There is one minor clutch-related adjustment task that requires attention sometimes and that is to check that there is the right amount of free movement at the pedal. This is so that there is no pressure on the hydraulics when the pedal is at its idle position. Constant pressure would be similar to “riding” the clutch and risks allowing undue wear because the driven plate is not held fast and spins in normal use. However, as the workshop manual makes clear, the only time you need to check the free movement is if new components have been fitted in the system and the original setting may have been lost. The free movement of the release push-rod should be the tiny amount of 30 thousandths of an inch or 0.76mm. To make life easier, this translates into 3.9mm depression of the pedal before the resistance of the master-cylinder piston is felt. This can be tested with hand pressure and has the advantage that the hand is sensitive to the point at which resistance begins. If adjustment is required, it is a fiddly job because the locknut and adjusting flats are located between the pedal and the master cylinder. Access with two spanners calls for much grovelling in the footwell.
Wear in the hydraulics is best dealt with at the same time as the brakes. If there is seepage from the master cylinder, whether from the clutch or brake side, it will require removing from the car and at the very least the rubbers will need replacing. The bores of the cylinders may need a light honing to reface them but if badly corroded they will need to be bored out and resleeved by a specialist. There is enough give in the rubber parts to tolerate a light honing without affecting fluid-tightness. The slave cylinder can easily be re-rubbered after a good clean. Bleeding the system is generally easy because the pipe and hose run is short but occasionally you may have a problem because the new rubber is stiff in the master cylinder and the piston does not move freely. This prevents the piston from moving back far enough to expose the small hole that lets new fluid into the cylinder and so it is not pumped down to the bleed nipple. You can overcome this by using one of the bleed kits that uses air pressure, usually from a tyre, to push the fluid through.
If you encounter any trouble getting the slave piston out, a solution can be fabricated. Obtain a bolt that fits the hose hole. Drill the bolt along its length with a small drill-bit. At the head end, open the hole out and thread it to take a grease nipple. Fit the bolt and the nipple and use a high-pressure grease-gun to force the piston out. Take care if you are working on an old unit that has been out of use for a while. Soak it with penetrating oil and when applying the pressure, put it in a cloth bag or something else that will catch the piston when it lets go and emerges from the cylinder like a bullet!
Because replacement of a worn clutch parts requires separating the gearbox from the engine, it is not difficult to understand why best advice is always to replace both, together with the carbon release bearing, every time the engine or the gearbox come out.
If the clutch fails, it is possible to remove the gearbox from the rear of the engine with the engine left in situ, but it is not really a job for the faint-hearted or those with limited garage facilities. It requires lifting the car safely so that adequate space is created underneath. A proper garage lift is the best solution. With the rear of the car raised, the engine mounts need to be released from the support brackets so that the engine can be raised with a jack at the front. Then the propeller shaft must be removed and the gearbox supported on a jack. Unbolt the clutch slave-cylinder from the top off the bell-housing with the flexible hydraulic hose still in place and tie it to one side, out of the way. Remove as many of the bell-housing bolts as can be easily accessed and remove the starter but leave a couple of bolts on the bell-housing flange to hold it in place until you are ready to separate engine and gearbox. It is vital that the first motion shaft should never take any lateral forces or bear the weight of the gearbox. Inside the car, remove the gear-lever trim and extract the lever from the gearbox remote control by using circlip pliers to squeeze the lock ring until it can be lifted out of its groove. Carefully remove the bolts from the gearbox support cross-member and lower the rear of the gearbox, ensuring the weight is properly supported. By raising the front of the engine, the angle of tilt on the gearbox is increased to the point where it has a clear path down past the bulkhead. If you attempt to drop the gearbox without lifting he engine mounts, the engine mounting rubbers will shear off. Remember to disconnect the speedo cable and reversing light switch wiring when they become accessible. Once the angle of tilt is achieved and the gearbox is still properly supported, release the remaining bell-housing bolts and gently withdraw the gearbox until the first motion shaft is completely clear of the clutch cover.
Re-assembly, as they say, is a reversal of the dismantling process. But if the work is being carried out under a car on axle stands it is hard work. In these circumstances, one can find oneself lying on one’s back, with the gearbox cradled in one’s crutch using pelvic thrusts to persuade the first motion shaft to engage! If this is likely to be beyond your physical endurance, then it is better to bite the bullet and pay someone with a four-post lift to do the job or resign yourself to taking the engine and the gearbox out the conventional way.
Removal and replacement of the clutch components is adequately covered in the workshop manual. Take care when removing and refitting the clutch cover. The bolts that secure it to the flywheel should be released and tightened together progressively and evenly so that no biased stress is applied that might distort the cover.
While the gearbox is off, check the condition of the flywheel face and clean it with meths or a brake-cleaner aerosol. Check for undue scoring: it should be smooth and even. Any corrosion can be removed with emery cloth. If the clutch previously worked smoothly and without slipping, harshness or the smell of hot oil the chances are that there are no other inherent problems and only normal wear has occurred. However, look for heavy contamination that may point to a more serious oil leak from the rear crankshaft bearing. A little leakage is harmless but excessive contamination will soon lead to other clutch problems, especially slipping. The condition of the old driven plate facings is a good indicator too. If there is obvious oil contamination or an unduly glazed, burnt appearance it is pointless reassembling the clutch until the underlying leak problem is dealt with, even if this means getting the engine out after all.
If your gearbox has been behaving itself, then it can be replaced after no more than a good clean. But take the opportunity to check the first motion shaft bearing (inside the bell-housing) for wear. The shaft protruding into the bell-housing should not be loose enough to allow excessive lateral movement. Also examine the rear end of the gearbox. The oil-seal that accepts the sliding end of the propeller shaft is prone to wear, which leads to heavy oil loss. The clue is that the underside of the car will be liberally sprayed with oil. It is easier to replace the seal with the gearbox off the car. (See Gearbox article).
When refitting the clutch plate, it is important to align the new clutch driven plate correctly, so that the first motion shaft will pass easily through it and engage the bush in the flywheel. Misalignment will cause much frustrating difficulty refitting the gearbox to the engine. The favoured device for aligning the plate is an old first motion shaft from a dismantled gearbox, but if you don’t have a dismantled gearbox lying around in your garage, a tool can be acquired from motor factors and specialists. There are two types of tool. The first is a universal tool for owners who often have clutches of different sizes to realign. It comprises a shaft and a set of bushes of different diameters that can be slid onto the shaft to match the flywheel bush and the hole in the plate (which is splined to match the first motion shaft). The second type, probably more practical for most owners, is a plastic moulding specifically designed to mimic the shape of the shaft. The latter is most likely to be obtained from an MG specialist. Various sizes are offered and for a standard Magnette, the tool listed for the MGA 1500 is the one you need. Take care if you have a non-standard engine because the splines on the tool must fit the splines on the new plate and the front end of the tool must engage with the flywheel bush. Later B-series engines had different set-ups.
Although the workshop manual treats the clutch cover plate as a repairable component, it is a false economy to re-use one that has seen long service or has an unknown history. Better to treat it as a disposable item and simply replace it with a new one.
Similarly, although the workshop manual refers to the re-facing of the driven plate, this is pointless when a new one can be bought off the shelf. Take care, also, when fitting the new driven plate. It will only work one way round and that is with the larger side of the splined centre facing outwards towards the gearbox. Keep it clean and avoid touching the friction surfaces with greasy fingers. A small amount of graphite grease can be applied to the central splines to avoid binding in use.
Always fit a new release bearing and new securing springs and make sure it is dimensionally identical to the one you removed, (always bearing in mind that the old one will have lost carbon thickness in use). Again, there were various types and the risk is that if you use one where the distance between the bearing face and the pivot axis is wrong, you will disturb the geometry and the correct adjustment of the clutch release will be lost. Either it will not release far enough or it will “over-throw” causing the release ring to be depressed too far and noisily foul the workings of the cover plate.
Check the condition of the release fork pivot bolt and its housing on the gearbox front cover. It may be worn enough to allow lateral movement, which in turn will also disturb the relationship between the release bearing and the release ring on the clutch cover. The fork itself can be re-bushed and the bolt replaced if it shows signs of wear.
When re-mating the gearbox and the engine, make sure the weight of the gearbox is never taken by the first motion shaft. Support the weight of the box until the shaft is fully inserted and the bell-housing flange is flush with the engine back plate. Get a couple of bolts in place as quickly as possible to avoid having it slip out. As the final stages of reassembly are reached, it may be necessary to twist the gearbox a little to get the shaft to fully engage. Alternatively, engage first gear before you start so that you can rotate the first motion shaft into position by twisting the final motion shaft at the rear.
Before you bolt everything up and replace the slave-cylinder, do a basic check of the top end of the release fork, to make sure that the point at which it contacts the cover plate looks right in relation to the opening in the bell-housing. If there seems to be too much movement before you feel resistance, there may be a problem with the release bearing that will require dropping the gearbox again (nightmare scenario!).