I won't go into a discussion of the merits/arguments for and against this mod except to point people to this discussion: http://www.miataforum.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=27;t=000109

I fitted a 1996 rack to my 1990 RHD car. It's a big change in the character of the car. Gone is the need to muscle it into a corner, it now requires a very delicate fingertip touch. Gone too is the load through the wheel under hard cornering, which seems to have reduced the feedback to the driver (though it would appear to now be just whispering subtly rather than shouting at me). The faster rack is great though, very quick into tight corners. Parking is light and easy; my partner loves it.

The installation can be gleaned from the Enthusiasts Manual (Grainger) but it requires jumping between at least 4 different sections. This article is largely a summary of what is written there, however I strongly recommend you also reference that book. There are additional instructions regarding the airbag, but my Australian model car does not have one. Essentially, there is a requirement to not turn the steering wheel when the rack is removed, or you'll need to reset the clock spring.

Parts required:
· PS rack.
· PS pump and tension adjuster mechanism.
· Pump mounting bracket (cast) and hardware.
· Fluid cooling pipe (bare metal loop)
· Fluid reservoir.
· Connecting hoses (hopefully already attached to the parts).
· Mounting hardware (hopefully supplied with the other parts as a complete kit)
· PS belt (I used a Bosch, Part Number 4PK940, on a 1.6 car with AC).
· PS fluid (or ATF, Dexron II or III) - about 1 quart/litre (capacity is 0.85 l).

Tools required:
· Jack, jack stands, wheel brace
· Tape measure
· #2 Phillips head screwdriver
· Sockets (metric) - 10, 12, 14, 17, 21mm plus a short extension and a flex/universal coupling.
· Spanners (wrenches) - 14mm, 22mm (open ended)
· Torque Wrench
· Small pliers
· Hammer
· Funnel

Before installation:
· Start by laying out all the parts and seeing how they connect together. Ensure all hose fittings are clean of dirt.
· The pump mounts to the side of the engine block (where, if you have AC, the tensioner pulley currently is).
· The PS rack replaces the manual one and mounts in the same fashion.
· The cooling tube (a loop of metal tubing) mounts in front of the radiator, to the rear face of the front crossmember.
· The reservoir mounts to the chassis, between the PS pump and the left headlight motor.
· Ensure you have all the connecting hoses and mounting hardware; if not, now is the time to get them. The main fluid path is as follows:
· Reservoir outlet (bottom of reservoir) connects to pump inlet (top of pump) with a rubber hose.
· Pump outlet (high pressure fitting) connects to the rack inlet with a special hose (attached to rack).
· Rack outlet pipe connects to the cooling pipe inlet (longer end) with a rubber hose.
· Cooling pipe outlet (shorter end) connects to the reservoir return port (side of reservoir) with (yet another!) short rubber hose.
Hopefully the hoses are already attached to the associated parts, otherwise study the diagram from the Enthusiasts Manual.

· If the new rack includes a universal joint on the input, there should be a paint mark on its pinch collar. This paint mark lines up with a groove in the input shaft. Mine didn't have the universal.
· If your new rack does not include a universal joint on the input shaft, I suggest the following steps:
· On the input shaft, there is a black plastic collar with a radial ridge on it. Turn the rack (with a rag on the shaft for grip) fully to one side, and (with a marker pen), mark on the rack housing where this ridge ends up.
· Turn the rack fully the other way (2.8 turns) and repeat.
· Estimate (or better, measure) the midpoint between these two marks, and make another mark here.
· Turn the rack ~1.4 turns back from its endstop and align the ridge with your centre mark. The rack is now centred.
· Pick a straight groove in the tyre tread, and (with the steering wheel straight) measure the distance to the same groove on the opposite tyre, as close as possible to the front face of the tread. This will help you set the toe alignment roughly until you can get to a suspension shop. Remember this number for later. It's easier to do this job with the undertray removed.

Engine bay:
Let's start with the easy stuff.
· Remove the rubber section of the air intake tube (immediately after the air flow meter) - Loosen the two hose clamps with a Phillips head, and yank it off.
· If you have AC, loosen the screw on the front of the tensioner pulley, and fully slacken off the tensioner. Remove the old AC belt.
· Remove the three 14mm screws holding the tensioner bracket and remove it.
· Attach the PS fluid reservoir with two 10mm screws.
· Attach the PS pump bracket to the engine block (three 14mm screws). Torque to 50Nm.
· Fit the steel sleeve into the large bore on the pump bracket. Push the long bolt through the front hole, and run the nut all the way on to it. With the hammer, hit the head of the bolt to drift the sleeve into the bore - until there is enough room for the pump to fit in. Remove the nut and bolt.
· Lift the pump into place and run the long bolt through from the rear (through the sleeve). Attach the nut (through the slot in the pump pulley) but do not tighten yet.
· Screw the adjuster mechanism link to the bracket. Do not tighten yet. Set the tensioner mechanism to fully slack.
· Fit the belt over the PS pulley (and AC pulley). Feed it on to the crank pulley carefully. If necessary, use the 21mm socket on the crank nose to slowly turn the engine over and pull the belt onto the pulley.
· Adjust the belt tensioner appropriately (8-9mm belt deflection at 10kg force). Tighten all adjuster screws. Tighten the long pump mounting bolt. It might help to cough the engine over (ie flick the starter on momentarily) to access the nut through the pump pulley.
· Attach the hose from the reservoir outlet to the pump inlet. Fit hose clips using pliers.
· There should be an unused connector cable tied to the top of the thermostat - this plugs in to a pin on top of the PS pump.

Under the car:
· First, loosen the front wheel nuts, and raise the car onto the jack stands. Remove the front wheels.
· Remove the plastic undertray (lots of 10mm screws and nuts).

Install the cooling pipe:
· The ends of the pipe feed through the left swaybar mounting bracket (this is tight and tricky). Be careful not to get dirt in the ends (tape or cap the ends if necessary). Feed the loop up in front of the radiator. This may require some gentle bending or forcing of the pipe, it's reasonably flexible, but don't kink it! I loosened off the black plastic radiator intake trim, but didn't have to remove it entirely.
· Fasten the cooling pipe in place with four 10mm screws (two on the front crossmember, two on the bottom of the left chassis rail). From the engine bay, plug the reservoir return tube into the shorter end of the cooling pipe.

Remove the manual steering rack:
· At the end of the tie rod, remove the split pin from the castellated nut. Apply WD40 or penetrating oil to the threads. Remove the castle nut (17mm), invert it, and run it back on until the nut is level with the end of the thread.
· Hit the nut with a hammer (downward blow) to break the balljoint taper free. Remove the nut and disconnect the balljoint from the upright.
· Repeat the procedure on the other balljoint.
· Remove the (12mm) pinch screw on the rack input shaft universal joint.
· Remove the four 14mm screws mounting the rack in place. Lift the rack out and slide it off the steering column spline.

Install the power steering rack:
· Lift the new rack into place, guiding the high pressure line up past the swaybar. Ensuring the rack and steering wheel are both centred, guide the rack on to the steering column splines.
· Install the four 14mm rack mounting screws. Fit the tie rod ball joints to the uprights and attach the castle nuts.
· Check the hubs are pointing straight ahead and the steering wheel is centred. If not, remove the rack mounting bolts, pull the rack off the shaft, and realign the splines until it is straight.
· Tighten the 14mm screws (46-59Nm). The socket drive universal is needed to access the back screws.
· Strike the balljoints from below with a hammer to seat the tapers. Tighten the nuts to 29-44Nm and fit a split pin (ideally new ones, but they can be reused once or twice)
· Install and tighten the (12mm) pinch screw on the steering column.
· Install the (14mm?) screw fastening the pressure pipe bracket to the chassis.
· Re-fit the plastic undertray (10mm screws and nuts)

Nearly there!

Back under the hood:
· Attach the high pressure line to the pump (22mm open spanner). Torque spec is 31-47Nm but you might have to estimate it as a socket won't fit the nut... Attach the line to the bracket on the pump (12mm?).
· Connect the rack outlet pipe to the long end of the cooling pipe. This one's hidden under an AC line down beside the engine. Pliers access for the hose clip is tricky but it's possible.
· Reinstall the air intake rubber tube.

Fill and bleed the PS fluid:
· With the funnel to help, top up the PS reservoir.
· With the engine off, turn the steering wheel from lock to lock several times; top up the reservoir if the fluid drops.
· Start the engine and repeat the above step at idle, until the fluid level no longer drops or froths.
· Top up the fluid level to the top mark on the dipstick/filler cap. Don't overfill or fluid will gush out when it warms up and expands!

Alignment:
· Refit the front wheels and lower the car. Tighten wheel nuts.
· Ensure the steering wheel is straight.
· Measure your toe as before (hope you wrote that number down somewhere!). Assuming that your alignment was good beforehand, try to replicate that measurement.
· Adjust the tie rods as necessary by loosening the 17mm lock nut and turning the shaft (12mm spanner across the flats). One full turn on the rod changes toe by about 7mm.
· As a rough guide, if you eyeball past the outer edges of the tyre to the outer edge of the rear tyre, all three points should line up. This will give a small amount of toe in (the rear track width is fractionally more than the front).
· Lock the 17mm nuts.

You're done. Enjoy! Drive carefully at first, as your car will feel quite different, especially if your alignment is out. The faster steering rack and lighter effort will turn in to corners much more quickly. Readjust your toe (equally and in an opposite direction on each side) if the steering wheel is not straight - ideally you should have a professional alignment as soon as possible.