SACHS Workshop tip:

Grabbing Clutch.

General note

Our useful tips provide only an overview. The installation instructions and operating instructions provided by the vehicle manufacturer and the warning and safety instructions contained therein must be observed! All work must be performed by a trained professional. The pictures used and the procedure described in our tips are examples and may vary depending on the vehicle manufacturer and axle design.

Clutch grabbing – what is it?

When alternating torques occur in the slip phase (e.g., due to friction value fluctuations) and causes vibration of the driveline, this is called clutch grab. Instead of slipping evenly, the clutch grips suddenly, then loses contact. The driver experiences these oscillations as vibrations, rolling or bucking. A grabbing or juddering clutch produces a severe vibration motion and can have various causes.

Why does a clutch grab?

In order to know how to stop the clutch grabbing, it is necessary to find out what causes the juddering problem. Apart from the clutch itself, poor engine setting or worn engine or transmission mounts can prevent smooth clutch engagement. Other possible causes for grabbing clutches are installation of the wrong clutch disk or incorrect installation.

Check:

Correct parts for the vehicle?
Associated system components / check all parts for wear and correct settings
- Clutch release system?
- Driveline bearing?
- Engine management?
- Deficiencies in the driveline?

Facings slightly contaminated with oil or grease

Cause:

Damaged transmission or engine sealing
Excessive grease on the transmission input shaft or pilot bearing
Leakage in hydraulic actuation system
Contamination of the friction surfaces due to incorrect handling

Consequence:

Even minor traces of oil or grease have a significant adverse effect on friction values, and thus start-up performance when the clutch is engaged.

Facings slightly contaminated with oil or grease

Hub spline damaged

Cause:

Transmission shaft and clutch hub forced together during installation
Excessive angular movement during transmission installation

Consequence:

Clutch disk does not move or moves jerkily on the transmission input shaft.

Comment:

Also often causes drag.

Hub spline damaged

Housing deformed

Cause:

Attachment screws not professionally tightened during installation. Not tightened in a cross-wise, over-center sequence.
Clutch pressure plate not correctly centered in the flywheel.

Consequence:

Lop-sided pressure plate lift

Comment:

Drag may occur if the problem is severe.

Housing deformed

Tangential leaf springs deformed

Cause:

Incorrect counter-holding technique, e.g., with a screwdriver, when bolting down clutch pressure plate (MX pressure plate)
Damage during transport, storage or handling

Consequence:

Lop-sided pressure plate lift

Comment:

May also cause drag.

Important:

Secure the flywheel against turning with a suitable tool provided by the vehicle manufacturer for this purpose.

Tangential leaf springs deformed

Worn engine / transmission mounts

Cause:

Worn parts

Consequence:

Leads to pseudo grab (bonanza effect) in driveline during setting off and gear changing or load changing.

Comment:

Always check these components for signs of wear (e.g., cracks in the rubber-metal joints or damaged joints).

Worn engine mount

Related SACHS tools

SACHS Clutch Tool Kit for Passenger Cars and Light Commercial Vehicles

The clutch tool kit is ideal for disassembling and installing XTend and conventional clutches as well as for centering clutch disks.

Find out more about the SACHS clutch tool kit

SACHS Lateral Run-Out Testers for Passenger Cars and Trucks

SACHS offers lateral run-out testers for clutch discs with diameters of up to and starting from 240 mm, depending on whether passenger car or truck clutches need to be tested.

All about SACHS lateral run-out testers