Ideas on slight clutch pressure loss? Slave cylinder?

[silver50]

My 2001 1.4 mpi has a noticeable drop in clutch pedal pressure after (approx) an hour of city driving or carrying heavy weight in the car.

 

It's been like this for a long time but I'd quite like it remedied. The car still drives ok but the biting point will feel lower and sometimes the pedal doesn't even quite spring back up properly. There is no leaking fluid and a few weeks ago I got my local garage to bleed the clutch. This seemed to help a bit for a few days...

 

The brakes are A1 but I must admit I don't know when the fluid was last changed. Would my clutch bleeding have introduced new fluid into the clutch part of things? Can't understand brake pressure seeming perfect if old fluid was the cause of this. I'm sure I ascertained a long time ago that the clutch doesn't require much pressure compared to the brakes.

 

I'm thinking of trying a new slave cylinder as they are not too expensive. What does the slave cylinder do,any advice or ideas on this? 

 

I'd appreciate any advice on it or how the system works in relation to clutch/brakes.

 

Many thanks

 

 

[Tech1e]

If bleeding improved the pedal feel then it's logical to assume that the system is drawing in air. As the slave cylinder is the easiest component to change I'd do that. Make sure you pressure bleed the system correctly afterwards to purge the air from the system.

[KenONeill]

To confirm this, with engine running and handbrake off fully depress clutch pedal and select first gear. If the car starts moving within about 5 minutes, your slave cylinder is starting to leak.

[silver50]

Many thanks guys.

 

I'll try the above test. I actually almost wondered if the car did try to draw forward a couple of weeks ago when my foot was on the clutch in gear.

 

Is the slave cylinder just to do with the clutch?  Would you agree it seems related to a clutch part of the hydraulic system if the brakes seem totally fine?

 

...for some reason this forum never sends me reply notifications even when selected..

[bigjohn]

Many thanks guys.

 

I'll try the above test. I actually almost wondered if the car did try to draw forward a couple of weeks ago when my foot was on the clutch in gear.

 

Is the slave cylinder just to do with the clutch?  Would you agree it seems related to a clutch part of the hydraulic system if the brakes seem totally fine?

 

...for some reason this forum never sends me reply notifications even when selected..

 

The only thing the brake and clutch hydraulic systems share is the brake/clutch fluid reservoir

 

The Clutch hydraulic system is very simple consisting of a slave cylinder with bleed nipple , flexible hose, metal pipe and master cylinder. Presuming pipes not leaking then it's either the slave or the master cylinder. 

 

As it's easier to change replace the slave cylinder first but my gut feel is this will probably be the master cylinder which can fail in a way that doesn't leak but fluid pushers past seals (pedal down)  but is drawn back into the system  (pedal up)

[silver50]

Thanks for explaining, I have a question though just to clarify. I always thought a car's master cylinder for the brakes and clutch but does the clutch have it's own master cylinder? Is it what the clutch pedal pushes into?

 

From someone I was talking to earlier, they thought the slave cylinder would be leaking if it was at fault. It would appear changing both would probably fix this, but I was hoping not to have the expense of both! My MOT just cost me £300!

[Tech1e]

Clutch and brake have seperate master cylinders.

The slave can take in air when it retracts without leaking.

[KenONeill]

Clutch and brake have seperate master cylinders.

The slave can take in air when it retracts without leaking.

Exactly. Also, to clarify, when I said "leaking slave" earlier, I meant that the pressurised hydraulic fluid leaks past the internal seals so that the clutch "lets out" without the pedal moving rather than air being drawn into, or hydraulic fluid lost from, the slave cylinder.

[sepulchrave]

The clutch and brake both share the same reservoir but the clutch inlet is higher than the brake so if the level gets low your brakes will work fine but the clutch will start sipping air as the fluid sloshes about.

[silver50]

Thanks for your help today everyone who responded.

 

I'll see if I can get a new slave cylinder to try. Can possibly do it myself with care regarding bleeding etc. I'll see if I can read up on it.

[Tech1e]

Gunsons easibleed is fine for the clutch.

[bigjohn]

The clutch and brake both share the same reservoir but the clutch inlet is higher than the brake so if the level gets low your brakes will work fine but the clutch will start sipping air as the fluid sloshes about.

 

Isn't it the other way round? - [Edit] mis read post sipping is not slipping! - should have gone to Spec$"^£"

 

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As you get air in the clutch hydraulic system you will have to press the pedal further to the floor as the air can be compressed(lower biting point)  - eventually you won't be able to disengage the clutch (Initially hard to get into lower gears and reverse - getting worse) 

 

Fortunately because you only have on slave cylinder and pipe and its lower than the master cylinder it will tend to self bleed(air rises) - but it needs doing as it will only get worse and let you down at the wrong time!

 

Brake fluid is [Edit] Hygroscopic (absorbs water) which eventually can cause corrosion in the master and/or slave cylinders. It's worth occasionally adding the changing of the clutch fluid to the service schedule , possibly every other brake fluid change

Edited 3 January, 2016 by bigjohn

[sepulchrave]

Brake fluid is ascorbic (absorbs water) which eventually encourages corrosion in the master and slave cylinders. It's worth occasionally adding the changing of the clutch fluid to the service schedule , possibly every other brake fluid change

 

Hygroscopic.

 

Ascorbic acid is vitamin C.

[bigjohn]

Hygroscopic.

 

Ascorbic acid is vitamin C.

 

Having a bad reading/typing day-  it is indeed Hygroscopic (suitably edited!)

 

Orange juice as clutch fluid?  

 

Can't even blame drink being taken - back to reality/work tomorrow!!!

Edited 3 January, 2016 by bigjohn

[Alexandru]

To confirm this, with engine running and handbrake off fully depress clutch pedal and select first gear. If the car starts moving within about 5 minutes, your slave cylinder is starting to leak.

 

Is it safe to keep the clutch pressed for that long? I think that if it's not dead yet, this would be the final cut.

[KenONeill]

Is it safe to keep the clutch pressed for that long? I think that if it's not dead yet, this would be the final cut.

That's a test for a slave cylinder with an internal leak, nothing to do with clutch wear.

[Alexandru]

Will it not premature wear / overheat the clutch ?

[KenONeill]

Will it not premature wear / overheat the clutch ?

It's a one-off test, conducted at idle revs. I've never felt the need to do it, but I'd do it with mine which is on 120_000 miles.

[felicia16v]

It's not going to hurt anything unless it's Dragging badly, which should be obvious really.

The pedal sticking down sounds like air is getting in or the mastercyl is on its way out.

[silver50]

I'm going to try the test but will hang on until the clutch does it's small loss of pressure thing it's doing i.e. after driving in traffic for an hour. Seems sensible to try it then.

 

Perhaps a bit miserable of me but I dunno about spending the extra £20 on the gunsons eazibleed as a bit of a one off job. I believe it can be done without with care, I'm still to read up on it.

 

Been great all the replies. Thanks folks

[sepulchrave]

I'm going to try the test but will hang on until the clutch does it's small loss of pressure thing it's doing i.e. after driving in traffic for an hour. Seems sensible to try it then.

 

Perhaps a bit miserable of me but I dunno about spending the extra £20 on the gunsons eazibleed as a bit of a one off job. I believe it can be done without with care, I'm still to read up on it.

 

Been great all the replies. Thanks folks

 

You won't do it without the eazibleed, I tried without and it simply didn't work at all, I changed the master cylinder and the slave at the same time though, so both were bone dry.

[Tech1e]

It won't work without a pressure bleeder. Simply pressing the pedal up and down won't flow enough fluid. The fluid just sits there going up and down the pipe.

[silver50]

Ah right, ok thanks. It's a bleeder then! 

 

I see screwfix do them, I'll pick one up