Hi everyone!

Clutch pressure loss then comes back when pumped few times

This is my Audi A3 2.0TD| Cab I recently purchased as a project car. Previous owner sold it with a suspected slave cylinder issue (CSC ones inside the clutch housing)

However after further inspection the metal pipe for the master cylinder was bent and the master itself had damage, so I Purchased a new pedal (with master cylinder) and a new pipe from a breakers yard-£40 for the set, managed to fit this all up nicely and put some PTFE tape on the rubber seal for an extra seal. The master itself does not leak and the clutch does have pressure. However the issue I'm facing now is the clutch can sometimes go flat and loose 80% of its pressure, I then re pump the clutch and the pressure returns (not very ideal stuck at a traffic light lol) and it remains fine until the next few gear changes where I have the repeat the process. There is no leaks as the brake fluid reservoir does not loose any fluid and I have checked the master whilst the clutch is being pumped on the inside again no leaks. What could my issue be ?

The problem could well be air in the hydraulic system, however cylinder seals, both master and slave, can pass fluid without leaking out of the system. If air bleeding does not solve the problem I suggest you renew the slave cylinder.

8 hours ago, cliffcoggin said:

The problem could well be air in the hydraulic system, however cylinder seals, both master and slave, can pass fluid without leaking out of the system. If air bleeding does not solve the problem I suggest you renew the slave cylinder.

Thanks for your reply, what are the chances the internal seal has failed on the used master that came with the pedal ?. Also I have bled the system a few times now so I doubt it would be trapped air.

Hello Adam,

Without further ado, my money is on the slave cylinder being the culprit here - highly likely why the previous owner passed it on.

If replacing clutch components I would use LUK parts. Cheaper parts would not be my route on this labour intensive job.

Regards,

Gareth.

Hi Gareth and thanks for your reply. I shall try a new master cylinder in the next hour and see if this does the trick. I have just been to the car and pedal was soft- pumped it around 15 times and pressure returned nicely and drove it round the block, I will go back to it and see if pressure is still there and then change the master out for a new one if this does not work after that pretty stuck tbh as I wouldn’t mind doing the job but just do not have the time.

Update

Went to the car yesterday and pressure was perfectly fine for 40 mins of driving. Then started to loose but one pump and it came back. Starting to think I can rule the csc slave cylinder out would that be realistic?

No.

Wondering what the latest is on this Adam-?

Regards,

Gareth.

3 hours ago, Magnet said:

Wondering what the latest is on this Adam-?

Regards,

Gareth.

Hi Gareth, tbh I’ve bled the clutch a few more times after that and the issue is still there but very rarely- so currently am just living with it tbf. Don’t see the need to do such a big job for one or two pumps once every drive or so. But thankyou all for all your help.

Good luck with that Adam. You'll need luck when the clutch fails miles from home and you can't engage any gears without grinding them.

1 hour ago, cliffcoggin said:

Good luck with that Adam. You'll need luck when the clutch fails miles from home and you can't engage any gears without grinding them.

Cost me £150 for the car and £50 on repairs. More than happy to scrap it if it fails. Drove me 1,500 miles since my last post so had my moneys worth out of the vehicle. Thanks for your concern 👍

Thanks Adam,

It’s last minute revelations such as these that make a nonsense out of spending time to advise on such things, when the real answer is to do exactly what you are doing - waiting for it to pack up rather than pay money out to sort it!

3 hours ago, adama078 said:

Cost me £150 for the car and £50 on repairs. More than happy to scrap it if it fails.

A pity you did not mention that earlier. Given how cheap the car was, you must have wasted almost as much money on the new pedal and the new master cylinder. Money you could have spent on a slave cylinder.