Clutch Disengagement

[Lutz Kramer]

After the clutch of my BJ8 sometimes kept hanging when the clutch was disengaged, i.e. the pedal comes back but the clutch remains disengaged and the car is not driven, I first bled the clutch hydraulics. I then replaced the master and slave cylinders a year ago. So it's unlikely that there is a defect there, but you never know. Last but not least, I have just installed a new clutch and the release bearing. However, it still happens every now and then that the clutch gets stuck in the disengaged position. Maybe someone has an idea where the error could be.

I also noticed that the clutch fork returns relatively slowly when you take your foot off the pedal. It takes about 1-2 seconds until the slave cylinder has completely retracted.

 

[Bob_Spidell]

Did you inspect the clutch fork and its bushings? They do wear, eventually, and possibly bind the fork. It's remotely possible the seals in the slave cylinder are possibly inhibiting movement. The slave cylinder is returned by the strong diaphragm springs in the clutch cover; weak ones might cause the problem, but your clutch would likely slip a lot.

What kind of clutch/brake fluid do you use? I have seen glycol fluid gel; that could cause a problem.

 

[Lutz Kramer]

Bob, the clutch fork is moving freely. Of course under pressure it might be a liitle different
I use DOT 4.
You might be right considering the slave cylinder being the problem, even it is only 1 year old. The same goes for the main cylinder.
Tomorrow I first will make a video of the movement of the fork. I don't have any feeling if the movement is realy slow or normal.

 

[GregW]

How old is the hose that attaches to the slave cylinder?

 

[Lutz Kramer]

I had in mind to post a Video where you can see how long it takes for the clutch to close. But unfortunately the forum server doesn't accept mp4 videos that are longer than a view seconds.

 

[Lutz Kramer]

Instead of the video I post a view fotos of the ineterior of the slave cylinder.
Maybe smebody can tell me if I better would replace it or still can use it. Of course all seals will be replaced.

 

[Bob_Spidell]

I (personally) would re-sleeve or replace the cylinder; some say they can be honed, some say no way (the piston can be cleaned up). But, it's not likely the pitting is the problem; it will eventually cause leaks past the seals. Greg's suggestion of the flexible line causing the problem is the most likely. If your car happens to have the original brake and clutch flex lines they should all be replaced.

 

[Jack T]

Yes, the flexible hose connected to the slave cylinder may be deteriorated internally, acting somewhat like a one-way valve.

 

[Lutz Kramer]

Bob, the clutch fork is moving freely. Of course under pressure it might be a liitle different
I use DOT 4.
You might be right considering the slave cylinder being the problem, even it is only 1 year old. The same goes for the main cylinder.
Tomorrow I first will make a video of the movement of the fork. I don't have any feeling if the movement is realy slow or normal.

Is it normal that the passage (port) to the brake fluid reservoir is only opened by the piston when it is about 1mm in front of the snap ring at the end of the cylinder? This might cause the problem, that the port is sometimes open and sometimes not and is therefore preventing the clutch to engage.

 

[Patrick67BJ8]

It sounds like the slave cylinders hose.

 

[Bob_Spidell]

The 'passage' to the reservoir--sometimes called a 'foot valve'--is spring-loaded should be open when the pedal is at full height so the M/C can refill. Then it closes when you press the pedal, sealing the flow to the reservoir. If it's stuck open you won't have pedal and your clutch won't disengage; if it's stuck closed the M/C won't refill with fluid and the clutch won't operate properly for long.

 

[Lutz Kramer]

It sounds like the slave cylinders

I will definitely dismantle the hose today and check it

 

[Lutz Kramer]

The 'passage' to the reservoir--sometimes called a 'foot valve'--is spring-loaded should be open when the pedal is at full height so the M/C can refill. Then it closes when you press the pedal, sealing the flow to the reservoir. If it's stuck open you won't have pedal and your clutch won't disengage; if it's stuck closed the M/C won't refill with fluid and the clutch won't operate properly for long.

The foot valve is sometimes open and sometimes closed. The difference is just 0.5 mm of movement of the piston, because the rubber seal is in a "plastic basket" at the end of the cylinder and only has 0.5 mm of play. Maybe the seal has extended or swollen by the years or however you want to describe it. I already have ordered new seals and will find out.

 

[Lutz Kramer]

I think I have found the main problem for the slow clutch engagement. It's probably the flex hose that is connected to the slave cylinder, which seems to be the original. So Greg seems to be right. There is still a tiny pin-sized opening that you can't see on the photos, but that's not enough to allow brake fluid to pass through fastly when engaging the clutch (almost no backflow). Therefore, the clutch fork only moves very slowly. But I won't finally know until the new flex hose and the two cylinders are here. I will report again then.
I have cut the hose into 4 pieces to find out where it is clogged. The complete hose is swallen and almost clogged.

 

[GregW]

To avoid future problems, you may want to put your car on a statin.