Project Miatabusa Part 5 - De-Powering the Steering Rack

By Dave Coleman

That's right; this installment of Project Miatabusa has nothing to do with putting the engine in the car. This may be the only Miatabusa strory where I don't mention the 11,000 rpm redline at least 3 times. Don't get used to it.

Motorcycles don't have accessory drive belts. The alternator is driven directly off the nose of the crank, the water pump is driven internally, and there's nothing else that usually needs power. No A/C, no power steering. We have some plans for making a drive belt system for Miatabusa 2.0, but this first one won't have, or need, any belts. 

That means it's time to de-power our steering rack. De-powering racks is pretty common in the Miata world. The cars are light enough not to need power steering, and power steering was actually an option on early cars. Still, depowering is not a change a normal Miata driver takes lightly. Manual steering gives a lot more feedback, but the change in effort is drastic enough to really change your driving style. The effort causes you to slow down your inputs and become a more deliberate driver, and the feedback makes it easier to drive right at the grip limit. But the weight also makes it a lot harder to keep up with a wagging tail, especially with instincts honed on power steering. With a power-steering Miata, I'm sideways all the time. With manual steering, I drive clean.

Whether you'll like manual steering depends not only on how much time you want to spend sideways, but also what kind of manual rack you use. There are three basic options. 

The factory manual rack seems like the obvious choice, but I'd argue it's actually the worst. To keep parking effort reasonable, Mazda used a slower steering ratio on manual racks. Yes, the effort is lower, but the slow steering really adds an unwelcome bus driver element to any twisty road.

The quick-and-dirty de-power involves simply removing the pump and looping the power steering lines on the rack. This is effective, but it's less than ideal for two reasons. First, there is a fair amount of friction in a power steering rack, thanks to all the seals and the hydraulic piston. The hydraulic system is still in place, and every time you turn the wheel, you're pushing air and residual fluid through the system. This is why you have to loop the hydraulic lines. If you just capped them, you'd basically hydro-lock the rack. The piston seal is weak enough that the steering wouldn't actually lock, but it would really, really suck.

The friction isn't that big a deal, and if it were the only problem, there would be no reason tear down the rack and fix it. The real problem with the quick-and-dirty de-power is slop. The valve that controls power assist relies on deflection of the pinion shaft to act as a torque sensor. That deflection is still there when you de-power, and you can feel it most right at turn-in, or as you transition through some esses. 

This quick-and-dirty manual rack is actually what we run on the Frankenmiata. The conversion is so quick and easy, we did it in about a minute in the middle of a race after a power steering fitting cracked and covered the windshield with oil. Until then, we were afraid manual steering would cause too much fatigue in an endurance race. Turns out it was no problem at all.
Project Miatabusa de-power miata steering rack with welded spool valve

The third, and best, option is the one we're taking. Tear down a power rack, remove all the power-steering nonsense, and weld the spool valve solid. Here's how you do it:

First of all, Mazda has used several different suppliers for steering racks, and all of them come apart just a little bit differently. The objectives are the same no matter which rack you're de-powering, but many of the steps to accomplish those goals might be different. This one is a JKC rack...

OK, so the first thing you want to do is pull off the driver's side tie rod. You can leave the passenger's side inner tie rod in place through the whole rack teardown. To get the driver's side off, you'll have to bend back the lock tab with a screwdriver.

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


Now, when I say that's the first thing you want to do, I mean the FIRST thing. DO it while the rack is still in the car. On the bench, it's a pain in the ass. On the bench after you've already removed the pinion shaft, it's an even bigger pain in the ass. 

The inner tie rod end is threaded onto the rack, usually with lots of Loctite, and if there's a whole car attached to it, it's reasonably easy to get a big wrench on it and turn it. Without the car, the whole rack housing spins. Without the pinion shaft, the rack spins inside the housing. Learn from my mistake.


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


Next you'll want to remove all the hydraulic lines and throw them in a bucket. You won't need them again, but you might want to use the ends as plugs. I'll get to that in the end. 


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


Now you wanna pull out the support yoke dongusmajiggy. Start by loosening this massive lock nut.

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


Then just unscrew this framus here.

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


The giant spring behind the support yoke lets you use the adjuster to change the load on the rack without accidentally clamping it so hard you jam it. Needless to say, this would be a good time to start organizing all the stuff you take apart so it goes back together in the right order.

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


The support yoke itself is this little shoe that presses against the rack. Its main purpose is to sit opposite of the pinion gear and hold the rack in place when the loads on the gear teeth try to push the rack away from the pinion. When you put the rack back together, the adjustment of this shoe is critical. Too loose, and the teeth will be damaged. Too tight, and the rack will feel sticky. Follow the adjustment instructions in the service manual as a starting point and then fine tune until you're happy. We'll re-visit this once the car is actually running.

Steering friction is a funny thing. Generally you don't want much of it, but just a little friction does make it easier to hold a smooth line through a corner.

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


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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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