Interesting feature of 36-40 clutch hub

[Steve Little]

Hi.
I’m piecing together a 38 Knuckle and at the moment I am refurbishing a 1936-40 clutch to go in it.
I noticed that a previous owner had done some hammer work on 3 of the long studs. The only stud they hadn’t worked on was loose, rotating and wobbling slightly.
I fitted the soft jaws to the vice and clamped the stud nice and tight to peen the back to tighten it to the hub. Instead of using a 40oz hammer and smashing it like previous owner, I got all fancy smancy and got out my rivet peening tools. I picked the correct size and gave it a three measured taps to see what effect the peening tool would have. Instead of the desired result, (a nice tight mushroom head) the head popped off the stud.
After a millisecond of regret, I could see there is a rusted crack section on one side of the head, meaning it has been cracked for a while.

Interesting feature I didn't know, the studs have a 5/16 thread and are screwed into the hub before Harley peened the back.

Unlike the later hubs, these studs aren’t listed as a separate part from the hub.
Mine are all bruised along the shaft from the spring retainer rubbing on them so unless someone knows of a supply for them, I will turn up 4 new studs and replace all of them.
Are they available?
Regards Steve

[Steve Little]

[Bruce T]

G’day Steve, after reading your post I went out to the shed and rummaged through my box of early clutch parts. I found a drive disc (2489-36) without the stud and it is threaded. Something I had not noticed before.
On the topic of the early clutch, someone may be able to comment on the following. I have noticed two styles of the drive disc (2489-36). Refer to photos below. One has an “open” riveted tin cover where the outer rim is flanged outwards and the other is flanged downwards and is "closed". In addition the style of the threaded plate studs and spring retaining studs, where they are peened at the back, also varies slightly with the two drive discs. All the peened studs are rounded on the “closed” drive disc and only the threaded studs are rounded on the “open” drive disc.
P1100305 (2).jpgP1100304-Optimized (2).JPGP1100306 (2).jpgP1100307 (2).jpg

[Steve Little]

Uhh-ohh, Am I mis-terming the part? Not a hub but a "drive disc?
Watch how quick I recover....My drive disc is the open flange type.
While we are on the what's, what. What purpose does the copper wire reinforced, gauze (perhaps asbestos?) play in the operation of the clutch? Mine has it but yours are both clean of any matting.
Bruce. Any ideas what it's for?
Regards Steve

[Bruce T]

Steve, possibly the only complaint from owners of machines fitted with the 36-40 clutch was their susceptibility for overheating, or at least according to Palmer, the clutch springs overheating. I think that the drive disc that I have that is “closed” is an early one (36-37). In response to the overheating issue HD did two things. They opened up the tin cover to try and assist air flow and hence cooling and they also fitted an asbestos – copper gauze to insulate heat transfer to the springs. That’s my guess anyway. You are right Steve the “closed” drive disc does not have this gauze. The open one does. Its just hard to see in the photo. I have a couple of others (open drive discs) and they have the gauze also.
If you want that 37 drive disc for you’re EL Steve you’ll have to beg……or you could swap me a taillight perhaps??

[Steve Little]

Nice info on the insulator Bruce. Thanks for the kind offer of the early style drive disc for my 37 but due to the brutish horsepower that the old girl generates, I will stick with the 38-40 ventilated style. Regards Steve.