Power Steering 110 - Dirt Sports UniversityPosted in How To: Body Chassis on August 4, 2014
Welcome to the 29th class in Dirt Sports University Series and the 10th on power steering. During our last class, we reviewed issues that seem to pose ongoing problems for some vehicles. Then, we looked at three cap designs for the power-steering oil reservoir. Next, we examined proper oil line fittings and hose sizes to ensure the correct oil flow in your system. The last segment revolved around how to check the power-steering system oil flow and pressure in your vehicle with the engine running. That’s where we left off. From there, we will see about connecting the steering system to your hands with the steering wheel, along with the connections in between. With this class, we will wrap up the University Series on Power Steering, and will focus on a new subject in the future. Let’s see what the last class in this subject has to offer.
Calibrating the System:
We ran short on time during the last class and breezed through the last section, called “Checking The System.” It’s vitally important to use a flow meter and pressure gauge to ensure you match the performance of your power-steering system while your vehicle is in use. Essentially, you are calibrating your entire system to the specified oil flow and pressure of the power-steering pump, and the remainder of the system matches it. If the numbers don’t match, the overall steering performance degrades and typically runs much hotter oil temperatures than necessary. Other issues may also pop up when least expected.
You can only determine how your vehicle’s power-steering system is performing by actually checking it. Do not assume it’s all OK because the engine starts and you can drive the vehicle away. Work with a top-notch steering company to get the right flow and pressure check. If you do not own the proper gauges yourself, see if the company can provide this checkout and system inspection for you. It only takes one oil line with a flap of rubber from a misassembled fitting to cause a problem.
Connecting the Steering:
Congratulations, you made it through the past nine classes on steering! At this point, you should have a pretty good idea how to make the entire system work correctly. All that is left is to connect the steering system to the steering wheel. Although, this might seem simple, this step often involves more than one would think. Hopefully, you have accumulated all your vehicle steering system components from a well-thought-out source. You can’t run down to the corner off-road store and buy a bunch of stuff, hoping it all works together as a matched system. Now focus on putting together the proper components in the way of U-joints for the steering column and applying the proper mechanics to make the steering wheel rotate smoothly.
Packaging the Shaft:
Take a look at the picture of this steering shaft that has to wrap its way around the engine headers. Try to use a heat shield to reflect that blistering heat away from the U-joint. It’s rarely an easy straight line to connect the steering box to the steering wheel in a front engine vehicle. Generally, any rear or mid engine buggy has ease of packaging, giving the steering shaft room to spare, and just about any front engine vehicle will be a challenge. A steering gear box like a Saginaw, which is mounted on the left frame rail, usually isn’t as much of a problem. Compare that to a steering rack where the input pinion shaft is right under the center of the front of the engine. However, both can test your skills at getting it all to fit.
The Shaft Path:
The shortest distance between two objects is a straight line, but the last time I can remember this being the case with a steering shaft was quite a long time ago. Back in the 1980s and earlier, it was possible to build a SCORE Class 8 truck and use one straight piece of tubing to connect the steering wheel to the Saginaw steering box mounted on the outside of the stock frame. We even used the stock rag joint coupler at the steering box. Times have changed. The trucks have gained more wheel travel and use custom frames with rack-and-pinion steering boxes mounted down below the front of the engine. This presents a real problem. Although, it is usually not noticed, cared about, or addressed until the last portion of fabrication during the vehicle build. Suddenly, you have a problem. Check out the picture of the steering U-joint right next to the header tube with the bronze bushing shaft mount and to understand some of the issues at hand. Packaging the steering shaft assembly in many vehicles takes careful thought.
Builders rarely incorporate a slip shaft into the steering shaft, but many times, it is not needed. However, many vehicles would be better off if they used one. Often, there is a little flex between the truck cab where the steering wheel is mounted and the steering gear box mounted on the frame. This vehicle flex can cause bind in the steering shaft assembly. The heat around the engine headers can cause the steel tubing to grow slightly in length while it is roasted by the exhaust headers. Howe Performance makes a nice solution. Look at the picture with the U-joints and splined shaft with slip collars. It is part of a complete telescoping splined steering shaft kit, which includes a nice rubber bellowed boot to keep the grease in and clean, and the dirt out, while sliding nicely. This collapsible section also provides additional safety during a front-end collision. It presents a solid object. You could otherwise have the steering wheel and shaft end up in your chest. Something to consider for drivers into safety.
Several companies sell quality steering U-joints like the ones pictured here. Avoid the small Apex joints used in small aircraft controls. They have a much smaller pivoting joint size, are weaker than the larger cross pin U-joints, and wear out quickly. Sweet, Borgenson, and Flaming River are all good brands and look about the same. Most use rebuildable-style U-joints that come in kits. They come in several smooth bore inside diameters to fit varying sizes of steering shaft tubing and several spline diameters with different spline counts. It’s critical to ensure the different splined shafts in the system receive the correct mating spline.
Size & Tooth Count:
When shopping for steering U-joints or spline couplers, use great care to select the proper diameter and the correct spline diameter and spline count. This might seem simple, but surprisingly, the wrong sizes can slip together and appear to be correct. On two occasions, I worked on vehicles that drove perfectly for quite a while. In both cases, as the vehicle was being pushed around the shop with a helper pulling firmly on the steering wheel to maneuver a tight corner and a popping noise came from the steering shaft. This left the steering wheel in a weird position. A close inspection found the Saginaw servo input shaft spline count was slightly different than the spine in the U-joint that was slipped onto it. The finer spline in the U-joint seemed to fit perfectly onto the slightly courser splined shaft of the servo. We had assumed it was correct and the vehicles left the shop. I would hate to imagine the scene if this pop and slip had happened while the vehicle was travelling at high speeds on a mountain road with a cliff.
Steering Shaft Size:
Yes, size matters. During a build, the steering shaft tubing material, diameter, and wall thickness is not the place to scrimp to save money or weight. The connection between your hands grabbing the steering wheel all the way down the connection of the steering shaft assembly at the steering box is demands all your attention. This steering shaft points your vehicle in a particular direction, allowing you to control it as all that big horsepower propels it, possibly at high speeds. Without that control, things go bad in a hurry. Generally, a minimum tubing size of 0.75x0.095 inches works well. The steering shaft can act like a torsion bar. If the tubing size is too small, you can end up with a springy feel in the steering wheel.
Steering Joint Angles:
Most steering shafts need at least two U-joints, as it is almost impossible to get from the steering box to the steering wheel without them. To get around an obstacle, you may need more than two U-joints, as well as some sort of frame mount or pillow block along part of the steering shaft to prevent flopping around. Often, the steering servo is mounted to the roll cage in the steering shaft assembly to provide a solid mounting point for the steering shafts. Check the manufacturer-provided information on your chosen U-joints to determine the angle limits of that specific joint. If you exceed the angle limits, you end up with a slight to severe bind in the steering shaft assembly.
Constant velocity steering joints can prevent the steering shaft bind associated with extreme U-joint angles. Unfortunately, the CV joint size might cause a packaging issue. Forward thinking can help you avoid complicated steering shaft systems. Put as much thought into the steering as you would maximizing your wheel travel to minimize problems.
Modern race trucks do have obstacles that the steering shaft must weave around. In many cases, the U-joint is used in extreme angles to get where it needs to go and the steering shaft typically ends up with two bind spots 180 degrees apart. This is caused by a whip action in the steering shaft as the U-joint crosses rotate at the same time, which slightly shortens and lengthens the shaft length. Some folks leave the U-joint’s spline-side screw loose to reduce the binding feel. This is only a Band Aid to the problem that causes premature spline wear and slop in the spline coupling.
U-joint manufacturers recommend varying fixes. One manufacturer suggests: Clock the U-joint end yoke caps on the shaft 90 degrees apart from each other like in the picture of the high U-joints angle here. This is called re-phasing the U-joints. According to one brand, the dimension of two or three spline clicks of rotation on the shaft between the U-joints should fix it. A third brand advises a 15- to 30-degree offset in phasing. You might need to do this same fix for multiple steering shaft sections outside the U-joint angle parameters set by the manufacturer. I advise starting with tack welding the steering shaft and U-joint assemblies together as a test in the shop to see where it binds and re-clock the shaft ends from there. Do good welds and keep the U-joints cool with a wet rag when welding the steering shaft.
I was involved in several vehicle projects that required an offset or 90-degree gearbox as the simplest means of routing the steering shaft around the engine and connecting it to the steering rack. One prerunner truck required two separate 90-degree gearboxes to connect the steering rack because we had to fit the shaft around a big-block Chevy engine. When using a gearbox that has two internal gears, the steering shaft coming out of the angle box rotates in the opposite direction. This can be a problem if you have no way to adapt. In the pre-runner steering shaft, the counter-rotation issue canceled itself out with the use of two separate boxes.
You might think any steering wheel can be used in an off-road vehicle. Well, think again. I’ve seen many types of steering wheels bent too easily. I’ve also seen the outer ring broken off the center spokes lots of time. Many off roaders leave their shoulder straps a bit loose and rely on the steering wheel to hold their upper-body weight while pounding through the bumps, jumps, and whoops. Always use a center pad on the wheel for safety and to help prevent your body from being injured. The outer ring and spokes of the wheel will bend in a crash, but the center hub area does not move much. Keep in mind your steering wheel lifecycle, just like you would other key vehicle components, and get a new steering wheel regularly.
This concludes our power-steering classes. We hope the information and knowledge was helpful and informative. Please investigate the correct and safe way to apply our lessons, procedures, and ideas on any project you plan to undertake.
If you have missed previous classes, track down a friend with a trusty subscription to Dirt Sports. You can purchase back issues from www.DirtSportsNation.com. While you’re at it, setup your own personal subscription, which can come right to your mailbox or over the internet.
We’ve taught valuable lessons on power steering, shocks, suspension, and other topics here at Dirt Sports University. Take the time to learn as much as you can about the off-road world. We can only assume you love it as much as we do. Thank you for allowing us into your life. We look forward to our next subject.
Professor Tom Morris
Dirt Sports University and School of Hard Knocks