Miata Suspension Interchange

Published: March 14, 2017; updated: March 27, 2018

NA vs NB:

Front Subframe

NA and NB subframes are different. Per Keith Tanner, the front NB subframe does have some improved geometry: The lower A-arms are moved forward. The steering rack has better mounts. The front uprights have the steering arm moved up about 7mm.

Steering rack must match the subframe (NA or NB). Per Keith again: The NA rack is held on with two U-shaped brackets that clamp the rack to the subframe. The NB rack has one of the brackets and two bolts that go straight through the rack housing itself. The bolt sizes are different at the very least.

Steering Rack

NA and NB steering racks have different mounts which are cast into the rack on the NB. Hence the steering rack must match the subframe (NA vs NB). Keith says: "Judging by the feel, there were other changes as well as I'm a much bigger fan of the NB manual rack than the NA version."

And:

I'm guessing the NB rack has slightly less throw. Mazda's own specs say the ratio is the same.

The NB manual rack is definitely better than the NA one. Rare, though.

As for differences in the power racks, the NB rack has a bit less assist for a given line pressure/volume. We noticed that in the V8 swaps, the NA racks feel lighter. We modify the orifice on the pump outlet to match the pumps to the Miata racks.

Steering ratios on NA and NB racks are the same. NB racks, both power and manual, have fewer turns lock to lock which widens the steering circle of NB compared to NA. MSM steering racks have the same ratios as NB racks and even less turns lock to lock, to limit turning angle to prevent wheels/tires rubbing the intercooler piping.

All manual steering racks have 18:1 ratio, all power racks have 15:1 ratio.

NA manual racks have 2.80 turns lock to lock, NB manual racks have 2.65 turns lock to lock. NA power racks have 3.36 turns lock to lock, NB power racks have 3.17 turns lock to lock.

Steering Column

NB has a larger steering U joint and a different intermediate shaft to accept the larger U joint compared to NA. These are parts 32-850 and 32-090B on this page. The rest of the steering column accepts either NA or NB intermediate shaft.

Rear Subframe

NA and NB rear subframe differ in exhaust hanger mounts and subframe brace mounting points. NB rear subframe brace is thicker than the ladder-style 94-97 rear subframe brace.

Sway bar end link mounts are different. NA uses a double shear U bracket. NB uses a single shear L bracket. Despite being single shear, NB bracket is much thicker and overall stronger.

The end link mounts are located on lower control arms on both front and rear, hence these control arms are different between NA and NB chassis.

NA and NB OEM sway bar end links are different. NA end links use two through bushings:

NB links use ball joints on both ends:

NA end links will mount in an NB control arm. NB end links will not fit into an NA control arm.

Aftermarket adjustable end links typically use a through bushing design and thus fit both NA and NB control arms:

Front Upper Ball Joints

Front upper ball joint tapers are different on NA and NB. Front uprights must match front upper control arms. NB front upper control arms have more reinforcements than NA arms.

Control Arms

Front upper control arms are different between NA and NB due to ball joint taper. Using NA arms on an NB or NB arms on an NA requires upper control arms and spindles to be matching (either both NA or both NB).

Front lower control arms are different between NA and NB due to sway bar mounts. NA arms can be used on an NB if using NA or aftermarket sway bar end links. NB arms can be used on an NA with any sway bar end links.

Rear upper control arms are identical between NA and NB.

Rear lower control arms are different between NA and NB due to sway bar mounts. NA arms can be used on an NB if using NA or aftermarket sway bar end links. NB arms can be used on an NA with any sway bar end links.

Front Spindles

  • 90-93 non-ABS spindles are identical;
  • 93 ABS spindle is the same except it has a bump and is drilled for the ABS sensor;
  • 94-97 spindles are geometrically the same as the 93 ABS spindle, they all have the bump but the holes are only drilled in ABS-equipped cars;
  • 99-05 spindles are different and have the larger upper ball joint hole.

Rear Uprights

  • 90-97 uprights have the same geometry, ABS cars have holes drilled for the ABS sensor.
  • 99-05 uprights give additional 10 mm of track width (5 mm wider per side).

At some point non-ABS NA Miatas switched to ABS-style uprights. 90 non-ABS uprights do not have ABS ears and are thinner in the top half of the upright, which also makes them lighter. 97 non-ABS uprights have ABS ears (not drilled for ABS though) and are thicker in the top half. 99-05 uprights have the same thickness as 97 uprights, but have the extra track width built in. It's possible that the switch from "early" to "late" upright style happened in 94 with NA8 but I don't know for sure at this point.

Rear Bearings

90-05 rear wheel bearings are all the same.

Rear Hubs

90-93 rear hubs are the same and use the small knurl wheel studs. 94-05 rear hubs are geometrically the same but use larger knurl wheel studs.

Several aftermarket companies have stopped producing 90-93 hubs and instead list the same part, which is the 94-05 larger knurl hub, for all 90-05 cars. These hubs fit into 90-93 cars but if you are installing extended studs you would need to get the 94-05 rear studs with the larger knurl.

Axles

  • 90-93 axles are a two piece design, only fit the small 1.6 diff;
  • 94-95 axles are a two piece design, they look like 1.6 axles but are not interchangeable with the 1.6 axles;
  • 95-05 axles are a one piece design and can be interchanged with the 94-95 two piece axles;
  • Mazdaspeed turbo cars use a larger inner spline and hence different axles. They also use a larger outer joint that requires the removal of the wheel bearing seal.

Shocks, Top Hats

NA shocks should work with NB top hats.

NA shocks have a vertical cut on the top threaded portion of the rod; NA top hats have a corresponding flat added to the center hole. NB shocks and top hats have no such cut.

NB shocks can be attached to NA top hats if the center hole in the NA top hats is drilled to be a full round hole.

NA top hats are physically larger that NB top hats. The corresponding chassis holes on NA are larger than the ones on NB. As a result NA top hats are not usable in NB chassis; conversely, NB top hats fit fine in NA chassis.

NA shocks have a flat bottom spring perch. NB shocks have a curved bottom spring perch to match the springs which are not ground flat on either end. When using NB shocks with NA top hats, care must be taken during assembly to correctly orient the top hat with respect to the bottom mount eye.

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