Quote:
Originally Posted by AKA_951
That's a really good idea. I think I might try that. Another concept is how much to raise the front or rear of the car. Ideally, you want both to point up. The master is already pointing up and the slave is close to neutral. Maybe raising the rear just enough to have them both point up is ideal. Then I can't get under the car.
I was also thinking my pedal, right now, could be under vacuum since the last time I closed the system, the pedal was in. I doubt that vacuum pressure could affect clutch spring force though. Who knows
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I've had every component of the brake system open and disassembled on my bench. The slave cylinder has a nipple at the top rear and an inlet at the front. With the rear of the car elevated (or the slave cylinder dismounted and tilted back end up, you will get all air out if bleeding from the top down. Since the fluid wants to drain out from the master to the slave, you can push fluid up, which will clear bubbles from the tubing and push them into the master, then let gravity drain the fluid back and close the slave nipple. This clears the slave and tubing.
The master is trickier. The outlet is low at the front. There is a piston inside (with a spring in front to push it to the rear) that divides the master cylinder into multiple compartments. Air bubbles can get trapped around the piston. Finally, there's a hole at the top of the master that leads to the reservoir. The hole is connected in front of the piston (and from there to the slave) when the piston is full back (foot off pedal and pedal up). The system seals itself with the hole behind the piston as the pedal moves to the floor. When you lift off the pedal, the spring in the master slides the piston to the rear and eventually connects the front half to the hole letting in more fluid. If you forget to move the pedal when bleeding, you don't bleed the rear half. If you leave the pedal down, you tend to trap air around all this.
If someone tries to adjust the brakes at the pedal, and removes the clearance (so the pedal pushes on the rod all the time, the piston can't move far enough back to open the system to the fluid reservoir. As the clutch wears, it can't get the additional fluid it needs (unless the internal master cylinder seals leak) and you get problems - pedal won't come back up, etc.
In theory, it should be possible to pump out all the air with the pedal, if the rear of the car is up, and I have done this, but it just isn't reliable enough, at least not for me. The only thing that worked repeatedly for me was to bleed in both directions. I was able to do it with a large syringe (came with a master cylinder I bought for another car) and with an oiler (clean/new - the type that holds a cup of oil and pumps it out with a trigger), but the easiest method for me was what I described above. It let me see when air stopped bubbling out.