The Ford F53 Chassis – Taming the Beast:

If you own a recent model gas-powered class A motorhome (a “gasser”), more than likely it is built on a Ford F53 chassis with the V10 engine. This chassis and engine have undergone several minor changes from model year to model year but overall the major components have remained the same. The good news is that the V10 power plant and F53 chassis have decent reputations for reliability and long service life. The bad news is that it is – and rides – like a truck.

Many first time motorhome owners are only familiar with how their passenger car or SUV handles and rides down the highway. When they first get behind the wheel of a motorhome it drives a little differently and has higher noise levels but it doesn’t seem so bad on the newly paved road in front of the dealership. Then comes the big road trip. Several states have the reputation of not repaving major highways in decades and the potholes to prove it. The crosswinds in the Midwest seem stronger than anyone ever remembered before. At the end of the day on a long trip everything is rearranged in every cabinet, anything not strapped down is somewhere else, and the driver and passengers feel like they have been riding roller coasters all day.

What happened on the road trip? Take a look underneath your class A motorhome. The first thing you will notice is that the coach body is supported by heavy duty truck leaf springs, not by cushy coil springs that are typical for a car. All the suspension components are bigger and heavier compared to a passenger car. What can be done to improve the ride and the handling of your motorhome? This is the subject for the rest of this article: “Taming the Beast”.

The information on modifications presented below is organized from the easiest and little or no cost progressing in complexity and expense. Many of the simpler modifications can be executed by someone with basic tools and equipment. As usual, your results may vary with the individual modifications to your chassis. Most of these changes I have performed on motorhomes I have owned over the years and have achieved positive results. I will also explain the expected results of each modification and why your individual results may not be the same on a particular coach.

Tires

Tires are the first line of defense between the pavement and the chassis. They probably take the most abuse and impact of any suspension component but are often the most ignored. People don’t tend to think of tires as part of the chassis suspension but they play key roles in how the motorhome rides.

Tire pressure is the simplest and often overlooked parameter on most rigs on the road today. Many motorhome owners are becoming smart and installing tire pressure monitoring systems (TPMS). It is noteworthy that federal law requires TPMS systems on all newly manufactured cars but not on larger vehicles such as a motorhome. A TPMS system will not only keep track of individual tire pressures, it can indicate potentially more serious problems such as a leaking tire, or a tire that is getting excessively hot due to a wheel bearing failure or dragging brake. Proper tire pressure is specified and should always be measured when the tires are cold, and even a few miles of driving can warm the tires significantly. It is not unusual to observe a 20 psi increase in tire pressure from sitting cold in the morning to afternoon driving on a hot interstate highway.

What is the proper tire pressure for your model of motorhome? The best starting place is to find the sticker supplied by the manufacturer located somewhere around the driver’s seat. This will indicate various weights and capacities of the motorhome and the recommended tire pressures. If you get your motorhome weighed with your typical traveling load, then go to your tire manufacturers web site and download their tire pressure versus loading charts. In almost all cases the recommended cold pressure is not the maximum pressure listed on the sidewall of the tire.

Tire pressure makes a significant difference in how your motorhome rides. Unlike a passenger car, over inflating RV tires will result in a harsh, bumpy ride. In the past I over inflated tires by a few psi thinking this will compensate for any natural slow leaking over time and the “old school” thought that over inflation will make your tires wear less and last longer. When I did some experimenting at different tire pressures I was very much surprised on how much tire inflation affected the ride. This makes sense when you consider that a tire actually absorbs much of the shock of a pothole or rough pavement. An over inflated tire is hard and unyielding. Even over inflating by 10 psi can change the way the coach feels on a rough road.

This brings up one final comment about tire inflation. From my experience by default, many RV dealers and tire shops will automatically inflate “truck” tires to 100 psi. I have spoken to RV dealers, tire shops, and truck depots over the years and verified this is the norm. While 100 psi inflation pressures are normal for a semi tractor-trailer, they are almost never the right inflation pressure for a gas motorhome. Even RV dealers, who should know better, have told me just put 100 psi in the tires and I should be OK.

After setting proper inflation, the next common issue with tires is balancing. Tire unbalance usually shows up as excessive “bouncing” or “vibration” on one corner or side of the motorhome at particular highway speeds. At low speeds the ride is fine, but at higher speeds there suddenly developes excessive vibration on one side and / or end of the rig. It can even smooth out again as speed is increased beyond a certain point. If you suspect tire balance is a problem, go to a trusted tire shop with high-speed balancing equipment. Make sure the shop has the proper equipment to handle large RV tire sizes, many smaller dealers only can take car tire sizes on their balancing equipment and cannot perform a true “high-speed” balance.

Tire balance can also change over the life of the tire. Tire balancing weights can come off or shift. I had an experience where I purchased new tires for an older motorhome and experienced vibrations at highway speeds on the front left wheel. I took the tire back to the dealer and they re-balanced the tire (most dealers will re-balance a new tire for no additional charge). The technician admitted the tire had not been balanced properly initially and was quite a bit off on the high speed balance machine. The bottom line is tire balance can affect the ride significantly at highway speeds and should be checked before digging into other suspension problems. A high-speed balance at a tire dealer is usually not expensive and many shops will not even charge for re-balancing if you purchased the tires there.

Alignment

The next subject that also involves tires is front end alignment. Alignment in its simplest form is how straight the tires point down the road. Ideally you should be able to take your hands off the steering wheel when traveling down a long, flat highway and the motorhome will continue forever on a straight line without pulling to one side or the other. In reality alignment is more complicated than this. The discussion in this article will be focused on the most common alignment problem that is called “toe”. A full alignment check also includes caster and camber but these parameters are usually not a problem on most vehicles unless it has a defect or has experienced severe frame stress as in the case of an accident, mishandling or frame modifications. The term “toe” in alignment refers to the slight angle of the front wheels pointing inward (toe in) or outward (toe out). On the rear-wheel drive F53 chassis, it is normal and specified by Ford to have a slight toe-in angle.

Misaligned toe can cause a variety of drivability issues and excessive tire wear. A strong indicator of bad alignment is to run your hand over the surfaces of the front tires. Is the inner or outer tread wearing more on one side than the other side? Do you feel ridges or “feathering” on the tread? If these are present it strongly indicates alignment could be off.

Errors in the toe setting may not be as obvious when driving the vehicle but can contribute to drivability problems. Excessive toe-out can make the vehicle seem to “wander” around the road and have poor cornering response. Excessive toe-in may not have many symptoms (other than excessive tire wear) but can seem to make the vehicle turn harder on sharp turns. It is interesting that the F53 and most other rear-wheel drive vehicles specify a slight (only 0.06 degrees) toe-in setting. This slight toe-in helps to firm up the steering and helps return and keep the wheels straight traveling down the highway. Excessive toe-in or toe-out will also cause your tires to scrub on the road since the outer treads of the tire are turning at a different rate than the inner treads. This causes the excessive wear and can negatively affect gas mileage since part of the tire is being “dragged” down the pavement in small but significant amounts.

Toe alignment can be checked at a shop with proper equipment or even checked at home. The first difficulty is finding a shop with proper equipment that can perform truck chassis alignments. Most local shops can only take cars and SUVs. My experience is that even many truck centers will turn away motorhomes. I have had managers come out and try to tell me they cannot take an RV due to “extra equipment and plumbing” which is more of an excuse than reality since a motorhome is designed to meet all federal regulations for sizes and weights and is no more unusual to work on the chassis than a delivery truck. The bottom line is to call ahead and talk with the manager or knowledgeable person about servicing your rig of X feet long and Y feet high. Their service bay, lifts, and alignment equipment need to be big enough to handle your motorhome. A last comment is that the motorhome should be loaded with its typical operating weight (including water and propane) when having the alignment checked.

You may be intrigued about checking toe alignment yourself at home. This can be done if you have a level, even flat surface (not dirt) where you can park your motorhome and be able to move it back and forth a few feet. The basic procedure is to use an accurate measuring device such as a good tape measure or rigid pole and measure the difference between the same tread location on the back of the front tires versus the distance on the front of the tires. For the F53 chassis this difference is nominally 1/32″ +/- approximately 1/8″ toe-in. Please note this measurement (the toe) is different depending on the chassis year, weight rating, and tire size. Make sure you look up the specifications for your particular chassis before making a determination on your setting. However this simple measurement is a good indication if your alignment is significantly off and needs resetting. A +1/2″ (approximately 1 degree) toe-in definitely needs servicing and will cause excessive tire wear if not reset. There are many instructions and videos on the web with more details on how to make this measurement and even how to adjust the toe setting yourself. Note if the toe-in is off by an excessive amount this could signal a more serious problem with the chassis that may require additional analysis and adjustments (caster and camber may also need adjusting). As a part of yearly maintenance on my motorhome, I check the toe setting for any large changes that may indicate a problem.

Sway

Excessive sway is a common complaint with motorhome owners that is not usually experienced on passenger cars. This is not surprising since motorhomes are tall, top-heavy vehicles. Sway is the leaning when going around a corner or the leaning on a sharp-curved exit ramp. It is also the tipping motion that is felt when a large truck passes on either side at a much higher speed that you are traveling. The F53 includes devices called “sway bars” or “stabilizer bars” at the front and rear axles which are steel bars (these actually serve as torsion springs) that basically connect from the left to right sides of the chassis. These sway bars provide a counteracting force to the frame when the vehicle starts to lean to the left or right. This helps the frame not to lean excessively to one side or the other.

It is interesting to note that a vehicle would be still fully operational with all the sway bars removed. If you only drove straight down a road with no crosswind (or semi trucks) sway control is not needed. Some rugged vehicles disconnect or remove sway bars for off road operation. Before starting any modifications to the sway bars I strongly recommend that you check all the brackets, especially the rear axle on the F53. On several model years, the rear sway bar brackets are notorious for coming loose on the F53. This seems to have been a problem with the bolts not fully tightened at the factory and falling out. There are many reports of this issue on various RV forums. It only takes a few minutes underneath the motorhome to check these brackets.

The first and easiest modification to the sway bars on the F53 is commonly called the “cheap handling fix” or “CHF”. On the f53 chassis Ford provides a secondary set of holes on the front and rear sway bar brackets that results in a stiffer setting. This modification is very easy to perform with basic mechanic tools and can be done at home in about an hour. I will not get into the details here but there are many excellent guides with pictures and videos on the web linked on all major RV forums. This modification is totally reversible, will not cause extra suspension component wear, and is approved by Ford (it will not affect the vehicle warranty). There are many discussions on major RV forums with direct references from Ford that this is a standard acceptable modification, and not harmful to the vehicle which was a rumor with some earlier forum posts.

The question then comes up about the CHF modification is why Ford does not set the sway components initially to the stiffer setting at the factory. The reason is that Ford sells F53 chassis for many different applications, it is not just a motorhome chassis. On the highway you will no doubt see many small and medium-sized delivery trucks that are about the same size as your class A motorhome. Ford’s response is that they do not know what kind of application a particular chassis is going to end up in. A lighter truck application may perform just fine with the standard sway setting. A motorhome by the fact that it has near maximum weight on the chassis at all times is a heavily loaded vehicle.

For many people the CHF improves the F53 chassis sway to an acceptable level. Individual motorhomes do have different sway responses. A motorhome with 2 or more rooftop air conditioners and high level cabinets containing heavy items will be more top heavy and more prone to sway than a rig with only 1 air conditioner and minimal high level storage. Additional stiffening of the sway response involves adding aftermarket devices either in tandem or replacing the factory sway bars with more rigid components. Many people have found additional improvements with these units and again the RV forums can supply information on various manufacturers.

Steering Stabilizer

Steering stabilizers have become a popular aftermarket product among many class A owners. A steering stabilizer is a device that attaches to your steering linkage and provides dampening and additional resistance to turning. Most of these units are composed of a large spring with a shock absorber. A good steering stabilizer will help the steering to feel firmer, reduce the feeling of “sloppiness” thereby reducing over-steering, and help keep the wheels pointed straight down the road with uneven or grooved pavement. A steering stabilizer also helps to keep the wheel from jerking out of the driver’s grip when hitting a large pothole or running off the pavement. It can help to keep the vehicle stable when being passed by a large truck or in the case of strong crosswinds. From personal experience I have found that I have less driver fatigue at the end of a long day of driving.

Steering stabilizers are available from many aftermarket companies and can be installed with standard mechanic tools. Installation by a professional mechanic is straightforward and should only involve an hour or two at the most in labor. There are typically no modifications to the chassis and the stabilizer can be easily removed if the owner decides not to use it.

Shock Absorbers

Shock absorbers, or “shocks”, are another key component of the suspension system. Shock absorbers, as the name implies, dampen and dissipate the transient energy transmitted from your tires when hitting a pothole or  bump in the road. By smoothing out the sharp jolts from traveling at highway speeds the ride is more enjoyable to the occupants and there is less rearrangement of cargo!

On a truck chassis such as the F53 the primary suspension component connecting the axles to the frame are leaf springs. These are large steel bands that provide “give” when one or more wheels are higher or lower than the others. When hitting a pothole, the shock of the tire suddenly falling into the hole or jumping up on the other side of the hole is transmitted by the tires up through the axle, to the leaf springs, and then to the frame. The mass of the chassis frame and vehicle helps to ride through the pothole but there is still a large energy spike transmitted to the motorhome body. Shocks are located between the axles and the body and attempt to smooth out and absorb the sharp impacts transmitted through the leaf springs.

Shock absorbers also help to modify the low frequency movements of the vehicle. In the case of hard braking, the body of a vehicle will attempt to “bobble” or “porpoise” up and down when coming to a stop due to the energy storage/release in the springs. The low frequency response of the shocks will counteract this motion.

A vehicle can operate without shock absorbers, as may be the case with worn out or defective units. A shock absorber will almost certainly be bad if it is leaking fluid (oil) which indicates internal seals are blown. There is debate when to replace shocks on a motorhome from normal wear, some owners say to replace them at 30,000 miles while others claim their shocks are still effective at 100,000 miles. There is a great amount of variability of shock absorber life depending on the vehicle weight, how and where it is driven, the brand of the of the shocks, and even personal preference on how the rig should feel on the road.

One brand of shock which I have had good results with is the Koni FSD. “FSD” stands for “frequency selective damper” and Koni has a version designed especially for the F53 motorhome chassis. The FSD series has special internal valves that help to dampen out sharp impacts such as expansion joints more effectively than the factory supplied shocks on the F53 chassis. I can attest that these shocks do provide noticeable and significant improvements when driving over older highways with expansion joints and rough roads under construction.

Shock abosrbers are accessible and can be easily changed on the F53 chassis by do-it-yourself mechanics. However, you should be aware of large sized bolts and high torque ratings required for removing the old shocks and installing the new units. An impact wrench with suitable sized sockets is recommended before tackling this job.

Air Springs / Urethane Springs

The next category of modifications for the F53 chassis involves adding springs or replacing the stock leaf springs altogether. The new “springs” in this case are air springs (air bags similar to those found on diesel rigs) or urethane foam based springs. The intention for adding or replacing the stock leaf springs is to provide additional support and control over the suspension stiffness, leveling control, and/or ride comfort.

Many motorhome owners that purchase add-on springs are towing a trailer or car behind the RV. The extra weight on the back of the RV can cause the rear end to sag and the coach will no longer be level on a flat road. Air springs can provide additional support to level the vehicle.

True air springs or air bags are identical in function to their big cousins on large semi tractor-trailer trucks. Air pressure can be added or removed to provide more or less support from the air bag. The bags can be pumped up via a standard tire type Schrader valve and compressor, or more expensive installations include a permanently mounted on-board compressor with remote control on the dashboard. The driver in this case can adjust the ride height and stiffness going down the road. Urethane springs are similar to air bags in that they are permanently mounted in the same locations but are not adjustable. They are made of high-density urethane foam that resists compression. Urethane springs never deflate, do not need a compressor to inflate, and do not need maintenance.

While the addition of springs will level out a loaded motorhome, the ride improvement is variable. Many operators are happy with the improved handling performance and some improvements in road noise and pothole response (in this respect they provide a dampening effect similar to shock absorbers). From talking to owners and information on forums, increasing spring capacity can actually make the overall ride harsher due to adding the equivalent of more stiffness to the rig despite manufacturers claims to the contrary. It is good advice to read reviews from actual owners before investing in a particular product. The advantage of air bags is that they can be run at lower pressures when not towing to give a softer ride but can be pressurized when needed. Another solution offered by at least one aftermarket company is to replace the standard leaf springs on the F53 with lighter leaf springs and air bags. In this case some of the harshness of the stock leaf springs is removed and the air bags provide the rest of the support. Even other companies remove all the leaf springs completely and rely solely on air bag suspension.

Adding air springs is a more complex modification than the others mentioned so far. The installation usually involves drilling the chassis and raising the motorhome off the ground. In some cases brackets may need to be custom welded to the frame. If existing leaf springs are modified or removed, proper equipment is needed to handle the removal of suspension springs. Check the installation instructions carefully before attempting this at home or approaching a shop to perform this work.

Other Chassis Modifications

I will briefly mention that there are a few aftermarket companies offering what entails a complete overhaul of the existing F53 suspension. These are usually extensive modifications which involve cutting and welding to the existing chassis and removing and replacing most of the stock suspension components including the springs, sway bars, brackets, etc. A truck suspension service center may be able to perform these modifications or you may need to make a road trip to the aftermarket manufacturer’s facility. These types of modifications are generally not reversible. There are videos on the web that can take you through the modification process. These extensive modifications are not as common since they cost thousands of dollars and can be a significant percentage of the value of your RV. Owners at this point may decide to upgrade to a diesel pusher motorhome with full air bag suspension instead of investing significant costs to upgrade a gas chassis.

Final Comments

I hope the descriptions above help to explain the most common modifications that a motorhome owner can perform to improve the ride and handling of their F53 based rig. The modifications can range from free (or minimal cost of a couple hours labor for a mechanic) to thousands of dollars at a specialty aftermarket facility. On my current class A motorhome, I have added a steering stabilizer, Koni shocks, a tire pressure monitor system, wheel alignment and stiffer sway setting (CHF). All of the modifications I have listed are discussed in detail on various RV forums and there are numerous on-line videos available to watch. However, much of the information outside of forums that do not permit commercial manufacturers from posting are heavily biased toward a particular brand or product. I will add that I do not have any business interest in Koni, I have mentioned them by name since they are the only manufacturer at this time in my opinion that has an effective variable frequency dampening shock absorber customized for motorhomes.

When considering modifications to your F53 gas chassis take it one step at a time. No one wants to spend hundreds or thousands of dollars for little or no improvement. Make sure you understand what each suspension component does and does not do. For example, a steering stabilizer cannot dampen the thump-thump of expansion joints but it can help to minimize the steering wheel from being jerked out of your hands when going over an extreme expansion joint or pothole. Some producers of aftermarket products embellish claims of what their products can do.

I emphasize again to start from the simplest, and take one step at a time before jumping into major modifications. I have witnessed instances where motorhome owners start with changing shock absorbers and adding suspension springs without analyzing their tires and front end alignment. Changing shocks will not correct an out of balance tire. A poor steering coach with bad alignment will not be magically cured with a steering stabilizer. When I was researching shock absorbers on forums I saw approximately 9 out of 10 people praised Koni shocks for good to excellent improvements. What was up with the other owner that said there was absolutely no difference with the new shocks when so many others had great results? There was no mention and I suspect no checking of tire balance or pressure and front end alignment. These basic items as I emphasized previously can make a large impact on the drivability and comfort of the motorhome. Remember that many of these suspension components interact to large degrees and the end result will be no better than the weakest one.

Ford is a trademark of Ford Motor Company. Koni is a trademark of ITT Corporation.

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