Suspension Upgrades

Enhance your coach’s ride and handling qualities and enjoy relaxed driving.
By Jim Brightly, F358406
Technical Editor
February 2006

It’s a bright and breezy morning. You’re heading north on Interstate 15, leaving the Los Angeles basin behind and looking forward to spending the first night on the road in Las Vegas. You’re doing 65 mph across the open desert, and you’re fighting gusting side winds. You constantly are trying to anticipate the next motorhome movement, quickly twisting the steering wheel to compensate for the wind, but all you’re really doing is playing catch-up “” and you’re barely able to keep the coach in your lane.

How can you correct this condition? How can you have your original motorhome back again? It definitely was never intended to drive like a sports car and it’ll never corner like a Jaguar, but it used to be two to three times easier and more enjoyable to drive than it is now. Can its handling be improved?

Absolutely. With a few qualifications “” mainly its weight “” virtually every motorhome can get its groove back. If your coach is within its gross vehicle weight rating (GVWR) and, more specifically, within its gross axle weight ratings (GAWRs), and is not too old to be supported with repair parts, its ride and handling can be returned to its showroom quality.

There are so many different kinds of coaches, chassis designs, and suspensions that Family Motor Coaching magazine could never cover them all in one article. However, using a 1998 General Motors P-30 chassis (built the year before Workhorse purchased GM’s chassis division) as an example, I will demonstrate what can be accomplished without just throwing money at the problems. You can then transfer that knowledge to your particular chassis. If you are unable to perform the repair tasks yourself, this information should prove helpful as you discuss your coach’s problems with a technician.

As you begin, you’ll want to perform one modification at a time. You may end up, as I did, changing out almost everything, but you don’t want to do that at the outset. You should approach the project one step at a time, because each repair may be the last one you’ll need to perform to achieve the desired results.

Test Drive
With that in mind, the first task I performed “” which is a good idea for anyone concerned with the handling and drivability of his or her coach “” was a baseline test drive. A word of warning, though: if you’ve been “chasing” your chassis’ steering for quite a while, you likely have become accustomed to its road manners and will correct for them automatically. So, approach this test drive with a jaundiced eye. Try to perform the evaluation as a technician who’s not familiar with your coach’s characteristics, being very critical when identifying its idiosyncrasies. After each step in the forthcoming sequence of repairs, repeat the test drive. This will determine just how far you need to go or at what point you’re comfortable stopping.

My test loop covered almost 125 miles on Interstate 40, a brief portion of historic U.S. Route 66, a bit of city driving, in and out of fuel station driveways, and some open-desert two-lane roadways. In other words, nearly every type of driving you’ll likely encounter in a motorhome. It included three different states, with flat road surfaces and highly crowned country roads.

On the initial test drive, I found that the coach swayed around curves, constantly pulled to the low side on the crowned surfaces, responded to every zephyr, and porpoised over dips. It also wallowed over driveways like a slow boat with a following sea, thumped over every seam and expansion joint in the freeway, and seemed very slow responding to movement of the steering wheel. I want to make note here that even though the chassis was 7 years old, it had less than 10,000 miles on the odometer. The coach had been stored in an Arizona barn for most of its existence. Years of sitting in the desert heat and weather extremes and lack of proper maintenance had taken their toll on the various components, both moving and sealed. Luckily, there are many new products to improve older P-30 chassis “” from heavier antisway bars to more efficient shock absorbers.

Tires
Of the seven tires on the coach (including a spare), five were original equipment; the two front tires had been replaced. If you’ve shopped around for tires, you know that all tire manufacturers agree on two things “” their tires are the best, and you should replace any motorhome tires that are more than 6 years old. If you’re running on tires older than six years, you’re driving on pins and needles, and a flat tire could punch a hole in your travel plans at any time. My first chassis change was to buy new tires.

I chose the Goodyear G670 RV 225/70R19.5 load range F tire, an all-position tire that has been designed specifically for type A motorhomes. The design of this tire differs from tires used on standard regional service usage vehicles (delivery vans, etc.), which require high mileage without much regard for ride.

The development of the G670 tire, however, focused on improvements in ride, handling, and vibration “” critical attributes for motorhomers who spend many hours on the highway and consider comfort a more important attribute than extended mileage. Most motorhome tires will succumb to old age long before they wear out. According to Goodyear officials, the tire also has a durable casing that provides improved fuel economy, and its specific rubber compounds enhance traction and improve tread wear for RV service. The tread pattern is said to produce lower heat, improved toughness, and reduced squirm for better handling, while the circumferential groove pattern and increased notches and sipes improve traction on wet or dry roads.

Using Goodyear’s inflation table and the coach’s weight, it was determined that the tires could be safely operated at less pressure than the recommended 95 psi maximum.

With the tires mounted, balanced, and properly pressurized, it was back to the 125-mile test loop. The first thing I noticed was the decreased noise level in the coach. I wish I’d had a decibel meter to provide specific numbers to demonstrate the improvement, but all I can give is my personal observation. No more dish rattling, pan pounding, or glass clinking. The tires produced a softer, more comfortable ride over the expansion joints and less vibration on other road surfaces. The first upgrade produced a definite improvement.

Shock Absorbers
The next project was to install new Bilstein shock absorbers. In my opinion, whenever you mount new tires on your coach, you also should consider replacing the shock absorbers, or at least have them checked by a qualified technician. Poorly operating shocks can drastically shorten the life of your motorhome’s tires by allowing them to skip and bounce over the road surfaces. Even though your tires will more than likely need to be replaced because of age before they wear out, you’ll still want to give them as many miles as possible until they’re switched out.

On a car, it’s relatively easy to check the shocks’ ability to absorb the jouncing and bouncing; you can push down hard on a bumper and watch the car bounce up and down “” it should return to normal ride attitude in one to one-and-a-half rebounds. If it takes more than that, the shocks need to be replaced. But it’s not that easy to perform a similar test on a motorhome, since the weight, the springs, and/or the air bags won’t allow you to bounce the vehicle. However, you can get a strong indication of faulty shocks if the coach wallows over driveways and porpoises over hill and dale. To make certain, you must remove the shocks. After the shock is removed, if you can slide its piston rod in and out by hand, it needs to be replaced.

Secondly, unless just one shock out of the group is broken and/or leaking, and the remaining shocks test okay, replace all the shock absorbers at the same time. There is a strong theory that one bad shock, like one bad battery, can bring down all the rest more quickly. Plan on replacing them all, not just one at a time.

I chose gas-charged Bilstein shocks for a couple of reasons: their lifetime warranty and because many motorhome manufacturers mount Bilstein shock absorbers as original equipment. According to Bilstein, their motorhome shock is not a generic heavy-duty shock with ultra-stiff valves and unpleasant ride characteristics. It’s a shock that’s designed for specific motorhome applications, which provides the coach with a safe, precise, and comfortable ride.

Normally, changing a shock is merely a matter of removing two nuts, discarding the old shock, positioning the new shock, and tightening the two nuts to the specified torque. That’s why I’ve always changed my own shocks instead of paying someone else to do the task. However, the installation was not quite so easy with this particular chassis.

There’s a legend “” perhaps urban, perhaps not “” that you shouldn’t buy a car made on a Friday, especially on Friday afternoon. If the lack of alignment on all four shock mounts on this chassis is any indication, this probably was the last chassis built on the GM assembly line before construction was switched to Workhorse “” and it probably was built on the last Friday of the month.

On all four corners, the lower shock mounts had almost no relation to the upper mounts, except that they were below them. In the front, the U-shaped lower mounts welded to the lower A-arms were totally misaligned with the upper mounts. This misalignment and the force needed to compress the gas-pressurized Bilsteins created some mounting problems. On the rear, I had to enlist the assistance of another person and two pry bars to align the lower bolt holes.

On the front, I used a motorcycle tie strap with a ratchet to compress the shock. I bolted the bottom loosely, lowered the coach’s wheel and A-arm assembly as much as possible, allowed the shock to expand until its length aligned to the upper bolt with its hole in the frame, and forced the bolt into the hole. Using a ratchet and socket, I drew in the shoulder of the shock to its proper position. I then torqued the upper mount’s nut and tightened the nut on the lower mounting bolt.

If I had more time and a welder at my disposal, I would have removed the two lower mounts from the front A-arms and repositioned them correctly, but that’s a job for another time.

Remember that any time you crawl under the coach, make absolutely certain that it is fully supported safely, and wear safety glasses. If your coach is older, always use rust cleaner on all the nuts and bolts a few hours before starting any project.

Once the shocks were in place, it was back to the test loop. Now we’re getting somewhere! No more wallowing over the fueling station driveways and porpoising in the dips or over the hills. Even though the coach still swayed a bit around the curves “” especially on highly crowned two-lane desert roads “” it felt much better and gave me an improved sense of control. I was able to increase my comfortable driving speed over the entire test loop approximately 5 to 7 mph.

Antisway Bars
The next problem was how to eliminate the side-to-side sway. On a 1998 P-30 it’s easy “” change out the original-equipment front antisway bar. For this I conferred with an ipd Inc. technician, who told me that when the chassis was built by General Motors, the size (diameter) of the antisway bar was computed using automobile and light truck weight ratios. (ipd recently was sold to Roadmaster Inc. and now operates as RSS, Roadmaster Suspension Solutions.) Fairly recently, however, it was discovered that these ratios are inadequate for motorhome chassis. In other words, with the height, width, and weight of motorhome chassis, larger-diameter bars can be used without causing undue stress and possible damage to the chassis components. Therefore, the ipd antisway bar for the P-30 chassis is 1-5/8 inches in diameter, which replaces the original 1-1/4-inch bar At the same time, I replaced the dried-out and hardened rubber bushings on the rear bar with new neoprene bushings from ipd.

Is installing a new antisway bar difficult? No. But it is normally a two-person job, only because the component is big, awkward, and heavy. Since all my neighbors and friends were traveling by the time I was able to replace the antisway bar, I used a short length of wire in the bar’s center to suspend it in place during its removal. I used the same wire to suspend the new bar (its ends were resting on the ground), and I was then able to hold the ends in place while I secured the brackets and bushings. Using the supplied bushing compound, I quickly replaced the rear antisway bar’s bushings one side at a time. (Watch where you touch when applying the bushing compound; it will stick to anything and everything and stretches like Silly String.)

Once the antisway bar was installed it was time for another test drive. Even before reaching the test loop, I knew the project was coming together. While each individual component improved the coach’s ride and handling, the new antisway bar and stiffer bushings on the rear antisway bar kind of tied the whole project all together. Side-to-side sway was gone. The swaying caused when passing big rigs in a stiff side wind was also almost completely eliminated, and the average comfortable speed around the loop improved by 3 to 5 mph.

Steering Stabilizer
At this time I thought that I had only one more item to go: the steering stabilizer. Blue Ox was the choice here. Initially, I wanted to install the electronically programmable stabilizer, but I discovered it was available only on the wider-stance P-30 chassis or later chassis from Workhorse. If you have a chassis that’s compatible with the programmable stabilizer, you should explore the possibility of having it installed. When fighting a steady side wind or steeply sloping road surface, you actually can program the stabilizer to automatically correct for this situation and relieve the stress on your arms and shoulders.

At this point I had reached the summit of my mechanical skills. I wasn’t comfortable installing and adjusting the Blue Ox stabilizer myself, so I took it to a local RV shop for installation and a front-end alignment.

One more pass around the 125-mile test loop. After all these new parts were installed, I still had some rut follow and slow steering response “” albeit greatly reduced from the stock setup “” so I drove the motorhome to Grants Pass, Oregon, for some final testing and fine-tuning at Henderson’s Line-up, Brake & RV Inc.

Final Fine-Tuning
During the Henderson road performance assessment (RPA) “” a much shorter test route than my 125-mile loop “” performed by John Henderson (shop foreman, head of company research and development, and brother of company president Robert), it was discovered that several original-equipment components were malfunctioning. The hydroboost pump and brake master cylinder were leaking, and the power steering pump was providing insufficient assist pressure at low rpm. These problems combined to make it feel as though I didn’t have power steering below 1,200 rpm, and the brake pedal would depress almost all the way to the floor during hard stopping. These items would definitely need to be replaced, but there were still other issues related to the steering and suspension. (By the way: Robert Henderson is working on setting up a nationwide network of approved RPA centers, so if you’re having handling problems, give Henderson’s a call and they may be able to direct you to a center fairly close to home.)

After weighing each front wheel and each set of rear duals separately, and determining that the coach’s weights were well below its GVWR and GAWR (and, front and rear, both side weights were within 100 pounds of each other “” can’t get much better than that), the air pressure was set at 75 psi in all six tires, which is the proper pressure for the weights involved. With John driving and me observing, we performed the RPA. John made appropriate notes on the RPA form that Henderson’s completes for each customer’s coach, which then remains in the coach after the repairs are completed.

On the RPA report, John determined that:

• The original-equipment front coil springs with air bags inside had collapsed from stock height nearly 2 inches, even with the air bags fully inflated.
• The drag link was bad.
• There was excessive play in both bell cranks. It was determined later that the bushings had worn badly even with the low mileage on the chassis.
• The coach had a slight pull to the left, which was determined to be caused by the Blue Ox steering stabilizer being out of adjustment from the original installation.
• All wheel alignment specifications were outside GM parameters, even though the motorhome had been professionally aligned just a few thousand miles earlier.

A detailed discussion of the RPA followed, after which I approved the following repairs to be made:

1. Replace the drag link.
2. Replace both bell cranks with SuperSteer aircraft-grade replacements.
3. Replace the front coil springs with SuperSteer custom-fitted coil springs.
4. Realign both axles.
5. Install a rear track bar.
6. And, of course, replace the hydroboost pump, power steering pump, and master cylinder.

As normal wear occurs, minute problems that start at the working end of the steering, such as the wheel bearings, tie-rod ends, gearbox, bell cranks, etc., are increased many times before they reach the control end of the system (the steering wheel). Each tiny problem multiplies until you’re constantly chasing control in the driver’s seat. By that, I mean you’re continually playing catch-up with the coach’s reactions with the steering wheel. This deterioration in the steering can occur so slowly that you may never realize things are going wrong until an uninvolved expert takes the wheel during the RPA. Once the new parts are installed, you’ll find during the follow-up assessment that there is now a world of difference in the driving.

The first components replaced were the coil springs. Original-equipment P-30 coil springs are 7/8-inch diameter, while the new SuperSteer springs are either 15/16-inch or 1-inch, depending upon application, and do not include air bags. Upper and lower A-arms have casted grooves or pockets to properly locate or “time” the coils. SuperSteer coil springs are shot-peened, compression-tested, and powder-coated for a long and stable life. Each SuperSteer coil spring is tested at an 11-inch height for the amount of weight it will support, and then it is marked with that weight. This enables Henderson’s to match springs to each other and to utilize the proper set of springs to support the actual axle weight after weighing a coach. (Be aware, however, that heavy-duty coil springs do not change the GAWR, because that weight rating is made up of all the front suspension components, including the tires, the wheels, the hubs, and the A-arms.)

Next up was the installation of the two bell cranks and the drag link between the steering gearbox and left-hand bell crank. If you’re watching a technician perform this task, make sure the tie-rod ends are greased before their installation. On a truck chassis, the steering gearbox is positioned where the bell crank is located on a motorhome. Both SuperSteer bell cranks have the same part number, the difference being that there are four mounting bolts on the driver’s side and three bolts on the passenger side (there is less torque stress on the passenger side mount).

SuperSteer bell cranks are far superior to the original-equipment bell cranks on the GM P-30 chassis. They’re built with an aircraft-grade chro-moly steel shaft and Timken tapered roller bearings. Original-equipment bell crank bearings use bushings that can wear rapidly, even when properly lubricated. (Remember, this chassis had less than 10,000 miles on the odometer, and both original-equipment bell crank shafts could be visibly moved within their bushings.)

This particular motorhome, a 25-foot type A, didn’t really need a rear track bar, since track bars work most effectively on longer coaches, especially those with an extended rear overhang. But since I tow an 18-foot transporter trailer with a vehicle on board, and I wanted to prevent any possible rear leaf spring realignment or improper flexing in the future, I decided a SuperSteer rear track bar was needed. At the same time, the rear bump stops were dropped down 2 inches (this distance depends on the spacing between the axle and the frame). Dropping the bump stop “fools” the suspension into thinking it’s leaning more than it is. This better controls side sway in curves by the bump stop actually “resting” against the leaf spring. (On some chassis it may be necessary to cut and relocate portions of the exhaust system’s tailpipe to clear the track bar.) In addition, make sure the full weight of the coach is on the suspension when the track bar is installed. If not, the bar may be installed incorrectly and be put in a bind when the full weight is rested on the suspension.

A final wheel alignment, headlight readjustment (the new coil springs raised the front bumper 2 inches, necessitating the readjustment), and follow-up RPA, and the coach was ready for the road. What a difference! It tracked straight and true. I actually could relax behind the wheel and enjoy the ride home to Arizona. I continually found myself trying to decide whether to whistle or smile “” I ended up doing both.

Here are several notes about the project and on suspension problem remedies in general:

1. Don’t forget to use a torque wrench on all the nuts and bolts involved in this project. Each item’s manufacturer lists the proper torque settings for its product.

2. On some longer and heavier coaches, it could be helpful to install quad shocks in the front (two on each wheel). In this scenario, both Bilstein and Koni shocks are used in conjunction with each other, because the Bilstein controls rebound slightly better on the upward push and the Koni have slightly more control on the downward pull. This type of combination can greatly improve the steering and handling of larger motorhomes. (Henderson’s can suggest which size coaches this will benefit.)

3. Workhorse W20, W22, and W24 chassis have virtually the same components available as the P-30 and P-32 chassis, and you can expect the same driving and handling improvements on those chassis as illustrated in this article. The actual mounting brackets and specific details may vary, and the components may be larger and more heavy-duty, but the actions and reactions will be the same.

4. If you’ve been “chasing” your chassis’ steering for quite a while, it may take several hundred miles to retrain your steering reflexes. Relax, and you’ll find that your normal driving reflexes will return more quickly.

5. Alcoa aluminum wheels, especially on the shorter chassis (they were not used in this project) also may greatly improve ride and handling because of their lower unsprung weight.

6. Interestingly, while I was at Henderson’s I met a couple from Culver City, California, in a fairly new 34-foot gasoline motorhome who were sent there by their coach’s manufacturer to correct their coach’s steering and handling problems. None of the shops in Southern California could correct their problems, but Henderson’s did.

7. Henderson’s Line-Up, Brake, & RV Inc. is an approved dealer for Workhorse, Spartan, Blue Ox, Safe-T-Plus, Interstate Batteries, and Banks Power, and is a member of several trade associations.

Glossary

Air Bags “” P-30 chassis are equipped with heavy-duty air bags inside the front coil springs. Air pressure can be used to adjust ride firmness.

Alignment “” All axles on a coach must be aligned properly, not just the front wheels. Misalignment can require the driver to compensate and continually turn the wheels in the front to keep the vehicle going down the road straight.

Antisway bar “” More commonly called “sway bars,” antisway bars are attached to the coach’s frame and rear axle and the front A-arms via bushings made of rubber or neoprene. A standard formula, which is based on the coach’s weight, is used to determine the size (diameter) of the bar. Using the unsprung weight of the axle assemblies, the antisway bars minimize the side-to-side body sway caused by road surfaces, side winds, and cornering.

Bell crank “” On a P-30 chassis there are two bell cranks, one mounted to each frame rail. Because of the width of the front steering track (tire to tire), steering would be very haphazard were it not for the bell cranks. Bell cranks change the movement direction (parallel to the frame rails) of the Pitman arm and drag link to a movement perpendicular to the frame rails. They also stiffen and stabilize the tie-rods to minimize or eliminate flex in the tie-rods and independent side-to-side movement of the two front tires.

Bump steer “” When the coach reacts to hard bumps by changing direction. In severe cases, bump steer can be frightening.

Bump stops “” Rubber bumpers that protect the steel frame from being damaged if struck by the cast-iron differential (rear axle) or A-arms (front).

Camber “” The inward and outward lean of the tire at the top. Positive camber is when the tires lean outward.

Caster “” Determined by the location of the wheel in relation to the axle on which it is mounted and aids in a vehicle’s directional stability. When the lower part of the axle is ahead of the top, it’s called positive caster. Positive caster, a very important angle, assists in returning the steering to center.

Dog tracking “” Occurs when the rear wheels of the vehicle do not follow or line up with the front wheels. This is another result of misalignment.

Drag link “” Provides the connection between the Pitman arm and the left bell crank.

Gross axle weight rating (GAWR) “” The maximum allowable weight each axle assembly is designed to carry, as measured at the tires, therefore including the weight of the axle assembly itself.

Gross vehicle weight rating (GVWR) “” The maximum allowable weight of the fully loaded vehicle, including liquids, passengers, cargo, and the tongue weight of any towed vehicle.

Pitman arm “” Connects the steering gearbox to the drag line and is made from cast iron.

Porpoising “” Uncontrolled fore-and-aft bouncing after traversing railroad crossings or dips and bumps in the roadway. This is usually caused by worn or broken shock absorbers.

Pull “” When a vehicle drifts to one side of the road or another and the driver must continually compensate. External to the vehicle, pull can be caused by side winds and/or excessive road crown.

RPA “” Road performance assessment, a term developed by Henderson’s Line-Up, Brake & RV Inc., is a thorough diagnostic road test by a Henderson’s technician. The RPA is based upon the coach owner’s complaints or driving experience, which is given to the service manager.

Rut tracking “” When the coach follows the grooves worn in the road (often created by heavily loaded semi-trucks, especially in hot weather areas) or ridges that are created when an asphalt surface meets a concrete surface, and it is difficult to correct or change the path of the coach.

Shock absorbers “” These components absorb road shock before it can be transmitted to the vehicle and keep the tires in contact with the road surface. Without shock absorbers, the tires would just bounce and bounce, wearing more rapidly, and road surfaces would be more aggressively transmitted to the vehicle’s occupants. As the shock is compressed or extended during its task, fluid is forced through a piston in the shock. As this fluid flows back and forth, it is forced through a valve. The size (diameter) of this valve “” plus some other internal components “” determines the stiffness of the shock. Fluid being forced through this valve can become aerated (cavitation) and the air bubbles could cause the shock to lose its integrity. Several manufacturers use nitrogen gas to pressurize their shocks and reduce this aeration. Contrary to what many people think, the shock absorber does not support any of the coach’s weight.

Springs “” The P-30 chassis uses multileaf rear springs and coil front springs with air bags inside.

Steering play “” Indicates an excessive amount of “play” in the steering wheel “” failure to respond immediately when the driver moves the steering wheel to the right or left.

Steering stabilizer “” Provides additional centering torque to return the steering to straight-ahead after cornering and absorbs side-to-side road shocks to the steering in much the same manner as a shock absorber controls vertical movement.

Sway “” The coach leans or rocks in a side-to-side motion during quick lane changes, cornering, in side winds, or entering driveways.

Tie-rods “” Rods that connect the two front wheels together, control the steering, and are adjusted to maintain toe-in alignment.

Toe “” The main tire angle, which is toe-in (the forward edges of the tires are adjusted closer to each other than the rear edges). If this angle is off, it will cause tread wear faster than anything else, because it causes the road surface to scrub off rubber.

Track bar “” This item is attached to the coach’s frame and the rear axle and works to more precisely align the rear axle perpendicular to the chassis frame. It is mounted parallel with the axle and perpendicular to the rear leaf springs. A track bar is especially effective with motorhomes that have longer-than-average rear overhangs and on older, high-mileage coaches where the rear springs have become weak and allow the rear axle to torque out of alignment while reacting with the road surface and drivetrain demands. The track bar can negate these misalignments on the motorhome.

Unsprung weight “” Consists of all weight on the outside of the springs including lower A-arms, axles, axle housing, brake assemblies, wheels, and tires. The unsprung weight is controlled by the shock absorbers.

Contact List
Bilstein Shock Absorbers, C5209
14102 Stowe Drive
Poway, CA 92064
(800) 537-1085
www.bilstein.com

Blue Ox Inc., C2903
P.O. Box P
Pender, NE 68047
(888) 425-5382
www.blueox.us

Goodyear Tire & Rubber Co., C9158
1144 E. Market St.
Akron, OH 44316
(330) 796-2121
www.goodyear.com/rv

Henderson’s Line-Up, Brake & RV Inc. (and SuperSteer products), C5009
417 S.W. Henderson Lane
Grants Pass, OR 97527
(800) 245-8309
www.hendersonslineup.com

Roadmaster Suspension Solutions, C4034 (formerly ipd Inc., C2986)
5602 N.E. Skyport Way
Portland, OR 97218
(800) 669-9690
www.roadmasterinc.com/rss_sway_bars.html

Workhorse Custom Chassis Inc., C8291
850 Stephenson Highway
Suite 510
Troy, MI 48084
(877) 294-6773
www.workhorse.com