Overdrive, replacement

Overhaul instructions

Applies to: 1991–1994; M46

Special tools: 999 2834, 999 2836, 999 2709, 999 5244

New overdrive is a mix of type J and P

The overdrive of type J has been taken out of production and has been replaced by a new J/P-combination with a larger center hole.

The change is a consequence of introducing the larger main shaft in the M46-transmissions from 1987

The larger main shaft is also used in gasoline turbo models from 1986 that has overdrive of the P-type.

New hydraulic pistons in overdrives of type J, J/P and P

Hydraulic pistons with improved seals were introduced successively in overdrives of type J, J/P and P during 1988.

The new seal consists of a heavy-duty O-ring that replaces the existing O-ring and the seal ring made of Teflon. The seal is of a type that lasts longer, which reduces the risk of leakage.

The change takes place from and including the part and serial number.

Overhauling

When overhauling overdrives of type J and J/P with hydraulic pistons of the earlier type, where the Teflon rings are worn out, the pistons shall be replaced with the new type (part number 6 814 454-2) with the new O-ring seal (part number 6 814 455-9). (See instructions below).

Clutch disc 3 502 761-4 shall be installed when slipping occurs. This applies to overdrives with the part numbers noted above.

The service kit (part number 261 183-6) shall be installed to correct defects on overdrives that do not have the above part numbers. The overdrive mechanism and the clutch (that is, reducer valve springs and return springs) must be pressure-adapted. These are included in the service kit.

Replacing hydraulic pistons

Remove the overdrive (see L1-L2 (Unloading)).

Tool 2709

If tool 999 2709 has to be used on a drive flange with three pins, it must be changed as follows:

Drill the two indicated holes to 16 mm.

Remove:

gasket

Pressure plates

Remove the hydraulic pistons

Use pliers when removing

Install:

1. New hydraulic pistons and O-rings
2. Pressure plates, with new nuts

Tighten the nuts crosswise with 10 Nm (1.0 kpm).

Install the overdrive (see Installation ).

Replacing clutch discs/installing service kit

Remove the overdrive (see L1 ).

Tool 2709

If tool 999 2709 has to be used on a drive flange with three pins, it must be changed as follows:

Dismantle the overdrive

Dismantle the clutch unit

Remove the lock rings and pull out sun gears and the clutch disc from the bearing carrier.

Replace the clutch disc

Lubricate the facing on the new clutch disc with ATF-oil, type F or G.

Assemble the clutch unit

Install:

1. the clutch unit
2. springs (new springs if the service kit is used)
3. gasket between the rear housing and the brake drum, so that the gasket ends up in correct position
4. brake drum

Replacing reducer valve springs (when installing service kit)

Remove the oil sump and primary filter

Remove the reducer valve's plug

Use plug wrench 999 2836. Tap on the plug with a plastic mallet to facilitate the work.

Remove the reducer valve and the components

Remove all adjusting washers

Install new valve

(Install the latest version with new, internal spring 6.)

Tighten the plug with 22 Nm (2.2 kpm).

Install the overdrive

See work steps L1-L3 Unloading.

Install the overdrive

See work step L3 Installation

Connect the oil pressure gauge 2834

Remove the plug under the solenoid valve and connect oil pressure gauge 999 2834. Run the engine when the car is lifted and supported.

Read off the pressure when the car runs in high gear (direct gear) at approx. 70 km/h (44 mph). The value shall be approx. 0.15 MPa (21.8 lb/in² ).

Engage overdrive and read off the pressure.

Correct values:

Unloading

To facilitate removal, the car should first be driven with overdrive engaged, then the overdrive is disengaged with the clutch pedal pressed down. The latter is important to avoid torsional stresses in the shaft between the plane carrier and the free-wheel (on the condition that the overdrive works). Any stresses disappear even if the oil with 2.0-2.5 MPa (20-25 kp/cm2) pressure is connected to the outlet at the control valve. With this pressure connected, the overdrive is engaged and disengaged.

Removal

Remove the propeller shaft from the drive flange with tool 999 5244. (999 5244 is not needed for rubber joint.)

Remove the transmission's cross member and lower the transmission.

Disconnect the cables to the control solenoid.

Loosen the screws that hold the overdrive to the transmission. Pull the overdrive unit straight back until it releases from the transmission's main shaft. Use extractor 999 2709 if the overdrive is stuck.

Installation

Move up the overdrive on the transmission's output shaft and tighten the nuts.

Install the transmission member

Connect the cables to the control solenoid.

Plug in the connector for the monitoring function of the torque limiter.

Install the propeller shaft.

Fill oil.

Test-drive the overdrive with the rear wheels off the ground.

Check the oil level.