Clutch Master Cylinder Question

[tcndeb]

Replaced the master cylinder on the slave on my daughter's 06. Trying to bleed the master, but I can't get ANY resistance what so ever, even though the hose isn't connected to the slave yet. According to my reading, there should be a check valve and the pedal should be stiff until I release the bleed valve. What am I missing?

[fdryer]

If I'm not mistaken, no check valve in the master cylinder so pushing the rod should result in brake fluid flow without any resistance. Service manuals describe connecting everything before bleeding procedures. There's a bleed valve to use for bleeding the system.

Where is your information from?

[fdryer]

Here's a reprint from the fsm. The master is supposed to be reconnected before bleeding procedures.

[tcndeb]

Originally Posted by fdryer

If I'm not mistaken, no check valve in the master cylinder so pushing the rod should result in brake fluid flow without any resistance. Service manuals describe connecting everything before bleeding procedures. There's a bleed valve to use for bleeding the system.

Where is your information from?

http://www.saturnfans.com/forums/sho...ave%2Acylinder

ETA: I believe the check valve is at the connection to the slave. One of the diagnostic checks said to unplug that line , and the check valve should prevent you from pushing the pedal down if the master is in good shape.

[fdryer]

PM waiter21 if you believe a check valve exists otherwise the service manual doesn't mention a check valve.

Another (partial) reprint from the fsm;

Hydraulic Clutch Operating Members
The clutch system consists of the following components:

• A master cylinder with a reservoir
• A switch
• An actuator cylinder connected to hydraulic tubing
• The pressure plate
• The clutch cover
• The diaphragm springs
• The clutch disc
• The torsional springs

With the depression of the clutch pedal, the clutch master cylinder becomes pressurized from the force of the push rod into the master cylinder. This forces hydraulic fluid into the tubing from the master cylinder to the actuator cylinder. The actuator cylinder then pushes the release bearing into the diaphragm spring to disengage the clutch. A hole in the cowl panel accommodates the master cylinder. A quick connect coupling helps route the hydraulic tubing. The actuator cylinder is inside the transmission and on the input bearing retainer. The hydraulic control system can be replaced without having to gain access to the clutch system internal components, simply engage the quick connect coupling mounted through the transmission housing. No adjustments to the clutch system are necessary. As the clutch wears, the fluid level in the master cylinder reservoir changes to compensates for clear wear. A new system will have fluid in the reservoir. An electrical switch on the push rod has two functions. One function is a clutch interlock, ensuring the engine does not start unless the clutch pedal is engaged, positioned to the floor. The second function is to cut off the cruise-control system, if equipped, when the clutch pedal is engaged. Some systems may have a clutch pedal hold down assist spring. Its purpose is to keep the clutch pedal depressed. This reduces driver fatigue during stop and go traffic.

[waiter21]

Take a look at the procedure I used.

There is a check valve on the master cylinder disconnect. When the hose is removed, it will prevent flow. If your master is bleed properly, you will not be able to move the pedal if the hose is disconnected from the slave....

You should be able to bleed the master cylinder while its disconnected from the slave.. After you successfully bleed the master, connect it to the slave, and you may then also need to bleed the slave.

http://www.saturnfans.com/forums/sho...d.php?t=222577

[tcndeb]

Originally Posted by waiter21

Take a look at the procedure I used.

There is a check valve on the master cylinder disconnect. When the hose is removed, it will prevent flow. If your master is bleed properly, you will not be able to move the pedal if the hose is disconnected from the slave....

You should be able to bleed the master cylinder while its disconnected from the slave.. After you successfully bleed the master, connect it to the slave, and you may then also need to bleed the slave.

http://www.saturnfans.com/forums/sho...d.php?t=222577

Is the check valve on the fitting at the slave cyl or at the master cyl end of the hose? Cause with the hose connected to the master, but NOT connected to the slave I get zero resistance.

[waiter21]

The check valve is part of the connector. It allows you to pre-bleed the master cylinder prior to connecting it to the slave cylinder..

By pre-bleeding the master cylinder, it makes it a lot easier to bleed the slave.

Connect your bleed hose to the bleed port, then twist the bleeder valve to open/close the bleed valve, Its just like a bleed port on a brake cylinder.

With the connector disconnected from the slave.

1) Top off the fluid.

2) Connect the bleed hose and the other side in a clear bottle. Use a wrench to knock the valve lose, then re-tighten by hand.

3) Have someone press the pedal as far as it will go and then hold it.

4) Lossen the valve, then re-tighten the valve. Then release the pedal.

5) continue to do this.

6) The pedal will start getting harder, and will not push down all the way. Hold light pressure on the pedal, then do the release / re-tighten the valve.

When this happens, the pedal will go to the floor and you'll get a squirt of fluid out the bleed hose.

7) Keep doing this until the pedal stays at the top when you attempt to press it. Check the fluid level constantly (every two or three strokes. If the fluid goes empty, you need to start over again.

WARNING - DO NOT use a lot of force when pressing the pedal down.. (use normal clutch force).. If you press real hard, you will break the plastic plunger, and ruin your day...

[tcndeb]

Thanks for the info both waiter and fdryer.

[Bruce Rock]

Originally Posted by fdryer

PM waiter21 if you believe a check valve exists otherwise the service manual doesn't mention a check valve.

A quick connect coupling helps route the hydraulic tubing. The actuator cylinder is inside the transmission and on the input bearing retainer. The hydraulic control system can be replaced without having to gain access to the clutch system internal components, simply engage the quick connect coupling mounted through the transmission housing.

[/I]

Since all the quick disconnect coupling I've seen (Air, hydraulic, and beer tappers) had check valves I assume all quick disconnect couplings use at least one check valve and sometimes two.

[fdryer]

I agree but without knowing this system, I did not assume the master has a check valve. From pictures shown on rockauto.com, the master has a feed from its reservoir and a plastic fitting I presume is the pressure output. Without presuming this master has a check valve, the fsm doesn't state anywhere to bleed this master by itself. Procedures state to connect everything then bleed using procedures as written. If I go by procedures and how the op cannot build pressure with his new master not connected, there may be several reasons for this. A) the new master is assembled dry so it cannot develop pressure until fluid is poured in, b) the fitting doesn't have a check valve and fluid would come out without pressure as soon as the master is filled and pumped a few times to prime the piston chamber - without any connection, pumping the master by hand may result in fluid simply coming out without any pressure since its not connected to the rest of the hydraulics. In order to build up pressure. Hydraulic systems components must be connected then hydraulic pressure can build up in a closed system to bleed out any air. The clutch master cylinder without a check valve cannot build up any pressure until its connected to the rest of the clutch hydraulics.

If I'm not mistaken, brake master cylinders do not have check valves on the output ports - bench bleeding requires setting up a way to prevent brake fluid from simply pouring out the output ports by way of plugging the ports temporarily to allow building pressure to fill each piston chamber until both chambers fill with fluid and comes out both ports before mounting to the car and connecting brake lines for more bleeding. This can become an oily mess if the output ports aren't temporarily plugged and removed just before reconnecting brake lines. The clutch master cylinder may be designed the same as brake master cylinders and with far less lines to bleed, simply easier to connect to the hydraulics and bled using the bleed screw.

[tcndeb]

OK, Finally gotten back around to this job after being out of town for a bit. Problem remains. I have been trying to get this master cylinder bled on and off maybe 5 different times. Still no resistance at the pedal what so ever. Any ideas on what I am missing?

[jcperezma]

Did you ever figure it out?

[tcndeb]

Originally Posted by jcperezma

Did you ever figure it out?

Basically just kept bleeding it until it built up resistance. Took all day.

[tcndeb]

While we got this car up and running a while ago, my daughter says there is an issue still. It seems every now and then, especially when the pedal is pressed quickly, the pedal goes down a little and then seem stops like it hit a brick wall. Can't press it all the way down no matter what. Let the pedal up and try again and it will go down normally. She broke the MC plunger the first time it did this.

Question is, could this be the check valve where the pipe connects to the MC going bad? I can't think of anything else that might be causing this issue.