Ok, this is where things really start varying from rack to rack. The pinion shaft on some of the other Miata racks is held on with a big nut on one end of the shaft. This one is held on with two allen bolts. Here, I'm using a Harbor Freight dead blow impact wrench to break them loose.

Project Miatabusa de-power miata steering rack with welded spool valve


Make note of the shims you find under the pinion housing. If you don't see any here, look down in the hole and see if they're stuck in there. These guys are important, and you'll want to be sure they go back where they belong.

Project Miatabusa de-power miata steering rack with welded spool valve


Now, how to get the pinion shaft out of the pinion housing? I got stuck on this step for weeks, since every rack de-powering guide I found used some other kind of pinion design, and even my factory service manual disagreed with what was supposed to be in my car. After digging through several manuals, I finally found one that matched. According to the book, you just press it out. Duh...

Project Miatabusa de-power miata steering rack with welded spool valve


And there it is, finally freed from his housing. That block with the 5 black rings on it is the control valve assembly that actually controls hydraulic pressure in the rack. Honestly, I have no idea how this crap works. Power steering is kinda like automatic transmissions. Shit that makes cars suck. I don't need to know how to make cars suck. 

Let's get that thing off...

Depower miata steering rack weld the quill miatabusa


The valve assembly is trapped between two bearings, so we have to remove one. In theory, this bearing should just slide off the shaft by hand. In reality, it's right up against some rust, so it had to be gently pressed off. After sanding the rust down, the bearing slid back on by hand.

Depower miata steering rack weld the quill miatabusa


Finally, you'll need a pair of snap ring pliers to free the spool valve assembly from the pinion shaft. Once the ring is off, this part really does slide off by hand. Keep the bearing. The rest of that crap is going in the trash. 

Depower miata steering rack weld the quill miatabusa


Finally, we have reached our goal. This is where the slop in a power steering rack comes from. See the splines? The pinion shaft is actually an upper and lower shaft splined together. Normally when two shafts are splined together, they rotate as one, but these splines don't do that. They're sloppy, and they're that way for a reason. 

The splines are really only there as a backup. They're the bump stops at the end of a clever little hydraulic suspension system of sorts. Hidden down inside this interface is a little torsion bar valve thingy (remember, I don't really know what it looks like). When you turn the wheel, it twists the bar, which opens a little passage that lets hydraulic pressure into the rack. That pressure helps push the rack the direction you were turning. With that help, you then don't exert as much torque on the pinion shaft, and that takes some twist out of the torsion bar, closing off the hydraulic pressure. It's an elegantly simple, self-regulating mechanism.

But once you remove the hydraulic assist, that elegant system turns into a bucket of slop. Turn the wheel now, and you just bend the torsion bar. That's it. Ok, maybe the car turns a little, but not with much vigor, and certainly not with any direct connection to your hands. After a few degrees, the bar is maxed out and you run into the splines. Then, and only then, do the two ends of the pinion shaft move as one.  

Depower miata steering rack weld the quill miatabusa


Just how much slop is this? Spend a few seconds watching the moving pictures:



Miata spool valve slop. from Dave Coleman on Vimeo.


Time for the scary bit. Let's weld this crap together and get that rigid connection once and for all.

This is scary, of course, because, well, steering is important. There's always that little voice in the back of your head saying that someday your weld is gonna fail, and with it your steering. Maybe it will. I'm guessing it won't though, and here's my reasoning.

1: if the weld fails, the splines are still there to connect the two ends of the shaft.

2: Unless, of course, the failure comes from the weld screwing up the heat treat of the shaft, and the shaft itself snaps. Maybe, but consider how much torque this shaft sees. It sees exactly as much torque as you can exert with your hands. You have one steering wheel's worth of leverage, now go break this 1" thick steel bar. Yeah, I didn't think so. Finally,

Angry hamster sway bar3: It was TIG welded with mad skillz and Weld Mold 880 filler material, which is a Ni/Cr filler material made for repairing giant forged stamping dies that are too big to be heat treated after welding. Unlike most welds, a proper weld with this stuff remains ductile, so it can handle all the bending I'll be doing with my huge muscles.

This happens to be the same filler material, and the same mad welding skillz, used to make the Angry Hamster's front sway bar 6" narrower. There is no better proof of a weld's ductility than welding a sway bar together... 

Depower miata steering rack weld the quill miatabusa


Now, when the pinion shaft goes back in the housing, don't forget all those shims you were keeping track of when you took this thing apart. 

Depower miata steering rack weld the quill miatabusa

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Sunday, October 31, 2010 7:09 PM
Haha, Dave you're funny. Great article, and thanks for explaining step by step the whole process. Very easy to understand.
I have a question though: I removed my PS on my DD Civic '93. Took off everything, like u did; lines included. Instead of looping a hose and allowing the oil to recirculate when the piston moves left and right, I just left the two holes open.
I did this about three years ago. And while doing it, I was thinking: "how about if dirt goes in? Or worst, it it locks up, I'm screwed."
To these days, I haven't had a single issue. Although the steering IS hard to turn when parking (maybe FR cars are a bit easier?).
Sunday, October 31, 2010 7:11 PM
Any thoughts in regard?
Dave Coleman
Dave Colemanlink
Sunday, October 31, 2010 7:24 PM
You'll certainly be sucking dirt into the rack, but it will be trapped between those two seals where its mostly harmless. Eventually, it will probably wear the seals out and start getting into the support bushings on the end and the rack and pinion gears themselves, but that will probably take a long time.

And yea, manual steering is really heavy when you're parking. That's just physics.
Monday, November 01, 2010 3:51 AM
You just need to park faster lol.
@ Coleman
Gotta say everytime I read an update on Miatabusa it makes me want to tackle something on the same level of ingenuity. And as always your funny as hell! Keep up the good work and I cant wait to see the next installment.

Der Bruce
Der Brucelink
Monday, November 01, 2010 11:14 AM
Miatabusa is one of the most radical, in a good way, projects anyone has come up with Dave! I've look forward to all updates since part 1 and can't wait for the eventual test video on Youtube!?

Did you ever think about doing an electric power steering conversion? I'm pretty sure a few companies have a kit. In fact, wouldn't Miatabusa be the ultimate test bed to try and apply something like this or an electric AC/heater unit. Although, I'm pretty sure you're going for Go-Kart status!?
Monday, November 01, 2010 12:52 PM
So will it still rev to 11k, given this radical steering change?
Dave Coleman
Dave Colemanlink
Monday, November 01, 2010 2:08 PM
@Der Bruce
There really is no need for power steering on this car. Even a normal Miata doesn't need power steering, and we're taking at least 160 pounds off the front wheels, so we REALLY won't need it.

And who needs A/C when you have windows that roll down (for now...)?
Monday, November 01, 2010 5:52 PM
Windows? your going to have windows?

I wish this guide was around when I owned my miata. I ended up doing a "dirty" de-powering. I was going to do it like flyin miatas sight but took one look and thought what the hell? this looks nothing like what they are showing
Tuesday, November 02, 2010 11:23 PM
Almost certainly the first time I have, and last time I will, read technical information about power steering and enjoy it. I've been longing for a site to fill the void left by SCC and after finding MotoIQ and reading just about every article I just want to say thanks for creating such great content. Thanks!
Sunday, November 14, 2010 9:23 AM
I agree with JJ! Can we get a nice little MotoIQ tv show to replace all of the muscle cars and trucks on Speed's "Power Block?" Plllllleeeaaaasssee??
Sunday, November 14, 2010 9:29 AM
Anybody happen to know a good way to get the slop out of a 90 civic hatch manual steering system? I replaced that plastic "end bushing", along with both tie rods and tie rod ends, but it still seems far too sloppy.... I guess I need to figure out how to replace the two U-joints in the steering column.... any pointers on what to do about those floppity suckas? And yes I have replaced all of the suspension bushings and ball joints in the front already.
Tuesday, November 16, 2010 12:37 PM
Good show.

And yeap. Weld something. It'll put hair on your chest.
Tuesday, January 04, 2011 7:08 PM
Attention waning - add updates please :)
Thursday, May 23, 2013 6:17 PM
Need Help!

This was very helpful, but I have a question for all of you Miata experts... I've been having a clunking sound when I go over even small bumps ('90 Miata with power steering). I think I've narrowed it down to the steering rack. I have both tie rod ends AND the steering colum shaft connected (Rack is still mounted in car with fluid hooked up). If I push/pull on one of the tie rods, there's a clanking noise coming from the rack. I took the cover off the bottom of the pinion shaft and I can actually see the bearing moving up and down (parallel to the shaft axle) when I push/pull the rack.
Can anyone tell me why this might be? Thanks in advance.
Monday, December 16, 2013 3:42 AM
Hi this article saved me a great deal of time and pain in the butt. Couple of questions, after welding do you put the valve back on for assembly and do you refit the rubber seal on the shaft?
Cheers G
Monday, January 27, 2014 9:36 PM
Thank you guys for this article, all the attention to detail really shows you guys know what your doing. If It wasn't for your attention to detail, I would soon be driving with a sloppy rack. More car tuners, even just car enthusiast should come here so they can understand and really learn about what it takes to make & properly install aftermarket parts.

Justin R
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