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Independent.ie

Wednesday 26 September 2018

Fix it: how to repair a dumper clutch

After problems arose selecting a gear on a three-ton dumper truck, Jamie Casey set about fixing it. Costing just €230 for parts, here's how he did it

Jamie at work on the three-ton dumper
Jamie at work on the three-ton dumper
A: The clutch assembly itself is sandwiched between the gearbox and the engine, so to access it both of these components must be split apart. The gearbox was unbolted from the engine, and completely removed from the machine.
B: The release bearing was assessed and found to be badly damaged. It had been allowed to travel off centre, and had become unevenly worn. Note the difference between the new and old release bearings, left and right, respectively.
C: A new clutch kit was sourced. Note the pressure plate in the foreground, the clutch disk in the background and the release bearing to the right.
When the gearbox was removed, it was decided to service it. The oil was drained, and found to be of very poor quality. This warranted further internal investigation, so the gearbox was opened up.
E; With the top of the gearbox removed, the inner workings could be inspected. Surprisingly, the gearbox was in perfect condition inside, and was sealed up again without any major works.
F: Having discovered the eccentric wear on the release bearing, I realised that the cross shaft carrying the release bearing could wander side to side by about 12mm. This should not be the case, it should simply rotate when the clutch pedal is pressed.
G: The new kit is ready to be installed. Note the difference between new and old.
H: The pressure plate was bolted onto the flywheel, with the clutch disk clamped behind it, between it and the flywheel.
I: Having reinstalled the clutch assembly and gearbox, the clutch linkage was fitted. When the clutch pedal is pressed, this linkage turns the cross shaft (pic F) to disengage the clutch. Note the two silver 20mm washers between the crank arm and bell hous

Jamie Casey

A clutch assembly is a device which, when disengaged, interrupts the power from an engine or motor to a gearbox. This allows the machine to engage or disengage gears, start or stop, and move off smoothly.

A simple clutch assembly has three main parts; the clutch disk, the pressure plate and the release bearing. The pressure plate clamps the clutch disk up against the engine's flywheel, thereby transmitting the power from the engine through the clutch to the gearbox. To interrupt this flow, the operator presses the clutch pedal and releases the pressure plate, meaning the clutch disk is no longer clamped against the flywheel and the drive is interrupted.

There are generally two common faults with clutches. The first is clutch slippage, recognised as a sudden increases in engine revs without the proportional increase in ground speed, especially while pulling a heavy load. In this case, either the pressure plate is getting weak, or the friction surfaces of the clutch disk are becoming worn.

The second fault is a difficulty in selecting a gear, often without clutch slippage. In this case, the release bearing is generally at fault. What happens is the release bearing becomes worn over time, and is no longer able to push on the pressure plate to release the clutch and interrupt the power from the engine.

The clutch featured here is from a three-ton dumper used for muck shifting duties in a landscaping business. Recently it became very difficult to select a gear, so I knew we had some issue with the release bearings. The new clutch kit was sourced in the UK, and cost €230. The entire job took about six man hours from start to finish, and required pretty basic workshop tools, namely sockets, spanners and a hydraulic jack.

A The clutch assembly itself is sandwiched between the gearbox and the engine, so to access it, both of these components must be split apart. The gearbox was unbolted from the engine, and completely removed from the machine.

B The release bearing was assessed and found to be badly damaged. It had been allowed to travel off centre, and had become unevenly worn. Note the difference between the new and old release bearings, left and right, respectively.

C A new clutch kit was sourced. Note the pressure plate in the foreground, the clutch disk at the back and the release bearing to the right.

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D When the gearbox was removed, it was decided to service it. The oil was drained, and found to be of very poor quality. This warranted further internal investigation, so the gearbox was opened up.

E With the top of the gearbox removed, the inner workings could be inspected. Surprisingly, the gearbox was in perfect condition inside, and was resealed without any major works.

FHaving discovered the eccentric wear on the release bearing, I realised that the cross shaft carrying the release bearing could wander side to side by about 12mm. This should not be the case, it should simply rotate when the clutch pedal is pressed. Some washers would need to be installed during reassembly to prevent the problem from reoccurring.

GThe new kit is ready to be installed. Note the difference between new and old.

H The pressure plate was bolted on to the flywheel, with the clutch disk clamped behind it, between it and the flywheel.

I Having reinstalled the clutch assembly and gearbox, the clutch linkage was fitted. When the clutch pedal is pressed, this linkage turns the cross shaft (photo F) to disengage the clutch. Note the two silver 20mm washers between the crank arm and bell housing body. These were installed to prevent the lateral movement of the cross shaft.


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