Throw-out bearing: what is it for and how to inspect it

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Throw-out bearing is installed in engine clutch. The clutch is meant for passing of driving moment from engine crankshaft to gearbox input shaft. Besides, it also fulfills following functions: provides fast and reliable engine connection to transmission; removes engine load pulse from engine and gearbox in the moment of gearshift; provides smooth breakaway after speed shifting; smooth gear shifting on the move; disconnects engine and transmission immediately after pressing clutch pedal.

• What is throw-out bearing for?
• How to inspect a throw-out bearing.
Throw-out bearing: what is it for and how to inspect it

What is throw-out bearing for?

Throw-out bearing is one of the main components meant for reliable work of clutch. There are two types of throw-out bearing: mechanical and fluid. To mechanical refer bail and wheel bearings, which consist of bearing itself, clutch and springing clip that fixates connector. The throw-out bearing is installed on gearbox input shaft runner. Its cone moves freely longwise. Connector is attached to bearing. It receives the force, which applies driver while pressing a clutch pedal and which is passed by mechanic and fluid drive and also passes this force to throw-out bearing.

By gearing clutch and connector the bearing shifts along gearbox input shaft runner and presses release levers with ferrule. Overcoming the contact spring force it pushes off the driving disk from driven disk and detaches transmission counterbrace. Pressing the levers is performed by outer race. Through its rotation the driven disk is unloaded and, thereafter, gearbox. Releasing a clutch pedal, the throw-out bearing is unloaded through press levers with the help of contact springs. The bearing returns to original position, providing smooth torque transfer from engine to transmission.

Fluid throw-out bearing has the same function, but its construction is a bit more complicated. For its performance hydraulic liquid is used, which is passed to bearing under pressure.

Throw-out bearing: what is it for and how to inspect it

Fluid throw-out bearing consists of cylinder, bearing, piston plunger, rubber surrounds, dust cap, inflow input connection and drain connection. Pressing a clutch pedal, liquid comes under butt end of fluid bearing piston. The piston moves under liquid pressure, presses disconnecting levers, moves driving disk from driven, disconnecting engine and transmission counterbrace. After releasing a pedal a draining port opens in main cylinder and all components return to original position.

How to inspect a throw-out bearing

Despite their high reliability, throe-out bearings also break down. Their failures usually occur because of improper vehicle exploitation. The throw-out bearing comes into operation after pressing clutch pedal. In this moment it is under impact load, which causes increased wear and breakdown of rubbing parts.

One of the main mistakes of throw-out bearing exploitation is their continuous kick into gear, which starts after pressing clutch pedal or if driver is unwilling to put car with automatic gearbox in neutral especially while city driving with long traffic jams. Severe loads impact bearing and clutch while hard acceleration, wheel trailing, continuous rough road or off-road driving.

There is one more exploitation mistake: untimely replacement of breaking down throw-out bearing. There are no existing instrumental inspections for bearings. Their failures can easily be noticed by indirect indications and while visual inspection after its removing. Indirect indications of mechanic and fluid bearings are a bit different.

Throw-out bearing: what is it for and how to inspect it

If you suspect that your bearing is malfunctioning (noise in gearbox, impossible to shift gear etc.), then you should inspect clutch linkage adjustment and pay attention, whether there is lash between working cylinder rod and connector. After that you must check working capacity of throw-out bearing: start a car, press a clutch pedal and if there is noise (knock, whistle etc.), which disappears after releasing a pedal, then the bearing of your car works improperly. For further inspection you must remove the gear box, remove connector then remove bearing and crutch with gearbox input shaft runner.

Inspect carefully if there endfloats in bearing, jamming while spinning, intense noise, mechanical tearing. If malfunction occurred because of lack of oil or dirt, then you must clean it and oil the runner. Then install the bearing back and pay attention to absence of jamming, while its move along runner.

Install everything back, checking if there is no lash between working cylinder rod and connector. Check the work of throw-out bearing while engine is intact. If there are no bearing malfunctions or you have suspicions of other clutch parts malfunctions, you should do its diagnostics.

To indirect indicator of fluid bearing malfunction refer (except those mentioned above): clutch pedal fall due to bearing piston or driving gear parts depressurization. That’s why before removing gear box, it is necessary to inspect main and working actuating cylinder, also inlet tube. Check the liquid in tank, make sure that there is no air bound in clutch linkage.

Throw-out bearing: what is it for and how to inspect it

Tools for throw-out bearing inspection. As was mentioned above, there are no special tools or gears for bearing check. The way to do it is visual inspection or indirect indicators.

Experience has shown that if there are bearing malfunctions (overheat, increased wear, endfloat, cracks, disintegrations, etc.) it must be replaced. When the gear box is removed, check other clutch components. Such work is pretty dirty and responsible, also requires car ramp or inspection pit. So, it is better to be done on vehicle service station.

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