly. Hayden has a life time warranty on their fan clutch products if you find you ever need a replacement.



Is it time to perform some preventive maintenance and change those worn-out fan belts ? Don't be surprised if you can not get the exact replacement Belts from Gates. It seems that Gates has discontinued their 8 thousand series belts (11 mm width).
The listed replacement belts are 9.5-10 mm width belts which will recess deeper into the pulleys (close to bottoming out, which is highly undesirable). Therefore, an alternate source of high quality belts with the following results (455 Cid):
   Gates  Goodyear
 Power Steering  7450  1546
 Alternator  7570  15581
 Air Conditioning  7619  15634

You may want to take note to these replacement numbers, since it can save several trips to the auto parts house.



The proper technique for tightening the air conditioning compressor belt is to apply a pulley-to-pulley force {expander tool) to get the belt tight. A pry bar against the compressor will break the O-ring seals and release freon. The compressor housing has a thin metallic wall and is very fragile. Loss of freon will not occur with the use of a pulley-to-pulley expander tool.



Why carry a heavy spare alternator and starter when you can carry a small light weight repair kit for road emergencies. That's right, light weight & low cost repair kits are available from most auto parts stores for under $20.00:
80 amp Alternator: Repair Kit # GM 66-2303 {Blue Chip Co)
Starter (Delco):
Repair Kit # GM 67-2401 (Blue Chip Co)



How many times have you been able too connect your 50 amp service connection into a 50 amp shore power source? Probably not to often. However; we carry that huge big heavy and stiff cable(4 conductors, 6 AWG) with all those adapters and have a difficult time making it all fit back into its compartment (almost impossible on a cold day). Some coaches, such as the Royale, are more fortunate since they came from the factory with 30 amp service cables. Now this makes more sense from an owner view point. Many camp grounds and RV Parks have 30 amp service available and you only need one other adapter (30 amp to 20 amp) to carry around,
After fussing with all the coach power load consideration and the use of their coach for years in many parks & RV resorts, many have concluded that we are far better off replacing the 50 amp Service Cable with a 30 amp service cable (3 conductors, 10 AWG) & converting the Onan Generator with a 30 amp service receptacle. If you have a 6 KW Onan, replacement of the Generator's AC switch with a 30 amp circuit breaker is advisable for worst case short conditions, However; many of our used Orion's can't put out enough current to create a problem without incorporating the 30 amp circuit breaker.
Selection of the type of shore power cable is important since you want a reliable, small & flexible shore power cable. RV extension cords are temperature sensitive with respect to stiffness and therefore nat advisable. A good Electrical supply house can provide an excellent durable & flexible extension cord cable type SO or SOW which is ora small diameter and adding a clampon type 30 amp connector (available at RV supply) for the shore power source end works well. The coach end of the cable terminates inside the coach circuit breaker box. Note the wire routing and termination inside the circuit breaker box prior to removal. Green goes to box case (ground) at the right box side; white to neutral buss strip at the left box side; and red & black goes to the top of the main circuit breakers (2 center circuit breakers). Install the new 30 amp cable with the color wires terminating at the same place as removal. You will not have a Red wire in the new 3 wire cable and that's OK (3 wires vs 4 wires). A jumper wire now needs to be added between the two main circuit breaker (where the red & black wires terminated in the original cable). Another way of saying it is to add a jumper wire between the black wire main circuit breaker terminal and the circuit breaker without a wire (red wire location that was removed). The 30 amp cable clamp connector & Onan receptacle are clearly marked (via color code) for proper wire terminations. You have now changed your AC shore Power Service from a 240 volt AC 50 amp. into a 120 Volt AC 30 amp service which is protected at the service location (source) at 30 amps. You'll find this more than adequate 99 percent of the time as long as you don't try to run the heater, air conditioner, hot water heater & microwave all at the same time. This is no different than all those times you had to use an adapter (from 50 amp to 30 amp) for connecting to shore power. Placing the cable back into it's holding compartment is a joy after all those difficult days of the 50 amp shore power cables. You will also find as much as a 35-foot 30 amp cable will easily fit in the compartment where the 25 ft. 50 amp cable was located.



When was the last time you changed the power steering Oil? Do some preventative maintenance and change it now and every two to three years. Drain by removing one end of the power steering return line. It's been a long time since most of us have changed it (if ever). Clean fresh oil will help prevent sticking problems (loss of power assist) with your power steering pump control valve.



A great deal of 12 Volt electrical problems are associated with the ground (return) circuit. Most electrical units rely upon current returning to the battery and/or generator via the frame/chassis. Yet, very little attention, if any, is given to the return current path. The amount of aluminum contained in the GMC makes matters worse due to the amount of aluminum oxidation. Preventative maintenance of the ground/return circuit is recommended by cleaning to a shiny metallic appearance (sanding and scrapping} and applying a liberal amount of petroleum jelly (Vaseline) to both chassis and to wire connection. The petroleum jelly aids in maintaining a low resistive connection by reducing oxidation (it also prevents a current leakage path for + 12 volt connections). Both battery connections are the worst for oxidation (high resistant connections). So, if its an electrical ground {return) connection clean and paint with a petroleum jelly. This recommendation also applies to most +12 volt connections.



Several members have recently experienced battery cable failures which have prevented engine starting. Internal cable failures have been experienced at the cable to connector/lug interface. Oxidation at this interface has occurred over time & made a "high" resistive connection which can not carry the starting current. Heat is generally present during the starting cycle at the connection with the high resistance. Also, some cables have been reported to come apart with the slightest pull on the cable. Check the battery cables and replace them if they are a suspect,
Also, don't let significant oxidation to occur at the battery terminals. Shine up and apply petroleum jelly (vaseline} or other suitable material prior to and after attachment.



Each time you change your engine Oil Filter, it is wise to tighten the oil cooler adapter nut (l 1/2" Hex). The oil cooler adapter nut is located inside the adapter, just above the oil filter. It seems to work loose over time and engine oil leakage will occur. Also, periodical replacement of the adapter seal is suggested {about every other oil change). The seal (located on top of adapter) can be obtained from the removed oil filter since they are the same size {perfect fit). The seal gets hard & will leak, verify tightness each oil and filter change.



The lower portion of the Radiator is exposed to highway debris during normal driving. A protective screen {1/4" hardware cloth or other screen) should be added between the chassis frame & lower radiator frame to prevent road objects from hitting the radiator core and causing a coolant leak. This could be a very costly if not noted and corrected promptly.
Low coolant level could cost not only a new radiator but also an engine/transmission replacement. Best practice is to protect the radiator and not let objects hit the it. there are many coaches without any protection for the lower radiator section. Look under your front bumper and if you can see about 6" of the radiator hanging below the chassis structure, you need protection added before it becomes a major problem. Check it now and add your protection !


 Tech Info