Clutch - Bleeding & Diagnosis Procedures
Bulletin: 85-7-11Date: Sept 1985
Ref.. No.: 85-267-7
SUBJECT: HYDRAULIC CLUTCH - BLEEDING AND DIAGNOSIS PROCEDURES
MODELS AFFECTED: 1985 SKYHAWK AND SOMERSET REGAL
The bleeding and diagnosis procedures for the hydraulic clutch were omitted from the 1985 Buick Chassis Service Manual.
BLEEDING HYDRAULIC SYSTEM
The process of removing air from the pipe line and cylinders is known as "bleeding" and is necessary whenever any part of the system has been disconnected, or level of fluid in the reservoir has been allowed to go below the minimum level so that air has been drawn into the master cylinder.
NOTICE: Never, under any circumstances, use fluid which has been bled from a system to fill the reservoir as it may be aerated, have too much moisture content and possibly be contaminated.
1. Clean dirt and grease from the cap to ensure no foreign substances enter the system.
2. Remove cap and diaphragm and fill reservoir to the top with approved brake fluid only. (Brake fluid must be certified to DOT 3 specification).
3. Fully loosen bleed screw which is in the slave cylinder body next to the inlet connection.
4. Fluid will now begin to move from the master cylinder down the tube to the slave. It is important that for efficient gravity fill, the reservoir must be kept full at all times.
5. It will be noticeable at this point, that bubbles will appear at the bleed screw outlet. This means that air is being expelled. When the slave is full, a steady stream of fluid will come from the slave outlet. At this point, tighten bleed screw to a torque of 2 N-m.
6. Assemble diaphragm and cap to the reservoir, fluid in reservoir should be level with step.
7. The hydraulic system should now be fully bled and should release the clutch. Check vehicle by starting, pushing clutch to the floor and selecting reverse gear. There should be no grating of gears, if there is, the hydraulic system still contains air. If this is the case, repeat bleed procedure.
ON-VEHICLE SERVICE
NOTICE: The clutch hydraulic system is serviced as a complete unit, it has been bled of air and filled with fluid. Individual components of the system are not available separately.
CLUTCH HYDRAULIC DIAGNOSIS
FAULT CAUSE ACTION
Pedal travels to floor. No pressure Master or slave cylinder faulty, Hose/ Check components and replace.
or very little resistance. pipe burst or leaking. Connections Then bleed system.
leaking. No fluid in reservoir.
Pedal travels to floor. No pressure Rear seal failure in master cylinder. Service or replace unit. Then
or very little resistance. Fluid in bleed system.
master cylinder dust cover
Pedal travels to floor. No pressure Master cylinder center valve seal Service or replace unit. Then
or very little resistance. Fluid faulty. bleed system.
level in reservoir rises as pedal is depressed.
Fluid in area of master cylinder Rear seal failure in master cylinder. Service or replace unit. Then
dust cover and on pedal. bleed system.
Fluid in slave cylinder and on Slave cylinder plunger seal faulty. Service or replace unit. Then
cylinder body. bleed system.
Pedal feels "spongy" when Air in system. Check fluid level. Bleed system.
depressed. Check and replace parts if
symptom recurs.
Pedal effort high with long pedal Incorrect size master or slave Check and fit correct unit. Then
travel. cylinder fitted. bleed system.
Clutch mechanism faulty. Gearbox
Unable to select gears. Pedal
faulty. Check and replace clutch or gear effort and travel normal box components.
Clutch slip. Clutch plate worn. Master and/or Check and replace. Clean and
slave cylinder seal worn or dam- service or replace units. Remove
aged, Overfilled reservoir. excess fluid.
Pedal effort and travel normal. Clutch or gearbox mechanism Check and replace faulty or worn
Difficulty in selecting gears. faulty. Wear in clevis linkages. components. 520039-SB7