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Fabia 1.4 16V Clutch air-locked?


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#1 sepulchrave

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Posted 27 September 2010 - 21:53

Hello,

First post, here goes:

I simply cannot get my clutch hydraulics bled clean, I've bled forward and back, even replaced the master cylinder but to no avail.

I think it's all clear then after driving a few miles without using the clutch I go for the pedal and it's gone, I can only keep it working if I keep my foot slightly on the pedal all the time.

Each time I bleed it I get a little more air out but I cannot figure out where it's coming from, there is no leak or fluid loss at all.

How straightforward is it to replace the slave cylinder if this has gone?

I guarantee that when I start the car in the morning and press the clutch pedal it'll go straight to the floor and stay there.

It all started after I did the back brakes and allowed the fluid level to drop too low because I didn't spot that the clutch shared the brake reservoir.

#2 hap123ciu

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Posted 28 September 2010 - 15:14

Maybe try a full change of brake fluid in the proper order using some pressurising tool? As I remember is rear left, rear right, front left, front right, clutch, 0.2 l for wheels, 0.1 for clutch.

#3 Clunkclick

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Posted 29 September 2010 - 21:07

Sounds like the slave cylinder selas have gone,

Haynes says repair kits not available so you have to buy a replacemeny.

Haynes procedure (Which seems to be broadly in line with Elsawin):-

Remove engine cover.
Remove battery (Remove lead enough ?)
Remove air cleaner and ducting, where necessary.
Unscrew nut remove gear change lever from top of transmission (not sure whether that's neccessary)
Extract circlip and disconnect selector cable from relay lever.
Unscrew three bolts from support bracket
Clamp the rubber section of hose from master cylinder
Pull retaining clip from pipe union and disconnect pipe from union
Unscrew two bolst at slave cylinder.

Slave cylinder bolts tightened to 20NM (Elsawin agrees with Haynes).


Mild version of your problem on my 16v saloon. Sometimes when I release the clutch the pedal comes fully up but the slave cylinder sticks and then releases causing the clutch to thump home. I asked tthe dealers to bleed it off which they have done and it gets a bit better. Also the clutch on mine doesn't bite until really high-up on the pedal travel.

From what I understand the master cylinder reservoir is shared with the brakes and that's where the trouble may lie. Its the devil's own job to bleed it through properly and I think there's a tendency for water ingested into the hydraulic system to lay on the clutch side of the system, which is lower down in the engine compartment.

I think also the bleed nipple is plastic, so you might want to check that it hasn't cracked and is allowing air in.

According to Haynes the bleed screw is located on the clutch slave cylinder which is located on the left-hand upper side of transmission.

The procedure in Elsawin attaches a system pressurised to 2 bar to blow-out the system. Not necessary !

Personally, I'd bleed the whole system, brakes first, (Haynes says on RH drive, order is nearside rear, offside rear, nearside front and offside rear) and then the clutch (Because its lower down).

I always used to use heavy duty bleed rubbers to do brakes and it worked a treat every time. Bleed rubbers being a length of rubber tube with a finely cut vertical slit in one end. Take-off the hydaulic reservoir cap - leaving the filter in. Loosen the bleed nipple, attach the bleed rubber (opposite end to slit) to the nipple, fully open the nipple. Place the slit end of the rubber in a jar - with slits there's no need to immerse the slit (Open) end in hydraulic fluid.

Then pump the pedal slowly and methodically and on every down stroke the slit on the rubber opens up to let out some fluid/water/air and then closes on the upstroke to prevent re-admittance of expelled material and/or air. Leave about 10 seconds between the end of the last pedal upstroke and the next downstroke to allow the cavities of the master cylinder to completely re-fill with fresh fluid. Do this until clean fluid with no bubbles comes out the slit - Elsawin says keep doing until a further 100 Cm flows out - I think they mean 100cc. Whilst this is going on making sure to top up the hydraulic reservoir as you go - you got to keep a keen eye on the levels in this dual purpose master cylinder reservoir because the take-off which feeds the clutch master cylinder is half-way up the side of the master cylinder reservoir. So it doesn't take many clutch strokes before the fluid level is lowered in the master cylinder possibly exposing the clutch feed to the air. When you're satisfied that the system has been completely purged get someone else to operate the pedal on the final down stroke and, as they are doing so, you close-off the nipple.

Always worked a treat for me with brakes on other cars.

Nick

Edited by Clunkclick, 29 September 2010 - 23:54.


#4 sepulchrave

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Posted 30 September 2010 - 13:02

Thanks Guys,

I have fixed it now, it was indeed the slave cylinder, however I also replaced the master cylinder since the part was on the shelf so I did this while I waited for the slave to be delivered.

The master cylinder was £56 and the slave £36.

The master cylinder was tricky to do since it is bolted to the bulkhead in the footwell behind the clutch pedal, the toughest part was getting the return spring retaining clip back in place after changing the cylinder and then popping the return spring assembly back into the correct location, it took about three tries to get it right.

The slave was much easier and I only needed to remove the airbox to gain access to it.
The trick was to remove the bolt retaining the slave and the hose support bracket first so the hose could be disconnected and swung out of the way, then replacing and tightening that bolt before trying to removie the other one which is much more inaccessible.

Be aware, it took nearly a whole litre of brake fluid to flush out all the bubbles and is impossible to accomplish without a vacuum/pressure bleeder.

The pedal now feels great and is much quieter, far less squeaking and squishing.

#5 Clunkclick

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Posted 30 September 2010 - 16:45

. . . . is impossible to accomplish without a vacuum/pressure bleeder.


Dare I ask why ?


Nick

#6 sepulchrave

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Posted 30 September 2010 - 19:28

Ok, almost impossible. :yes:

Because the master cylinder shifts so little fluid and the air seems to get trapped in the master cylinder itself.
But mainly because the return spring mechanism seems to be designed to keep the pedal to the floor as well as at the top of it's stroke, presumably to reduce the apparent pedal pressure while holding the pedal fully de-clutched.
This means the pedal will not return during bleeding but stays on the floor unless you pull it up manually.

Frankly it was well worth spending £20 on an eezibleed kit, even at Halfrauds rip-off prices!

#7 Clunkclick

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Posted 01 October 2010 - 11:30

Ok, almost impossible. :yes:

Because the master cylinder shifts so little fluid and the air seems to get trapped in the master cylinder itself.
But mainly because the return spring mechanism seems to be designed to keep the pedal to the floor as well as at the top of it's stroke, presumably to reduce the apparent pedal pressure while holding the pedal fully de-clutched.
This means the pedal will not return during bleeding but stays on the floor unless you pull it up manually.

Frankly it was well worth spending £20 on an eezibleed kit, even at Halfrauds rip-off prices!


I'd favour suction over spring causing a pressure lock. EEzibleed is pressurised from the spare @ 30 PSI (2 Bar), then that is probably just enough to break the to break the vacuum.

Clearly, judging by the reports on other VAG sites this is another truimph of German automotive engineering. Save pence on production costs by doubling up the hydraulic reservoir and make servicing and ownership a nightmare.


Nick

#8 sepulchrave

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Posted 03 October 2010 - 18:23

I'd favour suction over spring causing a pressure lock....


Negative Captain,

While the old master cylinder was actually physically removed from the car I checked the spring mechanisms effect on the pedal action,
it actually does hold the pedal up until about half travel, then as the spring mechanism changes angle relative to the pedal dwell it acts in reverse and pushes the pedal flat to the floor.

I was surprised as well.