Manual transmissions are MORE FUN, but do require some maintenance and occasional replacement of parts. Most questions I hear have to do with bleeding the system or inadequate release of the clutch when the clutch pedal is engaged. The first of a three part series appears in this issue. Here are my tips on this subject!!!
Clutch Bleeding
You can do it your way, but this method always works for me. After checking to be sure there are no leaks in the clutch hydraulic system, complete ALL of the following steps before test-driving the car:
1) Install a helper in the driver’s seat to push in and let out the clutch pedal on command.
2) Remove the cover from the Master Cylinder reservoir.
3) Top off fluid in the reservoir.
4) During the course of this procedure DO NOT allow the "helper" to "pump" the pedal. The "helper" is to depress and release the pedal on command only, DO NOT PUMP THE PEDAL. (See theory below)
5) You will be opening and closing the bleed screw on the Slave Cylinder as instructed below. CAUTION: During this procedure protect your eyes from squirting brake fluid.
6) (Helper) Press clutch pedal in fully and hold.
7) (You) open the bleed screw to allow fluid to escape.
8) (You) Close bleed screw.
9) (Helper) Release pedal completely.
10) (You) Top off fluid in reservoir.
11) Repeat steps #6 thru #10 no less than 5 times before going to #12 below. NO PUMPING!
12) You have now bled the Master Cylinder and the hydraulic line. YOU ARE NOT DONE YET!!!!! We must now bleed the Slave Cylinder (this is what the manual does not tell you).
13) With no further action to be done with the clutch pedal, you can now remove the "helper" from the driver’s seat and have them help you do the following steps.
14) After topping off the Master Cylinder, completely remove the bleed screw from the Slave Cylinder.
15) Have the "helper" stand at the ready with the bleed screw and the appropriate wrench for installing the bleed screw.
16) PROTECT YOUR EYES!
17) With the bleed screw removed, use both hands to grab the push rod coming out of the Slave Cylinder and push it into the Slave Cylinder as far as it will go AND HOLD it in.
18) Your "helper" will now install and tighten the bleed screw while you hold the plunger in.
19) When the bleed screw is tight, release the rod and as it comes out guide it into the proper position on the clutch arm.
20) Top off the Reservoir and the job is complete.
If you have replaced the Master and/or Slave Cylinders with non-GM parts, sometimes they never will work even with repeated bleeding. What happens with the non-GM parts is that when doing item #19 above air is sucked into the cylinder past the piston and the cup seal. There is nothing you can do with this except to replace the cylinder with the correct GM Delco part. Several times I’ve tried to use the aftermarket parts and they have NEVER worked right. Trust me here, buy the Genuine GM parts and save yourself a lot of trouble.
Theory:
Why do I insist that you REMOVE the bleed screw when pushing the plunger in on the Slave Cylinder? This is simple hydraulics. Fluid or air will always go the direction of least resistance. When you are pushing the rod into the Slave Cylinder you will find that it is impossible to push it in at a slow and steady pace. If you push it in too fast with the bleed screw still in and just unscrewed a few turns, some of the brake fluid and/or air in the Slave Cylinder will go back up the hydraulic line that you just bled, thus necessitating your starting over.
When bleeding your clutch.... The biggest mistake or misconception a person can make is to pump the pedal.
The clutch hydraulic system, unlike the brake hydraulic system SHOULD NOT BE PUMPED. The only thing that happens when you "pump" the clutch is that you make any large air bubbles in the hydraulic system into a bunch of small air bubbles. By the way, these small air bubbles are harder to bleed out than larger bubbles.
You cannot "pump up" a clutch. If you have to "pump up" the clutch to make a shift then you have a leak and you can bleed the system a dozen times to no avail.
On the clutch, think about it now, if you could "pump-up" the clutch would not the throw-out bearing tend to invert the clutch diaphragm and travel toward the engine until it met up with something solid like the flywheel? On a braking system, when you "pump-up" the brakes you force the brake pads into the rotor until the line pressure builds up enough that the resistance you feel when pumping the pedal increases. Further, as you press harder and harder on the brake pedal the pads just increase their pressure on the rotors.
GM thought this through when they designed the system. To avoid "pumping up" the clutch hydraulic system, GM put in a small bleed back hole in the Master Cylinder (by the way, not an original idea, all hydraulic clutches have it). This bleed back hole relieves line pressure every time the pedal is at the top of the stroke. Did you notice when you "pumped up" the clutch pedal that it does not firm up like the brake pedal does?
The only thing you accomplish when "pumping up" the clutch pedal is to take any air bubbles that are in the system and atomize them into smaller air bubbles, thus making the problem worse. Remember when you were at the soda shop as a kid and your parents kept telling you to stop playing with you soda and straw? Same theory here! The more you move that soda through the straw the smaller the air bubbles become.
By the way, the "hand pumps" work ok, but I have never needed to buy one yet. With the hand pumps you still need to ensure that the Slave Cylinder gets completely bled.