Valeoscope Commercial Vehicles Clutch 2020

Diagnosis Hard gear shifting

3.1.2 External reasons due to the clutch linkage Vehicle behavior ●● Difficulty in gear shifting when running or when the vehicle stops. ●● Gear noise (scratching noise) in reverse gear engagement. ●● Difficulty or inability to engage or disengage the gear. ●● Vehicle jumps slightly when the gear is engaged from idle position. Reasons ●● Pedal system: Jamming Wear Adjustments (Pedal height, Travel stopper pin) ●● Clutch linkage: Mechanical: Cable, sheath and stopper articulation axis (wear and jamming) Hydraulic & Hydro-pneumatic: Master and slave cylinder (leakage, adjustment) ●● Release travel is too short: repair of clutch linkage Diagnosis Measure the release travel: To determine if it is the clutch which causes the issue, we have to check the fork travel to estimate the release travel. ò ò Release travel too short  Repair of the clutch linkage ò ò Release travel conforms to specifications  Disassemble the gearbox from the engine and clutch inspection. Attention Ɂ Ɂ Do not disassemble the clutch unless the release travel is not correctly set according to the manufacturer's specifications. Advice   To have a good estimation of clutch release travel, the measurement must be done as close as possible to the clutch.  Check the presence of air in the hydraulic system (Bleed the hydraulic system according to the manufacturer’s specifications).

The travel A of master cylinder is not long enough due to a wrong adjustment of the pedal travel stopper screw 2. 

Vehicle behavior ●● Hard gear shifting while driving or when the vehicle is stopped. ●● Gear noise (scratching noise) when reverse gear is engaged. ●● Difficulty or inability to engage or disengage the gear. ●● In idle speed with clutch in declutch position, the vehicle moves with the gear engaged. Reasons ●● Gearbox (poor gear conditions or synchromesh…) ●● Gearbox shifting system (wrong conditions or incorrect shifting system adjustments, fork, …) ●● Inertia (time to stop the rotation of input shaft) ●● Inertia sensibility depends on the gearbox's design and its conditions. ●● It also depends on the lubricant's quality and temperature. Diagnosis ò ò In some gearboxes, the gears cannot stop immediately after declutching. Gear scratching noise happens during a fast gear engagement (mainly reverse gear, non synchromesh gear). To define whether the reverse gear's scratching noise is due to gearbox inertia or to a wrong clutch release, we can do as follows: ● ● Declutch and engage the gear  scratching noise. ●● Remain in declutch position, move the gearshift lever to idle position. ●● Wait for 15 seconds and engage the reverse speed. If no scratching noise  Gearbox inertia If scratching noise  Wrong clutch release Measurement method 1. Vehicle stopped. 2. Gearbox and clutch at normal operating temperature. 3. Engine at idle speed. 4. Evaluate the necessary time to engage the reverse gear without the scratching noise or the 1 st gear. 5. Proceed by successive steps starting with a very short time (1 second) or with the max acceptable time (7 seconds).

Example ●● Declutch, wait 1s, engage the gear = scratching noise ●● Declutch, wait 2s, engage the gear = scratching noise ●● Declutch, wait 3s, engage the gear = scratching noise ●● Declutch, wait 4s, engage the gear = no scratching noise Engagement time without scratching noise in 4s = acceptable Attention Ɂ Ɂ If the time is more than 7 seconds, it is necessary to check whether it is due to gearbox inertia (gearbox lubricant, engine idle speed…) or wrong clutch release, which needs to be at 15 seconds. Ɂ Ɂ If the reverse gear can be engaged, the issue is not caused by the clutch or the clutch linkage. Advice   Check that all adjustments have been done according to the truck manufacturer specifications.  Even if the issue happens to only one or two gears, the conditions of the gearbox and its linkage have to be checked.

Pedal

Slave cylinder: The release travel C is not long enough due to wrong adjustment of release push rod X . 

Slave Cylinder

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