Timely Brake and Wheel Bearing Inspection and Service are Critical to Safe —
and Efficient —

by Bill and Jenn Gehr
October 24, 2013
Filed under Gear, Tech Tips


In the last two issues (Part I, Part II), we concentrated on maintenance schedules and procedures to help keep the chassis rolling down the highway without surprise interruptions. We stressed becoming familiar with the chassis owner’s manual, and hopefully, you’re keeping a detailed log of necessary scheduled maintenance items and services. Complete chassis maintenance on a timely basis is important to the reliability and durability of your motorhome — and promotes peace of mind while on the road.
Perhaps because their motorhome is not used on a regular basis, some owners pay less attention to the brakes than they should. However, it’s important to remember that brakes are not indestructible and are a normal wear item for all motorhomes. At some point in time, the brakes will need to be replaced. It is recommended to have a professional inspect the front and rear brakes annually — and be sure to have the emergency brake system checked out at this time as well.

Air Brake Systems


Most diesel coaches are equipped with an air brake system that includes an air storage tank. Even with an automatic moisture ejection system, it’s a good idea to manually drain the air storage tank by pulling on the valve lanyard every six months or so to remove any residual moisture.


The moisture ejection system (commonly called an air dryer, above) is equipped with one of two types of desiccant cartridges. Make sure you verify the type of filter your coach has before beginning the service procedure.


A brake rotor in good condition (like this one) should be free from any deep grooves (galling), heat spots or cracks.


Knowing how to measure (or at least see) brake pad wear is important. The brake caliper typically has an inspection port that shows the caliper (rust-colored part to the left), pad (black line in the middle) and metal backing plate (thin black strip).


If your motorhome spends a lot of time near the coast, keep an eye out for signs of corrosion. Rust and/or oxidation can hinder brake caliper function, causing loss of braking performance, uneven wear, or both.


Earlier hydroboost systems used pressure from the power steering pump (instead of a large vacuum booster) to provide proper brake fluid pressure. With that in mind, paying attention to drive belt wear is particularly important.


Brake fluid is hygroscopic so it should be flushed and replaced every two years under normal conditions (more often in very humid climates) to maintain the correct boiling point.


Depending on the environment in which you live, additives can help the performance of your diesel coach. Diesel fuel conditioners/supplements have various claimed benefits depending on the brand, while air brake anti-freeze inhibits moisture and corrosion in air brake systems.


Newer hydroboost systems utilize an electric motor to provide pressure to the brake system. If your motorhome is so equipped, you can often hear the motor running when the brake pedal is applied.


Regular front wheel bearing service is vital for long bearing life and safety. This bearing had been run so long without proper maintenance, it was on the verge of disintegration. Note the missing roller in the middle, and severe pitting in the rollers.


An oil lubricated front hub (aka oil bath) system allows you to visually inspect the oil level. Make sure you use the correct oil, and keep it at or near the fill line.

The majority of diesel motorhome chassis are equipped with an air brake system. Air brakes have their advantages over hydraulic brakes since there is no fluid to regularly check or replace. In addition, air brakes are not comprised of a master cylinders and wheel cylinders that can be prone to failure. The lack of high-pressure rubber hoses that eventually fail or deteriorate also simplifies overall maintenance.
In order for air brakes to function properly, air pressure needs to be maintained at 80-100 psi. Gauges are provided in the instrument cluster to monitor air pressure. An audible, low-air-pressure warning will sound at roughly 60 psi. If this occurs, pull over as quickly as safely possible. When the air pressure reaches 40-45 psi, the emergency brake — not the parking brake — will automatically engage. Low-air pressure stems from an air-pressure leak or failure of the system to provide compressed air.
Excess moisture in the air system can cause brake failure. Most air brake systems are equipped with a replaceable desiccant cartridge (an air dryer) designed to trap moisture and oil produced by the air compressor during operation. Low air pressure can result if the filter becomes clogged. Plan on changing the desiccant cartridge every two or three years; it’s a good idea to carry a spare cartridge in case of emergency. In fact, simply changing the desiccant filter may be just enough to get you rolling again.
There are a few chassis that utilize an air brake system equipped with an automatic moisture ejection system. Despite these built-in automatic systems, it may still be necessary to manually drain the air storage tank. Just to be on the safe side, it’s best to manually drain the air storage tank every six months to ensure that there is no moisture contamination, regardless of the type of moisture control system. Some manufacturers install a pull-style lanyard located inside a baggage door compartment for convenient draining of the air storage tank.
Modern diesel and gasoline chassis have anti-lock brake systems (ABS) that make routine inspections and maintenance even more critical. If the dash ABS indicator illuminates, don’t ignore it. The brakes may feel normal, but there can be a serious problem that must be addressed in order to avoid premature failure due to normal or abnormal wear and tear on one or more system components.

Hydraulic Brake Systems

Hydraulic disc brakes have changed considerably in the last few decades, from basic drum brakes on all four wheels, to powerful anti-lock rotors and discs at each corner. There’s little doubt that hydraulic braking has come a long way toward providing added safety and decreased stopping distances. Annual inspections must include checking rotors, pads, drums and linings (depending on the type of braking system) for excess wear, as well as the integrity of the entire hydraulic system.
For inspections, the starting point is the brake master cylinder. As brake pads and linings wear, the brake fluid level will diminish. Check the owner’s manual for the correct type of fluid necessary when topping off the reservoir. When adding fluid, be sure to inspect the cap and reservoir for any debris, moisture or rust. If any of these contaminants are present, have the hydraulic system flushed immediately. Since brake fluid is hygroscopic (absorbs water), it should be changed every two years to keep its boiling point high.
The brake rotors should appear smooth with no deep grooving, cracks or blue/purple heat spots. The inner and outer brake pads should be measured from the metal backing plate to the rotor surface; this is typically done through an inspection port in the brake caliper. The pads should also be measured top and bottom (leading and trailing edges) to ensure they are wearing evenly. The brake and/or chassis manufacturer has a recommended minimum thickness that must be adhered to; once the brake lining is worn away and the backing plate begins making contact with the rotor, you’re on your way to an expensive repair bill.
Chassis that are equipped with a hydro-boost system rely on pressure created by the power steering pump or electric motor to provide proper brake fluid pressure. Make sure the reservoir is filled to the correct level and that the drive belt (where applicable) is in good shape.
Take into consideration the environment that the coach — and dinghy vehicle — is regularly exposed to. For ex-ample, if you live near the beach, rust can be a problem. Make a point to have the brake system checked twice a year. This is essential when opting for the coastal lifestyle. Rust is a killer, especially on brake calipers where corrosive buildup will almost certainly restrict the action of the caliper, causing loss of braking or uneven wear.

Wheel Bearing Maintenance

Several years ago, an owner was complaining about a noise emanating from the right front wheel area. I drove the coach a short distance to the service bay, and to my surprise, the tire and wheel fell off. The bearings had literally disintegrated from lack of lubrication. The damage was extensive and the repair time consuming; the owner unfortunately lost two days of vacation time while waiting for replacement parts.
Front wheel bearings seem to be an “out of sight out of mind” maintenance item. Whether you have a diesel or a gas chassis, check the section in your owner’s manual that refers to wheel bearing maintenance for service intervals. Ford converted most of its Class A chassis to sealed bearings around 1999. The Workhorse W16 and W18 chassis have a spindle-less hub system with uni-pack bearings that don’t require maintenance or adjustment. W20, W22, and W24 chassis have an “oil lubricated front hub” bearing system. The oil level needs to be checked every year through a sight glass that is located in the center of the hub. Make sure the oil is up to the full line, and check for leaks if the oil level is low.
Be sure to consult the owner’s manual for the correct type and weight of oil if you plan to top off the oil level yourself. Remove the cap in the center of the hub adjacent to the sight glass and fill to the line. Inspect the condition of the oil once a year.
Chevrolet P-chassis utilize a conventional bearing system that requires periodic maintenance; they should be cleaned, inspected and pressure packed with a high temperature wheel bearing grease. Don’t forget to replace the grease seals. While the hubs are removed, the calipers, brake pads, brake hoses and overall condition of the brake rotors should be checked. Be sure to use a torque wrench when tightening the spindle nut, as the adjustment is critical. Ford E-350- and E-450-based Class C chassis require the same maintenance as the Chevrolet P-chassis.
Most modern diesel motorhome chassis use a wet hub (oil bath) front wheel bearing system that requires an annual inspection, similar to the Workhorse chassis. Prior to 2005, most diesel chassis required the same servicing as the Chevrolet P-chassis.
Basic service for any oil lubrication system is fairly simple. Remove the wheel covers and inspect the inner and outer parts of the hubs for any signs of oil leakage; it’s not necessary to remove the tires or wheels. The oil can be changed on a short-term basis by removing the rubber plug that is located to the right of the plastic inspection cover and sucking out old oil using a syringe. Another way to do this is to remove the plastic cover and allow the oil to drain into a pan. Drawbacks to this method: it’s a messy process and the seal on the plastic cover will need to be replaced before reinstalling.
Converting a conventional wheel bearing system on a diesel motorhome chassis to an oil bath system is simple and less expensive over the long run. Many experts agree that converting to an oil bath system not only lubricates more efficiently, but the changeover will save money in wheel bearing service.
With the proper maintenance, you can expect your brakes and bearings to be functioning at their best the next time you hit the road.

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