Phasing In: Splined. Double-D, or DD
Combination U-Joint/ Vibration Reducer
Remember the first steering system you ever built? It probably consisted of a 2x4 and about five feet of rope. Chances are youre looking for something a little more sophisticated for your street rod. If youre lucky, youll have a straight shot from the column to the steering box and wont need more than a universal-joint at either end connected by a single shaft. According to the guys at Borgeson and Flaming River, that description makes up the vast majority of their customers cars. For others, where clearances are especially tight, you may have to take a slightly more roundabout route, using more U-joints and shafts at various angles.
For that reason, your steering system should be planned early into the project, right after the engine has been installed and the steering box or rack-and-pinion and steering column are in place. The most common steering obstacle is the exhaust header. Design these components together so that both can be built efficiently.
If your steering system requires three (or more) U-joints, start by positioning the middle U-joint somewhere near the center at close to its maximum angle, swiveling the components to find the fit that requires the least amount of angles and material while maintaining plenty of clearance. Use wooden dowels or PVC pipe to mock up the system. Once everything has been set up correctly, the pipe can be measured to determine the precise number and length of shafts needed.
The fail-proof performance of your steering system is critically important. Todays aftermarket components are manufactured to be as safe as possible. Take no short cuts and overbuild your system if necessary.
Universal joints, or U-joints, transmit rotary motion at an angle, allowing you to route the shafts around obstacles. As the angle increases, the strength of the joint decreases proportionately. U-joint strength is rated at a maximum angle by the manufacturer. Build your system with the least amount of angle that allows adequate clearance, and never exceed the angle at which the joint is rated, typically 30 to 35 degrees; if a greater angle is necessary, use more U-joints. Flaming River recommends 15 degrees as the optimum angle.
A double U-joint, made of three pieces instead of two, doubles the angle possible (Borgesons double joint is rated at 70 degrees, Flaming Rivers is 60). A double joint can also be used to put a jog or offset of about an inch anywhere in the column, as you can seen in the photo above. The use of a double joint requires a steering support.
Only needle-bearing U-joints should be used for street-car steering systems since the non-bearing types require frequent lubrication. Flaming River offers needle-bearing joints in steel with standard or polished nickel plating, or in extruded aluminum. The Borgeson needle-bearing joints are available in steel, polished stainless steel, or aluminum.
The forks of the U-joint yokes at each end of a shaft must be in the same position, or phased in. In other words, the joints at either end of a shaft must be positioned in line with each other. If not, binding and wear can result.
Steering shafts are either the spline type (a round shaft with splines at the end) or the DD or Double D type (with two flat surfaces on opposite sides of an otherwise round shaft). The advantages of a splined shaft are that it contains more material and is therefore stronger and it can be rotationally indexed more accurately than a DD shaft, which can only be flipped 180 degrees. The advantage of a DD shaft is the fact that it can be cut to fit; splined shafts cannot be cut more than perhaps an inch from either end because the splining does not run the full length of the column. The type you choose is dependent on the style of column and box or rack you are using. U-joints and couplers are offered with ends to accommodate all shaft types. Borgeson makes shafts in steel, stainless steel, or aluminum, while Flaming Rivers are steel or nickel-plated steel.
Some aftermarket companies offer telescoping or collapsible shafts to protect the driver in the event of a collision. The collapsible shaft moves in and out 6 inches or more on impact. A telescopic shaft is similar and can also be adjusted during installation or removal, although telescoping shafts are not recommended as an alternative to the correct length single-piece shaft.
Collapsible shafts are more of a concern when the angle from the box to the steering column to the driver is a direct line. In typical street-rod steering with an off center box, multiple U-joints, and a more vertical steering column, the system is more likely to fold in on itself at the joints, pulling the steering wheel away from the driver in the event of a collision.
Couplers The coupler is a connection used to extend the shaft coming out of the box or column. It can provide an additional 4-5 inches of clearance when neededperhaps if the box is too close to a crossmember to install a U-joint. Couplers are available splined all the way through or with splines or a DD in just one end; the other end is left with a smooth hole so the coupler can be welded to a non-splined round shaft. Couplers with integral vibration reducers are also available.
Any time your steering-shaft setup uses more than two U-joints, a double U-joint, or a vibration reducer, it must also include a support bearing. The support bearing bolts to the frame and holds the system stable to prevent binding or flexing. Add a support bearing for every U-joint over two that you usefor example, a three-U-joint system would need one support bearing, a four-joint system would need two, and so on. The support bearing can be located on either side of the center U-joint, but should be as near to the center as possible to provide maximum stability.
Also called vibration resistors, these components work essentially the same as rag joints but are smaller and more convenient. They use urethane or thermoplastic rubber bushings to damp road vibrations, reduce steering wheel shake, and extend component life.
Using a vibration reducer requires a support bearing, and if youll recall the rod test of the Model A roadster in our June issue, our complaint of too much steering play as the result of using a vibration reducer was due to the fact that a support bearing was not included. The reducer should be located between the bearing and the column to reduce any vibration transmitted from the frame through the bearing. The resistor should be installed as close to the U-joint as possible. Since it adds weight, installing it in the center of the shaft can cause flexing and binding. A vibration reducer/U-joint combination mounted at the end of the steering column is probably the best-performing, best-looking, and most economical way to go.