Editing Swapping to rack and pinion steering

{{youcanedit}} The process of "swapping" to rack and pinion steering is not a simple task. Increased bump steer, reduced turning radius and altered Ackerman are just a few of the bad conditions that will be created by swapping to a non-compatible rack. There are many design factors that must be taken into account before this swap can be done effectively. The relationship between the inner tie rod pivots of the intended rack and the upper and lower A-arm inner pivots is very important to control bump steer. The amount of rack travel during steer is also important to keep the turning radius consistent with the vehicle's design. A decreased turning radius makes the vehicle hard to maneuver at low speeds and too much steer will cause clearance issues with suspension and body components. This article from Longacre Racing gives some insight into the requirements: [http://www.longacreracing.com/articles/art.asp?ARTID=13 Bump Steer]. This "swap" generally turns into a monster when a non-compatible rack is used to "improve" a suspension designed around a recirculating ball steering box. The diagram at the end of the article gives specific design considerations that are VERY important when doing any steering work. Trying to retrofit a stock rack to a current suspension, especially when the design constraints are not considered, is an exercise in futility and will only produce an ill-handling, dangerous vehicle. ==Cavalier Rack and Pinion install== This information specifically refers to an installation on a 41 Pontiac, but it is very similar on any early car with Upper and Lower Control Arm front suspension. The “Cavalier” rack comes on 88 – 92 Cavaliers, but is also used on Lemans, Sunbird, and Grand Am, some Mitsubishis, Opels and others. The main feature is the center take off provision. The center take off allows for the long tie rods necessary to eliminate bump steer. Note that this rack also comes in a “sport” version that has a quicker ratio. Apparently it works well on Corvettes, but is too quick for many older cars. It is available in both a manual and power version, with the manual more prevalent on Sunbirds than Cavaliers. [[Image:manual_rack.jpg|frame|none|Manual rack pictured.]] For this installation we used a power rack for two reasons. First, there was a concern that a manual Rack and Pinion (R&P)may be as hard to steer as the original manual Recirculating Ball (RB), especially with the weight (3500 pounds), big tires (225/75/15 radials) and the positive caster introduced with the suspension upgrade just completed. Second, the manual rack is approximately 28 1/2 inches long (mounting positions) while the power rack is about 5 inches longer; making frame mounts on both sides an easy install. The manual rack would require a substantial offset bracket on the passenger side. In retrospect, the steering is so easy a manual rack may be preferable to some. ==Mounting the rack== There are several decisions to be made on mounting location. Ideally, if the rack can be mounted in the exact location of the existing center link, and the new tie rods are the same length as the originals, bump steer will be eliminated or at least a duplicate of the original setup. The driver’s side mount is a fixed location on the rack and provides support up/down, front/back and side to side. The passenger’s side mount can be slid side to side and that mount only provides up/down and front/back stability. This conveniently allows you to move that mount to suit your frame width. [[Image:drivers_side_fixed_mount.jpg|frame|none|Drivers side.]] [[Image:passenger_side_mount.jpg|frame|none|Passenger side.]] Many aftermarket mounting kits are designed to mount below the left frame rail. This restricts the up/down choices and extends the end of the rack into the left wheel well. We chose to place our bracket on the inside of left frame rail. It barely protrudes into the wheel well and placed the rack within ½ inch of being centered on the frame. [[Image:Dr_side_bracket_hanging.jpg|frame|none|Drivers side bracket gusseted both ways.]] We fabricated the Rack mounts out of 12 inch pieces of 1 inch square tubing (11 gauge) which fits perfectly into the rubber mounting brackets on the rack. We predrilled the brackets and mounted the rack to them, then clamped the brackets to the inside of the frame rails. This allowed us to move the rack up/down and front/back as we determined the exact location we wanted. Once properly set, we welded them to the frame and added both front/back and side/side gussets to eliminate any movement of the rack on the drivers side. There will be a minimum amount of movement on the passenger’s side to allow for frame flex, but that movement is within the rubber mounts, not the bracket. [[Image:pass_side_bracket_welded_in.jpg|frame|none|Passenger side bracket gusseted front to back only.]] The exact location of the rack will vary depending on engine location, headers and other modifications. One of the first things to consider is turning radius. We need to digress here and discuss bump steer. There is an excellent article on the Longacre site http://www.longacreracing.com/articles/art.asp?ARTID=13 that explains bump steer and how to eliminate it. In a simple explanation; The lower ball joint, (connected to the lower control arm) and the outer tie rod (connected to the rack, center link, etc) are moving up and down through suspension travel together. They are connected by the steering arm. If the ball joint and outer tie rod do not follow the same arc (because one is longer than the other, or their inner pivots are in different planes) the steering arm will move in or out to compensate. This movement creates toe in or toe out on its own (bump steer). Bump steer must be understood, so it can be eliminated in the design/set up stage. ==Turning radius== Many cars suffer from poor turning radius after an R&P install. There are 2 basic reasons. Either the rack was placed too far left and interferes with the wheel, or no adjustment was made to the steering arms. On a typical RB type steering box the pitman arm has a “throw” of 7 inches, side to side. It is usually connected to steering arms effectively measuring 7 inches long. (The 7 inches is measured from the center of the steering arm mount, where the king pin or ball joint pivots the spindle, to the center of the outer tie rod where the steering pivots.) Typical racks (Cavalier) have 6 inches of throw and originally connected to the upper strut in a manner that represents about 5 ½ inches from center of the strut to the center of the tie rod. Connecting the rack to the original arms causes a loss of nearly 20% of steering angle. It is strongly recommended that this be dealt with before installing the rack. Changes to the steering arm can affect the steering geometry and introduce bump steer. So, if you are going to address this issue, (some people don’t) do it before the rack install. There are two acceptable methods of dealing with this issue. The preferred method is to replace the steering arms with shorter ones. On the 41 Pontiac upgrade covered in the wiki “37 - 57 Buick Olds Pont suspension upgrade” we were able to replace the original 65-70 Chevy steering arms with a set from a 64 Chevelle. The Chevelle arms are 6 inches long (using our measuring guidelines, not the actual arm length) and even though that is a front steer car, we were able to flip them over for our use. [[Image:Chevelle_arm_vs_chevy_arm.jpg|frame|none|Chevy 7inch/chevelle 6 inch.]] There is a difference in mount width between the BOP arms and Chevy arms, so they won’t work on BOP without the Chevy spindle upgrade. If you are unable to find shorter arms for your application, bending the originals is the next option. You will find mixed opinions on this issue. Some will insist that heating and bending steering arms compromises their structural integrity and should never be done. Others warn you to be sure they are forged and not cast arms. Bending forged arms is OK, bending cast is not. Others will swear that rodders have been bending arms for decades, with no failures. Please research this issue to your own satisfaction, as we did not bend the arms on our car and make no representations on the safety aspect. On a buddy’s car, (1949 Ford) we did bend the arms, his call. By putting an S bend in the arms we effectively made them one inch shorter, pivot point to pivot point. This also made them one inch lower than the original position. To compensate for this change in geometry, the rack was 1 inch lower than the original center link. A correction could also be made by fabricating the center bracket with a 1 inch drop in the inner tie rod mounting points. However you address it, by doing it first you will have 3 fixed points to work with. Inner control arm pivot point, lower ball joint pivot point and outer tie rod pivot point. This leaves you with the front/back and up/down location of the inner tie rods to deal with. We mocked everything up in this fashion and then designed our rack takeoff mount (inner tie rod mount) to fit. Once the inner bracket was welded up and mounted to the rack we installed the tie rods and checked for bump steer. The final, minutest, adjustments were made by tapping the rack mounts on the frame with a hammer. Remember, at this point the rack was just clamped to the frame. When we found perfection, we tack welded the frame mounts, removed the complete rack assembly and welded the mounts and gussets in place. To understand how crucial the height location is, follow this mathematical extrapolation. A 1/8th inch difference in height of the rack, caused a 1/16 inch difference in the location of the tie rod arc, (at full compression or rebound) compared to the ball joint arc. 1/16 of an inch at the tie rod (6 inches from the spindle center) becomes almost 3/16ths at the rear of the tire (typical 30 inch tire). This causes a reciprocal movement the other direction at the front of the tire. Now we are dealing with 5/16ths. The other wheel is duplicating this, so the toe in, or out, changes 10/16ths, or 5/8 of an inch during suspension travel, acceleration or braking, while you are trying to drive in a straight line. Height is the most crucial dimension in locating your inner tie rods. Duplicating your lower control arm length with your tie rod length is not nearly as critical. In fact many original setups were unequal length. The trick is to make the tie rod as long, or longer, than the lower control arm. When the tie rod is longer, it will have a flatter arc than the control arm. The flatter arc means the tie rod will move outside the ball joint at the extremes of suspension travel and create additional toe in. Up to ¼ inch will not be noticeable in handling or tire wear. If the tie rod is shorter than the control arm, the opposite will happen. ¼ inch of toe out will put you all over the road. On the 41 Pontiac the lower control arms are 18 inches pivot to pivot. We used the original Cavalier tie rods, which measured 21 inches pivot to pivot. [[Image:Center_take_off_pics.jpg|frame|none|rack with original tie rods/center take off..]] Our bump steer (toe in) changes less than ¼ inch at full suspension travel, and less than 1/8 inch in normal operating range. I’ve been told additional toe in is beneficial during hard acceleration or hard braking, as it tends to stabilize the front end. ==Inner bracket/inner tie rod mount== One thing not covered yet, is the angle of the mount for your rack. We chose to rotate the rack until the steering sector was pointed at the end of our steering column. This made a fairly straight on connection for the intermediate steering column link, with no extreme angle to deal with. It also made the connecting link less than 11 inches long, including the U joints, so no supporting heim joint was necessary. It did however, require the center bracket to be built with an angle mount. On the first bracket we built (we made the mistake of fabricating the bracket before we changed the steering arms) we had the mounts offset from the center of the rack. A 1 inch plate is necessary to move the bracket out beyond the bellows. Then we ground out a portion of a 1 inch square tube and welded it at an angle to the 1 inch plate. [[Image:Offset_bracket_side_view.jpg|frame|none|End view of a bracket with height and angle offset from original mounting position.]] [[Image:Offset_center_bracket.jpg|frame|none|Front view of the offset bracket.]] In the final install, we needed the mounts to be nearly in plane with the original mounting holes. This changed the design completely. In the offset bracket, the 1 inch plate can be mounted to the rack with the original bolts (12mm 1.25 {fine} thread bolts) in the second version, longer bolts were required. Rather than weld the flat bar at an angle, we chose to drill the mounting holes at an angle and then weld in some grade 8 12mm bolts for the cavalier inner mount to fasten too. [[Image:Straight_thru_bracket.jpg|frame|none|Nearly straight through, but at an adjusted angle. Note the mounts adjust for the rack being about 1/2 inch off center in the car.]] Rather than use the original Cavalier tie rods, you may decide to build the tie rods out of tubing with adjustable tie rods on each end. You will need a tapered reamer for this operation. [[Image:Power_rack_install_rear_view.jpg]] Power rack installed, rear view [[Image:Rack_front_view.jpg]] Power rack installed front view [[Image:Original_cavalier_inner_tie_rods.jpg]] Install using original Cavalier inner tie rods and fabricated bracket ==Steering linkage.== The original steering (37-57 BOP) consists of a manual box and the steering sector is a solid shaft all the way to the steering wheel. If you shorten the original column, be sure to relocate the end centering bearing in the shortened portion. If you cut off an early BOP column, there will be no centering bearing to use. Since the original column outer diameter is only 1 ½ inches, I believe you will have to fabricate the centering bearing holder. We took this opportunity to convert to a tilt column. Late 70’s to early 80’s GM vans have a nice clean column, 2 inch diameter. No key (it was on the dash) and look right at home in most old cars. This column has self canceling turn signals and in our case, (automatic trans) a lighted gear shift indicator and neutral safety switch. We were lucky enough to find a tilt column, but they are getting rare. (After markets always available from Flaming River etc.). A few general observations. The straighter and more direct you can make your steering linkage, the better. There is an excellent article here on steering linkage - Steering shaft assemblies from junkyard parts – or you can order up the pieces from Borgeson et. al. Different columns have different output shafts, so check carefully before ordering. There are almost too many options here to discuss. It would be prudent to look at the steering linkage hookup, before deciding on the final rack location. You may want to align the steering sector on the rack specifically to clear headers, etc. Multiple intermediate steering links can be used, just follow the manufacturers guidelines on maximum angles, center supports, joint alignment, etc. [[Image:New_linkage.jpg]] ==Power steering pump== If you are going to install a power assist unit, there are still a few more issues. The power pump for the Cavalier rack is designed to fit a cross mounted front drive 4 or v6, didn’t even try to make it fit my early 80’s SBC. Just went with an original pump that fit the original brackets. Piece of cake. The Rack will have a tube and O ring style connector for the high pressure hose (metric). There are adapters available that convert that to an old fashioned flare fitting, just like the early model pump. Because the pump and the rack sector end up so close together, you may want custom hoses made. Once every thing is hooked up and functioning, you can test drive your creation. It may not feel just right. A rack is more sensitive than a RB box. Higher caster will help keep it centered. If it is simply to “light” “soft” or “over responsive” you may want to address the flow and pressure differentials between RB and R&P. Most older GM pumps will have a pressure rating as high as 1350 pounds. 82 – 94 S10’s have the lowest at around 1100. The Cavalier rack was designed for a pressure of +/- 1,000 PSI. You can address this with a simple shim kit from Borgeson. The pressure relief valve is located behind the high pressure output fitting on the back of the pump. You may need a small magnet to pull it out of the recess. The shim kit comes with a tool to help with removing the end nut, a new O ring for the outer fitting, and several shims with a guide on how many shims to use to attain certain pressures. Basically, additional shims reduce the pressure on the spring, allowing the bypass to open sooner and recirculate the fluid, rather than force it to the rack. The kit allows for reduction to about 750 pounds, suitable for a mustang rack, which allows you to get well below the normal range for a Cavalier rack. Reduce the sensitivity to your own liking. In most cases, the pressure reduction valve can be removed and replaced with the pump in the car. Yes, you have to drain and refill the pump each time, but that’s pretty minor. The second adjustment available is flow rate. Determined by the size of the hole in the high pressure fitting (the one you took out to get to the pressure relief valve) on the back of the pump. The earlier pumps had an output hole of 5/32. The cavalier pump has an output hole of 1/8, (Approximately 40% less.) I could not find a fitting with the smaller orifice to fit the older pump. (Newer GMs are metric fittings.) Perhaps if you start with a later S10 pump, metric will not be an issue? As an alternative, it was fairly simple to weld shut the orifice in the original fitting and re-drill it to 1/8th inch. The experts contend; reducing the pressure will reduce the amount of assist provided, which can be reduced below factory specs to give it a more heavy feel. The system is designed to give more assist the further you turn the wheel, (parking for example). You can't harm it by providing less than factory pressue. The flow rate seems to be more of a factor in the sensitivity over center, where you really don't need any assist. Both changes were noticeable from the original test drive. [[Image:Pump_fitting.jpg]] Fitting in the back of the pump - high pressure hose connects here. [[Image:Orifice_hole.jpg]] weld up and redrill the center hole, not the side hole. [[Category:Steering]] {{youcanedit}}

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