Rebuilding a 319 Gearbox

A while ago I went on a very interesting foray to the former East Germany and came back with one complete 319 box and another casing with just the first motion (input) shaft and the layshaft in it.  The complete box had excellent gears with very little wear, so I rebuilt that one using new sealed bearings and put it on one side.

The gears in the second box were all covered in a thin film of red rust.  I had checked them carefully before I bought it but was still pleasantly surprised to find them nearly perfect when I bead blasted them.

I wanted to build up a good box by using as many parts of the car’s original box as I could and the gears from this second box, but I needed the third gear constant mesh pinion (on the output shaft) which was missing, and I also needed a new 1^st and 2^nd gear cluster.  The latter are straight cut and relatively cheap to have made, so that was put in hand at my usual gear cutter in Sheffield, and luckily Mike Dutton came up trumps with the third gear.  The gear was good but the syncro cone was badly worn.  The top gear syncro cone from the other box was bad as well so I decided to see what could be done about them.

The top gear cone is a separate piece so I took all the balls and springs out of it and built up the worn faces with silver solder and machined them back to what I thought they should be.  The third gear cone is bronze as well but is shrunk onto the shoulder on the gear, which is then peened over.  This I found out by destroying the old one from the original box!  I didn’t dare use the silver solder method as it would ruin the case hardening on the gear itself.  The only way to renew it is to break it off and cast a complete new one, machine it and shrink it onto the gear shoulder.

This isn’t as bad as it sounds because although the top gear cone has all the balls and springs in it, in the case of the third gear one they are all contained in the other,female part, so they don’t have to be considered.  I used the broken cone as a basis for the pattern to cast a new one, silver soldering the outer from an old ball race onto the back of it so that there would be enough metal to grip in the chuck when I machined it and used P38 body filler to increase its size to allow for both the wear and the shrinkage of the casting.  I got my brother in law to machine the final casting for me as it is pretty critical and he is a far better machinist than I am. In fact, after all that trouble he machined it from solid instead of using my casting, reckoning that the material he used was better suited to the task!

At this point I think I should set out the routine for dismantling and reassembly of these lighter gearboxes, which are not quite the same as the ones fitted to the 320, 321 and 328, which have an intermediate bearing supporting the middle of each shaft.

To dismantle. 

Remove all the selector mechanism including the stirrup which controls the top and third sleeve and the reverse selector.  The stirrup will only come out when in the top gear position.  Take off the cover plate from the inside of the bell housing; this reveals a circlip on the input shaft. Take this off.  Go to the back of the box and take off the drive coupling with its key and washer, then remove the outer of the two covers, then the speedo drive gear (which does not have a key) and the set screw locating the reverse gear shaft.  Remove that shaft (there should be a threaded hole in the end to put a bolt in if it doesn’t come out easily).  Next take off the inner cover plate.  This may or may not bring the layshaft bearing with it, but it will bring the output shaft bearing.

You should now be able to remove the whole of the internals by tapping both the layshaft and the input shaft through from inside the bellhousing.  You may have to hold the reverse gear pinion out of the way as you do this, but they do come out!

The layshaft is all one piece with the gears pressed on it, but the input and out put shafts are much more complicated!  To dismantle them start at the input end.  There is a large circlip which holds the top gear syncro cone in place.  Remove this with a pair of snipe nose pliers if you haven’t got circlip pliers, and separate the two parts.  Here I cannot emphasise too much that you should keep all the shims you find in their respective places!  Do the same to the third gear syncro cone.  Pull out the output shaft. You should now be left with the sleeve with a syncro cone on each end and the first and second gear cluster in the middle plus the ring for the selector with its two circlips,  Carefully knock the two cones off the ends, take off the circlips and the ring.  The third gear pinion is located on the shaft by three radial pins, which in turn are held in place by three axial ones, which are spring loaded.  Push the axial ones in with a Stanley knife blade and remove the radial ones with pliers.  Hook the springs out with a bit of bent wire; they are usually pretty shot, so it’s worth renewing them.  Likewise the selector springs if they aren’t too good either.  If the radial pins, which see to the location of the gear on the shaft, are very worn it is worth having new ones made.

Having got it all apart check all the threaded holes in the casing (it’s very aggravating to find a stripped thread when you’ve nearly finished re-assembly!).  Check the state of the gears.  If the constant mesh gears are badly worn you are in trouble.  If the straight cut first and second are shot you can get new ones made quite reasonably.  As both top and third gears are in constant mesh they should not wear unduly, but the teeth which engage them, both inside the gears and on the ends of the sleeve do wera quite badly.  Mark Garfitt can usually supply new sleeves but I am not sure that anyone has had any of the other parts made.  They would be rather expensive, I think.

Putting it back together is the reverse of that, but I think the best way about it is as follows.  First, put just the input shaft in place (all new sealed bearings of course!) with any shims that came off with it.  Check for end float.  If there is any at all make new shims to reduce it to nil.  Take it out and put it back with the layshaft and rear covers as well. Check the layshaft for end float, get rid of any you find and make sure that the constant mesh gears are running centrally to each other by shimming one end or the other.  Take off the end casing, remove everything once again and replace it, this time add the output shaft with the third gear pinion etc. Eliminate end float and check the pinions are central as before. 

I mentioned sealed bearings some where up above, I am informed by my bearing suppliers that it is accepted practice to use sealed bearings throughout a rebuilt gearbox.  They will outlast the gears and the seals are very good at keeping odd bits of gear teeth at bay!  Don’t be tempted to remove one or other of the seals, leave them all in place, they even help stop those annoying drips!

Before putting it all back together again with gaskets and so forth it is well worth checking the selector mechanism for wear and refurbishing it if necessary.  The first/second selector is fairly straightforward, it just needs checking to make sure that the sliding cluster is clear of its mating part on the layshaft when in the neutral position.  If necessary the whole selector mechanism can be moved bodily backwards or forwards enough to make sure the gears don’t clash by just pushing it one way or the other when tightening the holding down set screws.

The top/third selector is different.  There are three major parts to this; the stirrup which pivots on two set screws near the bottom of the box, the bridle (for the sake of anything better to call it!) which is a bronze casting and which pivots in holes in the stirrup and the disc which is located on the splined sleeve by the two circlips.  Considering that the movement between in and out for third gear is 9mm, it does not need much wear in the three components to lose most of the travel.  I reckon that the box I have just overhauled had about 4mm of lost motion because of wear.  I ran silver solder into the four holes in the stirrup and then reamed them out to their original sizes, which is 7mm for the pins in the bridle and 8mm for those in the bottom pivots.  I also squashed the lips of the bronze casting in a little using a 5mm disc to limit the amount of squash, having warmed the casting up with a blowtorch first.  On some boxes the disc is 3mm and on some it is 5mm with an undercut on one side if it.  Check which way round it is when you dismantle it.  I think it should face forward, but I’m not certain.  If the circlips are not a good fit in their grooves new ones should be obtained, as this is another lost motion possibility!  The other place where lost motion can occur is at the little radial pins which locate the third gear pinion onto its shaft. I haven’t had to renew these on my boxes, but I don’t think they would be too expensive to have made if enough were needed.  It is also worth making sure that the output portion of the main shaft is not being allowed to be pushed backwards due to not having the correct spacers behind it.  Obviously if it can move the teeth will be that much further from being correctly meshed

With luck you should now have a gearbox which has four good gears! However, if like me you found the waggly stick method of changing gear a bit hit and miss I can supply you with a casting, which when used with a Triumph Herald or Spitfire remote control, is relatively cheap, easy to fit and a much more pleasant to use! 

Gearlever conversion

The Herald remote needs some modifications to make it really effective.  The following instructions go with the casting I mentioned above; -

1. The dangling lever which engages the selectors has to be extended to about 60mms, this from the underside of the shaft to the tip of the lever.  It should then be about 8mm above the face of the new casting.  The sides of the tubular portion can also be relieved a bit to give slightly more movement backwards and forwards.
2. The bottom end of the Herald gear lever also needs extending to about 52mms, that is from the centre of the new actuating hole to the bottom of the plastic ball.
3. The bar, which connects the bottom of the lever to the joint at the forward end, needs bending downwards so that it connects with the newly extended lever.