Q&A Chassis by Peter Scalf

First published as a feature article in August, 1999 issue, RV View Magazine (Official Publication of Camping World's President's Club)

(No portion of this article may be reproduced without prior written consent of Peter Scalf)

Preface by Brent Peterson, Editor RV View Magazine (Woodall Publications Corporation):

People tend to ignore what they don't understand, and your RV's chassis is a prime example of this kind of neglect. When looking for anew or used vehicle, our attention is easily diverted to floorplans, amenities and the sea breeze color scheme; but unfortunately, the most telling part, the chassis, is often left to chance. Let's learn about it from someone who's seen the underside (as well as the darkside) of more than a few motorhomes in his day.

Peter Scalf brings 25 years of experience working on chassis to the discussion. He has been certified to service just about anything with four wheels and now owns RV Chassis Master in Clermont, Florida. You can find Peter dispensing much-needed advice on chassis performance, service and handling on-line at www.rvadvice.com


What's new in the field of motorhome chassis?

Newcomer Workhorse Custom Chassis (formerly General Motors) is changing the way people service their vehicles. The company offers consumers the ability to get their chassis, as well as their motorhome, serviced by the dealership (RV manufacturers and dealers must meet specific certification standards to be selected). This "one stop" method puts an end to customers' frustrations of running to different places to fix different components of their RV. This is already affecting the way others do business. I see Freightliner is running two shifts at most of their facilities and Cummins. Onan and Detroit Diesel and Allison are also starting extended service hours. In addition, the P-series chassis has always been a leader in coaches up to about 34 feet in length.

The Ford chassis is commonly used in coaches up to 37 feet but is extremely underpowered and overloaded when used for these larger motorhome designs, causing the end user to complain about low power and handling problems. Although the Triton V-10 is proving to be an exceptional engine and the new Ford Super Duty chassis is a very strong competitor, these bus-type Class A motorhomes in the 35-37 foot range are over-kill for a gasoline chassis.

What about diesels?

The range of diesel chassis has grown significantly over the past ten years for medium-priced motorhomes. The leaders, Freightliner, Spartan, Roadmaster, Magnum and Alpine Coach (in no particular order), have made a wider variety of options in Class A diesel motorhomes.

Upstart Alpine (Western Recreational Vehicles) designed their chassis with braking and handling as the main characteristics and have earned recognition for the superior handling brought on by the Toyo tires and i.P.d suspension products. They also were tested and rated on top of the industry by Bendix brakes (using a hydraulic braking system instead of the normal air brakes for a chassis this size).

I recommend 275 horse power for units up to 20,000 pounds GVWR; the 300-350 horse power will adequately power units up to around 26,000 GVWR. Your larger 40-42 foot motorhomes need the 400-500 horse power diesel engine for adequate performance.

For those interested in mini-motorhomes, what are the chassis options?

The Class C motorhome chassis is fairly simple since the choices are not near as broad as the Class A chassis market. Basically, there is Ford, Chevy and Dodge. Although there are a few Freightliner and others out there, these units normally are not in the same price range or ballpark as your other Class C motorhomes. These would be considered more of a "specialty" vehicle.

The Ford Super Duty chassis is by far the most popular in the Class C industry today, with options of the Triton V-10 or 7.3 liter Powerstroke diesel to power the Ford Super Duty chassis, Ford is able to offer the manufacturers a chassis able to handle $14,050 pounds GCWR, capable of powering some of the larger Class Cs on the market today.

General Motors offers both the Vortec 454 and 6.5 liter diesel for their Class C type chassis, but the GM diesel is much less popular in the industry. Dodge, on the other hand, offers the 360ci in the Class C model.

What is the most important part in deciding on the right chassis?

In all cases, weight distribution and weight capabilities will be the most important factor in your choice. Even though the chassis has weight ratings for the load, weight distribution is very critical on how the coach will handle. The rule of thumb is, if the overhang from the rear wheels to the rear bumper is excessive, you'll find the lighter the steering will feel on the road. Check the GVWR and GCWR to see how much weight you have left for a tow vehicle; and look to see if the overhang is going to cause consideration for air bags or heavy sway bars on the rear. Some coach builders add the air bags as standard equipment.

Class C chassis are heavy-duty van chassis and when the coach manufacturer constructs an excessively long body, it results in a long overhang behind the rear axle causing the handling to suffer. If the coach manufacturer cuts and stretches the frame rails between the axles, they can distribute the weight on springs more evenly for controlled handling. In other words, if they build it wide, high and long on a standard chassis, be ready to hang on and fight the road.

When it comes to Class A motorhomes and overhang, it really depends a lot on the chassis - whether it was built on a short wheel base chassis with manufactured long frame rails and springs to support the weight, or did the coach manufacturer extend the frame rails at the back to support the box?

If you see a greater than ten foot overhang from the rear axle to the back bumper, look at the frame rail and see if the coach manufacturer added frame rail extensions. You will only see this on gas or front diesel engine models. This same rule also applies to tag axles. Some manufacturers add a tag axle then stretch the frame at the back, leaving the coach with the same unstable handling.

Which is better for me, gas or diesel?

You might want to begin by first considering the maintenance needs for both gas and diesel engines. While a diesel unit normally gets better fuel mileage, the cost of service normally increases. The oil change service gas engine at 3,000 miles using seven quarts of oil will be far less expensive than the diesel at 5,000 miles requiring 20-40 quarts of oil. Lubrication intervals should be at 3,000 miles on both chassis and normal maintenance, i.e., brakes, differential, wheel bearings, etc., also have similar maintenance intervals.

As a rule, the larger the motorhome, the stronger the case becomes for a diesel engine; beyond the 35-foot range, front-mounted engines become impractical. Diesel pushers provide a quiet ride and plenty of power for larger vehicles. Newer entry-level diesel chassis are being produced by Spartan Motors.

What are some things I can do to get better handling?

A number of chassis manufacturers are using i.P.d. suspension as standard components and many RVers boast about their good handling. More and more folks are looking into i.P.d. to correct their handling problems.

Which is better, hydraulic or air brakes?

In my opinion, the hydraulic brakes are better than air brakes since the pads are locking on both sides of the rotor. What you end up with are more square inches of braking surface and superior cooling of the braking surface than with the drum brakes (air brakes use drums and shoes and require much more maintenance).

Both hydraulic and air brakes can fade from overheating, but more permanent damage can be caused to the drums and shoes in air brakes. Your average person looking at an RV has never been accustomed to air brakes and has little ideal of how they work and what effect low air pressure can have on the system. In a hydraulic system the front and rear system are separated and one should hold in the other fails. Alpine Coach put a lot of thought into building their chassis and safety was the reason for their hydraulic brakes. Safari also looked at both options and chose hydraulics when building their Magnum chassis.

What should I do to protect my chassis?

A few key points to look at in maintenance is rust lubrication. In the past, undercoating was done by specialty shops; now with the introduction of Amsoil's undercoat in spray bottles, the owner can now easily and efficiently fight rust while performing his/her normal chassis lubrication. Be sure to follow the directions explicitly. Take care to protect wiring harnesses, fuel lines and other components not compatible with undercoating products.

All fluid levels should be checked on a regular basis. The use of synthetic lubricants throughout the drivetrain can extend the normal maintenance intervals while adding extra protection and saving in the cost of yearly maintenance.

Be sure to look at all weather head electrical connections and seal with a spray protector to fight corrosion twice a year. Follow the owner's manual guidelines for regular maintenance that's beyond your capabilities.

When buying a used coach, what are some signs of chassis wear?

Inspect the chassis for excessive rust throughout the drivetrain and entire chassis. Check all fluid levels for irregular signs (i.e., color, smell, etc.), look for weak or sagging springs and check for fluid leaks. Inspect rubber hoses, bushings, belts and vacuum lines for weather cracking. Inspect tires for abnormal tread wear. Road test the motorhome for unusual noises, vibration, handling problems and other performance characteristics. Be sure all gauges and monitoring equipment is functioning properly. If in doubt, take along a trust mechanic or pay for a "Pre-Purchase" inspection by a professional.


This article posted to the Internet October 24, 2000

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