Clutch - Low Biting Point

[benmack99]

TLDR; I have replaced clutch, release arm/bearing, hydraulic master and slave cylinders, and pressure bled system, yet biting point is still too low. What have I missed?

Weird one this! Car is a 2007 VW Fox, 1.2 CHFB, with conventional clutch, hydraulic release. It has a very low biting point, with pedal about 1-2cm from floor, and drags while changing gear. It's been like this since we bought the car 2 years ago. Decided to fix it to avoid trashing gearbox.

I replaced clutch (friction disc and pressure plate), release arm and bearing, and master and slave cylinders.

But the biting point is unchanged, 1-2cm from floor, and drags with pedal on floor.

I've gone through the entire system, cannot see anything wrong. Pressure bled the hydraulics several times, fluid coming through clean, so I'm pretty sure there is no air in system. The flywheel looked clean, no wear or scoring. I checked end float on crank, around 0.1-0.2mm. The release arm ball joint inside the bell housing looked solid and clean. I've had a good look at the pedal assembly, can't see anything wrong there. The master cyl pushrod moves as the pedal moves, no slack or give, as expected.

There is no manual adjustment on this car, the hydraulics auto-adjust when clutch pedal is released, as follows:-
- pedal return spring pulls master cylinder to end stop, opening fluid inlet from reservoir
- spring on slave cyl holds it against release arm/bearing, removing all slack in system
So when you start pressing pedal, the clutch release bearing will start moving immediately.

What I find really weird is how precise the biting point is, 1-2cm above the floor, and unchanged despite having changed everything. This suggests the problem lies elsewhere. But where? I'm out of ideas!

Any suggestions welcome! Please heeelp!

[Panamax]

Is there any mechanical adjustment available beteen the clutch pedal and the pushrod into the master cylinder?

[benmack99]

No, there is no mechanical adjustment anywhere. Both master and slave cyls have fixed length pushrods. Pedal and release arm/bearing also have no adjustments. The entire system is auto-adjusting as described above. Thanks

[finlo]

There could be lots of end float on the crank like old Triumphs that were famous for it!

[benmack99]

Yeah, I did wonder, but I checked that, see above. Thanks

[TwinKam]

Have you had anyone observe the slave push rod whilst you press the pedal, to see if they really do coincide?
Before dismantling anything again, I would try other methods of bleeding the system, eg: conventional manual bleed, reverse pressure bleed, pump-up and open bleeder whilst pedal held down, or bleed at other points along the line first, eg: master cylinder, 'damper' if one is fitted, flexi hose connections).

[benmack99]

Good points, thanks. Unfortunately I cannot see the slave pushrod - the slave cyl mounts in a hole in the bell housing such that the pushrod (and release arm) are hidden inside the housing. I am thinking of unbolting the slave cylinder and making a test jig (e.g. pushing against a strong spring), so I can see it moving. Or as a last resort I can drill a hole in the bell housing and measure travel of release arm... I can calculate the expected travel based on ratio of cylinder diameters squared (master is 15.9mm, slave 19.0).

Re bleeding, I have tried various ways (manual, pedal-down, and pressure bleed using a Gunson Eezibleed). I'm 99% sure I've cleared all the air, because after replacing the master cyl (which was the last time I opened the hydraulics) I did a pressure bleed and saw all the air from the master come through, then put another few hundred ml fluid through without a single air bubble. And the layout is sensible, both cylinders are horizontal, reservoir above master above slave, no obvious air traps. And if the problem was air, I would expect variations in the biting point after each time I replaced a hydraulic part and rebled the system. And the flexi hose looks sound, no sign of swelling.

However I will try your idea of a reverse pressure bleed, I can connect the eezibleed to the slave bleed nipple.

Cheers

[Panamax]

benmack99 said:

No, there is no mechanical adjustment anywhere. Both master and slave cyls have fixed length pushrods. Pedal and release arm/bearing also have no adjustments. The entire system is auto-adjusting as described above. Thanks

I suggest you post a photo of how the pedal mechanism connects to the pushrod.

[oakdale]

Is there a flexi hose in the clutch pipe?
If there is, check it's not bulging when the clutch is operated.

[benmack99]

oakdale said:

Is there a flexi hose in the clutch pipe?
If there is, check it's not bulging when the clutch is operated.

There is, it looks sound, no sign of bulging (and the hydraulic pressure is pretty low on a clutch). But if I get totally stuck I will try a new hose. Thanks

[oakdale]

benmack99 said:

There is, it looks sound, no sign of bulging (and the hydraulic pressure is pretty low on a clutch). But if I get totally stuck I will try a new hose. Thanks

There will be several hundred psi pressure in a clutch hydraulic system but I wouldn't change the hose for the sake of it if it looks sound.

[benmack99]

Panamax said:

I suggest you post a photo of how the pedal mechanism connects to the pushrod.

Here's some photos of the pedal assembly, and a VW diagram





I have removed the blue switch to ensure it is not stopping the pedal, and the metal bar that crosses in front of the pedal does not touch it, so when released the pedal moves up until the master cyl hits its internal endstop (at which point the fluid inlet is open, allowing the system to auto-adjust).

As you can see from the diagram, the master cyl (item 20) has a fixed length pushrod, which clips into pedal using item 22. No adjustment. And I have fitted a new cylinder and clip (22) so no wear.

The return spring (item 13, with green end cap in first photo) is an over-centre arrangement - once the pedal is half way down, it actually helps push the pedal down, assisting the driver. But with pedal up, the spring pushes the pedal to the master cyl internal endstop.

There is minimal slack between starting to press the pedal, and the pushrod starting to move (though I will double check that when home this evening).

Also here's a pic of the slave cylinder on the gearbox (see red arrow), looking down at top of gearbox, from LH side of car (apologies for poor quality, I took it before dissassembly just as a reminder of where things go). As you can see, the pushrod is hidden inside the bell housing.



Also a pic of the slave cylinder, showing the pushrod (there is a spring inside the bellows that pushes it out against the release arm)



And a diagram of the clutch - the slave cyl pushrod pushes the top of the release arm (7) towards us, and the spring inside the slave cylinder holds the release bearing against the clutch (when the pedal is up, no hydraulic pressure), so there should be no slack anywhere in the system. I replaced items 1-8, and item 9 (bottom pivot for release arm) looked sound and solid.

[TwinKam]

Do you feel a resistance for the last say 5mm of insertion of the slave, ie the pushrod has contacted the release arm and is starting to compress its expansion spring?

[GreenV8S]

Presumably you had this problem before you started replacing stuff. How did the problem start - suddenly, or gradually?

[benmack99]

TwinKam said:

Do you feel a resistance for the last say 5mm of insertion of the slave, ie the pushrod has contacted the release arm and is starting to compress its expansion spring?

Yes, the pushrod is pushed pretty much all the way back in as I fit the slave to the car.

[benmack99]

GreenV8S said:

Presumably you had this problem before you started replacing stuff. How did the problem start - suddenly, or gradually?

It was like this when we bought the car, about 2 years ago. It might have got slightly worse over those 2 years, difficult to be precise, but the bite point was always very low. And the key point is that it has hardly changed at all between before and after replacing the clutch and hydraulics

[littleredrooster]

This is not the flexing bulkhead problem that some VWs had in the past is it?

[benmack99]

littleredrooster said:

This is not the flexing bulkhead problem that some VWs had in the past is it?

There's a thought. I assume the problem is the master cylinder assembly flexes downwards, thus reducing the pedal travel? I haven't noticed anything but I will double check

[Glosphil]

My wife's 2019 Skoda Fabia with the 1.0TSi (110) 3-cyl engine also has a low biting point on the clutch. So low that both of us have to set the seat further forward than we want. The local VAG specialist says no adjustment possible.

[Polome]

A good few years ago I had a similar problem with a gen 1 Renault Espace it was cable operated but gave the same symptoms as you. I set the adjuster a couple of times to no avail. A close look at the clutch peddle showed a crack opening up when peddle depressed thus reducing fulcrum movement. A new peddle cured it. When the Renault parts man handed me the new one I said it s exactly the same as my old one and will probably crack too yes they all do that sir see you in about a year! . last ever Renault. May be worth a check.

Edited by Polome on Friday 9th January 07:08

Edited by Polome on Friday 9th January 07:09