Clutch, sometimes it works, sometimes it doesn't.

Hi.
It's my neighbor's car.
Volkswagen Golf 4, 1.6 liter engine.
MKB = AZD
Gearbox = ERT
Sometimes, the clutch is not fully disengaged, which means the gear cannot be shifted properly when stopped at a traffic light.
When the engine is turned off, the gears engage perfectly.
If the engine is started with a gear engaged, it will already have some initial forward momentum.
Everything up to this point makes sense to me.
The problem is that it can be turned on perfectly again the next day.
You can easily drive around the city for an hour without any problems.
Sometimes you experience this effect, but it goes away again the same day.
It was also vented several times.
It's likely that the hydraulic clutch is drawing in air.
Isn't there supposed to be a leak somewhere?
Unfortunately, everything is completely dry.
The lever between the shaft and the release bearing was intact, but it was still replaced.
Does anyone have a suggestion for what should be traded next?
Donor cylinder or receiver cylinder?
What about the connection to the main line?
Can poetry be over?
Best regards, Frank.

Hi,

Your clutch isn't disengaging properly. You've already checked one possible cause.
Are there any mechanical damages to the clutch or its coil springs, or is there a problem with the needle bearing where the gearbox shaft connects to the crankshaft? I'm not sure if the latter applies to your vehicle.

Since separating the clutch from the engine is quite a complex process, I would suggest using a borescope to inspect the clutch bell.

You can usually tell if the clutch isn't fully disengaging due to a faulty slave cylinder or master cylinder.
The relevant part is the distance from where the clutch pedal becomes heavier to press to the floor.

Best regards, Rainer.

Hello!

If there is a defective slave cylinder on the transmission, there must be a leak of brake fluid from that location.

You should shine a flashlight into the footwell and check the master cylinder to see if any brake fluid is leaking from it. Or at least, traces of it are visible.

Based on the description, that would be my favorite.

I also have a Golf 4, and once the pressure plate of the automatic clutch broke. It just snapped verschandeln through. There were similar problems as the ones you're experiencing.

Normally, when dealing with such problems, you start by replacing the cheapest and easiest-to-replace parts. So, the donor cylinder.

While you can technically block a pipe using a plug, it's not a truly reliable solution. Sometimes it works, and sometimes it doesn't.

Okay, here's my advice:
new actuator cylinder
But be careful, bleeding the clutch hydraulics is the biggest problem.
It's not easy, and it requires patience and composure.
In an emergency, vent from the bottom up.

If there is a defective slave cylinder on the transmission, there must necessarily be a leak of brake fluid there.

Is it really mandatory?
The receiver cylinder is completely dry.
I need to check the donor cylinder again, but I believe it was dry as well.
I also vented from bottom to top.
If both cylinders are now dry, can we definitively say that both cylinders are definitely intact?

Could an air bubble sometimes become noticeable and sometimes not?
Is that possible?
I find it hard to imagine a hardware-related issue that would simply cause something to either work or not work.
I will take another, closer look at it this afternoon.

For comparison, again.
With the clutch fully depressed, the estimated distance required for the car to move forward slightly in my 1.4-liter engine is approximately 6 cm.
For the 1.6 version, this distance is approximately half.

I'm going to take another look at it today and ventilate it thoroughly again.
Best regards, Frank.

You can usually tell if the clutch isn't fully disengaging because of a faulty slave cylinder/master cylinder.
What is relevant is the distance from the point where the clutch pedal becomes heavier to press until it reaches the floor.

I have two cars here for comparison.
1.4, mine, and healthy.
Neighbor's 1.6-liter engine.

Depressing the clutch pedal until the slave cylinder/lever moves:
Both are approximately 1.5 cm.
When the pedal is fully depressed, the lever moves 15 mm in both vehicles.
With the pedal fully depressed and slowly released, the undamaged car begins to pull forward after 6 cm.
The 1.6 model starts doing it after about 3 centimeters.
Since the clutch pressure plate and release lever were replaced, the clutch has been working perfectly, except for one instance.
That specific '1' makes me think.
Sometimes it works, and sometimes it doesn't...
I'm going to bleed the system from bottom to top again shortly, and then I'll see how it goes.
As a last resort, the only option remaining is to replace the clutch, but it would be quite unfortunate if the problem isn't related to the clutch.
Best regards, Frank.

Hi,
If the hydraulics are working correctly, then the remaining possibilities are a broken pressure plate, a disassembled spring, or a clutch disc that is no longer sliding properly on the splines of the transmission input shaft.

Take a look at this.
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Postscript.
I've only experienced this once before, in an old Passat.
The pilot bearing in the crankshaft had disintegrated, which caused the transmission input shaft to continue rotating even when the clutch was engaged.



Best regards from Berlin,
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F B wrote:

Quote: If there is a defective slave cylinder on the transmission, there must necessarily be a leak of brake fluid there. Is it really mandatory? The receiver cylinder is completely dry. I need to check the donor cylinder again, but I believe it was dry as well. I also vented from bottom to top. If both cylinders are now dry, can we definitively say that both cylinders are definitely intact? Best regards, Frank

Hello!
Yes, that's correct.

The clutch slave cylinder on the transmission is like a piston in a tube.
If the seal is leaking, the liquid will come out. You can see that.

The master cylinder on the pedal assembly is somewhat more complex in its construction:
The piston builds up the pressure. If the seal is defective, it's possible that the pressure is leaking past the seal.
You step on it, but you don't really build up enough pressure. This also happens with a time delay.
You can sometimes wait for a minute there with the clutch pedal pressed down. Whether anything will change.

The master cylinder has a second seal behind the piston, which seals the area towards the reservoir. This is where the actuation rod passes through. That's due to the design, and there's no other way to do it.
Perhaps you've seen or disassembled a master cylinder from an old car or motorcycle before, and it works in a similar way.

I'll start by checking the rear seal, the one towards the footwell. If it's leaking from there, the master cylinder is definitely faulty. In such cases, there are often problems with air trapped in the system.


However, it can also be defective if it doesn't provide enough space for the feet. Then it won't maintain the built-up pressure properly.
You shouldn't expect any air to be trapped inside.

So, I also remember that about 20 years ago, I completely replaced the clutch on a BMW. However, that didn't solve the problem; ultimately, it was the distributor.
To be honest, I was a bit taken aback, like, "Just quickly put in a new clutch, and please have it done by tomorrow..."
It wasn't ready-made.
I noticed that you can shift gears immediately after pressing the clutch pedal, but a few seconds later, it's no longer possible.
In that case, the donor cylinder was also dry on the outside.
However, it didn't maintain the pressure properly.

We'll continue to monitor the situation for a few more days and then decide what to do.
Best regards, Frank.

Hi.
The master cylinder was replaced, and the clutch actuation has been working perfectly for days.
Apparently, an air bubble can actually form and hide.
I don't understand it, but it works.
Let's see how long it lasts.
Best regards, Frank.

Thank you for your feedback!

F B wrote:

Hello. The master cylinder was replaced, and the clutch actuation has been working perfectly for days. Apparently, an air bubble can actually form and hide. I don't understand it, but it works. Let's see how long it lasts. Best regards, Frank

Hello!

Air bubbles are compressible, no matter where they are located.
And not just occasionally, but always.

Let's assume that the sealing ring on the actuator piston is no longer sealing properly.
Due to its age, and there are also 1 or 2 holes in the housing for fluid drainage; the sealing lip constantly rattles over these holes.

It must have been like that. The system sometimes fails, depending on the temperature or how quickly the clutch is engaged.
Sometimes it happens, and sometimes it doesn't.

Air bubbles are compressible, no matter where they are located.
And not occasionally, but always.

The system sometimes fails, depending on the temperature, or depending on how quickly the clutch is engaged.
Or just like that, and then not again.

That's the contradiction that I'm having trouble with.
It would mean that the donor cylinder could potentially self-vent and draw in air again through the leaky seal.
But I'm probably just overthinking things.
Both cylinders were replaced, and it's working now.
Best regards, Frank.