A2 FSI Clutch slave cylinder replacement.

Last week my dash warning light came on to warn that brake fluid was low.
After ruling out the calipers and the flexible hoses that are common to fail, I scratched my head and looked into the engine bay for leaks.
The culprit was the clutch slave cylinder.
This part sits on the side of the gearbox, halfway down the engine on the passenger side (for a UK car!), you can JUST see it below the selector mechanism for the gearbox.
The slave cylinder is a "sealed" unit and is held onto the side of the clutch by two bolts.
The coupling for the hydraulic fluid is a quick release coupling (see photos).

Now a word of warning. You WILL need the dexterity of a gynaecologist and the patience of Ghandi to attempt this job. Access is virtually zero and you have to fiddle and fail repeatedly to work around the maze of pipes and obstructions. But it can be done, and that is the main purpose of this how to! To let you all know that it is possible without removing any pipes or other components.

The only tools needed is a 1/4 inch ratchet spanner, a 13mm socket (for the bolts) and a selection of extension bars to do the trial and error task of reaching the bolts.

Removal starts with the bolt nearest the bulkhead.
This bolt also holds in place the support bracket for the hydraulic pipe.
With this bolt out, I used a small flat bladed screwdriver the pop open the quick release on the hydraulic coupling.
You need a small plastic sandwich bag next.
With the quick release wire in the open position, the coupling just pulls out of the slave cylinder (friction fit).
You need to put the end of the hydraulic coupling into the plastic bag as it will leak brake fluid everywhere (about 50ml in total came out of mine!).
You can swing the whole pipework of this out of the way and tuck it up somewhere near the suspension tunnel.
Now onto the other bolt...this is REALLY difficult for access, but by now you should be getting practiced!
As you undo this bolt the plunger on the slave cylinder will push the cylinder at an angle and impede access, the spring on the slave cylinder plunger is probably 2-3kilos to compress.
With the last bolt out the whole slave cylinder is easy to remove, as you can see, mine was knackered on the bellows.

To fit the new slave cylinder I first fitted the bolt nearest the bulkhead temporarily WITHOUT the pipework bracket.
I tightened this bolt enough to pull the slave cylinder into place against the weight of the spring.
I then fitted the second bolt (nearest radiator) and did this up tight.
The bulkhead bolt then needs to come out again.

At this point, I connected the hydraulic coupling to the new slave cylinder and popped the release wire back into place.
With the coupling in place, you can position the support bracket to align with the hole on the slave cylinder.
Thread the bolt through bracket, and slave cylinder and tighten up.

This sounds really easy, and mechanically it is. But just be ready for lots of failed attempts at getting bolts in and dropped spanners and scraped knuckles.

Last job is then to bleed the entire brake system, including the nipple on the slave cylinder. I guess if you are reading this then you know how to bleed brakes.











 
That is a great post, thank you for taking the time to post this, it will certainly help others who need to do this.

I will add it to the "How To" index.

Cheers
Steve B
 
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Car is back on the road now and drives well. I am not sure if its some form of placebo effect, but freshly bled brakes always feel better.

One further bit to add to the "how to".
Above I said that about 50ml of brake fluid drained out of the pipe while disconnected.
I didn't think this mattered as I intended to do a full bleed anyway.
When I came to bleed the clutch, there was a huge amount of air in the system and no amount of conventional bleeding would shift it.
In the end I popped to my local motor factors (ASK in Kippax) and picked up one of those Gunson pressure bleed kits (overpriced but they do work).
With the kit connected an pressurised and with the bleed nipple on the slave cylinder open, I had my assistant (well grumpy teenager) repeatedly pump the clutch pedal. After about 300ml of fluid, all the air was gone.
So my advice would be to try not to let all the fluid drain from the pipework, maybe keep either the old or the new slave cylinder connected at all times.
 
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