Synchronicity

A question that regularly crops up is which is best, synchro or 'dog' selection gearboxes. Well,hold on to your hats - here comes the explosion of a myth.
It would appear that a very large majority of people racing Minis believe that a 'dog' engagement box is the ultimate. Sorry, but this is not necessarily so. Much of this depends on the ability of the user. Before we go any further, some background information may be useful... ...
Moons ago there were 'crash' boxes. Aptly named because if you didn't get it right on the gear change, the gears used to crash into each other. Thus causing an horrendous wear rate. You can not have hard metal objects bashing into each other constantly without causing some kind of wear. This was the fore-runner of the 'dog' box, or at least the drivers ability to use one successfully. After all it was down to the drivers ability to 'synchronise' the changes - or identify the right r.p.m. at which to engage the next gear without all that graunching noise.
Briefly, early gearboxes operated on non-constant mesh principles. This essentially meant that the gears were only engaged by sliding the teeth of the gear pairs together. On later constant mesh engagement, the main gears were permanently engaged, selection was made by the introduction of an independent hub. The use of this hub allows the speed of the selection gears to be more evenly matched to the speed of the mainshaft, thus vastly reducing the crunch associated with the much earlier crash box syndrome. Consequently a far superior and much less damaging gear selection  process was sporned. Now, as far as race cars are concerned, some slightly differing parameters are involved - which is where all this seems to fall apart, so first a little history lesson .. ...
Formula One used to race with helical gears and synchromesh - yes, really, they did. Until the mid sixties that is when a certain Mr Hewland saw an opportunity to produce a gearbox that was easier to use and vary 'in the field '. Motorbikes had been using dog engagement gears for some time. The overlay being a rapid system of altering gear ratios without the hassle of synchro hubs shedding their selection balls and springs all over the pits. Working on the situation where money was not of primary importance against lap times, this was the way to go for the Formula One boys. The most important point to bear in mind at this point is that motorbike gearboxes work at between 1/2 to 1/3 engine speed, whereas car engines work at practically 1 to 1 engine speed. And this is where some of the problems lie. Why is this important ? Wear rate. Much like the early crash boxes, unless perfect rpm selection was made by the driver severe damage was experienced - meaning very short gearbox life. Basically we are talking about inertia and impact. Try to consider two gears revolving at several thousand rpm, then pushing them together to engage and hope this will happen first
time. As there are more than a few teeth to engage right off it must be appreciated that if both gears and hub are not rotating at the same speed, engagement first t ime round is unlikely - practically impossible in fact. This situation is made worse by having more than a few teeth to engage (reasons for this later).
Onto synchronisation, or 'baulk' ring engagement then. This term 'baulk' is used to describe what actually happens. Instead of trying to get a bunch of teeth on a gear to match up first time round, a mediator is introduced between the gears. Commonly known as the 'baulk ring' - whoa, surprise, surprise!! So what does it do ?
It speeds up or slows down the engaging gears to the speed of the mainshaft and hub so that selection is smoother and massively less damaging than the old crash engagement. OK, hopefully we now have a grip on what type of engagement is best suited - Uh-oh,1 can see frowns ...... Right, real basic stuff coming up - but don't feel insulted.
You are not alone in this .......
What we are talking about here really is driver ability. A dog box in the hands of a poor user is a sight worse than a synchro box in the hands of just about anybody. Unless the driver is able to make the required adjustments to driving technique and style to maximise the potential of a dog type box, gear changes are likely to be slower, and accrue far more damage (and thus a severe reduction in reliability). So the myth of dog boxes being more reliable ends here. It is not the product - more the user. A bad user of a dog box will create as much servicing as a poor user of a synchro box. The underlying factor here is that a synchro box is more user friendly. Next up is the question of speed of change. Once again, it is down to the user. Effectively the only reliable change after the synchro type is the semi-automatic or air-shift gear boxes as automatic adjustments are made to correct/match gear/hub speeds to ensure a perfect first time gear selection as used on all current Formula 1 cars. Dog manual selection relies heavily on human input.
Essentially, until the driver is used to and can make the relevant adjustments to using a dog type box, rebuilds will be as frequent as a synchro box to keep the unit in peak performance. Unfortunately, due to the nature of the design, synchro boxes require frequent maintenance when used in competition to keep in good working order. But far less expensive than rebuilding a badly used dog box. Hopefully it can be seen from this that a dog box is not the be all and end all. They can be more trouble than they are worth - they are some three times the price of a synchro kit.
Most drivers would not benefit from such a large financial outlay-so consider this before taking the plunge. One element that can be used to illustrate the wear/rebuild problems is the number of 1/2 selector forks we sell. Those running dog boxes seem to need to replace these at alarmingly frequent intervals - suggests that some less than perfect gear selection is going on. Especially off the line - where I suspect most of the damage is being done. As an aside to this - our redoubtable gear manufacturing specialist has designed a dog engagement box that literally selects itself. Point the gear in the relevant direction and it practically selects itself. It is totally fast. The only draw back is that Mr. X is worried because it may need a rebuild after 800 competition miles........

Keith Calver.