Transmission Assembly

REMOVAL & INSTALLATION

Manual Transmission

1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
2. Remove the negative battery cable.
3. Drain the transmission oil.
4. Remove or disconnect the following:
   • Shifter knob
   • Center console
   • Gearshift lever
   • Engine undercover and the performance rod
   • Exhaust pipe from the manifold
   • Entire exhaust system as an assembly
5. Matchmark the driveshaft flange at the rear.
6. Remove or disconnect the following:
   • Driveshaft
   • Clutch release cylinder and set it aside, without disconnecting the hydraulic hose
   • Starter
   • Speedometer cable and wiring from the frame member
7. Support the transmission and differential with jacks.
8. Remove the transmission-to-differential frame, also called the Power Plant Frame (PPF), as follows:
   1. Remove the frame-to-transmission bracket.
   2. Remove the bolts from the underside of the frame at the differential end, noting their location. Pry out the spacer from the frame.
   3. Remove the differential mounting spacer from the underside of the differential.
   4. Insert a 14 x 1.5mm bolt through the frame hole and turn it into the sleeve. Twist and pull the bolt downward.
   5. Install a 6 x 1mm bolt in the side hole to hold the sleeve and remove the long bolt. Remove the short bolt.

      NOTE: Do not remove the spacers from the end of the PPF. Doing so will reduce the performance of the frame. If the spacers are removed, the PPF must be replaced as an assembly.

   6. Remove the transmission side bolts and the frame member.
9. Remove or disconnect the following:
   • Bolts from the clutch housing
   • Transmission from the vehicle

   To install:

10. Lightly lubricate the main shaft spline and the release bearing fork contact points with molybdenum grease and install the fork. Place a wood block on a floor jack and use it to tilt the engine up in front.
11. Install or connect the following:
    • Transmission. Tighten the bolts alternately, in several passes, to 48–65 ft. lbs. (64–89 Nm).
    • Transmission to the differential frame. Tighten the bolts to 76–91 ft. lbs. (104–124 Nm).
    • Bracket. Tighten the bracket-to-transmission bolts to 27–40 ft. lbs. (37–54 Nm) and the bracket-to-frame bolts to 77–91 ft. lbs. (104–124 Nm).

    NOTE: After the frame installation, position a straightedge between the body frame members on each side of the vehicle. Measure the distance between the bottom of the frame to the straightedge; it should be 2.403–2.797 in. (61–71mm). If the distance is not as specified, reposition the frame member at the transmission.

    • Speedometer cable and wiring
    • Starter
    • Clutch release cylinder
    • Driveshaft. Tighten the nuts to 22 ft. lbs. (30 Nm).
    • Exhaust system using new gaskets. Tighten the nuts to 34 ft. lbs. (46 Nm).
    • Performance rod and engine undercover
12. Fill the transmission with oil.
13. Install or connect the following:
    • Shift lever
    • Rear console
    • Shift lever knob
    • Negative battery cable
14. Refill the transmission.
15. Verify proper operation of the transmission.

    Fig. 1: Measure distance "A" after installing the transmission-to-differential frame member — Miata with N4A-HL and NC4A-EL transmissions

Automatic Transmission

1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
2. Shift the selector lever to the N position.
3. Disconnect the negative battery cable.
4. Drain the transmission fluid.
5. Remove or disconnect the following:
   • Engine undercover
   • Shift rod
   • Performance rod
   • Complete exhaust system from the exhaust manifold
6. Mark the position of the driveshaft on the rear axle flange.
7. Remove or disconnect the following:
   • Driveshaft
   • Speedometer cable
   • Vacuum hose from the vacuum diaphragm
   • Electrical connectors from inhibitor switch, kickdown solenoid, overdrive cancel solenoid, oil pressure switch and lockup solenoid
   • Dipstick and dipstick tube
   • Oil cooler lines
8. Support the transmission and differential with jacks.
9. Remove the transmission-to-differential frame as follows:
   1. Disconnect the wiring harness from the frame.
   2. Remove the bolts from the underside of the frame at the differential end, noting their location. Pry out the spacer from the frame.
   3. Remove the differential mounting spacer from the underside of the differential.
   4. Insert a 14 x 1.5mm bolt through the frame hole and turn it into the sleeve. Twist and pull the bolt downward.
   5. Install a 6 x 1mm bolt in the side hole to hold the sleeve and remove the long bolt. Remove the short bolt.
   6. Remove the transmission side bolts and remove the frame member.
10. Remove or disconnect the following:
    • Torque converter bolts
    • Starter
    • Transmission mounting bolts
    • Transmission, being careful not to drop the torque converter

    To install:

11. Be sure the torque converter is fully installed in the transmission. The distance between 1 of the bolt hole lugs and a straightedge laid across the bell housing should be 0.89 in. (22.5mm).
12. Install or connect the following:
    • Transmission. Tighten the bolts to 48–66 ft. lbs. (64–89 Nm).
    • Starter
    • Torque converter. Tighten the bolts to 27–40 ft. lbs. (36–54 Nm).
13. Install the transmission-to-frame member as follows:
    1. Install the differential mounting spacer on the underside of the differential. Tighten the mounting bolts to 38 ft. lbs. (52 Nm).
    2. Position the jack under the transmission so the transmission is level.
    3. Position the frame and install the transmission side bolts. Snug the bolts.
    4. Be sure the sleeve is installed in the block. Install the spacer and bolts with the reamer bolt in the front hole. Snug the bolts.
    5. Tighten the transmission side bolts to 77–91 ft. lbs. (104–123 Nm), then tighten the differential bolts to the same specification.
    6. Connect the wiring harness to the frame member and remove the jacks.

       NOTE: After the frame installation, position a straightedge between the body frame members on each side of the vehicle. Measure the distance between the bottom of the frame to the straightedge; it should be 2.023–2.417 in. (51.5–61.5mm). If the distance is not as specified, reposition the frame member at the transmission.

       Fig. 2: Sleeve and reamer bolt positioning — Miata with N4A-HL and NC4A-EL transmissions

14. Install or connect the following:
    • Oil cooler lines using new gaskets
    • Dipstick tube and dipstick
    • Electrical connectors and the vacuum hose
    • Speedometer cable
    • Driveshaft by aligning the matchmarks. Tighten the bolts to 22 ft. lbs. (30 Nm).
    • Exhaust system
    • Front pipe to the exhaust manifold using a new gasket. Tighten the nuts to 34 ft. lbs. (46 Nm).
    • Performance rod
    • Engine undercover
    • Shift rod
    • Negative battery cable
15. Fill the transmission with fluid.
16. Start the engine and check for leaks and proper operation.