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Master Cylinder: Constantly squishy or NO pressure.

  • Thread starter Thread starter DannyMotor
  • Start date Start date
D

DannyMotor

Guest
78' GS750, Earls braided lines, new seals in both front calipers, rebuilt the M/C, clubman bars, new crush washers.

Bled the brakes just fine, did the 'upside-down' air tube trick to watch all those little bubbles come out... and tightened everything up. No issues with weeping, or leaks what-so-ever.

The MC is full, and I tried the zip-tie trick on the lever over night. It's fine for about 5-6 pumps, but then it goes back to floppy and will only build pressure about 1 1/2 inches from the grip, it operates OK, but it's quite nerve wracking riding around, knowing you've got to pump the brake twice before even thinking about stopping.

Pumping, as stated, will bring the pressure back to normal operating travel, but will go away after a few minutes.

Is this because I'm running a MC of a bike that used to have 1 disc/caliper setup, and now I'm trying to run it with 2? Or is due to the low angle of the bars sloshing the fluid away from the inport hole?

Or is it a mix of everything and I should just go find an MC off any-old dual-disc Suzuki?
 
Never had a problem with single brake MCs running dual brakes. If anything they give you more pressure from a given lever force. An inch and a half is pretty far, the lever has to move far enough to close the return port before it can make any pressure, but the pumping thing doesn't sound good at all.
 
"Normally" having to pump any hydraulic brake is a classic indication of air in the system. Time to rebleed and test again.
 
koolaid_kid said:
"Normally" having to pump any hydraulic brake is a classic indication of air in the system. Time to rebleed and test again.
Click to expand...

Or leaky seals in the master cylinder. Try this, put just a very very slight finger pressure on the lever, as light as you possibly can. Will the lever slowly move all the way in?
 
tkent02 said:
Or leaky seals in the master cylinder. Try this, put just a very very slight finger pressure on the lever, as light as you possibly can. Will the lever slowly move all the way in?
Click to expand...

It will NEVER get to the bar. Ever. I can do just that... slight pressure, allowing it to come back, but it stops about 1-1.5 inches from the bar... if I just ham-fist it, I can't even pull the ball back to touch the grip... so there's pressure there... it's just like the lever is 100% dead to about 1/2 way and then ALL the brake is in the last 1-1.5 inches of travel.

If I don't pump the brakes... I can be going 40, grab a fist-full of brake, and just about lock the front tire, but it just puts the fear of God in you when the lever gives up THAT much and then puts on the brakes within an inch of the bar... all be it you get just about all the stopping power the bike has... I just don't know if my underwear budget can take it.
 
That's about how motorcycle brakes work. I have ten bikes in the garage now, all are like that, from the oldest cable brake Yamaha to the brand new BMW. The first half inch or more of lever travel does nothing, keep pulling harder and harder, the lever goes to about an inch from the bar.
 
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Yep, ham-fisted as hard as I possibly can, I can get it to touch the grip, but can't hold it there.

NONE of my other bikes do that... haha. I can feel pressure from about 3mm of pull to the grip with all of my other bikes...

- 87' Suzuki Intruder
- 05' Kawi KLR650
- 01' Triumph Tiger 955i
- 74' Honda MT250
- and my fiance's 92' Yamaha Seca II...

I helped a buddy rebuild a 79' CB750K with single front disc that you could feel drag as soon as you started pulling.

Hence my worry. *shrug*
 
Aww... really?!?! No stick-figure picture of a meme with a disapproving look? For shame admins. For shame.

Anyway... if you could see my face... I was disapproving of your comment.

Out of the bikes sitting in my garage, and ones I've owned in the past... 00' GS500E, 84' CM200T, hell, even Puch and Tomos mopeds I've owned... all start to 'feel' the brakes engaged within 3mm of pulling the lever... they don't get HARD, but you can hear them and feel the bike slow down...

Much like in a car.

really+a+pony+version+of+a+meme+some+bronies+really+_2fb4eedd3de7d2f02ac5b5b683891f6d.jpg
 
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I dunno... I'm still feeling like a new/used more modern master cylinder may be needed. Just for piece of mind.
 
Would you know if they all banjo bolts are universal?

I'm probably going to stop by the 'motorcycle graveyard' tomorrow and see what they have kicking around. Last time I was there there were a few GS850's and some 80's GS750 TCCD's there with the bolt-on cover M/C's... We'll see.
 
Dang it. Well, I don't want to go with some 'universal' bs... so I'll have to take one of my bolts with me and double-check everything I find.
 
People have had good results with the new MCs from Ebay, just get the right thread pitch.
 
Those $80 units? I like the look of those. I may just pop for one.

Also, new development. Just realized there IS a leak...

Took the handle off and the boot around the piston is leaking. The whole end of the lever that sits in the master cylinder was wet.
 
Good thing you found a fault, there is nothing good about the feeling when your gut says there is a fault but nothing can be found. Not trying to teach old dogs new tricks, but I've found that not everyone knows that sometimes you also need to bleed the brakes at the master and not just at the calipers. Good advice can not be repeated enough, so if you did know let it slide, for the people who didn't know, well, now you know :)
 
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