bled brakes, still spongy

hey, forgive me for not searching and reading thread after thread until i find the answer i'm looking for - but i used up all my patience on my bike (81 seca 750).

my breaks were dragging, so i rebuilt the calipers and installed new seals. i bled everything and they are still spongy. i'm getting fluid with no bubbles coming out of all 4 bleeders (calipers and anti-dive).

any input is appreciated.

 

See what happens in the Reservoir when you Pull the Brake Lever.

If a BIG Steam of Fluid makes it look like Old Faithful ...

You have to rebuild the Master Cylinder,
The Seals in the Master Cylinder are supposed to Pump Fluid doen the Lines.
If the Main Seal is NOT Pushing the Fluid Out ... the Secondary Seal is Pushing Fluid against the back if the Main Seal.
It needs a place to go.
So, ... It "Fountains" in the Reservoir.

 

this is unfamiliar territory for me here - looking into the filler hole, while i pump the brake lever it appears to draw fluid down inside. and, like i said, it does put enough pressure to the calipers to keep me from rotating the wheel by hand (front of bike is raised off the ground).

do you mean to say that i should remove the MC and take the cover off the reservoir and then pump it by hand on the bench and see what happens?

i just pulled it off the bike and when i was loosening a mounting bolt (shouldn't have anything to do with it but . . .) i heard a slow hiss like something let go.

 

No.
It would have been an ovservation to have made during Bleeding.

If the Master Cylinder nneeds servicing, ... the MC fails to move the volume of Fluid OUT of the MC.
The Primary Seal does not Push Out Fluid.
It lets the Fluid leak by the Seal.
The Secondary Seal pushes Fluid against the Volume that DID NOT Move ... causing Fluid to need to escape from the tiny hole that keeps the MC replenished.

 

well, bein that i already pulled the MC off - i looked inside the reservoir and saw a teeny amount of crud - but not as much as i was expecting. i also *loosely* plugged the hole that the steel brake line connects to with a bolt (i figured the actual connection is flared like a hydraulic line so i didn't want to bugger up any threads). any how i put some fluid in the reservoir and was able to build enough pressure to hiss out past the bolt.

figuring that i either a)needed to wait for a rebuild kit to arrive or b)there's nothing wrong with my MC, i put it all back together, bled the brakes and it acted the same way.

then it occurred to me to tighten the free play on my brake lever. i tightened it up while watching the other end of the cable and spinning the front wheel. i tried to get it as tight as it would go without moving the piston and without feeling any increase in drag on the front wheel.

it still feels spongy, but it takes quite a lot of effort to get the lever down to the grip now. i notice that the brakes start to grab when the lever is pulled between 1/3 and 1/2 way down to the grip.

does this seem normal? i'm wondering if i'm getting spoiled by more modern brakes on more modern bikes. or maybe this is a symptom of old brake lines?

for what it's worth, i also took the anti-dive out of the picture. i used the shorter banjo bolt from the anti dive to connect the brake line up if ya catch my drift. just trying to pinpoint what's going on, ya know?

 

It can be difficult getting all the air out of the lines using the normal technique.
I use a syringe (20cc) and a small piece of clear hose to pump fluid through the bleed nipples and back up to the MC. This way you're not fighting gravity.....and you can re-fill the syringe over and over by using the fluid out of the reservoir :lol:

 

Th stock seca brake set up can feel a bit spongy, even when everything is right, combination of th cable and original lines. So long as you know its foibles it's easy to live with and will stop you when it should. I recently put on braided lines which was a definite improvement but still have a cable.
Th remote master is only a pain about twice a decade, and I like that there's no blob on my bars. Get it all working and go for a shakedown cruise,see how it feels. after checking all of ^^^^^^ help.

 

well, bein that it's about 20 degrees outside and i have 3 miles of snow and ice before i get to any salt encrusted pavement, i'm gonna have to pass on that shakedown cruise.

however - is there a MC rebuild walk through somewhere on this sight? i know there's really nice walk throughs for valves and carbs but was wondering about MC?

if there is, could somebody point me in the right direction? when i had it off last night, i got as far as "remove the rubber boot from the piston" and wasn't sure how to get it off without ruining it so i quit taking it apart.

(also, moderators, in my humble opinion, it would be very nice if the valve adjustment walk through with lots of pics and the church of clean carbs rebuild were both stickies at the top of this sub-forum - including the MC rebuild walk through (if there is one (sorry about all the parentheticals)))

 

Never re-use the fluid once it has been through the lines, it's toast.........

 

old rubber brake lines = spongy brakes

 

well polock, you're right, but I cleaned the calipers and mc, and bled the brakes, and mine feel really firm, I was planning to switch to steel lines, but I'm going to test them, and if they're ok, i wont change them until I find an fz or more modern front end

 

final synopsis is that it feels like i'd be locking up the front brake with the brake lever pulled to about 1.25 inches from the grip. definitely mushier than my other bikes, but possibly doable. i'll have to wait until it thaws out around here to take a test drive and see if i change my mind.

 

Depends wiz - if I'm filling a fully re-built system from dry then I'll re-use the fluid. If I'm "flushing" a system I'll throw the fluid out :wink:

 

I installed stainless lines last year and the sponginess went away. I also rebuilt the caliper and did a very thorough bleed. I can't say for sure if it was the lines that did the trick.

Don't use those speed bleeders. IMO they don't work.

 

The Bleed Nipple is where Brake Fluid and Air Bubbles EXIT the System.
You should not be able to introduce Brake Fluid at the Bleeder if the Master Cylinder's MAIN Hydraulic Seal is Fluid and Air Tight.

The Master Cylinders Main Hydraulic Seal is a ONE-Way Seal.
The Seal Pushes Brake Fluid OUT of the MC and DOWN the Lines and INTO the Calipers.

The Bleeder allows the System to be Opened and to Vent.
As the Master Cylinder pushes Fluid down the Lines and Air in the System will collect in the Caliper Piston Bore.

Opening the Bleed Screw allows the Volume of Fluid pumped by the Master Cylinder to move down and out ... forcing air to be pushed out the bleeder and the Bore to become filled with fluid ONLY.

The long-standing Standard Operating Procedure for Manually Bleeding Brakes is tried and true.
Wrap the Bleed Screw with several layers of Teflon Tape to make the Threading air tight.
Puncture the Bleed Hole in the Screw after wrapping the valve.

Attach an Air Tight Hose to the Bleed Nipple and place the Open End >> Submerged << in a quantity of Clean Fluid.

If the Open end of the Hose is equipped with a "One Man - One Way Valve" submerge the One way Valve and PUMP the Brake Lever while adding Fresh Fluid to the MC as Brake Fluid is forced out.

If you are NOT using a One Way Valve.
Close the Bleed Valve.
Pump the Brake Lever to raise Hydraulic Pressure.
Open the Bleed Valve.
Allow the Fluid or Air to escape.
Keep the Brake Lelver held firm to the HandleBar.
Close the Bleeder ...
>>Repeat until Air Bubbles are no longer visible.

 

you sure about that ?

 

When you pull the brake lever it pushes fluid from the M/C, but when you release the lever the fluid flows back. Ergo, if you are not applying pressure the fluid must be able to flow back UP the lines..

 

No.
At the Back of the MAIN SEAL are a pattern of Metering Holes in the Plunger.
The Main Seal Applies Pressure and releases it.
Fluid passes through the holes in the Plunger and gets Pushed > One Way > past the MAIN Seal to replenish the Fluid needed to keep the System pressurized when the Pads wear-out or if there is some small leak.

Fluid can only pass around the Main Seal to Balance the System
If the Main Seal allowed fluid to pass BOTH Ways ... There would be NO Hydraulic Pressure achieved.

 

Of course it can pass both ways or the callipers would explode............

 

The Calipers would explode?
Don't be silly.
When the Brake Lever is applied ... The MAIN Seal Pushes on Hydraulic Fluid until the Movement of the Caliper Piston presses the Pads against the Rotor.

Upon releasing the Lever ... the Hydraulic Pressure is relaxed.
Fluid does NOT fill any space by getting pushed beyond the MAIN Seal.

When the MAIN Seal Fails. Hydraulic Pressure cannot be achieved.

If the Fluid is not held by the MAIN Seal its time to Rebuild the Master Cylinder.

Think about it ... IF the Main Seal was a two-way situation there'd be no pressure in the System.

The integrity of the Master Cylinder Main Seal to hold pressure and not allow fluid to flow two ways is why there is Hydraulic Pressure and, ...

Basically <--- BASICALLY ... WHY there is Hydraulic Brakes.
Fundamentally.
Principally.

 

when your bleeding the brakes and a little squirt of brake fluid and some bubbles comes up out of the master cylinder reservoir, where did that come from?
the brake line, so the main seal is sealed but the line has a passage to
the reservoir
so you can push fluid UP the line, from the wheel cylinder thru the line to the master cylinder reservoir
method 5 here
http://www.ibmwr.org/r-tech/oilheads/brakes.shtml

 

Rick - I have used a syringe to push fluid through the bleed nipples and back up into the reservoir on all the bikes I've owned since an old bike mechanic showed me the trick about 15 years ago. It works 8)

And once you get the "hang of it", you'll NEVER bleed brakes the normal way again :wink:

 

This DOES work but I'm always leery of pushing crud or contaminants that were on their way out, back into the system.

I get the best results with a Mity-Vac followed by some good old-school conventional bleeding; then after a few "heat cycles" I bleed them again (and ALWAYS get at least one good bubble.)

That being said, the best-bled Yamaha system in the world WILL be a bit spongy with the stock rubber lines, even brand new. If you want "grab a rock" brakes (I love em) go stainless.

 

Hav'nt done th reverse method yet but next time I need to..I'll be giving it a go. We have th technology.

 

Rick, obviously, exploding callipers is hyperbole, but to 'explode' your theory, just force one of the calliper pistons back, with a screwdriver, or whatever & see what hapens to the displaced fluid..........

 

Speaking of explosions... maybe he was throwing crackers (fireworks) in th fire again.

 

Forcing a Caliper Piston back against the Seal is NOT a recommended practice.
You force the Master Cylinder to do what is is designed NOT to do.
The recommended Practice for Moving the Caliper Piston back into the Bore is to relieve the Pressure by opening the Bleeder.

Forcing the Caliper Piston back against pressure is a harmful practice.

There is no need for me to be instructed on the operation of the Hydraulic Braking System.
I thoroughly understand the Brake System from top to bottom.

 

Hands up all those that ease the pistons back to fit new pads.........

 

At least a dozen times

 

Yes.
It's done.
I confess to taking that shortcut, too.

But, this does not alter the fact that in doing so, we deliberately defeat the Seal and force Brake Fluid back against a Hydraulic Seal.

 

There is NO way you can force fluid back against the seal, it by-passes it & BTW brake fluid is incompressable, unless it has air in it..........

 

I think you're tap-dancing on the Titanic with this one Rick :lol:

The relief hole in the MC reservior is between the piston and the brake line. When the brake lever is at rest the brake line is not pressurised and fluid is allowed to flow either way through the system. When the brake lever is depressed, the piston moves over the relief hole and seals the system - allowing pressure to be built and the calipers activated.

You are not defeating any seals by pushing fluid back up the lines when the system is idle.

 

Here, let's resolve it this way.

"In My Opinion, a belief of mine, alone, I maintain that the Main Seal is a "Pump" Seal. Not two-way. This, I disclose, is only my personal opinion and not widely accepted to be true by others."

 

not to stir a bees nest here - but in the interest of learning about how brakes work - is it correct to say that a bad main seal in the master cylinder will make the brakes feel spongy - but if the seal is bad, you will also see brake fluid squirting up into the reservoir?

 

If the seal in the M/C is worn when you hold pressure on the lever, it will gradually move towards the grip.....

 

Yes.
You will see Brake Fluid spouting from the Replenishment Port.

When the Main Seal fails ... The Brake Fluid is not Pumped to the Caliper.
No Pressure to halt the travel of the Brake Lever allows the Secondary Seal to move further than it would normally travel, causing pressure to develop between the two seals and the Brake Fluid to seek any point of least resistance.

The Fluid comes squirting-out of the Replenishment Hole looking like Old Faithful.

 

so, if your brakes feel spongy, but you can't pull the lever to the grip (and don't see a geyser in the reservoir) then you know your MC is not to blame and it's either air in the lines or old lines, right?

 

you have a 750 seca i will put money on that "spongy" feeling you are getting is totally because of the inferior braking system that bike has (cable - hydraulic) my whole system was completely perfect and it never felt right compared to a "normal bike brake system".


this is why i now have a bar mounted master and stainless lines

 

Schnarr, Bushy has a 750 with the remote M/C & I tried his f brake at the weekend, it was as possitive as can be, he has, however, just fitter S/S lines.................

 

that's what i'm telling myself if the snow ever melts around here, i'll take it for a spin and see if i change my mind.

you wouldn't happen to know where i can find a reasonably priced aftermarket handlebar mount front brake do ya?

one of these days i plan to put different bars on the bike (among some other things) and would like to upgrade the brakes when i do this - but i can't seem to find anything under $300 - and i don't want new brakes that bad.

 

Try ebay. FJ1200, FZR600/1000 are a good choice (they have Yamaha written on the caps :wink: )

 

i'll check it out

 

Goodness I've been mentioned in despatches from Wizard HQ skeeter..
it sounds to me like.. you may still have air in th line OR you are not used to th feel of th system as I said earlier it can feel a bit soft when everything is right yet still stop you as needed.
I found that moving th bars to one side then th other and let it sit for a while each way allowed small air bubbles to settle and be pumped/bled out.Then ride it for a coupla days, being mindful that your brakes may not be right yet, and do it again and you'll probably get a little more air out (as Fitz said as well),
I reckon that if you've got other things to do..do 'em and wait till you ride it for th final decision on th brakes.

 

i'm pretty sure it's just a symptom of old brake lines - i don't think a cable actuated MC helps the situation either, however. but i was thinking about trying to bleed again after i get done with midnight shifts and the bike has had a chance to sit for a few days.

it did occur to me that using a syringe to fill the MC could be aerating the fluid a bit.

i had some friends over the other night and i had them try the brake lever and they both thought the brakes felt fine, but then i had them squeeze the brake on my '07 KLR and they were like, "oh yeah, i see what you mean there"

i've got a couple months to wait for the roads to be clear and salt free around here, so i'll just have to keep myself occupied with other things until i can get that test drive in.

i'm just glad i've ruled out the MC as a culprit.

however . . . before we put this baby to bed . . . any thoughts about the anti-dive? i know it's not the culprit in my situation as i removed it from the equation and had the same symptoms, but i thought maybe for completeness and to help someone that's stumbled across this thread?

is there anything in the anti-dive that can cause brakes to feel spongy?

 

I thought the same thing myself. The anti-dive system is a joke in my book and just gives a false sense of security. If it were such a good idea, why don't they put it on bikes now?
The only thing that will make your brake spongy is air in the system or poor rubber brake lines. Go put preasure on the brake lever and feel the rubber brake lines. They actually EXPAND when you put alot of preasure on the lever. That's where the steel lines are far superior. I hate the cable over hydraulic system on my Seca and am in the process of finding a handelbar master cylinder and steel lines to make the system the way it should have been from the factory. Although I can get it to stop alright, I just hate the spongy feel, and the inconvenient location of the master cylinder for maintenance.

 

Yes .. after breaking a bleeder in th anti-dive I could only bleed it by loosening the allen (hex' ? )screw--which holds th little piston that makes it work-- at th front of the unit after taking it off th fork to allow gravity to do its thing. Then putting it back after it's bled, fiddly ..yes. So it must be possible to have air and crud in there.

It's worth dismantling th whole thing to clean it. It's very simple inside, just be careful with th smallness of th pieces, there's a C clip that may break.

 

i curently have a bar mounted master from a 91 fj1200 and 2SS lines straight from the master to calipers, no splitter i chose that master because the banjo exits forward rather then some that exit to the left which caused an issue with my euro bars, it would have put the master to close to the guages, to be able to put in the banjo.


it looks pretty much factory now

 

there is a small piston in there that the brake fluid pushes on, to change the valving in the forks
it's not very big but some of the fluid volume moves that piston and not the brake piston