General description
The manual transmission fitted to all Mini models covered by this manual is of the constant mesh type containing four forward and one reverse gear. The transmission is housed within an aluminium casing bolted to the lower face of the engine and also shares the engine lubricating oil. The differential assembly is contained within a separate housing bolted to the rear of the gearbox casing.
Originally, cone type synchromesh was fitted to second, third and top gears only. This was replaced by an improved baulk ring synchromesh fitted to all models from October 1962. Four-speed baulk ring synchromesh was introduced to the Mini Cooper range in 1964 and was later fitted to all Mk II models.
Automatic transmission became available an Mini Saloons from 1965 as a factory fitted option. Further information on the automatic transmission- will be found in subsequent Sections of this Chapter.
Gearboxremoval and refitting
The gearbox is removed from the car together with the engine and differential assembly as described before. It is then necessary to separate the engine from the gearbox and full information on this procedure is also detailed before.
The procedure described below covers the early three-speed synchromesh gearbox with either cone or baulk ring synchroniser assemblies and also the later four-speed synchromesh units. Any differences in the dismantling instruction will be detailed where necessary.
Position the gearbox on a strong bench so that it is at comfortable working height and easily accessible from both sides. Alternatively place the gearbox on a clean floor preferably covered with paper.
Begin dismantling by removing the differential assembly as described elsewhere.
Undo and remove the large hexagon headed plug and washer from the front of the gearbox casing and then lift out the spring and reverse check plunger.
Note; On some models a reversing light switch maybe fitted in place of the hexagon plug.
Take off the idler gear from the side of the gearbox casing together with its thrust washers. Ensure that the thrustwashers are kept in their correct relative positions on either side of the gear.
Unscrew the clamp bolt and washer securing the selector lever to the gearchange shaft. Slide the gearchange shaft off the selector lever and withdraw it from the casing. Take care not to lose the Woodruff key from the shaft (photo). Now lift out the selector lever and prise out the shaft oil seal if required.
Undo and remove the speedometer pinion housing cover retaining screw and lift off the cover and bush assembly. Now lift out the pinion.
Undo and remove the nuts and spring washers and lift off the engine mounting bracket and front cover.
Now lift out the interlocking change speed gate (photo).
Knock back the locktabs and undo and remove the two bolts securing the oil suction pipe blanking plate to the rear of the casing. Lift off the blanking plate and gasket.
Knock back the locktabs and undo and remove the two bolts securing the oil strainer and suction pipe support bracket to the lug on the gearbox casing. Pull the suction pipe out of the oil strainer and remove it from the gearbox (photo). The oil strainer cannot be removed at this stage.
From the flywheel housing side of the gearbox, extract the small circlip from the first motion shaft (fitted to later gearboxes only) and then using a puller or two screwdrivers withdraw the small first motion shaft roller bearing from the end of the shaft.
Engage two gears simultaneously by moving two of the selector rods in or out. This will lock the mainshaft and prevent it from turning as the large retaining nuts are undone.
Tap back the lock washer and undo and remove the first motion shaft retaining nut from the flywheel housing side of the gearbox. This nut will be very tight and it may be necessary to place the gearbox an the floor and have an assistant stand on the casing as the nut is undone. Now slide the first motion shaft gear off the shaft.
Tap back the lock washer and using a socket and extension bar inserted through the open end of the casing, undo and remove the final drive pinion retaining nut. This nut will also be tight Eind your assistant may be required again. With the nut removed, slide off the final drive pinion (photos).
Knock back the locktabs and undo and remove the bolts securing the mainshaft bearing retainer to the centre web of the gearbox casing. Lift off the bearing retainer and shim followed by the (ayshaft and reverse shaft locking plate (photos).
Measure the endfloat of the laygear using feeler gauges. If the endfloat exceeds 0.006 in (0-152 mm) or is less than 0.002 in (0.0508 mm) then new thrustwashers must be fitted on reassembly.
Unlock the two previously locked mainshaft gears by moving the selector rods back to the neutral position.
Using a brass drift, tap the layshaft out of the gearbox casing towards the flywheel housing side, and lift out the laygear together with the two thrustwashers (photos).
Undo and remove the two plugs from the lower rear face of the gearbox and lift out the springs and interlocking plungers. Sludge in the bottom of the casing may prevent the plungers from being removed but this will not affect the dismantling procedure. Take care that they are not lost or dislodged when cleaning the casing after dismantling.
Extract the large circlip from the flywheel housing side of the gearbox which retains the first motion shaft bearing in position. Now very carefully, using a brass drift, tap out the first motion shaft and bearing from the casing (photos).
*Mini-list comment* There *IS* an easy way to get that blasted diff pinion double roller bearing out! Haynes says to drift at an angle. This has busted 3 bearings on 3 attempts. This other book (Autodata) shows the use a special horse-shoe shaped spacer (special tool 18G1127) which is inserted in between first gear and the bearing and then the mainshaft is drifted the other way and "pop" out comes the bearing intact.Using a brass drift or soft-faced mallet, tap the mainshaft toward the flywheel housing side of the gearbox until a gap of about 1 in (25 mm) exists between the bearing and first gear. Now using extreme care tap the outer race of the bearing away from the flywheel housing end and out of the centre web of the casing. Tap each side of the bearing alternately to prevent it from binding and take care not to impose any load on the teeth of first gear. When the bearing is clear of the centre web slide it off the end of the mainshaft and withdraw it from the casing (photos).
Now carefully lift the complete mainshaft assembly up and out of the gearbox (photo).
Lift out the oil strainer assembly (photo).
Tap out the reverse gear shaft (photo) and withdraw the gear and selector fork.
Slacken the locknuts and then undo and remove the selector fork retaining locking screws (photo).
Slide the selector rods out of the forks and withdraw the rods and forks from the gearbox.
Remove the circlip from the reverse gear shift lever pivot pin and remove the lever (photo).