I have a 1936 600cc Aero model undergoing one of those long protracted restorations. One of the last sub-assemblies to be dealt with is the transmission, and evil things have been done unto it. Until I get around to it, it resides in a cupbord. it is a P/ prefix 4-speed.
I just recently came across another Aero box of the same vintage, this time a M/ prefix, which according to Jeff Clew's book is for the 500cc Aero. Now I am not sure what the difference between the 500 and 600cc gearboxes were, to warrant individual prefixes. Not the internal gearbox ratios, because they are the same. (The 600 pulled an overall higher gear, of course.)
One thing that is different between the two gearboxes is the mounting clamp. The one for my P/prefix box is the same clamp as used on the 600EW models. Now I do not know if this is the right clamp, but it is clearly been with the bike for a long time, as there are chafe marks on the bottom of the gearbox shell from the ribs. Anyone that has experience with the EW transmission clamps knows these are not very robust castings and are frequently found broken. It is possible the clamp was replaced very early on in the machines life with an older style replacement. I would think that once the bike was exported to the USA (whenever that was) it would have been much more problematic to replace the clamp, and more likely it would have ended up with a piece of flatiron made by the local blacksmith. For the moment I am inclined to believe it is the original clamp, as the rest of the machine was in a very original, albeit weathered, condition; right down to the electrics.
So then we has this clamp that was fitted to the M/ series gearbox. It is a much more robust design, and honestly what they should have been making all along. So when did this style clamp come into existence? I do not have a 1936 spares list to see if the gearbox clamp shared the same number as the 600EW (part #9355). I do have a spares list for the 1938 600cc model, and it list the gearbox clamp as, #9355! That suggests Douglas never superseded the clamp design. So is this an aftermarket item? Anyone seen something similar?
Another question is the M/ series gearbox is painted black, except for the end cover which is lightly polished. In the catalog illustrations it is usually pretty clear in which instances they painted the transmission end cover black, or left it bare aluminum. Not so the rest of the transmission. So far as I know, it was Kingswood's practice not to paint the gearbox shell. While most of the paint has come off, whoever painted it made a fairly thorough job of it. I have to believe they had the gearbox out of the frame to have gotten at all the surfaces they did. Anyone else seen what might be original examples of painted cases?
-Doug
