I'm quite interested in the front fork and brakes used on the group 1 (1932 TT), group 2 (Atkins track bikes) and group 3 (c1934 mostly sidecar bike) "big tank" Douglases. Sad, isn't it?
Forks first:
The Group 1 bikes, at the TT, used a fork that was referred in the Motor Cycle of the day as "Druid". The "Thorpe Douglas" article in the Classic Motor Cycle refers to Thorpe fitting a set of "racing Druid" front forks, presumably from the ex-Atkins cache of "ex-TT bits". Indeed the fork on the grass-track Thorpe Douglas looks very similar to the 1932 TT fork. Although the 1932 TT Douglas fork looks very "Webb-ish", it is different from the Webbs used on other TT entries (e.g. Norton), so let's assume it is a rather unusual Druid racing fork. I've looked pretty hard but can't see an identical fork on any other machine of the period. A distinguishing feature is the friction damper on the lower fork spindle, controlled (in the TT versions) by a hand wheel on the right side. An additional friction disc is anchored to the front fork leg, a couple of inches below the spindle.
Atkin's track racers (group 2) used the Druid ES (Enclosed Spring) fork: very vintage and often used on the outer circuit at Booklands, notably by track expert Bill Lacey on his Nortons. A very distinctive fork, and quite different from the "racing Druid" fork on the 1932 TT bikes.
As for the group 3 bikes, mmm... shortage of period photos. The Reheis bike uses the "racing Druid" pattern, albeit modified in the links and with added struts. Nothing visible in the photos so far of the Babl bikes. The Bury brothers bike used - at least in 1937 and when it was restored many years later - the racing Druid, BUT in its early life (Donnington 1935) it is pictured with its front brake on the left, rather than the 8" Enfield brake on the right as it had from 1937-on. Was the brake the only thing changed, or was the front fork changed too? The ex-Clifford bike ("no 34", reputed to be ex Jack Douglas) uses the 1934-on Douglas heavyweight fork, with the Douglas brake on the left. I don't know what this means, since in Doug's early-ish photo the bike has an OW gearbox, it's hard to say if the front fork and brake came from the same OW or was fitted when the bike was built.
And the front brakes:
The group 1 bikes used the 8" Enfield, on the right. Of the three in the TT, one, Johnston's bike [Edit: not Longman's as I wrote originally], was different from the other two in that his brakes were linked: the front brake was applied when the rear brake was applied, or independently from the handlebar lever.
The group 2 bikes were brakeless at the front.
The group 3 bikes that we have photos of (Bury, Reheis, Babl x 2) started life with brakes on the left. The Reheis bike used a drum outside of a spool front hub, so was probably - more or less - a 1934 heavyweight Douglas brake. Period photos of the Bury and Babl bikes, show no detail of the brake, other than it being on the left. From 1937, the Bury brothers bike used an 8" Enfield brake on the right.
Doesn't sound like much of a story? Here's an observation that makes it a bit more interesting.
The first photo below shows the Bury brothers at Donnington in 1935, the debut year for their "big tank" racer. It's detail from a very small photo in the Motor Cycle, so it's rubbish quality, but it does show the front brake on the left.
The second photo is from The Best Twin, and shows the Bury brothers at Donnington two years later, in August 1937. The front fork in 1937 is racing Druid, and the brake is now 8" Enfield on the right, as per the spec of the 1932 TT bikes. But there is something else to note: the front brake has two operating cables - one linked to the rear brake pedal, and the operated by the hand lever. Just like Johnston's [Edit: not Longman's] 1932 TT entry...
Late photos of the Bury bike, post serious racing and after restoration, show the double drilled brake arm and the double cable anchor on the Enfield brake plate.
Let me unleash some wild speculation. The Bury and Babl bikes (listed in the appendix of Clew) were delivered with "OW" fork and brake. As an upgrade, some time after 1935 but before 1937, did the Bury bothers get the front end of the 1932 Johnston [Edit: not Longman] bike - racing Druid fork, 8" Enfield coupled brake - from the factory as an upgrade??
Cheers
Leon
[Edit: It was Johnston's bike that had the coupled brakes: Motor Cycle, 2 June 1932: "Unlike the other Douglas models [in the Senior TT], Paddy's [C.W. Johnston's] machine has interconnected brakes." No idea why I wrote Longman.]