Mivec Owners Group

This is a popular conversion in the Miata community, and I've long been wanting to do this, so I have. My car is a gen 1, but the steps apply to most modern rack-and-pinion setups.

(For the original inspiration, see article here: http://www.flyinmiata.com/tech/depower.php?x=1)

This conversion is not about swapping the power rack and pinion assembly for a manual rack and pinion assembly. I have done that on my Del Sol, and was not satisfied with the increased lock-to-lock ratio of the manual rack, which in turn slowed down steering response. Rather, this conversion retains the power rack and pinion (and the quicker steering ratio) by modifying the internal mechanism of the power rack.

If you've seen my build thread (viewtopic.php?f=28&t=7362&p=60443#p60443), I had been running my car for a while with the power steering pump and lines removed, simply looping the lines through a small fluid reservoir to keep the rack lubricated. While this works fairly well, the rack is still pushing fluid around inside the housing and lines - increasing steering effort and clutter in the engine bay (lines, reservior). I wanted a clean setup like a true manual rack, without the need for fluid and lines to keep the rack lubricated.

The theory behind this mod goes like this. Inside a power steering assembly, there is a piston (a disc-shaped divider) attached to the rack. This piston moves left and right inside the housing, and separates the housing into left and right chambers. When there is more fluid pressure in the right side chamber (coming from the pump/lines), the piston is pushed to the left, thus moving the rack to the left, providing power assist. When there is more fluid pressure in the left chamber, the piston/rack moves to the right.



While removing the fluid pump and looping the fluid lines removes active pressure to the chambers, the piston still moves left and right when you steer. This displaces the fluid inside the chamber and squeezes them through the lines, creating passive pressure. This translates into increased steering effort.

The de-powering coversion gets rid of this passive resistance by removing the internal piston. Essentially, I will disassemble the power rack and pinion assembly, cut the piston off, clean the internal parts, lubricate the rack and pinion gear with multi-mileage grease (so as not to require power steering fluid), and re-assemble it.

This is my previous setup. The lines are simply looped, and I have added a small reservoir for the fluid.

First, start by unscrewing the tie rod ends and removing the steering assembly from the car. Removing it with the engine still in the car is a pain, but manageable. Once out of the car, remove the rubber bellows boots. One of the boots is already removed in this pic. Try to drain as much fluid out of the rack as possible while the lines are attached, to minimize the mess on your garage floor. This is done by cycling the rack left and right to pump out the fluid. Be careful where you point the outlet, as it may queef in your face.



Once most of the fluid is drained, start removing the fittings at the rack.


Once again, cycle the rack left and right and empty any remaining fluid into a container.


Next, un-fold the tabs on the washer that locks the inner tie rod in place. Use a hammer and chisel, or similar, to accomplish this.


In the next step, you realize the impossibility of removing the inner tie rod without the right tools. (If you are doing this with the engine out of the car, I recommend removing the inner tie rod BEFORE unbolting the rack assembly, so you don't have to find a way to keep the assembly from flopping over while you try to wrench the tie rod off). I didn't have a big enough wrench to unscrew the tie rod end, and I didn't have a vise to secure the assembly, so I had to think a bit.

Fortunately I McGyvered a solution (not recommended unless you are in my situation).

Clamp tie rod with vise grips.

Cover the pinion splines with an old sock (so as not to damage it), and slip a pipe over it.

Slip another pipe over the vise grip handle, so it looks like this.

Step on the pipe covering the pinion shaft, and pull on the pipe covering the vise grips to unscrew the inner tie rod from the rack.

A close-up of the inner tie rod, the tab washer, and the rack end.

Remove both inner tie rods, and set them aside. Part 2 is next.

Now remove the end plug with a 24mm socket.

Once the end plug is removed, you will see a 17mm nut. remove this also.

Here you can see the nut removed, showing the bottom of the pinion shaft, and the bearing.

Once again, I find myself not having the right tools. There is a huge locknut on the rack support cover, something like a 42mm. After a bit of thinking, I used a locking pipe wrench to get it off. But that's not all. Once the locknut is removed, a 19mm hex key is needed to remove the rack support cover nut. Again, I don't have the right tool to get it off.

After a bit of thnking, I McGyvered a solution. I used a 19mm Honda lug nut and a 19mm wrench, I was able to remove the rack support cover without a hex key.

Inside, you will find a spring. Remove this.

Behind the spring is the rack support piece. remove this also.

Now get a pair of needle nose pliers to remove the rack stopper plug. Stick the pliers into the two holes, turn it to the right until you see the end of the retaining clip snap out of the slot.

Then turn it to the left to remove the retaining clip and unscrew the rack stopper.

Once this is done, carefully remove the rack itself from the housing.




Here is a picture of the piston on the rack that needs to be cut off. It's the thin disk on the right with the white rubber seal around it. We will be using a Dremel cut-off tool to cut into it. I will update later with part 3.

Here is the disassembled steering assembly with the piston disk in question cut off the rack.

A close-up of the cut piston.

After thoroughly cleaning all the pieces, it's time to put them back together.

Here's the rack greased up. Slide the metal piece to the right onto the rack when you're ready.

Next, slide the rack into the cleaned housing. Get the rack housing end plug (in my hand) ready to install.

Install the end plug, and insert the circlip end into the slot/hole, and turn the plug counter-clockwise with needle nose pliers to install the circlip.

Clean and grease up the valve housing, and install it into the rack. Install the two bolts that hold the valve housing, make sure it all looks sharp and tidy.

Next, take your clean rack support, and install it in the hole.

Install the cleaned rack support spring on top of it.

Use a 19mm hex key, or do the old lug nut trick like me to install the rack support cover bolt.

At this point you're supposed to adjust the rack tension by tightening or loosening the rack support cover. There is a procedure to this, but I just tightened it by feel. As long as it doesn't bind or feel unreasonably loose, it should be okay. Install the big ass locking nut.

Install the 17mm pinion shaft end nut. I recommend torquing this one to spec, as there's a bearing underneath it that you don't want to compress too much.

Install the 24mm end plug, and you're practically done re-assembling the assembly. The tie rods and bellows boots remain to be installeed.

Great post

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93 Cyborg R (race car)

Waikato@Heart - supporting heart kids through life
Bart Dinger Electronics

Great stuff. I can now confidently say that i'll never try this...

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1993 CB4A Lancer MR Mivec - The world's fastest Gen 1 black Lancer Mivec in Auckland with white wheels. That I own. Probably.

wont this make your steering hard to turn?

Excellent step through guide. Plus 1 for not wanting to try this though.

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96 Mirage RS

Finished product:




I guess one's mother might say so. I've been daily driving with just the pump removed on sticky 205/15s and it doesn't break me a sweat. Road feel is excellent, so much that I would personally never go back to power steering.

hmm i should really do this and get rid of that piston free as a bird now with no lines and the top holes welded up while having the rack two joined together but who knows seizing would suck something bad , thanks alot for this post and i agree non power steer is nice and much better having all the gear out of the engine bay is much neater

This is awesome! I'm guessing it would be the same for the gen 2 rack then? I might do this too my rack while the engine is out.. What did you use too cut the piston off and what grease did you use?

how does this affect low speed turning?
like for gymkhana events and with rear wheel biased death traps trying to kill you where you need to react and counter steer quickly?

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The procedure is exactly the same on a gen 2 rack. A Dremel (high speed power tool) with a cut-off wheel was used to cut the piston disc off the rack. I used some wheel bearing grease that I had off hand to grease the rack, but anything from multipurpose automotive grease to crisco should do fine for rack lubrication.

Tight steering manoeuvres at speeds under 5km/h will require some effort. Tight parking spaces would be an example. If you want to get an idea of what it feels like, try going to a go-kart track. That is the sort of feedback you might expect. Sometimes I get confused driving my car after go-karting because the steering feels so similar.

I don't have any problems with controllability when the car oversteers either. In fact I find it easier to forsee a slide before it happens because of the increased feedback through the steering wheel. The steering also seems to return to centre quicker, so it's easier to catch the car back in from a slide. If you do gymkhana on a regular basis, it will probably tire you out and it will suck. It will, however, train you to speed up and keep a low steering angle which I suppose leads to faster driving.

I like this modification, I'm hesitant to do it for the harshness that can put the steering wheel at low speed, I have a question, the lines of fluid that they are on the right and left are removed and gets a plug and ready?


I use my car for daily management and running with the friends, not be if only to remove the pump and fluid tank worth for weight savings

hmmm very interesting and informitive , i have a cyborg r here setting up to do road rally and circuit racing , i can see the gains already with reduce hp loss from the engine but i wonder how this set up would handle through the long and twisty roads we have here , i was gonna de power my rack and run an electric power steering , this set up is much simpler , i guess there is no harm in depowering it and see if i am competitive with in under race trim