Swapping to rack and pinion steering
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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. | 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 | + | 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. | 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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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. | 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 | + | [[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. | 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 | + | [[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. | 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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==Power steering pump== | ==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. | 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, | + | 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:Pump_fitting.jpg]] Fitting in the back of the pump - high pressure hose connects here. | ||
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