© 2012 Delmar, Cengage Learning Clutch Diagnosis and Service Chapter 70

© 2012 Delmar, Cengage Learning

Clutch Diagnosis and Service

Chapter 70


Objectives• Diagnose clutch problems before disassembly• Adjust a clutch• Install a replacement clutch• Inspect worn or damaged clutch parts and

determine the cause of the problem


Introduction• Early automobiles

– Produced with manual shift transmissions• Required clutch

• Some new model cars and light trucks have manual transmissions– Utilize a clutch as well

• Common to have at least one new clutch installed• Clutch work is not difficult to learn• Diagnose problems before and after disassembly


Diagnosis of Clutch Problemsand Clutch Noises

• Clutch will normally last more than 100,000 miles– City driving in heavy traffic reduces clutch life

– Diagnose problems before disassembly

• Listen for unusual noises and isolate them– Noise when clutch is first engaged: due to

problem with friction lining

– Noise only happens when foot is resting lightly on pedal: release bearing is probably at fault


Transmission Noise• Sometimes noise occurs only when engine is

idling in neutral with clutch engaged– Front transmission bearing on input shaft and

mainshaft pilot are only bearings rotating• One of these bearings is probably the noise

source


Pedal Problems and Slipping Clutch

• Diagnosis on basis of pedal feel– Pulsating pedal: something internal in clutch

– Pedal is hard to depress: binding linkage or cable

• Slipping clutch– Tested by putting it in the highest gear range

• Several possible reasons clutch slip– Partial engagement

– Partial disengagement


Dragging Clutch• Clutch drags: does not release properly

– Disc stays attached to the flywheel

• Test for a dragging clutch– Start engine and run it to normal operating

temperature

– Engine at idle and transmission in neutral: depress clutch to floor

– Wait ten seconds

– Shift transmission into reverse


Oily Clutch Facings• Oil leaking onto clutch disc:

– Causes clutch slipping• Disc may overheat and burn its friction surface

• During repair:– Disc and pressure plate are replaced

• Rest of the parts are thoroughly cleaned

– Determine and repair oil leak source• Oil on front side of flywheel: crankshaft rear seal

or external engine leak• Oil on rear side of flywheel: bad front transmission

seal or overfilled transmission


Damaged Friction Surfaces• Damage to friction surfaces of clutch cover or

flywheel can cause clutch to slip– Clutch slips: heat is generated

• Flywheel or pressure plate can be warped• Flywheel, pressure plate, or disc can all become

glazed• Flywheel is commonly resurfaced


Chattering or Grabbing Clutch• Chattering clutch

– Occurs when pedal shakes as clutch is engaged

• Grabbing clutch – Occurs when friction disc does not slip normally

but grabs all at once

• Causes of clutch chatter or grabbing– Oil on friction lining

– Worn or broken motor mounts

– Worn or bent clutch fork


Clutch Service• Includes:

– Checking and adjusting free play and travel

– Hydraulic component service

– Clutch replacement

• Some clutches require adjustment– As the disc wears, it becomes thinner

• Results in release levers moving closer to the release bearing which means less clearance


Servicing Hydraulic Components• Internal hydraulic system problems

– Usually the result of dirty or aging internal rubber sealing parts

• Master cylinder and slave cylinder– Either can develop leaks

• Different methods can be used to bleed air from a clutch hydraulic system– Gravity bleeding


Clutch Replacement• Includes replacement of several parts

– Disc

– Release bearing

– Clutch cover

– Pilot bearing or bushing

– Sometimes a flywheel and/or front transmission seal

• Often come in a clutch parts kit


Remove a Transmission or Transaxle

• Follow instructions in service manual– Rear-wheel-drive cars, mark and remove:

• Driveshaft• Vehicle speed sensor• Crossmember

– Front-wheel-drive cars, remove:• Halfshafts• Transaxle


Clutch Removal• Major steps

– Remove fasteners between housing and engine• Do not lose the dowels

– Mark parts before disassembly

– Use an aligning arbor to hold the disc while removing clutch cover

– Inspect part for damage

– Clean parts with hot soapy water, break parts cleaner, or alcohol


Flywheel Removal• Major steps

– Before removing: mark it

– Inspect for damage• Surface is flat: sanding disc can be used to

deglaze surface• Heat from slipping clutch causes cracks and

warpage• Flywheel can be resurfaced


Flywheel Starter Ring Gear Replacement

• Sometimes a ring gear will be damaged due to starter motor problems– Remove worn gear

• Use hammer and punch

– Install new gear• First heat to make it larger• Chamfered side of teeth are aimed to same side

of flywheel as old teeth


Flywheel Installation and Inspecting New Parts

• Important considerations– Use correct quality screws on flywheel and clutch

cover

– Tighten screws to specified torque

– Always compare new parts with old ones• Take the old parts to the parts store

– Different sizes of release bearings, diameters of clutches, and numbers of input shafts

• Available within same mark of car


Pilot Bushing Service and Clutch Disc Service

• Pilot bushing or bearing in crankshaft – Often replaced as part of clutch job

• Bushing removed: use a puller

– Check fit on transmission input shaft before installing

• Clutch disc – Normally replaced any time clutch is apart

– Replacing will often result in like-new clutch performance

– Relatively inexpensive



Clutch Cover/Pressure Plate Service

• Clutch cover assembly: replaced with disc– Clutch cover may be reused

• Inspect pressure plate to see that it is flat


Clutch Installation• Important considerations

– Be sure to clean your hands

– Thin film of grease is applied to input shaft splines

– Install disc in the right direction• Attach disc and clutch cover on flywheel• Align the clutch disc to pilot bearing

– Tighten all clutch cover screws

– Use a jack to lift transmission into place


Release Bearing Service• Release bearing sometimes fails

– Clearance-type release bearings when driver rides the clutch

– Usually replaced on a preventative maintenance basis

• Sometimes collar is reused

• Major steps– Check front bearing retainer

– Lubricate release mechanism contacts



Clutch Housing Installation• Major steps

– Install sheet metal pieces that might fit between engine block and clutch housing

• Be careful nothing is trapped between the surfaces of clutch housing and engine block

– Install transmission and remaining parts

– Perform adjustments and fluid level checks

– Test-drive

Documents

© 2012 Delmar, Cengage Learning Clutch Diagnosis and Service Chapter 70