Readers, I thought you might be interested in a picture of the final stage of my Morris 850 transmission rebuild. The picture is a little unusual because it shows the unit with oil fill. For a long time, I had thought that the oil level in these cars was a result of careful attention to a balance between the pump not running dry on hard cornering (oil level too low), and the amount of frothing and spray from gears and crankshaft (oil level too high). But I was amazed to find that the drawings show that the power unit oil level is nothing more than the centreline of the gearbox/final drive bearings/ gear train. So before putting my rebuilt gearbox into storage, I filled it will oil (a little over the centre line is 5 litres) spun the geartrain around by hand, and then drained the oil out again. When the gears are rotating, there is an interesting build up of pressure where the teeth mesh and oil at this point is forced through holes in between the gear teeth to lubricate the bronze bushes on the main shaft.
The 850 gearbox is unusual because, not only does it have the old style bronze cones (not "brass", as you might read somewhere), but because there are two versions. An early version was fitted from 1961 up to some time in late 1962, and then a later version from late 1962, both with the cone type synchromesh, up until the advent of baulk rings in 1964. What's the difference? Well, in the early version the leading edges of the first/reverse/laygear spur teeth are rounded. That is, they are intentionally machined with a rounded profile. (I had seen on some youtube video that the guy doing a rebuild thought that this signified that the gears had worn because the replacement he got had chilseled leading edges). It is the later version of this early gearbox that has chiseled edges on the spur gears. The main shaft also differs because the early one doesn't have a groove for the plunger which is included in the later first gear hub. Subtleties like this make it a challenge to obtain the correct replacement parts. I've detailed all this in an article on my web site if anyone is interested in more information.
I thank some people for helps in sourcing hard-to-find parts and making suggestions: Chris Katsikas, Andrew Bergan, Chris Miller and a some businesses in NZ (
https://www.classicminispares.co.nz), UK (Somerford Mini), Portugal (Oliveira and Valentimida) and USA (
https://www.sportsandclassics.com) and our own Craig Martin at Newport Motors and Andrew at Mini and Moke World Brookvale.
Tony Cripps
