Manky's XS650 Yamaha

[Manky Monkey]

I was chatting to my brother, Mr Brock, at his workshop in Wiltshire this afternoon, & we spoke of that very thing.
He pulled  a 6mm fitting out of a drawer, (possibly a brake pipe union), & said One of these, (a short length of hex bar bored & tapped to M6), with a length of 6mm stud in each end with locknuts, would do it. Stupidly, I didn't pocket it before he put it back in the drawer. I've got to go back next week though. The pushrod's only maybe 3" long, so not a lot of room for adjusters & once I know the necessary length it won't ever need adjusting again, so probably easier to trim the original down until it works -assuming it does. Just time consuming as it means constantly removing & refitting the linkage, then trying to bleed it each time. I'll get there eventually. 

[Sid_Vicious]

If you get an coupling nut for alltread bar they are about 40mm long X 10mm and treaded for M6. And a with piece of alltread you can determine the length you need then make up one in one piece .     

[Olds]

He pulled  a 6mm fitting out of a drawer, (possibly a brake pipe union), & said One of these, (a short length of hex bar bored & tapped to M6),

Sounds like a threaded bar (studding or all-thread) connecting nut. Looks like a normal plain nut, but much longer. Screwfix have them in stainless steel @ £2.49 for a pack of 10.

[kapri]

Normal practice for brake pushrods is slightly free ie about 1mm ,just  enough to feel as slop. This allows for heating = expanding of brake fluid without locking itself on as it expands

[Manky Monkey]

Hadn't thought of the expanding fluid -I just assumed a little clearance would make sure the piston fully returns.
Yup, sounds like that's what Steve showed me. As I said, it's just a fiddly, time consuming job & I need some daylight to do it in, but hopefully it'll cure the problem.

[Manky Monkey]

Back to Steve's workshop this afternoon to collect my bike parts -there were some scuffs in the rear mudguard & a few other small parts needed painting, he just happened to be painting parts for his race car in black, so he did mine too. Thanks bruv. 
Mudguard & kickstart re-fitted this evening, then I had another go at the back brake. With the rebuilt master cylinder, I now have what appears to be a working brake, but the pedal's travelling right to the floor before it works. So just to see what happens, I'll pick up a pack of bicycle ball bearings from Halfords tomorrow & sit one on top of the pushrod in the master cylinder to temporarily extend the rod. Maybe the brake will bind, maybe it'll work perfectly. we'll see.

[kapri]

Is it  possible you need a shorter pushrod ? ie you are not using the full swept volume of the m/c and not allowing the fluid to replenish the cylinder hence you are always moving too small a volume to operate the brakes correctly and fully.

[Manky Monkey]

Yeah, that was my first assumption Kev. Not really sure, but bunging a ball bearing in, (anything would do but I've just bought a pack from Halfords for 2 quid), will eliminate that possibility first.

[Manky Monkey]

Not a particularly good afternoon.
I added a 6mm ball bearing on top of the pushrod that operates the master cylinder. Result the brake was binding.
So I left the bearing in place & trimmed 3mm off the pushrod. Result -the brake works but only right at the end of the pedal travel. Too far to be comfortable to use & I'm sure the MOT man would call it excessive travel.
I messed about, trimming a little more off the rod, adding a 2nd ball bearing -no improvement.
Really fed up with this now. Apart from the wiring, it's the last bit to sort out & it's fighting me all the way. I enjoy fabricating stuff but the faffing about trying to make it work ain't my thing. To top it all off, while leaning over the bike & straining to line up the cylinder with it's mounting holes, I suddenly got a nose bleed. At that very moment Big Darren strolled in from his garage next door
-How's it going?
I looked up, dripping blood ....not well, not well.
So I've been to Screwfix Dave, bought a pack of those threaded joiners & found a 6mm bolt in my spares box. Tomorrow I'll weld the joiner to the clevis, in place of the pushrod & make an adjustable rod.
If that fails I'm seriously thinking of cutting the whole damn brake assembly off the frame & fitting one of those direct push Harley cylinders, as I should've done in the first place, though it'll mean major surgery to the frame & repainting.

[kapri]

Refresh my memory on parts used on the brake and what's modified ?

[Manky Monkey]

I'll take some photos today Kev.
Standard Yamaha pedal, standard Yamaha master cylinder.
The pedal's attached to a cross shaft, running across the frame in a tube with bronze bushes at each end.
At the other end of the shaft is a short arm with a return spring attached to it. The pushrod's welded to a clevis that pivots on the end of the arm, (actually a modified Pop brake rod).
Push the pedal, the shaft turns, the arm at the other end turns & the pushrod pushes up into the piston in the master cylinder.

[lunatic]

I think, maybe, the lever at the cylinder end is too short. Or maybe not!

[Manky Monkey]

Pedal ratio! Yeah, I'm guessing it'll be that, simply because it'll be the most awkward bit to fix. If I make that arm longer, I'll have to move the master cylinder, which'll mean cutting the bracket off the frame, which'll mean taking the chain off to reach it. Then I'd need a new brake hose & probably have to modify the electrics box again. Really hope it isn't that.

[Manky Monkey]

Off to the lock-up to take some photos & kick the bike.

[Manky Monkey]

O.K, I resisted the urge to hit it with a hammer & took some photos.
So. More or less standard Yam' brake pedal.