Making a Ribbed Gearbox Fit an A30 Bodyshell by Richard Johnston

Making a ribbed gearbox fit an A30 bodyshell by Richard Johnston 1. Introduction The smooth gearbox. I described the recipe for converting A30 gearboxes to use A35 smooth gearbox gears in the Autumn 1982 Spotlight (republished Spring 1995). This is a pure “assembly of existing parts” process. With the aid of a workshop manual it is not difficult, though deciding whether something is too worn to use needs experience. Most wear takes place when the lower gears are in use, and there is more or less no wear when in top gear as it is direct drive gear. On the whole most A35s have not spent much time in the intermediate gears and so the main damage to them is usually to first gear and the first gear spur on the layshaft through engaging first while moving, and to the engagement dogs on the gears if the synchromesh has been abused, or the synchroniser springs have broken, which is a common cause of failed synchromesh but a simple repair. The gears themselves rarely have serious wear, unless the gearbox has been run without sufficient oil. These considerations mean it is fairly easy to find a A35 gearbox with minimal damage to use as a source of gears. Ribbed gearboxes are better for many applications than the earlier smooth gearboxes for these reasons: a) they use a later design of synchromesh that uses baulk rings to prevent premature gear engagement. Baulk ring synchromesh is used in modern gearboxes. It does not require special gear changing techniques to achieve silent gear changes - an advantage for those who only drive an A30/A35 occasionally. b) the gears in them are designed to transmit more power than the smooth boxes, so that they last longer. The gear set used in the later 1098cc and all 1275cc Sprite/Midgets has the so- called “type B” gears, which are also more energy efficient as the angle of the helical gears was reduced, resulting in less lateral thrust. c) the gear ratios are better suited to modern traffic conditions and for engines with more power. The “standard” gearbox as used in later A35 vans, Morris Minors and the A40s has a higher second gear than the smooth A35 gearbox, while the Midget gearboxes have closer gear ratios that suit more powerful engines. Unfortunately making a ribbed gearbox to fit an unmodified A30 bodyshell is not just an “assembly of existing parts” procedure, as some parts have to be made or modified. However it is possible for someone with relatively modest workshop skills and equipment. 2. What parts do I need? a) A ribbed gearbox in useable condition. Irrespective of type, as with smooth gearboxes, many ribbed gearboxes have damaged first gear teeth which makes them noisy. Midget gearboxes are likely to have been used hard in the intermediate gears and may be particularly badly worn. Also, especially on Midget gearboxes, the more sensitive synchromesh cones may have been damaged by the use of gear oil with EP additives. If there is any doubt about the state of the gearbox it should be stripped down and checked or sent for reconditioning. b) A gearbox tailshaft cover from a Series II Morris Minor. This is the same as an A30 cover but longer. This item may not be easy to source. c) a sheet of 4mm thick aluminium – this needs to be as large as the front face of the tailshaft cover. I sourced a piece 200mm square on ebay. d) clutch fork from 1098cc/848cc Austin A35 van, or the equivalent created by welding two forks together (see figure 1), and, if using a thick engine backplate a 1098 clutch thrust bearing (for thin engine backplate use the 803/948cc clutch thrust bearing) Figure 1 Comparing the smooth gearbox clutch fork (top) and a ribbed box fork modified for the A30. Note the different position of the fulcrum, which is why the rod is made longer. e) A35 propshaft f) Speedometer drive and gear from A30 but only if using the original A30 speedometer. g) (Ideally) the tailshaft spacer from a smooth gearbox that separates the rear main bearing from the speedometer spiral gear. If you do not have this, the ribbed box one can be spaced out with washers to avoid the speedometer drive fouling the tab washer. h) gaskets for the rear cover (ideally 3 of these – one is for cutting the spacer) and, possibly, front cover of the gearbox 3. Procedure 3.1 Preparation of the Morris Minor rear cover. 1) Place the Morris minor cover in a position where a rear cover gasket can be laid upon the front flat surface it and a hole drilled into it. 2) Place the gasket carefully on the cover, so all the holes round the edge line up exactly. Centre punch the centre of hole indicated by the point of the pen on figure 2, and drill a hole with a 9/32” drill about ¼” deep. It does not matter if the hole is made too deep. Figure 2 Gasket showing the hole for the rear bearing housing peg 3.2 Preparing the gearbox 1) Unbolt the remote gearbox casing (8 nuts) from the gearbox extension. 2) Remove the speedometer drive. Undo the 9 setscrews that hold the gearbox extension to the main gearbox case, and remove it – you may have to turn this to and fro to disengage it from the selector fork rods in order to remove it. 3) Remove the drain plug on the bottom of the gearbox to allow access to the rear fork. Make sure that all the fork rods are in neutral (i.e. they all line up). With a 7/16 inch box spanner or suitable socket, undo the locknut on the retaining bolt that retains the reverse fork, by turning anti-clockwise about a whole turn. With a 3/8” socket undo the bolt enough so that the rear fork rod can be rotated 180 degrees – this comes out around 1/8” – do not take it out. When doing this be careful not to pull the rear fork rod out of the casing at all. Retighten the bolt just enough to stop any further turning movement of the reverse rod. 4) A step must be added into the reverse fork rod to prevent reverse gear being engaged accidentally. In a used gearbox there will be a shiny line at the place where the top of the step should be placed. See the line as shown on figure 3. This is 5/16” below the top of the fork. Figure 3 – reverse fork rod, showing the line that corresponds to the top of the needed step 5) The step can be made in different ways according to the skills of the mechanic: a) The step can be made up with weld, and the top of step made level with a dremmel tool and suitable grinding tools. b) a piece of steel can be cut to make a step that can be pressed into place as an interference fit, and then welded from the underside of the step, or fixed in place using JB weld. The result from using this method as shown in figure 4. Figure 4 Reverse fork rod, after installation of step Whatever procedure is adopted, the completed step must be firmly and permanently placed, made to be flush with the surface that faces the third/fourth fork rod (there is very little clearance), with the step 5/16” down from the top of the fork. It does not matter if the step is set a little higher as the gearstick will still clear the step.. 6) Cut or grind 1/8 inch off the rear end of the reverse fork rod (otherwise the rear fork will be pushed towards being in mesh when not in use). 7) Release the reverse fork rod by undoing the reverse fork rod retaining bolt (3/8 inch) a little. Return the reverse fork rod to its normal position, align the retaining bolt with the hole and tighten the retaining bolt. Then tighten the locknut (7/16 inch) [Some people may find the above work easier to do off the gearbox. In which case the reverse fork can be removed without otherwise disturbing the internals of the gearbox as follows: 8) Turn the gearbox so you can access the bottom surface, so that the clutch housing is on the right. You will see the drain plug – and to the right of it in line there is a setscrew, and below that is another setscrew.. Remove that lower setscrew. This retains a spring and a plunger. These need not necessarily be removed, but be careful that they are not accidentally lost. 9) Remove the clutch fork and front cover. 10) Do step 3) above but do not retighten the retaining bolt. 11) Using a spare A-series gearbox fork rod (any sort) or a dowel the same diameter as a dummy rod, carefully push the reverse fork out of the gearbox, always keeping the rods in contact, until the dummy rod replaces the reverse fork. 12) When the alterations to the reverse fork rod are complete, with the same careful procedure use the reverse fork rod to push the dummy rod out again. 13) Retighten the reverse fork retaining bolt as described in 7) above 14) reinstall the front cover with a new gasket, making sure that the layshaft is correctly aligned with the cover and pushed home from the rear end, and the shim is in place. 15) Replace the bolt removed in 8) above, making sure that the plunger and spring are present.] 16) Fit the Late Austin A35 van clutch fork, and fit a 1098cc clutch thrust bearing (if engine has the thick backplate).

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