Main.TrailIndexPage | Transmission and Clutch | Clutch

Clutch

This component is part of Transmission and Clutch.

Definition

The clutch (German: Kupplung) is a critical component in the manual transmission system of the vehicle. It is comprised of several parts: clutch disc, pressure plate, throwout bearing, master cylinder, slave cylinder, and the clutch pedal assembly. All are located at the interface of the engine and transmission, with hydraulic lines facilitating actuation. Its technical and common name is simply “clutch” or “clutch assembly.”

Function

The clutch enables a temporary disconnect between the engine and the transmission, allowing for smooth gear changes and safe starts and stops. Depressing the clutch pedal pushes fluid from the master cylinder to the slave cylinder, which moves the throwout bearing, disengaging the clutch disc from the flywheel. Unique to Mercedes is the “over-center return spring” for the clutch pedal, which assists the driver:

  • At the top of the pedal stroke, the spring pushes up.
  • At the bottom, it aids the driver in keeping the pedal down.

This design reduces driver effort during clutch use.

Maintenance

Routine Service

Regularly change the clutch fluid! Older Mercedes often stay parked for long periods; sitting can cause the master cylinder’s valves to stick and let the pedal drop to the floor at stoplights. Dirty or old fluid accelerates corrosion and sticking. If you acquire a car that’s been unused, start with a full fluid flush.

Bleeding the Clutch

Air in the hydraulic system leads to insufficient pedal return and disengagement problems. Bleeding is best performed by:

  • Using a pressure bleeder attached to the bleed screw of the slave cylinder (forces air up/out).
  • Alternatively, connect a hose from a front brake caliper’s bleed screw to the slave and use the brake pedal as a pressure source.
  • Pumping the clutch pedal to bleed is largely ineffective.

Diagnosis and Adjustment

If the pedal doesn’t return fully (sticks halfway), there’s likely a hydraulic issue—replacing the pedal spring will not help. This is usually due to:

  • Incorrectly adjusted slave cylinder
  • Air or moisture in the system
  • Sticking master/slave cylinder valves

Check for leaks and pedal feel. If the pedal sticks 2" above the floor, it may be an issue with the over-center return spring or pedal bushings—often solved with lubrication and adjustment, not parts replacement. A master or slave cylinder rebuild may be needed if leakage or internal wear is present; rebuild kits are inexpensive ($20) and the job can be completed in less than two hours.

Rebuilding Cylinders

  1. Drain fluid at the slave cylinder.
  2. Remove the master and slave from the car; disassemble.
  3. Clean thoroughly with alcohol; remove surface rust.
  4. Replace seals with care, flanges facing fluid; reassemble with brake cylinder paste.
  5. Refill hydraulic system from below using a pump; top-fill often traps air.

Clutch Replacement

Before starting, gather:

  • Clutch disc
  • Pressure plate
  • Throwout bearing
  • Crankshaft centering bearing
  • Front/rear transmission seals
  • Shifter bushings (good time for replacement)
  • Transmission flange lock plate (#186-262-0173)
  • Driveshaft flex disc and rear transmission mount kit (#113-586-0024), if needed

A clutch alignment shaft and a four-pronged spanner socket for the transmission flange are necessary special tools. Be sure to tighten the spanner nut properly—an incorrectly torqued nut can damage the transmission and render the speedometer nonfunctional.

Often, resurfacing or balancing the flywheel is warranted for smooth clutch operation, but this isn’t always necessary. Flywheel balancing requires specialized equipment and may be expensive, but can yield significant improvement in drivability.

Symptoms When Faulty

  • Pedal sticks to the floor or doesn’t return fully.
  • Rough or hard gear engagement, especially reverse.
  • Pedal must be lifted with your toe.
  • Fluid leaks at the master or slave cylinder; pedal sinks at stoplights.
  • Unusual noises or vibration with the pedal in or out.

How to Test for Faults

  • Check for hydraulic leaks and pedal free play.
  • Inspect fluid clarity and level; flush if dirty.
  • Depress and release pedal—feel for smoothness, sticking, or loss of resistance.
  • Persistent issues after bleeding/adjustment may require cylinder overhaul.

How to Fix/Change

  • Bleed the system per above if pedal is spongy or slow to return.
  • Rebuild master/slave cylinders as needed.
  • Lubricate pedal bushings and check freeplay at the slave rod.
  • Replace clutch disc, pressure plate, and bearing as described if slipping or chattering occurs.


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