There's one or two YouTube vids on VAG group cars, but nothing very wonderful to help me see exactly what's involved/how it's done. I've been losing pressure at the pedal BTW, but months go by with it ok. I bought a slave and master. I fitted the slave today.

 

Anyone? Anything here.. 

 

I can't see a knee airbag on my car for example, is that right? Thanks

Edited 9 December, 20241 yr by silver50

If months go by without the problem manifesting then you should wait longer than one day before deciding to change the master cylinder.

 

Was the slave cylinder a concentric one requiring gearbox renewal? They are the most common cause of clutch problems, they will draw in air but not leak so I can understand if you replaced yours, saw no leakage so now suspect the master cylinder.

 

The master cylinder is very simple, far simpler than a traditional one, it has one piston with a fixed O ring contained within the bore, it operates by displacement, if the seal leaks then the fluid will leak out and be visible, it cannot go past the seal and back to the reservoir like a traditional one.

 

Master cylinder replacement is tricky because you are working blind and by feel most of the time, its very easy to dislodge or misplace the seal for the outlet pipe.

 

I would bide my time.

Thanks for your reply. Mine had an external slave cylinder. 
 

I know what you’re saying. Indeed it could be fine for long enough again but I bought both last week AND have the car up for sale. It’d have been quite good to have peace of mind that it’ll be ok. The pedal did come back last time, pulled up by hand, but it completely lost pressure when I was about to turn right at a busy junction. This was after mild playing up on the same day.

 

I’m wondering exactly what does all need to come off/out to get the pedal out and replace the master. It doesn’t seem like a fun job though (understatement!).

Edited 9 December, 20241 yr by silver50

Have you bled the clutch and put new fluid in. Must add my mechanic did this not me.

 

Made a difference on my 1.4tsi

2 hours ago, solwood said:

Have you bled the clutch and put new fluid in. Must add my mechanic did this not me.

 

Made a difference on my 1.4tsi

Yes I’ve bled it but only a bit to get any air out. My car is less than 50k miles but the clutch has always felt a bit high as though a bit worn. It seems to feel a little bit different since bled. Slightly better. 

Well that’s the master cylinder changed today. Lo and behold it still seems to be playing up with the pedal losing pressure.

 

I’m not losing any fluid and it absolutely feels hydraulic like. Pedal feels a little soft and of course is occasionally going very spongy/not springing back.

 

I got a garage to do the master today. He’ll have bled it I’m sure as did I after the slave. Though it hadn’t felt fantastic after the slave, so I’ll try bleeding again.

 

All ears if anyone has any suggestions. Quite frustrating.

Its no surprise to me, I did the same, its the cheaper and easier job so worth a punt before having to bite the bullet and replace the slave cylinder.

 

Bleeding will resolve the problem (air drawn in though the O ring joint between the slave cylinder and feed pipe) but the frequency of failure will become shorter, at the end I was having to bleed every  miles in urban traffic.

 

Bleeding is easy, just open the thumbturn screw and close it as soon as fluid comes out, the air rises to a chamber right under the nipple.

 

Reading back I see that you had already changed the slave cylinder and have now changed the master cylinder, did you pay particular attention to the seal which fits on the end of the rigid pipe which is held in the master cylinder by the spring clip? The old one may have detached and remained in the old cylinder, the new one has to be pressed onto the pipe end with some force until it clips on with a positive action, its very easy to think that it just pushes on the end of the pipe, it sits there quite well but needs to go back further.

 

Of course that part is completely inaccessible and you are working blind.

 

More bleeding will be required with a new master cylinder, the best way is to put a long bleed tube on the nipple and run it up to just above the height of the fluid reservoir, open the bleed nipple and leave it overnight, any air will find its way out through the bleed tube or back up the line through the cylinder, the pedal should be in the upper position, no pumping required.

6 hours ago, J.R. said:

Its no surprise to me, I did the same, its the cheaper and easier job so worth a punt before having to bite the bullet and replace the slave cylinder.

 

Bleeding will resolve the problem (air drawn in though the O ring joint between the slave cylinder and feed pipe) but the frequency of failure will become shorter, at the end I was having to bleed every  miles in urban traffic.

 

Bleeding is easy, just open the thumbturn screw and close it as soon as fluid comes out, the air rises to a chamber right under the nipple.

 

Reading back I see that you had already changed the slave cylinder and have now changed the master cylinder, did you pay particular attention to the seal which fits on the end of the rigid pipe which is held in the master cylinder by the spring clip? The old one may have detached and remained in the old cylinder, the new one has to be pressed onto the pipe end with some force until it clips on with a positive action, its very easy to think that it just pushes on the end of the pipe, it sits there quite well but needs to go back further.

 

Of course that part is completely inaccessible and you are working blind.

 

More bleeding will be required with a new master cylinder, the best way is to put a long bleed tube on the nipple and run it up to just above the height of the fluid reservoir, open the bleed nipple and leave it overnight, any air will find its way out through the bleed tube or back up the line through the cylinder, the pedal should be in the upper position, no pumping required.

 

Thanks J.R. 

 

Appreciate the guidamce and suggestions. I got a garage to change the master cylinder I'd purchased yesterday so I can't say about the sealing into the master. However, owing to the fact things feel the same as before it was fitted I'd imagine it's probably alright. 

 

Did you end up having to change that feed pipe into the slave cylinder? 

 

I am thinking it's a must to make sure it's bled well so thanks for your suggestion with the long pipe. Would you know what size of tubing is right for it? 

Watching some videos I'm thinking back bleeding it might be a plan if I were able to do that.

 

This is starting to beg the question as to being anything wrong with original the slave/master..

I fitted a new old stock original suffix all aluminium one piece cylinder so no joint to fail.

 

The feed pipe is part of the cylinder, originally it was all one piece, when they changed to plastic it became two pieces, cheaper to mould and cheaper to transport in a much smaller box.

 

I created a thread on the subject showing photos of the failed 2 piece cylinder, the new 2 piece replacement where they had changed the material of the feed pipe and the aluminium one piece original version that I chose to fit instead of the plastic one that I did not have faith in.

 

It could be that the change to the same material (glass filled nylon) for both parts of the joint means the newer ones wont fail, I was not going to take any chances.

 

Use your eyes and hands to judge what tube diameter and material is correct.