Chaps,
Will Hogan at Stainless steel classics has kindly and beautiful supplies a new brake rod. It's for an A7/10 so is too long but I will adapt for my 1955 BSA M33 Plunger. The old brake rod is pretty bad and while it works to a fashion is not good. Can anyone measure their plunger brake rod and tell me their kink angles and dimensions. A couple of photos to explain how it gets around the plunger units would be superb. I have said to Will I will send these onto him to aid his supply specifications.
Many thanks
Hamish
My 1953 M33 brake rod doesn't seem to have any kinks in it, which I didn't realise before; that means it rubs on the plunger. However, measuring from the drive chain the offset is 3/4" between my brake pedal and the brake arm trunnion.
Measuring from the drawing in the parts book, one bend is halfway along the length of the rod, and the other one is half way between the first bend and the clevis pivot. Unless I hear differently on this thread, I'll bend my rod to those proportions and to a 3/4" offset. Shouldn't take long.
Anyhow, here's a photo of the end of my brake arm. Once I do the bending I expect a bit less thread will stick out the end. Also, I thought I'd cleaned this bike; I see I missed some bits...
That's excellent! Indeed there are probably a fair number in the same position rubbing and damaging the plunger unit. It would be good to have an archive of such details for other restorers or part makers.
In case you are leaping keenly out to the shed tomorrow, 3/4" isn't enough offset. 7/8" seems more like it, but I am yet to fully assemble the thing. More dimensions later, when it's all back together.
7/8" lines up very well with the trunnion, but it's very close to the plunger shroud. I made the first bend 4" from the centre of the hole in the brake rod clevis not 5", or the rod would be far too close to the brake light switch. I made the second bend 5" further along. The brake rod doesn't seem to rub on the plunger any more, and the pedal action is much improved; it's like a different brake.
I'm yet to determine if the rod misses the plunger because of the worn bit where it was rubbing on the plunger. According to what I find, I might make the offset 1" instead of 7/8", then make another very small offset of 1/8" in the opposite direction, to get good alignment with the trunnion.
If I did this again I'd make the first bend 3" from the clevis and the second 5" along from that, because the rod is still rather close to the switch.
At last I've been able to have another look; sorry for the delay. Yes, 7/8th" offset is spot on to line the rod up with the brake lever trunnion. An unworn rod would miss my plunger shroud by 1/64th". That isn't really enough, but the worn spot on my brake rod does give me a bit more of a gap. With a new rod, I think a first offset of 1 1/8th" one way with another of 1/4" the other would give reliable clearance. A bigger first offset might get the rod too close to the brake plate, so 1 1/8th" is about the maximum.
Anyhow, here's some photos. Despite appearances, the rod is nowhere near the drive chain in the first photo. I'll try and get some measurements up soon.
That is amazing, thank you so much.
Via Tim Jeffrey I have managed to secure a new old stock 65-6279 rear brake arm for the hub. I will send it across to the SJ engineering company in Northern Ireland to see how we get some made up. The other options of twins 42-6075 and the 67-6053 have the wrong offsets and dont work well. There seems to be a shortage of the 65-6279 and given they do wear out and are somewhat consumable it would be good to get some made up.
Hamish
Hi,
Thanks to Tim Jeffrey I know have a 65-6279 rear brake arm (maroon) and thought I would share how much of a difference from the larger 42-6075 (black) there is. Basically the larger 42-6075 impacts the rear sprocket and doesnt fit. Draganfly say its an alternative but it doesnt work. Same with 67-6053 which doesnt work.
There doesnt appear to be any 65-6279's about and I was lucky to score this one, so will send off to SJ engineering to get some more made up.
Thanks
Hamish
Here are some measurements and a sketch. The offset for the brake arm is only very approximate, because I measured it while it was still on the bike. There's no part number on my brake arm so it might be a pattern part. I'd be interested to know the offset on your M33 brake arm.
To be clear, my measurement of the brake rod (above) was the length when straight, before I put the two bends in it.