Brake Lever Travel

mrmach5

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So recently decided to upgrade my front brake system on my 75 XS650. I installed a new 13MM Master Cylinder from Hugh's Hand Built, and a one piece stainless brake hose, eliminating the two rubber houses and the brake light switch manifold etc.. Bled out the system a few times, and tied the lever back overnight a few times, with some improvement but,,,,,,,,, my issue is you need to pull the lever half way to the bar before any real firmness in the lever. Once that point is reached, good brake application , just uncomfortable using up that amount of lever deflection before getting brake. Not sure if there could still be air trapped somewhere in the system???
 
Possibly some air trapped but do yourself a favor and get an 11 or 12mm master from a Yamaha dirt bike. Made in Japan not China.
tim
 
An 11 or 12mm would be worse, it would travel more before anything happens. This just seems to be the way these smaller master cylinders operate - better "feel" and modulation but more travel before anything happens. I put an 11mm on my '78 and while it works fine, all that extra lever travel took some getting used to. On my '83, I decided to go a little bigger (1/2"), but still smaller than stock (14mm). I think I like this better. I get the benefits of the smaller MC (better "feel" and modulation) but not as much lever travel as the 11. You might benefit from a slightly larger one as well. The stock 14mm used on the '77 and later models might be just the ticket for you. I think your original was a 5/8" or 16mm.
 
yes 13mm might be a little small for an early dual piston caliper but...
remove the caliper and fully retract both pistons. Gotta watch that you don't overflow the reservoir. Then pump them out again maybe repeat one more time.
For 5twins; I recently changed the MC on Period piece from the stock special MC to an 11mm from a TT225 Yamaha, SS line of course. Did the typical bleed, then did the remove the caliper and retract the piston "trick". I did have the lever adjustment screw all the way out, but after the retraction/pump out had to run the screw back quite a ways to get the lever close enough to the bars to be a comfortable squeeze. No squishy lever here and great braking action.
 
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^Do you mean bleed as usual, then remove the caliper and push the piston all the way back with a clamp, the re-attach the caliper and bleed as usual again?
 
^Do you mean bleed as usual, then remove the caliper and push the piston all the way back with a clamp, the re-attach the caliper and bleed as usual again?
No leave everything hooked up. On the late model single piston it takes just the one 8mm bolt and the Phillips screw in the back to take the caliper off the carrier leaving the pads in the carrier, then use a c-clamp to push the piston in. You can turn the caliper so the line entry is the high point. If you have the reservoir cover off go slow on the c-clamp or you can make quite a brake fluid "fountain".
 
yes 13mm might be a little small for an early dual piston caliper but...
remove the caliper and fully retract both pistons. Gotta watch that you don't overflow the reservoir. Then pump them out again maybe repeat one more time.
For 5twins; I recently changed the MC on Period piece from the stock special MC to an 11mm from a TT225 Yamaha, SS line of course. Did the typical bleed, then did the remove the caliper and retract the piston "trick". I did have the lever adjustment screw all the way out, but after the retraction/pump out had to run the screw back quite a ways to get the lever close enough to the bars to be a comfortable squeeze. No squishy lever here and great braking action.
I have a 13 mm Brembo MC on my RD350A, same caliper as early XS, TZ, etc. Works very good. Another buddy had a 1/2" Grimeca master on his RD350, also with excellent results. 12 mm is as low as I would go, though.
 
No leave everything hooked up. On the late model single piston it takes just the one 8mm bolt and the Phillips screw in the back to take the caliper off the carrier leaving the pads in the carrier, then use a c-clamp to push the piston in. You can turn the caliper so the line entry is the high point. If you have the reservoir cover off go slow on the c-clamp or you can make quite a brake fluid "fountain".
I've wondered about bleeding with the caliper up high. You'd take the wheel off and lay it on the bench, then stick the caliper on the disk to keep the pads apart, and bleed as usual with the master close to the floor. Hard to see how it bleeds at all with the usual configuration since the air would be floating to the top, not toward the bleed screw.
 
XJ try this as I suggest, it works! Actually for the initial bleed do it the same way, don't put the caliper on the carrier with pads til AFTER it's all bled and cleaned up!
 
I usually don't force the piston back in unless I'm having problems with getting the system bled, but maybe I'll give it a try. But, both of my brake set-ups seem to be working fine. After their initial progressive engagement, they develop a nice, hard lever pull. It certainly doesn't feel like there's any air in there. I set my adjustment screw so there's just a small amount of freeplay between it and the MC plunger. I figure that gives the maximum amount of plunger travel. On these smaller MC set-ups, I think you need that seeing as how not much happens for the 1st half of the stroke.
 
I usually don't force the piston back in unless I'm having problems with getting the system bled, but maybe I'll give it a try. But, both of my brake set-ups seem to be working fine. After their initial progressive engagement, they develop a nice, hard lever pull. It certainly doesn't feel like there's any air in there. I set my adjustment screw so there's just a small amount of freeplay between it and the MC plunger. I figure that gives the maximum amount of plunger travel. On these smaller MC set-ups, I think you need that seeing as how not much happens for the 1st half of the stroke.
I'd really like YOU to try this and post up what happens. I'm pretty confident it's going to improve things. Like I mentioned after doing this I had to back out the screw cause the lever was hard TOO FAR from the bar for a comfortable squeeze!
 
Well unfortunately after going thru the procedure , no improvement . Lever halfway to bar before any braking resistance. Not sure where to go next? perhaps a different master cylinder?
 
Question, do the calipers on the 74-75 models have two pistons or just one? Schematic in the Clymer manual does not show it clearly. If two pistons , then one of mine is seized in the bore and may be perhaps the culprit in my issue.
 
Two pistons and yes, both must move. The brake will suck big time with only one moving, lol. I'm not sure getting both to move will have any effect on lever travel but it certainly will on function. I encountered this on an RD350 I was working on. The front brake worked but was very weak. Basically, it was only half working.
 
You'd take the wheel off and lay it on the bench, then stick the caliper on the disk to keep the pads apart,
A piece of metal the same thickness as the disc would save the extra step of wheel removal... just sayin'.... :sneaky:
 
Yes, I have a little "special tool" made up for this, a small piece of 1/4" thick angle. I stick it into the caliper between the pads whenever I remove it. This guards against me inadvertently squeezing the pads tight together should I screw up and grab the front brake lever while the caliper is off. Been there, done that, and it isn't pretty, lol.
 
Early calipers can taken apart and assembled "butterfly" c clamp tge good one so the stuck piston can be forced out.
 
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