Topic: Faulty brake bleeder screw = soft lever feel?

[Scott S]

 '71 CB 500

 The front brakes have been completely gone through, including:
-cleaned and rebuilt stock master cylinder
-new braided hoses
-new copper washers
-cleaned and inspected caliper with near new pads
-bench bled m/c
-new fluid (obviously)

 I've bled nearly a bottle of fluid through the system and get NO air bubbles.
 The m/c will squirt a stream of fluid an inch or two above the reservoir with the cap off.
 Caliper has been adjusted at least three times.
 I can lean the bike back on the rear wheel, spin the front and stop it with the lever. However, on the only shake down run I've taken, the  front brakes are weak and the lever feels soft/spongy. No leaks on the system that I can find anywhere.

 Yesterday, my Pop came by with a vacuum bleeder. This bleeder has a vacuum gauge on it. When we pressurize the system, the gauge will slowly leak down. When we open the bleeder screw we get lots of tiny bubbles (again, I get ZERO bubbles when bleeding conventionally). We tried several different fittings and hoses and always get bubbles off the bleeder, even for a short while after closing it.
 However, if we pressurize the vacuum bleeder and plug the hose with a finger or other plug, it will hold vacuum. Does that mean the bleeder screw is bad and causing the soft brakes?
 Lastly, what size is the Honda bleeder screw? Nothing in my Yamaha parts pile fits (too big) and I can't find anything locally at Pep Boys, etc.

 Any other thoughts/ideas?

[chickenman_26]

When you use a vacuum bleeder, you're going to see bubbles in the hose attached to the bleed screw due to air being sucked around the threads of the bleed screw, and possibly due to the rubber attachment being a loose fit on the bleed screw. This is not something that bothers the bleeding process, as long as you close the bleed screw before the vacuum bleeds off below 5".  You can eliminate most of the vacuum leak by covering the bleed screw threads with a few wraps of Teflon pipe tape. Still , it's a PITA, so I replaced the hand pump bleeder with a vacuum bleeder operated by compressed air.

Your spongy feeling may be due to air trapped in the master cylinder near the banjo fitting. Cover the area around that fitting to prevent brake fluid from getting on painted parts, then crack open the fitting slightly while holding pressure in the system. You shouldn't hear anything as fluid seeps from the banjo bolt area. If you hear little pops and crackles, that's air coming out. This is a frequent problem after the system has been completely emptied. Don't release the brake lever till you've tightened the banjo fitting.

Stu

[Scott S]

 Thanks, Stu. Thee instructions with the vacuum bleeder warned us that you may get bubbles, but I thought they'd eventually stop.
 One other "trick" that I tried is wrapping a rubber band around the lever and holding it in for a while. I was told this might allow any air to bleed back up into the reservoir. Didn't help.
 I'll try the banjo bolt trick today.

[GammaFlat]

Another thing to consider is that if your parts were really clean or new, they'll get "cling-ons" or air bubbles that want to stick to the insides of parts.  When you buy a new master cylinder for a car, there's always instructions to tap the MC with the handle of a screwdriver during the cycles of bleeding.  I've seen this happen first hand where you bleed the crap out of the system and get nothing... then you beat the crap out of the new parts (the handle of my Craftsman screwdriver has "evidence marks").  Suddenly you get lots of bubbles.  Just like shampoo, rinse and repeat

[Jerry Rxman Griffin aka MuthaF'er]

Search and you will find. In FAQ, brakes. The sizes such as 7100 refer to 7mm 100 thread

http://forums.sohc4.net/index.php?topic=259.0

[Scott S]

 Haven't tried bleeding the brakes anymore, but I did try letting the bike sit with the handlebars cocked left or right. No change.

 I did notice a "squeek" from around the handle or plunger area of the m/c. There's no sign of a leak up there. There's a small (very small) amount of dry, white, powdery stuff, but no fluid or wetness anywhere.
 I installed the rebuild kit myself and the plunger fit was tight. Very snug. Do you think it could be sucking air (or pushing air) from around the plunger and causing the "squeek"? It may just be normal...I don't know.

 I do plan on trying to bleed the m/c at the banjo bolt. I just need another set of hands to help out.

[Scott S]

 Tried bleeding the m/c at the banjo bolt. No change...no air, just fluid.

 Tried hooking up a syringe and pumping fluid UP into the system. Did this with the lever in the normal position AND depressed. It just builds pressure at the syringe. I cannot pump fluid past the bleeder screw.

 Tried bleeding the brakes the conventional way again. Just fluid, NO air. The lever still feels spongy. It's semi-hard at first, but gets softer as I pump it. I can't ride the bike right now (waiting on fuel lines), but last time I rode it and the lever felt like this the front brakes were weak.

 I'm at a loss. I tried contacting the guy on ebay who sells the 14mm masters and, of course, he's out of the style that everyone here has been using. A few months before they are restocked. He has one in chrome for $99.99 plus shipping. He has a similar style with the banjo fitting at the FRONT of the m/c, not on the side like an o.g. Honda m/c.

 I'm open to suggestions here....

[Spanner 1]

Scott your problem is that the new m/cyl. piston you installed is SHORTER than the original...... the cup seal with the correct piston sits just behind the fluid return hole ( the teeny one ) and when the lever is pulled the seal immediately passes over the return hole = no squirt into the m/c .... hope you still have the old piston, take the new-one out and compare..... good luck.

[Scott S]

 Well, I remember holding both pistons in my hand and comparing them. They sure looked the same to the naked eye.
 But you're right. I can see something (part of the piston) through the larger hole. When I squeeze the lever it disappears from view and fluid squirts up from the smaller hole (fluid return?).
 I do have the old piston. I guess I could take it all apart and measure everything.

 It sure seems like air, though. I can squeeze the lever and eventually make it go all the way to the grip if I keep squeezing or pumping. That seems like air to me, but I sure as hell can't find it in the system.
 I'm beginning to think I'm sucking air back in through the plunger seal at the lever end of the m/c. That's where I sometimes hear the "squeaking" noise, but you'd think there would be fluid all over the place if the seal was compromised. That's what was happening after the initial cleaning and why I installed the rebuild kit: fluid leaking from the plunger area where the lever hits.

[chickenman_26]

 It sure seems like air, though. I can squeeze the lever and eventually make it go all the way to the grip if I keep squeezing or pumping.

That particular symptom is indicative of ancient rubber hoses that need replacement. The harder you squeeze the lever, the additional fluid movement results in swelling of the hoses rather than extra pressure at the brake pads. You don't need any fancy braided lines, though. OEM style replacements from Siriusconinc.com work fine. About that old myth regarding a rubber band around the brake lever overnight, that trick doesn't bleed out any air. It just holds the brake pistons firmly in contact with the rotor long enough for the piston seals to relax. So when the lever is released, there's almost no pull back of the pads. As normal pad wear occurs, the rotor/pad clearance will return to normal, and the "spongy" feel will return.

Stu

[MCRider]

CM: From original post, he put braided lines on.

[chickenman_26]

CM: From original post, he put braided lines on.

Thanks for the heads-up. Guess I should read more carefully before wasting bandwidth. 
But honestly, most brake levers can be brought close to the grip, if you squeeze hard enough.
Hard to say without feeling it. Maybe it's completely normal.

Stu

[Spanner 1]

The early m/cyls. had a longer piston..... the re-build kit the OP used is a later one with a shorter piston which he has installed, not thinking that the new piston is any different... the dead-giveaway is in his first post where he says ' the m/c will squirt a stream of fluid an inch or two above the reservoir with the cap off '. ( when the lever is pulled ). The short piston holds the cup-seal well behind the return hole so that when the piston moves forward the pressure is just released thru' the hole and no brake action until the lever is maybe, 1/2 way pulled and the seal has passed over the return hole..... but I see the OP is already looking for an 'aftermarket' m/ cyl. to replace his original.... pity.

[Scott S]

 Well, I have a few options now....

 Brand new master cylinder from David Silver Spares is on the way. Only ~$43 and is done in the original style.
 Picked up a good, working m/c from a forum member for only $12 shipped (also on the way).
 Also still have the original piston for this one. One of these days I may be tempted to take it apart again and try re-installing the original piston with the new rubber bits from the rebuild kit.

 At any rate, I have three viable options now, right?

[Psychonaut]

Bringing up and old thread.

Scott, did you ever get your brakes firmed up? I have been through just as much fluid and still can't get the pre seal replacement feel.

[Scott S]

 Yep, the David Silvers m/c is the BOMB! Excellent brakes, rock hard pedal. I even installed one on my XS650!

[Psychonaut]

Ah, the are temporarily out of stock. I'll email them on when it will be back.
Thanks