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NB sub-frame in NA

Old 01-13-2014, 11:40 AM
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Default NB sub-frame in NA

is this worth the trouble? I have the front of my car completely apart at the moment and was thinking it was a now or never kind of time. I have access to all the parts for pretty cheap.

all I really need is the sub-frame and rack, correct?

thanks...
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Old 01-13-2014, 12:09 PM
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More caster, less play in the steering rack bushings. Bolts right in. Just the subframe and the rack is all you really need.
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Old 01-13-2014, 01:33 PM
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thanks. for some reason I thought I read the steering geometry was better on the NB set-up, helped with bumpsteer maybe???

my car is a anomaly. the last time I lined it up, I had 5* of caster and around -3.5* of camber. I can make the numbers with the factory sub-frame.
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Old 02-05-2014, 03:30 PM
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Isn't the tie rod attachment points on the front NB uprights higher (7mm or so) to help with bump steer? Isn't that why you don't need R-package outer tie rod ends on a NB? That's why I was planning on swapping in everything on my car, subframe, depowered rack, upper control arms, uprights, lower control arms.

IIRC, the upper and lower control arms are interchangeable (but the upper balljoint and upright are NOT) but the NB bits have better reinforcement?
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Old 02-05-2014, 03:36 PM
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Originally Posted by TheScaryOne View Post
Isn't the tie rod attachment points on the front NB uprights higher (7mm or so) to help with bump steer? Isn't that why you don't need R-package outer tie rod ends on a NB? That's why I was planning on swapping in everything on my car, subframe, depowered rack, upper control arms, uprights, lower control arms.

IIRC, the upper and lower control arms are interchangeable (but the upper balljoint and upright are NOT) but the NB bits have better reinforcement?
The difference in geometry is all in the front subframe rack and suspension mounting points. roll center hight is also different, slightly lower.
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Old 02-05-2014, 04:03 PM
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the uprights did change both front and rear on the NB. The steering arm moved up by 7.1 mm in the front.
While you can swap the whole subframe w/suspension most of the handling advantages of the 99+ subframe are from the uprights. They individually interchange too. The tie rod attachmment has been raised 7.1mm to help bumpsteer.
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Old 02-05-2014, 07:43 PM
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Originally Posted by TheScaryOne View Post
I believe those are poorly written and wrong.

The rack moved up a bit and the lower A-arm pivot points on the subframe moved down. The changes are is described in a Mazda published book on the NB. looks like they just slid the welded on tube the big bolt goes through for the upper A-arm back a bit to get more caster.

FWIW Im running an NB front sub frame with LE tie rod ends now.
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Old 02-05-2014, 08:20 PM
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But are you also running NB uprights? If what I've read is correct, the LE tie rod ends with NA uprights and control arms and NB subframe and rack will work fine. It's the LE tie rod ends with NB uprights and control arms that aren't needed, as both attempt to correct the toe curve.

Keith @ FM and Lance Schall both cited the same NB FSM.

NB changes to enhance steering response:
1. Smoother shock absorbers, particularly at small deflections. Revised mounting at car end for more direct action without NVH penalty.
2. Tie rod mount point at suspension upright raised 7.1 mm to reduce toe variation (the feature discussed above)
3. Increased caster trail by upper A arm mount moved back 3.0 mm and lower A arm mount moved forward 2.1 mm (This actually increases stright line stability at the expense of higher steering effort)
4. Lower front roll center by dropping lower A arm mount points 5.7 mm (decreased roll per given cornering force)
5. Increase anti-roll bar diameter in front from 19 or 20 mm to 22 mm. Rear from 11 mm to 12 mm (Hard suspension; normal stays at 11 mm)
6. Change mounting at steering rack from strap to ears (strap still at one end). This is intended to recover some of the feel lost by item 3 above.
I'd really like to know one way or the other, because if I don't have to go to all of the hassle of swapping uprights, I won't.

Last edited by TheScaryOne; 02-05-2014 at 08:22 PM. Reason: Bold
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Old 02-06-2014, 03:28 AM
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Originally Posted by TheScaryOne View Post
But are you also running NB uprights? If what I've read is correct, the LE tie rod ends with NA uprights and control arms and NB subframe and rack will work fine. It's the LE tie rod ends with NB uprights and control arms that aren't needed, as both attempt to correct the toe curve.

Keith @ FM and Lance Schall both cited the same NB FSM.



I'd really like to know one way or the other, because if I don't have to go to all of the hassle of swapping uprights, I won't.
I was wrong. the book does say the tie rod attachment point was changed on the upright. doesn't say by how much. ill have to dig up my collection of parts and see that.

I have NA uprights with LE tie rod ends and an NB sub frame and rack on my car.
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Old 02-06-2014, 01:00 PM
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Awesome. I wanted to use NB uprights so I didn't have to special order expensive R-package tie rod ends and could use OTS parts.

Now I just need a single upper control arm and a set of NB shocks and springs to do my swap.
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Old 02-06-2014, 01:10 PM
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NB plus LE tie rod ends?

It would be nice if it's a fail (adds bumpsteer), so I don't have to worry about it.
I have not measured my bumpsteer (lazy, as always), but if anyone have tried it would be nice to know how stupid it was.
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Old 02-06-2014, 01:19 PM
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That's a really good question, actually.

I'm looking at doing a complete front suspension update/refresh this year on my NB after I get another DD sorted out. As I was going to replace the tie rod ends anyway, I figured I would just do the LE ones "because they are better" but if that's not the case on an NB, I'd like to hear it.
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Old 02-06-2014, 02:09 PM
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Originally Posted by EO2K View Post
That's a really good question, actually.

I'm looking at doing a complete front suspension update/refresh this year on my NB after I get another DD sorted out. As I was going to replace the tie rod ends anyway, I figured I would just do the LE ones "because they are better" but if that's not the case on an NB, I'd like to hear it.
Pretty sure the LE ends don't shift as much as the NB upright does if the 7.1mm figure is correct. There is a sweet spot in there somwhere seems like mazda would have figured it out the first time or at least by the second time.
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Old 02-06-2014, 02:33 PM
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Hazarding a guess, I'd say the LE tie rod ends were a band-aid on the factory lowered (1" lower?) R-package car, and they fixed it when they upgraded the production to the NB. Maybe, knowing that they had to create a band-aid part, they found that the 7.1mm adjustment produced a better toe curve for both stock and lowered cars, and they chose to make it standard? I can't believe they'd R&D new parts just to cater to the performance crowd who lowers their cars, so it must be better at stock height too.

From what I can tell, the 90-93, 94-95, and 96-97 NA were all different heights, with the 96-97 being the highest. Some people have referenced 12.9" front as being Mazda's short end of the ride height specification range on both the 94-95 and the NB (per M.net).

Edit: Been thinking about this more, and the other changes made with the NB suspension must have contributed to this decision. I wonder what the toe curve looks like between an NA with LE tie rods, and an NB?

Last edited by TheScaryOne; 02-06-2014 at 04:47 PM.
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Old 02-06-2014, 05:41 PM
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If you buy the entire NB subframe assembly the swap is a breeze. Prior to the swap I was unable to get more than 2.5degrees of camber on right front. After 3+ is possible. Bump steer was never an issue for me but I figured why not take advantage of all of the upgrades and do the entire assembly. I got a real clean one for $300 complete.
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Old 02-09-2014, 03:09 AM
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I suspect the NB is pretty neutral with bumpsteer at stock height but most of us run quite a bit lower on the track so the LE ends with the NB rack and uprights might be the best combination until the drop spindles are widely available. Or I'm cornfused...
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Old 08-26-2018, 10:52 PM
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The spline on the NB rack is bigger than the NA miata rack, making the u-joint that connects the column to the rack not fit. Do I need to use an NB ujoint, or make something custom for it to work?
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Old 08-26-2018, 11:34 PM
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Nope. Na u joint fits the NB rack. Unless na manual and power are different.i know the manual na fits the power NB rack.
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Old 08-26-2018, 11:57 PM
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Originally Posted by Leafy View Post
Nope. Na u joint fits the NB rack. Unless na manual and power are different.i know the manual na fits the power NB rack.
My NA had a factory NA power steering. So, if I understand what you posted, is that the NA manual steering rack U-joint will work on the NB power steering rack. I believe I just confirmed that the NA power steering U-joint will not work on the NB power steering rack. Darn it.
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Old 08-27-2018, 03:38 AM
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NB lower U-joint will fit the NA shaft. That's what I have done on all the NB>NA swaps I've done.
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