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Thread: NB power steering swap into NA.

  1. #1
    6,000 rpm - mere mortals would shift JamieH's Avatar
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    NB power steering swap into NA.

    I've seen and read just about all the info I can find on doing this swap before doing it myself. But none of the threads and info I found were all that exact. So, I figured there should be a write-up discussing what's required and the differences in parts. This will include installing a power steering cooler line for '96-'97 cars as it was omitted during those 2 years.

    Being that this is a complete plug and play type of deal, if you can remove all the original NA parts, you can just as (nearly) easily installed the NB parts. It is very obvious where everything goes.

    I will point out the differences and why each part is needed. Pics will be for showing differences and to identify parts. I intend to add in OEM part numbers later.

    Install tips are at the end.

    Parts needed:

    • NB front subframe - Mazda part# NC72-34-800A

    • NB steering rack - Mazda part# NC10-32-110R-0K

    • NB rack to column U-joint - Mazda part# NC10-32-850

    • NB rack bolts

    • NB or NA outer tie rods (I recommend 93LE/R-package)

    • NB pump - Mazda part# NC10-32-600

    • NB pump tensioner/bracket - Mazda part# NC11-32-609A

    • NB rack the pressure line hardline/cooler (this usually stays attached to the rack when sold used) - Mazda part# NC10-32-460

    • NB pressure line - Mazda part# NC10-32-490J or N066-32-490 or N115-32-490

    • NB pressure line subframe bracket & line to line brace

    • NA return line (reservoir to pump) - Mazda part# NA02-32-684B

    • NA cooler hard line ('90-'95)

    • NA cooler line hoses ('90-'95) - Mazda part# NA02-32-682

    • NA reservoir ('90-'95)


    The cooler line/hoses will already be installed from the factory on '90-'95 cars. The OBD-II cars didn't have the cooler hard line, but the mounting points are there. Yet, a minor change was done to the reservoir on the '96-'97 cars (more on that later). But depending on the mileage of your car, you should probably replace all the soft hoses. Maybe irregardless of the mileage as NAs are all 20+ years old now.

    The break down of why each part is required to do the swap.

    The NB subframe is needed as the mounting points of the NA and NB steering racks are different in 3 ways.

    1. Distance between the mounting points.
    2. Left side NB mount is incorporated into the rack itself.
    3. NB rack bolts are larger

    The bonus of using the NB subframe is slightly better suspension geometry. If I have understood what I have read and found elsewhere, better chamber gain under compression.

    Bare NA subframe installed ('97 shown):



    Bare NB subframe installed (same '97 as above):



    The NB rack is self explanatory, it's the reason to do the swap. Even though all sources I have found say the ratios are the same 15:1 for the NA and NB power racks, the lock to lock is different, 2.8 NA and 2.6 NB. Which means the NB rack has a slightly larger turning radius or the ratio info is incorrect or some other explanation I have yet to find. But, according to Keith of FM, the NB rack has less assist for a given pressure/volume.

    The NB rack to column U-joint is needed because the NB rack has a larger input shaft than the NA rack. But, the column shaft size itself is the same between NAs and NBs.

    NA & NB racks side by side (NA top, NB bottom):



    NB rack to column U-joint installed in '97 NA:



    The NB rack bolts are larger than the NA bolts, in two ways.

    1. Larger diameter.
    2. Left side bolts are also longer.

    NA rack bolts:



    NB rack bolts:



    The NB or NA outer tie rods can be used. They thread on the same and will fit the steering knuckle the same. But I recommend the 93LE/R-package tie rods if you happen to be lowered a bit. They'll help with bumpsteer a bit.

    The NB pump uses a banjo like fitting rather than the NA's flare fitting for the pressure line. No banjo/crush washers are used. Instead, two O-rings seal the fitting.

    The NB pump tensioner/bracket uses a different bracket extension to brace/direct the pressure line towards the front of the car.The bracket itself has a stud as part of the assembly, whereas the NA bracket has a welded nut. The bracket extensions are also at different angles.

    The NB pressure line, as explained above, uses a banjo style fitting at the pump. But, it also uses a double flare fitting at the rack. The NA pressure line uses a single flare fitting at the rack. There is also a small bracket that secures the pressure line to the subframe as well as a small, two-piece line to line brace.

    NB pump, bracket, and pressure line assembled:



    NA pressure line fitting on pump:



    NB pressure line fitting on pump:



    NA tensioner/bracket assembled:



    NB tensioner/bracket assembled:



    NA & NB brackets side by side (NA left, NB right):



    From below:



    From above (NB left, NA right):



    Engine to tensioner bracket, NA on top of NB:



    Bolt holes are the same distance from one another.

    Engine to tensioner bracket, NA in front of NB:



    But the NB bracket is thicker than the NA bracket.

    Pressure line to pump brace/bracket:



    NB tensioner/bracket fully assembled:



    NA pressure line:



    NA pressure line pump side fitting:



    NA pressure line rack side fitting:



    NB subframe pressure line bracket:





    NB rack/pressure line, line to line brace/bracket:



    NB rack/pressure line, line to line brace/bracket installed:





    NB pressure line fitting installed on pump:



    Note that NO crush/banjo washers are used.

    NB pump, tensioner/bracket, pressureline installed in '97 NA:



    The NA return line is used as the pump and reservoir are in the exact same places, so the NA line is the correct length.

    NA return line:

    Last edited by JamieH; 04-27-2017 at 10:09 PM.

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  3. #2
    6,000 rpm - mere mortals would shift JamieH's Avatar
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    The following only applies to '96-'97 NAs.

    The '90-'95 NA cooler hard line was not installed on the '96-'97 cars. And they are the only NA/NBs to not have a cooler hard line as far as I know (unsure if the MSM does). The NA cooler hard line is used as it is the only one I have confirmed as fitting in an NA. Bolts used are M6x1.0 for all 4 attachment points.

    Cooler line installed, looking up into the mouth of the bumper:



    From inside, looking in from an opening on the driver's (left) side:



    Cooler line routing through the sway bar mount:



    The '90-'95 NA cooler hoses are used as they are the same on both ends. The NB uses one such hose, but because the NB's cooler hardline is slightly different, it also uses a different, longer hose on the other end.

    The '90-'95 reservoir is used as the tube that goes to the cooler is angled/pointed, more towards the ground. The '96-'97 reservoir, having to connect directly to the rack instead, the same tube is now angled/point more towards the rack itself. This change, even though ever so slight, is enough that an OEM cooler hose will not fit properly. Could it be bent to fit? Maybe, but at risk of damaging the reservoir. The only other solution is to use a universal length of hose. It is more sensible option, I'm just the kind of guy that likes some things to be/look as OEM as possible. Also, an NA reservoir is used as the NB reservoir does not have the required D-shape to clear the pop-up motor.

    '90-'95 reservoir left, '96-'97 reservoir right:



    Earlier reservoir installed in '97 NA:



    This also shows one of the cooler line hose connections. This is from the reservoir to the end of the cooler line furthest forward once installed.

    Bonus:

    This is not needed per say, but if you are keeping everything stock-ish you will likely want this.

    EVAP subframe nipple, part # JE16-13-298

    This part is the same for NAs and NBs. It only shows up as "CONNECTOR" in Mazda part systems.







    There's a good chance it will be broken or missing on the subframe you acquire for the swap. And you will very likely break the one on your NA subframe if you attempt to remove it. There is no way to access the back/inside of the subframe.

    OK, so some install tips.

    I suggest removing the rack separate from the subframe. It's a bit less weight than removing them together. You'll also be able to go ahead and get the U-joint disconnected from the column. Which it might be a total PITA to remove. It's not uncommon for the U-joint to be frozen to the column shaft. So, be prepared for a fight and consider yourself lucky if it comes out without much effort.

    Here's the big one, get some help for removing and installing the subframes. It's the most difficult and dangerous thing of the whole swap to do. You're going to be removing the lower motor mount nuts, supporting the engine with a jack with a piece of wood between the jack and engine oil pan, and then removing the 4 bolts and 4 nuts that attach the subframe to the chassis.

    The subframe will come out with only the lower motor mount nuts removed while leaving the engine side of the motor mount bolts in place. It's a little tricky, and requires a bit of finangling, but it's doable.

    You will need to lower the engine & subframe a bit in order to be able to maneuver the subframe just right in order to get it to clear the motor mount studs and the studs on the chassis. Be patient, keep an eye on everything and you should be able to get it off/out. The subframe isn't particularly heavy, but it is cumbersome. Hence why you'll need some help.

    Installation of the NB subframe is the opposite of removal of the NA subframe.

    For installing the earlier cooler line in a '96-'97 car, you're going to want to remove the air guide. It's the piece that sits in the mouth of the bumper and provides structural support for the bumper. Otherwise you'll have to remove the bumper entirely to get the line in. You may need to flex/slightly tweak the ling to get it to go in and slip through the sway bar mount. Be patient, you'll find the position that'll get it in.

    Also, it's wise to run a tap through the mounting holes for the cooler line. They're exactly where they should be on the '96-'97 cars, but because nothign was ever installed there from the factory, 20+ years of dust, dirt, rust, etc. has had the opportunity to build up on the threads.

    When installing the cooler line hoses, you may need to bend the cooler line ends a little to get things to line up just right. You'll be able to bend them a small amount without any concern of damaging them (use your better judgement). You may also need to flex/bend the hard line on the NB rack a little so things line up for the cooler line hose that connects to it.

    Do NOT attempt to bend/flex the small hard line on a '96-'97 reservoir in order to provide proper routing for the cooler line hose. You stand a good chance of breaking what is most likely a solder joint. Which will either create a leak or break the line altogether. Either swap the reservoirs or run a universal piece of hose.

    Not much else I can think of that should be of much trouble. It really is a bolt in affair.

    Oh, I guess don't forget to bleed the system of air. Fill the reservoir, leave the cap/dipstick out/off and start the engine. Then turn the steering from lock to lock a few times.

    Hope this helps anyone that is thinking of doing this swap or anyone that does do it.

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  5. #3
    3,000 rpm - starting to feel the power Rogue's Avatar
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    Thanks for this, I have bought about doing it since I have a new NB Rack on the shelf.
    Let me know how the feel is. I am not a fan of the over boosted NA power steering.
    This is why I have manual racks on 4 of my Miata's
    My wife won't go Manual so this may be a fix.
    1992 BnT, 93LE #737, 94M, 95M, 96M, 97PEP, and a few 90s

  6. #4
    6,000 rpm - mere mortals would shift JamieH's Avatar
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    The feel is pretty good. It feels exactly like an NB. Turns in like an NB too. And I'd swear the response is better as well. Off center response seems nearly immediate.

    I've not yet had the chance to really work it though. Only really driven with it for a day and a half. And half of that time I wasn't paying the steering feel much mind as I've been listening for tire rub up front with the taller 195/55/15s and just being mindful of other sounds and the such after the T-belt/WP maintenance and control arm bushing swap.

    But I'd describe it like I do any properly working power steering in an NB, solid.

  7. #5
    5,000 rpm - there be torque here! The Driver's Avatar
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    GOD bless you, OP! I too want to do this. SUBSCRIBED!!!
    96 Montego, replacing a 95M... I miss: My running peeps in Tampa, running barefoot @ Clearwater Beach and First Choice BBQ, in Brandon. In So Cal I miss: The Malibu Canyons, CA 33 and In & Out Burgers ! I'm from Tampa, if I was from Tampa Bay, I'd be a fish!

  8. #6
    Ninja Messiah kung fu jesus's Avatar
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    Love it! Thanks for the documentation!
    Thread sticky for you!

  9. #7
    6,000 rpm - mere mortals would shift JamieH's Avatar
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    Can't edit the original post, but here's some more part #s

    NA cooler hard line ('90-'95) - Mazda part# NA02-32-410A

    NA reservoir ('90-'95) - Mazda part# NA02-32-690A

    NB pressure line subframe bracket & line to line brace - Mazda par# Line to line brace/bracket: UC873218X & UC8732182 (subframe bracket is shown under the same part number as the pressure line itself)

    NA 93LE/R-Packae tie rod ends - Mazda part# MZ-N021-32-280A-2

    All of the part numbers are more for helping to identify and find the parts rather than buying them through a dealer. Only in the case of parts that can't/shouldn't be bought used, for whatever reason, should you get new parts (like the little subframe nipple for the EVAP).

    Some tips on acquiring the parts in general.

    I really recommend either finding a donor car yourself to pull the parts from or contacting one of the several Miata wreckers of the community by phone. The smaller parts can get overlooked (the pressure line brackets particularly), and some parts are sold as being for all years but really aren't. I've seen several ebay sellers list the '90-'95 or '96-'97 pump reservoirs as fitting all years, '90-'97 or simply listing them as '90-'97 reservoirs.

    Contacting by phone will give you the chance to speak with a person and you'll be able to let them know exactly what you're doing and everything you're wanting. It's also handy, if like me, you're after the best condition + lowest miles parts. Which when it comes to steering components really matter. Example, my original NA steering pump with 184K miles had (well still has, I didn't repair it since I did the swap) a blown rear body seal and was leaking, but only under pressure. On the up side, there's some real quality Miata parts wreckers in the community who won't even bother selling you junk.

    A donor car is great if for nothing else to show you exactly how everything is suppose to be routed and/or bolted together. Beyond that, it's an oppotunity to get everything you need from an NB at once.

    Oh, just remembered this about the subframe. Measure it before installing, preferably before buying if possible. You can take several measurements side to side and cross to cross at the bolt holes. You're checking for squareness, insuring that the subframe isn't bent/warped/tweaked. You can have about a 1/16" or so of difference and still be fine.

    Last thing you want to do is find out you have a screwed subframe after everything is together and have trouble getting the front end aligned or start noticing odd handling behavior.

    Here's an image swiped off of M.net showing the measurements to take. This is of an NA subframe, but the attachments points are the same on an NB subframe (except for the rack, but I've already gone over that).



    I just thought that someone may be wondering about the control arms. You can use your original NA arms. NA and NB arms have the same geometry, NB arms are just a bit beefier. Thought there is one thing you need to be mindful of, the upper ball joints are different. Just in case you want to use NB arms anyways, you should know you'll need to swap the upper ball joint for an NA one. The NB ball joint is longer and has a different taper.

    The good news is that it is possible to swap in an NA replacement ball joint in an NB arm. Moog part# k500210, which is the go to NA upper ball joint replacement will fit in an NB arm. A fellow on M.net recently posted results of it working for him.

    Which, I feel as if the only reason to go full hog and swap in the NB control arms is if you just really, really] gotta have every NB part possible on your NA. Though, I guess if you want the improved bump steer geometry of the NB you'd need the upper NB control arms with their NB ball joints and the NB knuckles. As the change is in a raised position of the steering arm on the knuckle.

    But, 93LE/R-Package outer tie rod ends will get you pretty good results instead of going through all of that. Then again, I have to imagine that a combination of the NB knuckles and 93LR/R tie rods could give the best results. Could, but maybe not.

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  11. #8
    Ninja Messiah kung fu jesus's Avatar
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    I bought NB knuckles when I switched to NB control arms.

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