Hi all,

 

2014 2ltr tdi Estate. Clutch pedal losing pressure regularly and I have to manually pump pedal to gain pressure. 

 

I have replaced the slave but no joy. Now looking at doing the master and while going that far may aswell do clutch plate so before incurring this cost are there any other possible causes? Is there a non return valve somewhere in the system getting stuck or will I just go ahead with the full job?

 

Any thoughts are welcome 

 

Thanks

 

Niall

7 hours ago, Niall83 said:

 

 

I have replaced the slave but no joy. Now looking at doing the master and while going that far may aswell do clutch plate so before incurring this cost are there any other possible causes? Is there a non return valve somewhere in the system getting stuck or will I just go ahead with the full job?

 

 

 

Is the level of the brake/clutch fluid going down in the reservoir?   Any fluid dripping from the bottom of the gearbox bellhousing?

 

It sounds like you have actually changed the master cylinder? - this is the one mechanically operated by the clutch pedal. The diesel version has a concentric slave cylinder inside the bellhousing where you have to remove the gearbox to fix so you might as well replace the whole clutch assembly -  it'll be contaminated anyway if fluid leaking from the slave cylinder. Also consider the condition of the Dual Mass Flywheel.

 

 

 

 

Edited 1 November, 20214 yr by bigjohn

Bigjohn,

 

Appreciate the reply. Sorry i keep mixing them up, yes it's the master i have replaced and the fluid level in reservoir is not dropping which is confusing me

37 minutes ago, Niall83 said:

Bigjohn,

 

Appreciate the reply. Sorry i keep mixing them up, yes it's the master i have replaced and the fluid level in reservoir is not dropping which is confusing me

That doesn't mean the slave isn't leaking. You can get an internal leak which loses pressure on the slave piston without losing fluid from the system. To test this:-

 

1. Start the engine on level ground. You'll see why.
2. Select first or reverse gear and leave your foot on the clutch.
3. Wait 5 minutes and see if the car starts to move off (or stalls). If it does, then you have a slave cylinder leak.

I'm not sure that will give me an accurate diagnosis. I may lose pressure once a month or at times a few days in a row. Sometimes one or two manual pumps and I'm away, other times I may have to pump for 3 to 5 mins before O gain pressure and it may or may not go quickly again

The concentric cylinder is a known fail point though - don't think there is an inline valve but not 100% sure. I discovered mrs BJ's Panda had a strange valve on the end of the external slave when clutch was making a funny squeak when hot - in the end the pedal stuck to the floor. New slave & valve restored normality.  I can't peek on my own Superb as the clutch is rather different on the 1.4tsi.

Edited 1 November, 20214 yr by bigjohn

Been there done that got the T shirt.

 

Bleed the slave cylinder, its very easy all you have to do is turn the knurled thumbnut 1/2 a turn and close it as soon as fluid come out, you dont even need to remove the air filter but advisable the first time to know what is what, after that you can do it by feel. Towards the end I had to do mine several times a day and on any journey have to find somewhere to pull off before any junctions or roundabouts after cruising a few miles.

 

They dont leak fluid but draw in air, against all logic given that they have a hydrostatic head of fluid above them, but thats what they do, it come in via the O ring joint where they went from a one piece casting to two plastic mouldings, replacement is a gearbox out job and you are advised to try and find a new old stock aluminium VAG one and not the later plastic one that will likely fail again.

 

With the knowledge of how the parts seperate it may even be possible to replace the O ring working through the starter motor aperture, you might need to withdraw the gearbox a few cms.

 

If you get a new cylinder which will be plastic you will see the joint that I am speaking of, I reckon sealing around the inlet pipe where it protrudes from the bellhousing with Sikaflex would stop the vibratory movement and prevent the new one failing.

 

Touch wood mine is 100% trouble free after I pulled the 4x4 transmission and replaced it with an early VAG cast ally one.

15 minutes ago, bigjohn said:

The concentric cylinder is a known fail point though - don't think there is an inline valve but not 100% sure. I discovered mrs BJ's Panda had a strange valve on the end of the external slave when clutch was making a funny squeak when hot - in the end the pedal stuck to the floor. New slave & valve restored normality.  I can't peek on my own Superb as the clutch is rather different on the 1.4tsi.

That is the clutch bleed block known by VAG as the clutch peak torque limiter, it allows fluid tobe pushed into te cylinder as fast as you like (depressing the clutch pedal) but throttles it on the return stroke, their logic being they would prefer the clutch to slip than the transmission to fail if you dump the clutch.

 

It causes big time problems of clutch slip on the higher powered TDi's when upshfting quickly to the higher gears from high revs with full boost and mashing the throttle, if you overtake someone and misjudge the relative speeds, change up and get on the throttle quickly to complete the misjudged manouvre you will have no drive when you need it most.