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Replacing a clutch slave cylinder.


Les Henson
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This thread is the replacement of the clutch slave cylinder on series 2A, 3, 90 and 110 vehicles (with a standard set-up)

Very messy job it is too and awkward, due the location of the slave - tucked down on the passenger side, between the starter motor and exhaust downpipe. All the work has to be done from under the vehicle - right in line of drips etc. This can be done with the vehicle sat on its wheels, but raising the front end does improve things somewhat. The fluid can all leak away due to the failure of the seal inside the slave, but also a rock solid pedal can also mean the piston has siezed in the bore of the slave body. On 90/110's there is also the possibility that the clutch fork has punched through, so determine the fault before hand. If the fluid has all gone, then look to see if fluid has been running down the clutch pedal shaft, or the pedal feels ok, but the clutch doesn't disengage - these are typical syptoms of master cylinder problems. The cause of a slave cylinder seizing is usually down to water getting inside the dust cap on the slave, this then corrodes the piston and bore and overnight or after being stood for a while, the piston locks up. The problem in this thread is failure of the slave seal, which then drained all the clutch fluid out into the flywheel housing. The pedal is very light and goes all the way to the floor with little or no resistance. Vehicle shown is a 1980 swb S3 with a 2.25 stinky diesel engine. (slave is the same for the petrol.

Ist pic is view down the passenger side of the engine from under the bonnet. The slave is barely visible and you can't get at it from under the bonnet. Raise it anyway to allow light in.

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Raise the front of the vehicle and place an axle stand under the axle close to the wheel so that it won't be in the way.

The slave can now be seen, tucked under the starter motor, with the downpipe in the way, making things a bit awkward.

Note that on a 90/110, the slave is less recessed, due to the different flywheel crossmember.

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To minimise fluid dribbling all over you, remove the bleed nipple and wait while the system drains down into a suitable container.

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Series vehicles have a rigid steel pipe that crosses over from the drivers side of the engine, round the back of the head, and then down to the slave - there's little available movement of the pipe when it's disconnected from the slave, so unscrew the pipe union of the slave (1/2" or 13mm spanner), and then carefully tie it back out of the way as shown. Be careful not to over stress the pipe - it may break or at least if it bends it'll be more difficult to line it up again to attach it to the new cylinder. 90/110 vehicles have the same set-up, but there's a lot more movement on the pipe that is fitted due to the flexi hose.

When the pipe is detached, some more fluid will leak out - some that remained in the lower part of the slave.

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The slave is now held to the flywheel housing by 2 x 1/2" or 13mm bolts. The top one is awkward, but a 5-inch extension bar is just the right length. On a series vehicle you can get your hand over the top of the chassis rail to guid the socket onto the top bolt.

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The slave can now be drawn off the operating rod, there should be a dust cap on the end of the slave, if not, then check it hasn't remained on the rod. The old slave, a right gunky mess!

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Remove the dust cap from the new slave and put a blob of grease on the top of the piston, this will help prevent water from getting at the piston and causing it to corrode in the bore.

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Replace the dust cap and carefully push the slave over the operating rod and so that the bleed nipple is above the pipe connection. There's some resistance in doing this as the new piston has to be pushed down the bore, and the dust cap is sometimes a tight fit through the hole in the flywheel housing. Replace both bolts and tighten - not too much, a stripped thread means the engine will have to come out of the vehicle and the thread repaired/flywheel housing replaced.

Leave the sealing cap in place until you are ready to replace the pipe to prevent dirt getting inside the new slave.

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The thread on the pipe fitting is very fine, so be very careful not to strip the thread, again don't overtighten, or you will end-up having to replace both pipe and slave. Make sure also that the pipe isn't in contact with the starter motor or other engine/body parts, vibration will cause a leak after a while as the two rub together.

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Fill the reservoir and get someone to sit in the cab, slacken the bleed nipple with a 7/16" or 11mm spanner.

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The pedal should now be pressed down and held. Tighten the bleed nipple and the pedal should then be released. Open, press, close, release, and so-on. After a few presses, fresh fluid will squirt out. close the bleed nipple and try the pedal, it should have little movement before you feel the system pressurise. You should also feel the clutch is working normally. Replace the rubber cover on the nipple, refill the master cylinder, and then take the vehicle for a test drive - generally if it feels ok, then it is. Clutches self-bleed to some extent, so if there is a very small amount of air in the system it will find it's way back up to the master cylinder. It's usual to notice that a clutch feels better after a day or two of use.

It's almost 100% certain that you will experience the thrill of clutch fluid running down your arm when you do this job :angry:

Les.

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Minor hijack but does anyone know what the thread is (my one looks like M12 Fine) and/or a part# for the pipe or part of that will go from my slave cyl (which I think is Series 3, anyway the union is 3/8" UNC) to that slave cylinder?

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Les,

you forgot the golden advice! Make sure you don't drop the push rod into the bell housing. The dust seal can sometimes get a good enough grip to pull the stupid clippy thing off the arm and sods law says if you aren't careful that it will drop in. I'm sure you know, just in case someone gets onto the job and wades in a bit too eagerly it could be a bad day in the garage :)

If the push rod does come undone from the clip I think the Fab forum has a tool to reattach it, or it can be discarded and by angling it in the rod can be put back in the right place without it (like my 90 is at the moment :( )

Only other tip I think is worth mentioning is that if you do the master as well then take a good look, there is an adaptor from the pipe into the master, which you need to retain and use on the replacement.

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