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Class A Motorhome Chassis Service

Preventative Maintenance For Your Class A

Mark Quasius
Jun 1, 2013
Photographers: Mark Quasius
Remember the old Fram filter commercial slogan, “You can pay me now, or pay me later”? That definitely applies to any Class A motorhome. Motorhomes are a sizeable investment and their chassis requires preventative maintenance or else you’ll wind up with some fairly hefty repair bills down the road. Maintenance on a motorhome chassis isn’t all that different from your pickup truck or passenger vehicle, except that everything is bigger and heavier.
Photo 2/13   |   Class A Motorhome Chassis Service Motorhome Engine Bay
The majority of costs involved in maintaining your motorhome will be related to labor rather than parts and filters, so making this a DIY project will save you lots of money. Servicing your chassis involves more than just running through the steps on a checklist, changing some fluids, and replacing filters. This is the best time to take a good look and inspect your chassis to see what is falling off, binding, or rubbing.
Before You Begin
You’ll need to have the service information that pertains to your motorhome before you get started. Many owners’ manuals have adequate information regarding capacities, oil grades, and time and mileage intervals for the various tasks. Check out forums online like ours at They’re filled with information from fellow RVers and can help eliminate service-related headaches.
Engine Oil
Changing the engine oil and filter is the first thing anyone thinks of when considering service work. Verify your engine’s specs to see how much oil it requires. If you have a diesel, chances are your drain pan won’t hold it all. Adding a Fumoto oil drain valve to your engine will help. This valve operates with a quarter twist and will allow you to stop the oil flow midway through the process so that you can change drain pans or buckets without making a big mess.
Photo 3/13   |   Engine oil and transmission fluid dipsticks are located at the rear of most diesel pusher motorhomes for easy accessibility.
Once the oil has been drained, it’s time to replace the oil filter. Diesel pushers have larger oil filters, so you’ll need a larger-size filter wrench to remove it. It’s recommended to prefill the filter so that you’ll have oil pressure immediately upon startup. Then, wipe a little oil onto the rubber filter gasket to prevent it from binding when you tighten the filter. Finally, add the correct amount of oil to your engine. Run the engine for a while to check for any leaks, especially at the filter, before shutting it down. Allow the oil to settle into the pan for a few minutes before checking the oil level via the dipstick.
Fuel Systems
Diesel engines depend on exact metering and timing of fuel and the heat of high compression to ignite the fuel mixture. The fuel systems required to do this are more complex than any gasoline engine, so it’s critical to provide clean fuel to the fuel-injection system. Small specks of dirt can plug injector nozzles, reducing performance, reliability, and economy.
Photo 4/13   |   Fuel filters are generally equipped with water drain valves to test for any water in the diesel fuel. Prefilling the filter before installing helps to eliminate air from the fuel system.
Most fuel systems provide two stages of fuel filtration. The primary fuel filter is designed to be a water separator and will most likely have a water-in-fuel sensor unit that will trigger a warning light. A petcock will allow you to drain the water out of that filter should that happen. This filter is designed to trap rust and other heavy particles, but a secondary fuel filter with a finer micron rating is located downstream. This filter is the final protection and prevents minute particles from entering the system.
Diesel fuel systems require a continuous fuel supply, so the system will become air-locked if you ever run out of fuel and you’ll have to bleed the air out of the system. The same holds true for when you change fuel filters, so you have two options available. One option is to prefill the fuel filters with fresh diesel fuel before installing them. If you choose to do this, make sure that you are using clean containers because any dirt that enters the filter can be harmful to your system if it gets into the injection pump. The second option is to prime the system to bleed the air out. Some engines require operation of a manual primer pump while others, such as Cummins, allow activation of the electric fuel lift pump by turning the key on and off in 30-second intervals a number of times to purge any air out of the system. Some owners prefer to prefill the primary filter only because the secondary filter will trap any particles that enter the system, and then use the primer pump to bleed the air from the secondary system. My personal preference is to keep a 2-gallon plastic fuel can that is dedicated to this purpose and always contains clean fuel and prefill both filters.
Air Filters
It only takes one tablespoon of dirt to ruin an engine, so air filtration is important to your engine’s longevity. Air filters eventually wear out from age or from becoming saturated with dirt.
Photo 5/13   |   Air filters must be changed regularly—dirty or not.
Most systems provide a filter-restriction indicator that specifies how many inches of vacuum your air filter is creating. Most filters are designed to be replaced when there are 15 inches of vacuum present. This is over the baseline of a fresh filter, so if you have 6 inches of vacuum with a fresh filter, you should replace it when the indicator reaches 21 inches of vacuum.
The second criterion is age. Paper elements don’t last forever, and they can fail if they get damp or old and allow particles to pass through and damage the engine. Most filters need to be replaced every three years, regardless of how plugged up they are, just to ensure that the filter material won’t fail.
Photo 6/13   |   Air filter restriction gauges indicate how much restriction is in your system so that you know when your air filter needs to be replaced.
Cooling Systems
Your cooling system will prevent your engine from overheating and melting into a pile of scrap metal. Both the coolant flow and airflow through the system need to be kept in optimum shape. Radiators can plug up with dirt, reducing the airflow through them and the ability to remove heat from the coolant. Motorhomes with rear radiators are especially prone to gunking up as the oil fumes coat the cooling fins. This gunk will need to be removed to restore proper cooling.
Photo 7/13   |   Steel coolant reservoir tanks come equipped with a sight vial to indicate proper coolant level when cold.
The coolant itself also needs to be replaced according to its specified schedule. If you have a heavy-duty coolant pre-charged with supplemental coolant additives (SCAs), you’ll need to use test strips to verify that SCA and nitrite levels are correct in order to prevent cylinder liner pitting from cavitation. You won’t have to worry about that if you are using the newer organic acid technology (OAT) coolant, but an extender needs to be added at three years and the coolant itself needs to be replaced at six years.
Finally, belts and hoses need to be checked. Rubber doesn’t last forever and the heat of an engine compartment doesn’t do them any favors. Belts may need to be adjusted, but the most important thing is to look at the inside of the belt to check for any cracking. Hoses get hard and cracked over time, so it’s good to inspect them and consider replacing them after five years of age.
Transmissions depend on transmission fluid to lubricate and cool them and to transfer power through the torque converter. Transmission fluid and filters have a definite service life, so be sure to refer to your service schedule to determine when these items need to be changed. When changing transmission fluid, be sure to wipe any deposits from the magnetic drain plug before reinstalling it.
Brakes are a critical component of your chassis because you aren’t going to be able to stop without them. Air-drum brakes are generally equipped with self-adjusting slack adjusters, which will maintain the correct adjustment on your brake shoes. However, you may need to manually adjust them if they fail to self-adjust. Do this by chocking the wheels and releasing the brakes. Adjust each slack adjuster to have one inch of free play when you pull on it.
Photo 10/13   |   Hydraulic filters are normally replaced annually, but a restriction gauge is provided to indicate any early filter failures.
If your motorhome has hydraulic brakes, the procedures aren’t that much different than on any other vehicle except everything is bigger. The biggest issue with motorhome brakes is that they are subject to fade after heavy use due to the weight of the motorhome. Brake fluid is hygroscopic, which means that it absorbs water. This water can turn to steam when the brakes get hot and create a spongy brake pedal with no braking action. Motorhome brake fluid should be bled and changed every three years to ensure that the fluid is water-free.
Photo 11/13   |   A pneumatic vacuum tank is great for changing hydraulic fluid. A hose is inserted into the hydraulic reservoir to suck out the fluid prior to changing the internal strainer element.
Disc brake calipers tend to freeze up over time, especially on a vehicle that isn’t driven that often, like an RV. Inspecting them and lubricating the slides will ensure that your calipers will slide freely and not bind. Sticky calipers can drag and cause damage to brake rotors, as well as affect your ability to stop.
Air System
Any coach with air brakes or air-ride suspension will be equipped with an air-supply system. This system consists of an engine-driven air compressor, various air tanks, an air dryer, and numerous valves and hoses. The brake diaphragms are rubber and the various valves also have rubber seals in them, so it’s important to provide clean air that has no oil in it. Moisture can freeze up in winter, rendering the brakes inoperable, so the air also needs to be dry. An air compressor tends to add a bit of oil to the air during normal operation and any moisture in the incoming air will also pass through the system. When mixed with the oil fumes, this forms a slimy mess that doesn’t do the rubber products in your air system any good.
Photo 12/13   |   Draining moisture from the air tanks is generally done by pulling lanyards in the wheelwells. This Allegro Bus has remote petcocks located in the basement compartment to simplify that task.
The air dryer combats this. This dryer will remove moisture and oil from the air and eject it out the dryer’s drain port. The filter on the air dryer is designed to last for three years, but this will vary as to how much air and moisture you pass through it. If you operate your RV frequently in a warm, humid area, your air dryer will need replacing sooner than an RV that spends its time around, say, Tucson, Arizona. The three-year recommendation is just an estimate based on average use.
Once your air dryer’s coalescing filter element is no longer capable of filtering out moisture, it will pass that moisture through to the air tanks. This is why it’s important to drain your air tanks regularly. Normally, you’ll pull the drain lanyards and hear the air blast out but won’t see anything because it’s clean. However, one day you’ll pull that lanyard and find that it’s starting to spit out moisture, which indicates that it’s time to service the air dryer. It’s not hard to do, but you will need a large strap wrench to unscrew the filter because it’s fairly large in diameter and you need to drain the tanks before removing the filter. When performing your regular air tank drains, don’t think of it as actually draining them or you may feel it’s a useless task. Think of it more as testing them for moisture, which is an important task.
Photo 13/13   |   The air dryer coalescing filter element is located near the rear of the coach. Be sure to drain all of the air tanks prior to removing this filter.
Suspension and Driveline
Your motorhome’s front-end suspension and driveshaft will have a number of grease fittings that will require fresh grease on a regular basis. Use a quality grease, preferably with a moly additive, and pump it until you see the old grease exit, then wipe off any excess. This will ensure that any water or contaminants have been flushed out of the cavity. Solid front axles have kingpins where the steering knuckles are attached. You need to jack up the axle to remove the weight from the wheel in order to effectively grease the kingpin bushings. This will allow the kingpin to float so that grease can thoroughly penetrate around the bushings and the thrust washer. Driveshaft universal joints on larger coaches may have two grease zerk fittings per joint, so be sure to grease both of them.
Tire pressures should be checked daily before each trip and be given a quick visual inspection for any defects. When you service your RV, you should carefully inspect your tires for any sidewall cracking or anomalies in the tread, such as feathering or scalloping, as well as tread depth. If this is evident, it’s probably time to have your RV’s alignment checked. Harmful UV rays from the sun damage tires over time, so protecting them with tire covers will help extend their life.
Taking time to do proper maintenance of your motorhome will result in some generous savings in the long run and will keep you on the road, enjoying your pride and joy.



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