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Pressure plate overhaul

CLUTCH REBUILD ON THE AUSTIN HEAVY 12/4

It was New Years Day and we were travelling on our way through rural Cheshire to meet up for lunch with a group of car club friends when everything went wrong. We came to a sudden and unexpected stop in the centre of a small village when the car in front braked suddenly. As I put my foot down on the clutch and braked, I heard a nasty, metallic noise from somewhere below me, and then the engine cut out. This should have been a pleasant moment to enjoy a country scene as a wave of foxhounds streamed across the road all around us, followed by people on horseback, as the local hunt had chosen that moment to set off from the village pub right in front of us. Unfortunately, I was too panic-stricken to enjoy it properly, as I resented the idea of breaking down in full view of about a hundred huntsmen and hunt followers!
When I tried to re-start the engine, I got a click from the starter solenoid, but the engine wouldn’t turn, although I could tell the starter motor wasn’t jammed. I already had my foot down on the clutch before I hit the button, but the gearbox was still in gear, so I shifted it to neutral and tried again. This time the engine turned and started. I was puzzled ! Although the clutch pedal felt normal, the clutch wasn’t disengaging and it was impossible to get into gear. We did get our New Years Day lunch with our friends, as we were just a mile from our destination when we broke down, and a couple of friendly and helpful locals found a tow rope and gave us a tow to ‘The Maypole’. Afterwards, we went home on the back of a breakdown truck, courtesy of the Austin Club’s own breakdown service, which was superbly efficient.
The next day, I investigated the cause of the breakdown, and as soon as I had the floorboards out, and looked into the clutch pit, the problem was there to see. One of the three de-clutching levers was detached from the clutch release bearing, and I found it was completely free where it should be pinned to the pressure plate, and it was possible to lift it right out. It was amazing that the whole thing didn’t fly out while the engine was running and cause a lot more damage. Pressing down on the clutch pedal had still been operating two of the de-clutching levers, after a fashion, although not squarely to disengage it, which explains why the clutch had still felt normal. Fortunately, the noise had made me decide not to run the engine for more than a few seconds.
So it was going to be a complete strip-down with the gearbox and clutch having to come out. This was rather annoying because I’d been through that whole process only a few weeks earlier to sort out a worn starter ring gear. The good news was that it was all still fresh in my mind, and should be simpler and less daunting second time around. I was also greatly relieved to find that I was not to blame for this problem as a result of my previous work !!!
So out came the gearbox and the flywheel cover assembly. This time it only took an afternoon, because I knew what I was doing. Two things had happened, but I have no idea which happened first. The clutch pressure plate withdrawing pin had broken at the top where the declutching lever pivots, although they managed to stay together. One of the photos shows this broken pin. At the lower end, the peg which holds the withdrawing pin into the pressure plate was missing. I found no sign or remains of these two items in the bottom of the clutch housing, so it’s a complete mystery where they went. There were aluminium shavings all around the clutch housing where the loose declutching lever had caught it while spinning, but no steel bits. It’s also a mystery how the peg came out. All the parts were badly worn and a very sloppy fit, but the pegs should be permanently held in position under extreme pressure from the clutch springs.

The first thing to do, with the clutch unit on the bench, was to separate the flywheel cover from the pressure plate to gain access to the individual parts and remove the declutching levers, pins and pegs. To separate them, the pressure plate has to be compressed fully into the flywheel cover using two heavyweight G clamps. When this has been done, the three pegs, or the two remaining ones in my case, which hold the withdrawing pins to the pressure plate can be drifted out, either from the inside of the pressure plate, outwards, or from the outside of the flywheel cover, inwards. I found it easier to drift them from the outside. There could easily be confusion over naming some of these parts, but I’ve tried to use the names used by Austin in the Austin Twelve Spare Parts List of about 1930. Incidentally the spare parts list is a very useful thing to have beside you when trying to work out how everything works and fits together.
Once the pegs have been removed, the G clamps can be loosened off, with the unit positioned with the pressure plate uppermost and the plate can then be lifted off, leaving the fifteen clutch springs in position in the flywheel cover. The three declutching levers and their withdrawing pins can now be removed from below.
Willie McKenzie, of Austin Reproduction Parts Ltd, can supply a set of pins complete with the six pegs, so as everything seemed to be very worn and loose, I ordered a set. The play in these parts couldn’t have done any good for the clutch action. The new pegs which hold the withdrawing pins in the pressure plate, had one end serrated and had to be driven in quite hard, whereas the old ones were plain, and I’ve no idea how tight they would have been originally. At the same time, I thought it would be as well to replace the clutch withdrawal bearing and collar, which comes as a complete unit. The original was very worn, and now one of the forks had been split slightly when the declutching lever came away, so it really wasn’t worth risking putting it back. They’re not cheap, but it would also be nice to get away from the terrible vibration it always suffered from since we’ve had the car. Willie also supplied this, and it looks to be very well made.
The re-assembly process is quite straight-forward. First, the pressure plate needs to be positioned accurately over the flywheel cover so that all 15 of the clutch springs are correctly located in their recesses. Next, the two units are compressed again using the G clamps, making sure that nothing slips. When the pressure plate is screwed down as far as it will go, turn the whole thing over and the declutching levers can be re-fitted with their pins. I assembled each de-clutching lever in turn to the new pin with the shorter top peg and slipped it into its recess in the flywheel cover. When fully seated you should be able to see right through the matching holes in the flywheel cover and the pressure plate, looking from the outside of the assembly. I found it was better to drive the long pegs through from the inside of the pressure plate, serrated end first. There was not such a good angle to swing a hammer this way, but it was easier to see when the pin was correctly positioned, flush with the inside surface of the pressure plate. When all three levers and pins have been pegged in, the G clamps can be wound out and removed, and if it was done properly, the whole assembly should stay together. Try pushing down on each of the de-clutching levers to check that they operate freely, and that the pressure plate moves in and out. If all’s well, it’s time to refit the clutch to the flywheel and refit the gearbox.

These notes have been written just weeks after stripping out the gearbox and clutch for another job, and the details of the removal and refitting procedure have been dealt with in detail there, so I haven’t repeated it. The notes were titled ‘Removing the gearbox and clutch Austin Heavy 12’ with photos. During the previous strip-down, I had replaced the clutch drive plate because it was loose on its centre boss, but this item should be checked while the clutch is out, and so too should the clutch friction rings. If these need replacing, it would be necessary to remove the flywheel too, as one ring is riveted to the flywheel and the other to the pressure plate.


Tom Stapledon

January 2007

Compressing the pressure plate
Broken declutching lever
Flywheel cover & pressure plate
The broken declutching lever
The 3 declutching levers
Flywheel cover with the pressure plate removed
showing reverse side of pressure plate
showing the mounting for the levers
new withdrawal pins mounted on declutching lever
the set of new pegs & pins
flywheel cover & pressure plate being compressed for reassembly
compress it evenly
old thowout bearing assembly
other side
new throwout bearing
old and new
new release bearing with oil tube fitted
clutch operating shaft
 
see a copy of the clutch parts below