Replacing Clutch Cylinders

You're at the traffic lights, tapping your fingers along to the radio when the lights go green. You press the clutch, grab the gear stick, and make that awful grinding noise learners make. Everyone points and laughs, and the taxi behind blares his horn. You ram the clutch pedal to the floor and eventually ram the gear home, but not before your face has turned redder than the traffic light.

In cases like these we often blame the clutch, and that's partly correct. What's most likely is that one or both of your clutch's hydraulic cylinders has failed. When this happens the clutch can't do its job, leading to all sorts of shifting issues. Fail to fix it, and you'll eventually burn out your clutch or do severe damage to your gearbox.

For the sake of a few quid and an hour of your time, both cylinders can be replaced by even the clumsiest of mechanics. Here's how.

Overview

This article is written specifically for RHD models. The principal difference being there is a specific reservoir for the clutch fluid, as marked in the pic below. For LHD models, the clutch uses a feed from the brake fluid reservoir.

The clutch system works on the same principal as the brakes, whereby two cylinders and some hoses transmit the force from the pedal, via clutch fluid (which is the same as brake fluid), to the slave cylinder and clutch release mechanism. The clutch slave cylinder is basically a small hydraulic ram with a piston on the end. When operated, the piston pushes the clutch release mechanism, or at least it used to until it broke. This system must be airtight with no leaks, and is bled from a small valve on the slave cylinder in the normal brake-bleeding fashion.

Diagnosing a clutch fluid issue is simple. Your pedal goes soft, it becomes very difficult to impossible to change gear, and you may have very little or no clutch fluid left. The two main culprits are the master clutch cylinder which sits behind your clutch pedal, and the slave cylinder which is bolted to the gear box. If you get clutch fluid around your pedals, then it's the master. If the slave cylinder fails, it leaks fluid into the bell-housing so there is no visible sign of leaks anywhere except for a drip from the bottom of the bell-housing (which most people assume is engine or gearbox oil).

It's recommended to change both master and slave when one fails. When your slave cylinder fails, the piston in your master cylinder would have travelled a little further than it has in the last twenty odd years, and this damages already fragile seals on the crud that has built up.

Procedure

Slave

If you are taking the slave cylinder off you want as little fluid in the system as possible, otherwise it will just end up in your eyes. You can do this by draining the reservoir or by removing the existing bleed valve on the slave. To gain access to the slave, remove the gearbox protective plate, which is attached by two screws to the front beam and two nuts further back. One of my front subframe screws couldn't be secured properly, so a cable tie through the beam holes sufficed.

Once you've got access to it, disconnect the slave cylinder via two nuts; one below, one on top. The top nut requires an extension to reach which can get past the hose - see below.

Don't let the cylinder dangle on its own or you'll damage the rubber pipe, so find a way to support it. Rather than trying to remove the hose from the cylinder, it's easier to disconnect the hose from its source, which is a standard metal pipe with an 11mm union nut. These are notoriously prone to rounding off, and if they do you are pretty screwed, so lots of patience is required. Soak it in WD40 overnight if possible, apply lots of heat if you can (heat guns are brilliant and cheap), and use a proper flared spanner which wraps around the nut, giving you less chance of rounding it off. Using a standard spanner on the hose end and a flared spanner the other side on the brake pipe nut, give the front spanner a few shock whacks to loosen the nut, and all being well you'll shortly wonder what all the fuss was about. After 20 odd years these unions will be seized to the hose, and are likely to be as soft as cheese.

With the hose and cylinder off, it's easier to take the hose off the cylinder using the method above in your hand or a vice, rather than underneath the car on your back. See the below picture which tells you all you need to know about getting these unions off! I know the hammer is in shot; don't go nuts with it, as it's just to give the spanner a few hard short shocks to loosen the union, which should then come off by the normal means. When you put the union back on the new cylinder, do the next chap in 20 years a favour by spraying the thread (not inside) with copper grease.

Re-attach the hose back to the car, and re-attach the cylinder to the gearbox with the bleed screw pointing upwards.

The system now needs to be bled. This is great with two people working in tandem, but it can be done by one person kneeling on the floor. The process is to press the pedal down and hold it while cracking open the bleed nut on the slave cylinder. Close the nut again and release the clutch pedal. Repeat this process until the pedal firms up. Pay attention to the fluid level in the reservoir, because if it gets low you'll suck in air and have to start the bleed process all over again.

The pedal stays soft at this stage. The moment of truth is when you tighten the bleed valve, pump the pedal once, then on the second press it should go hard. To test, lower the car off the front jackstands, move everything out the way of the front of the car, and start the car with the clutch down and 1st gear selected. You're looking for signs of the revs dropping or, worse, the car moving. If this checks out, do a clutch bite point check, then go through all the gears on a short test drive, and reward yourself with a plate of chips.

Photos and text by milescook with assistance from Brianmoooore and willnz.