Clutch Master Cylinder Failure After Replacement

Hello everyone,

I need a little inspiration from you.
I replaced the clutch on a Multicar M26 and afterwards I discovered that it no longer disengages properly. If I pump the pedal about 5 times, I can then engage a gear and start moving.
I removed the clutch slave cylinder and was able to hold it in place while a second person pressed the pedal.
The release lever is easy to operate and properly installed.

Am I correct in my diagnosis, and for what reason could the solenoid valve become defective after being replaced?
Could the donor cylinder have been moved to an unusual position because the receiver cylinder was fully extended, causing it now to allow fluid to pass through internally?

Best regards,
Thilo

Hi,

Either there's air inside or the seal is defective.

Best regards, Rainer.

Hello!
You can't really damage the master cylinder because, unlike main brake cylinders, it is constantly being fully depressed.

Did you have the hydraulic line open, and did you need to bleed it again?

So, if I read this, I think there's air in the system.

The hydraulic system for the clutch is usually very difficult to bleed.
In difficult cases, I have vented from the vent valve of the slave cylinder to the reservoir using a vacuum pump.

I've also replaced the clutch on an M 26 before, and I don't recall it being particularly problematic.

My first thought was that it might be air pressure, so I immediately tried to vent it, but no air came out.
I vented it at approximately 1 bar of pressure.
The system wasn't open, and that's also why I find the explanation given about the system's behavior to be implausible.

@Steffen
Did you build a special adapter for reverse bleeding, or did you just improvise something and work with low pressure?

Thank you.

Then I'm betting on a torn rubber seal...

Hello!

Previously, there was a method for bleeding the hydraulic system of the clutch.
by connecting a hose from the front brake caliper to the clutch slave cylinder. You would then simply pump it in a closed loop, and this worked particularly well with the electric brake actuators found in older VWs.

Based on the description here, I think there's air in the system. You know how it is: by repeatedly and quickly pumping with the pedal, you compress the air bubbles in the system, and they can't expand back out so quickly due to the long, thin lines.
After waiting for 5 seconds and releasing the pedal, the air bubbles expand again, pushing the brake fluid back into the reservoir.

Of course, that then raises the question:
Could the donor cylinder have been the cause of the repair?
During my youth, I once replaced the clutch on a BMW, but it didn't work with the new clutch. It turned out that the slave cylinder wasn't building up enough pressure.

Tip:
First, bleed the system from bottom to top. Air may potentially enter the system, perhaps through the receiver cylinder if it suddenly and quickly decompresses. I'm not sure, but I see this as a possibility.
"And yes, I've actually made an adapter for my ventilation device that allows me to do this. But it's nothing special, just two tubes pushed together and connected to a fitting that happens to fit."

If things get too difficult:
The clutch slave cylinder on the transmission should leak if it is defective.

The donor cylinder doesn't necessarily have to be used.
Let's see if everything is dry where the rod goes in. If it's dry there, then the inner seal could be broken (like it was with my BMW before).
"For cases like these, I've made some custom blind plugs that I use to seal off the line for testing. The pedal has to stay completely locked in place."

After replacing the clutch and gearbox on our Galaxy, I had to bleed the system multiple times before the clutch could be properly engaged again, and I also had to press the pedal frequently in between.

However, in this case, the cycle was necessarily open.

Hi there,
I completely agree with Steffen. Bleeding hydraulic clutch systems can sometimes be a really annoying process. We once had the same problem with an E30; it took about 10 bleeding attempts before the clutch started working normally again.
Ultimately, the hose leading to the left front brake caliper was also the problem.

Best regards from Berlin,
Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Greetings,

Thank you for your suggestions. I spent about an hour bleeding the brakes, but it didn't get any better. Then I bought a master cylinder for 100 euros, and after another hour of bleeding, it finally worked. Steffen's tip about reverse bleeding was ultimately what made it successful.
In the end, I had to add two bars to the device and check the expansion tank until no more air came out.

The clutch was only replaced because the engine had been removed and the torsion spring was broken.

Thank you again.
Thilo.

Here's some feedback again.

The clutch failed again six months later.
At that time, only the friction disc was replaced due to the broken torsion springs, which was a major mistake. The main reason for this was that there are no more pressure plates available for this vehicle. They have been discontinued, and a conversion kit for the subsequent model costs €1200.

After the printer broke down again, I visited all the authorized repair shops in the area, and surprisingly, the smallest workshop with the most disorganization actually had a replacement print head in stock for around €250.

Since then, everything has been working as it should, and the bleeding process was successful on the first attempt.

I explained my problem to the seventy-year-old owner, and he immediately understood. After being removed and reinstalled, the printing plate here no longer has the necessary tension, so it always needs to be replaced after a certain amount of use.

Best regards,

Thank you for your feedback.

At work, I have a new colleague who previously worked at a smaller truck repair shop in Schneeberg.

We were also discussing the new Multicar models during breakfast recently.
"He also complained quite a bit, calling it a chaotic construction that was impossible to repair and extremely expensive."