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Doing a Clutch job on the 12/4

GEARBOX AND CLUTCH REMOVAL ON THE AUSTIN 12/4

It was more than four years ago since I had a professional job done on ĎPrincessí, our newly-acquired Austin 12/4. Princess is a 1931 New Windsor saloon and she had a very heavy clutch, which caused my wife difficulty, because of a back problem. At the time I didnít feel up to tackling a major job like that, so I decided to leave it to the professionals to fit a new set of clutch springs, as supplied by the VAR. When it was stripped down, they reported to me that the clutch was in fairly good condition, but that the starter ring gear was rather badly worn. Did I want anything doing about it? As I hadnít had any trouble with the starter gear and it sounded expensive, I declined and said to just do the clutch springs as agreed. Of course very soon after, the starter did begin to jam in mesh occasionally. I found it was necessary to put the starting handle in and jump up and down on it with all my weight to free it.
We later started doing weddings with the car, and the jamming of the starter got more regular, so that I had to keep the starting handle very close to me at all times. Now this is inconvenient at the best of times, but when youíre dressed up in a suit and youíre outside the house with a bride in the back of the car timed to reach the church in ten minutes, it becomes seriously stressful! This has happened several times through the last, busy summer season, and you can never be sure if the starter pinion will disengage when you start jumping on the handle. On one occasion I couldnít disengage it while on a garage forecourt after filling up with petrol. We had to tow the car home and take the starter motor off. This is not a job to be attempted in the road with a bride in the back of the car!
So at the end of the wedding season, I decided that the problem had to be tackled to reduce my stress levels. Now Iím a novice who hasnít looked at a clutch since I was a mere youth when the clutch disintegrated on my Viva HB. I had to replace it then, as I didnít earn enough to pay someone else to do it, but I remember next to nothing about it except that itís a problem to line up the clutch plate so that the gearbox shaft will go back in. I vaguely remember something about a piece of broom handle being used as an alignment tool.
I made enquiries from friends and experts, and after much confusion and trouble with bad memories, it turns out that the starter ring gear on the 12/4 is not part of the flywheel or even shrunk on to the flywheel as I would have expected. Itís actually part of the clutch cover assembly which is a massive, heavy machined item, and not a flimsy pressed steel affair as I imagined it to be. This clutch cover is bolted onto the flywheel and at first sight it looks like part of the flywheel. This led to confusion as two people I spoke to were convinced that the starter ring was part of the flywheel itself. The Austin 12 parts list helped to clear that up before dismantling started, with some very clear drawings. Next ---what to do about it? Original clutch covers may still be around at a price, but might be in no better condition than my own. For those with the skills and the patience, Iíve been told the answer is to build up the damaged teeth with weld and to file them back to the correct profile which sounds very clever and incredibly tedious and long-winded. I think thereís a third option, but canít be sure until the strip-down. It appears that the clutch cover plate is held onto the flywheel by six bolts arranged around the circumference and equidistant. If this is right, then it should be possible to turn the clutch cover round to a new position on the flywheel.
The way I understand it, the engine, when switched off, will always come to rest in one of two positions, roughly with all four pistons half way up the cylinders. As the engine loses its momentum, one piston or other will be coming up to the top of its compression stroke, but wonít make it, and the crank will bounce back by ninety degrees or so. This leaves one of two areas of the starter ring gear, diametrically opposite, always at the position where the starter motor pinion will engage it. When the starter pinion flies out to mesh with the ring gear, this happens with a lot of force and so a small number of teeth tend to take all the hammering. If the clutch cover plate is still in its original position, there may not be too many damaged teeth and moving it round may be the answer. If itís already been moved before, this may not be an option. Time to strip it down and have a look.


I had decided to combine this job with the annual winter service on the car, so after a twenty minute run to warm up the oils, the car was manoeuvred into the best position in the garage for all-round access, the wheel nuts were all slackened off and the car put up on four axle stands. Then wheels off and drop the sump and gearbox drain plugs while the oils were still warm. Next, push the seats as far back as possible, take out the front carpet and lift out the floorboards. This gives quite good access on the Twelve. The batteries were now disconnected prior to removing the starter motor. Make a note of the electrical connections for later. I always seem to have trouble with the starter, as it has an odd-sized bolt, the hardest of the three to get at.
Although my ball-change gearbox has a large, open inspection hole in the top of the bell housing, itís not possible to see the teeth on the starter ring, but when the starter motor comes off, you can inspect the condition of the teeth through the opening. Next to come off is the transmission handbrake mechanism. First undo the big adjusting wing nuts on the top of the shoes and remove them with their washers, and the shoes will slide off the shaft. The two nuts and bolts which secure the bottom of the assembly to the gearbox should be removed and then the whole shoe assembly will lift away.
I made a mistake here which I realised soon after taking the handbrake assembly off. The next job is to remove the prop shaft, and itís much harder to undo the nuts, front and rear when you canít stop the shaft from turning, so I had to put a brake shoe back on to hold it. Next time, prop shaft off first.
There are just three nuts holding the front end of the prop shaft onto the fabric coupling, then four nuts and bolts holding the rear end to the diff. Now back to the handbrake lever which is held onto its shaft by a cotter pin. Once the cotter pin has been removed, the handbrake lever comes off to the right and its shaft pulls out of its mounting on the top of the gearbox to the left. The various other parts on the shaft need to be kept in their correct relationship for re-mounting onto the shaft later. Next to come off is the gear lever. This just pulls out of the box after unscrewing the large cup nut at its base.
Next, the clutch and brake pedals and their shaft must come off as there isnít enough space for the gearbox to pass. This looks like one shaft at first glance, but it isnít. A very short shaft comes out of the clutch housing and the longer one in line with it, on which the pedals pivot, is bolted to the chassis at its right hand end. A nut and bolt hold the clutch pedal to the clutch operating shaft via an adjuster for pedal reach. Mark the relationship between these and remove the nut and bolt, then disconnect the pedal stalk from the lever and remove them. Now remove the two nuts and bolts holding the brake pedal shaft to the chassis and unwind the main brake adjuster rod right out of the brake pedal lever, the one with the tap handle, (after marking its position). Next remove the return spring and disconnect the pedal stalk, and the brake pedal shaft can be taken out. Unscrew the speedo cable from the gearbox.
Now with everything disconnected from the gearbox, its time to undo the nine bolts around the bell housing. I had serious worries that there wasnít enough room between the rear of the handbrake drum and the brake cross shaft, (3 inches or less), for the gearbox to come out. I thought about taking the brake cross shaft out to give me more working clearance, but I didnít really want all the extra work, and it certainly didnít look as if the cross shaft had been out on the previous occasion that the gearbox came out. With the gearbox held just by the last two bolts near the top of the bell housing, I wound the trolley jack up under the gearbox drain plug to take the weight. I also used a steel bar across the car floor, hooked under the handbrake ratchet bar. With the last bolts out, I worked the box rearwards, but there wasnít enough clearance. The steel bar had to go so that I could lower the back end of the gearbox below the brake cross shaft. Eventually it came away and could be lowered down to the floor and out sideways. This was a lot harder than it sounds, and in hindsight I should have removed the handbrake ratchet bar from the top of the gearbox, but I thought it would make a useful handle. In fact it got in the way of my rearward movement of the gearbox. Once the gearbox was out of the way it was possible to see the clutch unit properly and examine the teeth on the starter ring. There were a group of about 12 teeth on each side that were very badly chewed up, but the rest were fairly good, which means that the clutch cover hadnít already been moved round. Also, the top dead centre markings lined up where theyíre marked on the clutch cover and the flywheel. When looking into the inspection hole, itís the marks on the clutch cover that you normally see, with the marks on the flywheel very difficult to see, right at the top. There are also TDC marks for No.2 and 3 pistons directly opposite.
A marker pen had already been used to mark the relative positions of the flywheel and clutch cover, so now there were six bolts, held with tab washers to be removed, to release the clutch unit, after first removing the clutch withdrawal mechanism. These should be eased off slowly and evenly to release the tension of the 15 heavy springs, making sure as you go that the seal has broken before finally taking out the last bolts. All the spring tension should be released before the bolts run out of thread. This clutch cover is a very heavy lump of steel and needs to be supported well before the last bolt comes out. If it drops on you, youíll know all about it. As it comes away, the clutch drive plate will also drop out. All the rest comes away as a single unit, the pressure plate, toggle levers and springs are all captive within the clutch cover.
Now the clutch cover and starter ring could be examined properly on the bench. With the TDC 1-4 mark at 12 oíclock there were about 12 very badly damaged teeth from that point in a clockwise direction, and exactly the same diametrically opposite, clockwise from the TDC 2-3 position. All the rest of the teeth were showing very little sign of wear or none at all. This backs up the theory that the crank always comes to rest in one of two positions, and that a relatively small number of gear teeth take all the wear. The six bolt holes were measured and were found to be equidistant, so there was no reason why the clutch cover couldnít be moved round by one bolt hole in either direction to put a fresh set of teeth in the right position for the starter pinion.
The clutch friction linings are mounted on the flywheel and the pressure plate inside the clutch cover and were found to be in good condition. If they needed to be replaced, it would be necessary to remove the flywheel to fit one lining, and to dismantle the pressure plate from the clutch cover to replace the other. I found that the drive plate and its centre boss were loose where they are riveted together. Having no idea how much wear had taken place to the rivets or the holes where they pass through the plate, I decided to fit a new plate. This came with six new rivets and had to be fixed to the original centre boss. The rivets were centre popped and partially drilled, and then the heads were chiselled off. As it turned out, there was hardly any wear, but better safe than sorry, and my centre plate was rather scored. The new plate was riveted down hard to make sure that doesnít happen again. I decided to file the rough edges of the damaged gear teeth just to minimise any possibility of problems if any of these teeth came into contact with the starter pinion, and then cleaned the clutch friction linings, ready for re-assembly.

It seemed odd to be putting everything back together so soon after a major strip-down, but all this was just for the sake of turning the clutch cover plate round by 120 degrees on the flywheel. I was lucky to be able to borrow a home-made alignment tool from a friend, to accurately centre the clutch drive plate during re-assembly. This is just in the form of a peg made of aluminium with a section turned down to fit the hole in the flywheel centre and a larger section to fit the centre boss of the drive plate. When the clutch drive plate is offered up to the flywheel, and the peg inserted, the drive plate will be accurately centred and held in place while the clutch cover is being bolted back on. This ensures that the gearbox shaft will push home through the drive plate and everything will line up properly. When the clutch cover has been bolted back on to the flywheel and the drive plate is firmly held between the friction linings, the locating tool can be removed.
Next, I clearly marked the TDC 1-4 point on the flywheel, on all visible surfaces with a marker pen, so as to make it easier to see in future when looking down into the bell housing opening. Then it was time to offer up the clutch cover to the flywheel, and I decided to rotate the clutch cover by 120 degrees anti-clockwise, (for no particular reason). Either way would have achieved the same result as I proved to myself again by rotating the whole assembly by 90 degrees from TDC. This is the position to which the engine normally comes to rest at switch off, and this now put a good set of teeth in line with the starter motor pinion. The six bolts should be tightened down evenly, a little at a time and then the tab washers need to be bent over. Next thing to do was to mark the new position for TDC on the clutch cover plate because now the makers marks are no longer in the right place, which could cause a lot of confusion for anyone trying to time the ignition at a future date. I marked the position very clearly with marker pen, in line with the marks on the flywheel, and hoped that Iíd remember what the red marks were for next time I needed to find TDC !!
While inspecting all the clutch parts earlier, Iíd noticed that there appeared to be a lot of wear on the clutch withdrawal mechanism where the clutch withdrawal levers bear. I know that a replacement mechanism is available, but rather expensive, and as the clutch was working well, I didnít intend to replace it this time. However, after seeing the amount of wear, I regretted not having marked the relative positions of the de-clutching levers and the withdrawal mechanism, so that I could put it back the same way. The wear on the parts concerned was probably uneven, and I was worried about the clutch operating unevenly after re-assembly. Anyway, there was no way of telling, and there were three choices, so I just had to put the withdrawal mechanism back in behind the three levers and hope for the best. Everything had to be put back together completely before the clutch operation could be tested.
So now itís time to put the gearbox back in. I manoeuvred the box, after cleaning it up, back under the car and roughly in position for lifting. Then I stared at it and stared at it. I walked all round it, I looked down onto it, I got under the car with it and I stood in the car astride it. There was no way I was going to lift it, and there was no way the reverse of the removal procedure with the trolley jack could work. At this point, I really felt the need for a small crane, but I didnít have one. A friend had mentioned using fan belts as slings, and so I decided to experiment with this idea. I found a couple of old fan belts in good condition and I had a supply of steel bars which were something over three quarters of an inch in diameter. I cut a couple of these down to the right lengths to lay across the floor of the car in the foot well and then I looped the fan belts round the gearbox, one near the front end and one to the rear. By placing a bar through the front belt and supporting on one side of the floor, I managed to lever the box up and rest the other end of the bar on the other side of the car. I did the same with the second bar, and now I had some leverage, it was possible to raise the box by lifting the steel bars onto wooden blocks to get it into roughly the right position. With the gearbox at the right height and in line, I could now wind the jack up under the drain plug to adjust the height accurately. The actual process of guiding the gearbox first motion shaft into the withdrawal collar and into the flywheel was not at all easy. I was very grateful that I had the gearbox with the large inspection hole as it was not easy to keep the withdrawal mechanism located on the three levers while turning the flywheel to get things to line up, and at the same time, guide the clutch withdrawal fork behind the collar. Eventually it went in, and the first bolts could be put in at the top of the bell housing.
The first thing I wanted to do was to check the operation of the clutch to make sure it would disengage properly, but to do this, there was a lot of re-assembling to do. The clutch canít be operated without the footbrake pivot shaft, so this was re-assembled first with the clutch pedal shaft and pedal arm. The clutch pedal linkage was re-connected to the marks I had made before dismantling. Next I re-fitted the starter motor and re-connected its wiring because I wanted to wind the engine over on the starter to check everything was OK. Then the battery was connected and the gear lever re-fitted. With all the spark plugs still out, I now turned the engine over, first with the starting handle to make sure there was nothing fouling anywhere, and then with the starter motor. It was a relief to see the engine turn over and the gearbox final drive shaft turning, and to see that it stopped turning when I put the clutch pedal down. This was as far as I could go to ensure everything was working properly without completing the re-assembly process. So now that I felt a little happier abut the clutch operation, I finished off the re-assembly of the footbrake mechanism by fitting the pedal stalk and then screwing the main ďtap handleĒ lever back in to the pedal up to the mark Iíd made on the screw thread. The return spring was re-fitted and then the brake light switch had to be reset, as this is mounted on the tap handle lever too.
Next, the handbrake mechanism was re-fitted, after Iíd cleaned it up and washed the brake shoes, which were rather oiled up. I adjusted the handbrake by pulling up the lever by one notch, and then tightening the large wing nuts on each shoe until the shoes were in contact with the drum. I then released the brake to check that the drum was free to turn. After this, the brake would be hard on when pulled up by two notches. Next, the prop shaft was re-fitted to complete the re-assembly process.
It would have been rather too easy to forget a couple of important things at this point, in my hurry to try the car on the road. The gearbox and engine needed re-filling with oil and the clutch withdrawal mechanism needed a few drops of oil down its oil tube. Then refit the spark plugs and the road wheels and drop her back down off the axle stands.
It was time to start up the engine and try a few tentative movements out of the garage and backwards and forwards on the drive, to feel the action of the clutch and the brakes. Everything felt right, so down with the floorboards and donít forget to tighten the wheel nuts, then itís off round the block for a road test. A lot of work for such a small adjustment, but everything seems to be fine. Now, only time will tell if the sticky starter problem is permanently cured.


Tom Stapledon
November 2006.

Floor boards out Floorboards out 2 Floorboards out 3
The transmission & brake Starter motor view Underside view
Underside Starter motor off Handbrake gear partly dismantled
Brake shoe assembly off Showing brake pedal shaft Brake & gear lever off
Brake & gearlever off 2 Pedals & shaft off Pedals out
Gearbox out Gearbox out 2 Gearbox out 3
Closeup of clutch release Area of chewed teeth showing some good teeth
After removal of chutch Clutch assembly 1 Clutch assembly reverse side
Clutch assembly 2 Closeup clutch release assembly Closeup of clutch release again
Clutch cover plate Clutch drive plate Clutch drive plate reverse side
Clutch drive plate LH side faces Gearbox New drive plate New drive plate riveted
Clutch assembled Withdrawal mechanism reassembled Refitting the box 1
Refitting the box 2 The clutch alignment tool The finished product

A big thankyou to Tom for sharing this with us

 

 

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