M96 & M97 Rear Main Seal Replacement

Rear Main Seal (RMS) Replacement

Applicable Models

Porsche 97–08: Boxster (986/987), Cayman (987), 911 (996/997) – M96 & M97 Engines

Overview

The rear main seal (RMS) prevents oil leakage between the crankcase and rotating crankshaft. Over time, seal material hardens and leaks develop. Replacing the RMS requires removing the transmission or flex plate.

Safety Precautions

• Allow engine and transmission to cool completely before starting.
• Wear safety glasses and gloves at all times.
• Work on a flat surface; engage the parking brake and chock wheels.
• Support the vehicle securely on jack stands if raised.
• Disconnect the battery negative cable before beginning.

Tools & Materials

Preparation

1. Chock wheels, raise the rear if needed, and support on jack stands.
2. Disconnect the battery negative cable.
3. Remove rear engine cover and any heat shields blocking access.

Step-by-Step Procedure

1. Remove Transmission or Flex Plate

1. Disconnect shift linkage (manual) or torque converter harness (Tiptronic).
2. Remove driveshaft or propshaft: unbolt flange (8 mm) and slide shaft free.
3. Support transmission with a jack under the transmission case.
4. Remove bellhousing bolts (10 mm) around the housing flange.
5. Lower transmission to expose flywheel or flex plate.
6. Remove TTY bolts (22 mm) from flywheel/flex plate; keep them organized.
7. Remove flywheel or flex plate and set aside on a clean surface.

2. Extract the Old RMS

1. Clean the bellhousing seal area with brake cleaner.
2. Center-punch the old seal at one of the molded dimples.
3. Drill a 2 mm hole through the seal material, using a spacer to avoid over-penetration.
4. Install a screw into the hole until firm.
5. Attach slide hammer to the screw and gently extract the old seal.
6. Clean the bore with brake cleaner and inspect for burrs; smooth if necessary.

3. Inspect Bore with Go/No‑Go Gauge

Before installing a new seal, it’s critical to verify the crankcase seal bore is within factory tolerance. An out-of-spec bore—due to casting irregularities or wear—will continue to leak even with a new RMS.

1. Insert the “Go” end of Tool 9699-1 into the bore; it should slide in smoothly to the seating shoulder.
2. Flip to the “No‑Go” end; if this end also enters the bore, the seal bore is too large and the case must be machined or replaced.
3. If the “Go” end fits but the “No‑Go” end stops at the shoulder, the bore is within tolerance, and you can proceed.

4. Install the New RMS

1. Verify the new PTFE RMS is mounted on its plastic support ring; do not touch the seal lip.
2. Install insert guide 9699-2 onto the crankshaft pilot.
3. Place the new seal (dimpled side away from the bore) onto the guide.
4. Attach the installation bell of Tool 9699 and turn the 19 mm bolt clockwise until it stops.
5. Confirm the seal has seated 13 mm deep from the crankshaft mating surface.
6. Remove the tool assembly, leaving the seal in place.

5. Reassemble Flywheel/Flex Plate & Transmission

1. Apply a small amount of Loctite #242 at least 8 mm deep inside each bolt hole.
2. Install new TTY bolts and torque to 19 lb‑ft (26 Nm), then tighten each an additional 120°.
3. Raise the transmission into position, align input shaft, and hand-thread bellhousing bolts.
4. Tighten bellhousing bolts in a crisscross pattern to factory spec (~25 Nm).
5. Reinstall driveshaft or propshaft and reconnect shift linkage or converter harness.
6. Reconnect battery negative cable and lower the vehicle.

Final Checks

• Start the engine; inspect the bellhousing for oil leaks.
• Listen for abnormal transmission noises during engagement.

Tips & Tricks

• Use the go/no‑go gauge before replacing the seal to avoid unnecessary labor if bore is out of spec.
• Keep the new seal in its packaging until installation.
• Never apply oil or sealant to the outer diameter of the PTFE seal.
• Always replace TTY bolts; they must not be reused.