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| − | 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.
| + | 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. |
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| − | 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.
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| − | 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.
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| − | 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.
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| − | ==Cavalier Rack and Pinion install==
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| − | 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.
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| − | 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.
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| − | [[Image:manual_rack.jpg|frame|none|Manual rack pictured.]]
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| − | 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.
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| − | 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.
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| − | In retrospect, the steering is so easy a manual rack may be preferable to some.
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| − | ==Mounting the rack==
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| − | 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.
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| − | 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.
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| − | [[Image:drivers_side_fixed_mount.jpg|frame|none|Drivers side.]]
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| − | [[Image:passenger_side_mount.jpg|frame|none|Passenger side.]]
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| − | 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.
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| − | 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.
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| − | [[Image:Dr_side_bracket_hanging.jpg|frame|none|Drivers side bracket gusseted both ways.]]
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| − | 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.
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| − | [[Image:pass_side_bracket_welded_in.jpg|frame|none|Passenger side bracket gusseted front to back only.]]
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| − | 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.
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| − | 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.
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| | ==Turning radius== | | ==Turning radius== |
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