Swapping to rack and pinion steering
From Crankshaft Coalition Wiki
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==Steering linkage== | ==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 | + | 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 1-1/2" you may need to fabricate the centering bearing holder. |
| − | We took this opportunity to convert to a tilt column. Late | + | |
| − | There are almost too many options here to discuss. | + | ===Tilt column=== |
| + | We took this opportunity to convert to a tilt column. Late '70s to early '80s GM vans have a nice clean column, 2 inch diameter. No ignition lock tumbler assembly (it was on the dash) so it looks 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 market columns are available from Flaming River, etc.). | ||
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| + | ==Other design considerations== | ||
| + | A few general observations: The straighter and more direct you can make your steering linkage, the better. There is an excellent article on steering linkage- [[Steering shaft assemblies from junkyard parts]], or you can order up the pieces from Borgeson et. al. | ||
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| + | Different columns have different output shafts, so check carefully before ordering. There are almost too many options here to discuss. | ||
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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. | 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]] | + | [[Image:New_linkage.jpg|border|left|400px|]] <br style="clear:both"/> |
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| + | ==Power assisted steering== | ||
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| + | ===steering pump=== | ||
| + | If you are going to install a power assist unit, there are a few more issues. The power steering pump for the Cavalier rack is designed to fit a transverse mounted front wheel drive 4-cylinder or V6; no attempt was made to fit it to an early '80s SBC engine for obvious reasons. Instead, an original type pump was used that fit the original brackets. Piece of cake. The rack will have a tube and O-ring style connector for the metric high pressure hose. There are adapters available that convert the metric fitting to a flare fitting, similar to the early model pump. | ||
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| + | ===Hoses=== | ||
| + | Because the pump and the rack sector end up so close together, you may want custom hoses made. | ||
| + | Once everything 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 settings will help keep it centered. | ||
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| + | ===Steering "feel"=== | ||
| + | If it is simply too “light”, “soft”, or “over responsive”, you may want to address the flow and pressure differentials between RB and R&P. | ||
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| + | ====Pressure relief valving==== | ||
| + | Most older GM pumps will have a pressure rating as high as 1350 psi. The '82–'94 Chevy S10 has the lowest rating at around 1100 psi. The Cavalier rack was designed for a pressure of ~1,000 psi. You can adjust the pressure with a simple shim kit from Borgeson. | ||
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| + | 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 the desired pressures. | ||
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| + | Basically, adding shims reduces the pressure on the spring, allowing the bypass to open sooner and recirculate the fluid, rather than force it to the rack- thus making the pressure lower. The kit allows for reduction to about 750 psi, suitable for a Mustang II rack, which allows you to get well below the normal range for a Cavalier rack. Reduce the sensitivity to what suits you. 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. | ||
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| + | ====Flow rate==== | ||
| + | The second adjustment available is flow rate. The flow rate is 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 20% smaller). I could not find a fitting with the smaller orifice to fit the older pump (newer GM pumps use metric fittings). Perhaps if you start with a later S10 pump, metric might not be an issue- but this needs to be confirmed first. As an alternative, it was fairly simple to weld shut the orifice in the original fitting and re-drill it to 1/8". | ||
| − | + | Note: The experts contend that reducing the pressure will reduce the amount of assist provided, which can be reduced below factory specs to give it a heavier feel. The system is designed with a variable ratio, that is, it is designed to give more assist the further you turn the wheel, like for parking maneuvers, etc. You can't harm it by providing less than factory pressure. The flow rate seems to be more of a factor in the sensitivity over center, where you really don't need any assist. In any event, both changes were noticeable from the original test drive. | |
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| − | [[Image:Pump_fitting.jpg | + | {| |
| + | |[[Image:Pump_fitting.jpg|thumb|370px|center|High pressure hose fitting from the back of the power steering pump]] | ||
| + | |[[Image:Orifice_hole2.jpg|thumb|310px|center|Weld or braze, then re-drill the center hole to change flow rate, not the side hole]] | ||
| + | |} | ||
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[[Category:Steering]] | [[Category:Steering]] | ||
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