Frustrating brakes

the fronts lock up.. rebuilt calipers master cylinder and new brake lines.. work good for a bit then grab.. I crack a bleeder open and all is good.. so weird.. any ideas? 750 seca

 

Did you do anything with the anti dives?

 

what did you do to rebuild calipers?
does the bleeder fix last for long ?
what brake fluid are you using?
by grab what exactly do you mean? grab and drag?
and as asked what did you do for the anti dive?

 

Either the bleed hole in the master cylinder is not clear or the cable from the brake handle is too tight and the master cylinder piston can't retract all the way keeping the bleed hole blocked . Maybe a combination of both. Do you still have the stock cable operated MC ?

 

Did you pull the piston out of the caliper and replace the inside seal of so did you clean the bore of caliper out real well? When I did mine one caliper had quite a bit of corrosion under the seal . Also mine were rock hard think original from 82.

 

Is your brake LEVER returning all the way out? I had one that I had tovalways remember to judge the rest of the way with the back of fingertips, or the caliper would drag

 

I had my mechanic friend clean and rebuild the calipers he completely broke them down and cleaned them and replaced seals. I didn’t touch the forks yet.. it’s the original master cylinder...the brakes grab and overpower my engine.. I crack a bleeder open and they r fine again.. it’s super weird

 

have you checked the runout of the discs?

 

What do you mean by that?

 

test for warpage of disc.

 

They r brand new.. I doubt they r warped but I can

 

They can still grab like that if the seal was not lubricated first. Also, did you check to see whether the lever is returning all the way back out?

 

Warped disc won't cause brakes to stick. They will cause a pulsing feeling when brakes are applied. Have you checked the MC cable to see if there is the proper slack to let the MC piston retract all the way?

 

Improper bleeding can cause this, as can overfilling the master cylinder (due to the nature of the Seca 750 master cylinder).

After checking the master cylinder return port, and the brake cable adjustment (and the cleanliness of the master cylinder lever that the cabel actuates (it's hidden under a rubber boot on the bottom of the master cylinder), then...

An excerpt from:
brake-help.108235

9. You aren't done yet. There will still be some air in the system. The next step cures that, no matter what method you use to fill and bleed the system.

10. Use a vibratory sander (no sanding pad) and slowly run it along the brake lines, calipers, and distribution block from bottom to top. This will move any remaining air bubbles up into the master cylinder. Tap (or vibrate) the master cylinder to get the air bubbles to come out of the return hole. This process can also be done with a box-end wrench or other similar tool, and tapping the calipers and lines (it just takes longer).

11. Do one final bleed normally, just to be certain that the calipers are fully bled.

12. Use a flashlight to check the fuid level in the master cylinder. It should be below the fill neck. Unfortunately there is no dip-stick or sight glass on this master cylinder, so unless you empty it and measure out the fluid you will need to just eyeball it. If the fluid level is too high the brakes can hydrolock and not release.

 

Quick question,
What is below the fill neck? My brake light has come on a few times but when I look down the fill there seems to be fluid there and the plug is quite long leading me to believe the level shouldn't be too high...

If I can confirm the level is correct I'll be looking at swapping or at least checking the sensor...

Attempt at a picture:

 

The level looks fine to me. It might be a tad high; it's hard to tell from a photo. If it were too high you'd have problems with the brakes dragging.

There is a float assembly in the master cylinder, and it only triggers the warning if the level is too low. It could just be unplugged, or have a broken wire, or even be stuck. I'd tap the master cylinder a few times before digging into it.

 

Sometimes I have to push the lever the rest of the way back out. I only have to push it out a teeny bit, but it sometimes hangs up, and then the brake hangs up. As soon as I push that last little bit out, the drag stopsl

 

No dragging thanks, not yet anyway...

I'm just concerned about driving around with low brake fluid. I haven't seen any leaks and I cleaned up a caliper that was rubbing the disc slightly the other day so cleaned the pads, slides, pistons, etc. and reset fork pinch on axle to get proper line-up. (Like a 1/16" move)

I've been riding the current brake fluid charge a year and a half (3000 miles?) and have had no issues whatsoever to this point.
I'd hate to grab a brake that isn't there however

 

That original description above is exactly what the Secas do when the little hole is the master cylinder is plugged. I think Chacal has a picture that shows the location.

 

brake fluid absorbs water and should be replaced yearly

 

Realy? Maybe if you live in a swamp?

 

http://brakemax.com/water-hygroscopic-brake-fluid-explained/

 

With all due respect, this guy is talking tosh, and if you think about it, you'll see why.

Since this system relies on friction, it will definitely get hot. If the hydraulic fluid boils, it is useless. Fortunately, fresh, new DOT 4 brake fluid has a boiling point of over 500 degrees so the chances of boiling are slim. However, brake fluid is hygroscopic which means it absorbs water and moisture which enters brake fluid through microscopic pores in seals, hoses, seams, and joints at a rate of approximately 3% per year. This water in the system now can reduce the boiling point from over 500 degrees to barely 300 degrees. As water continues to accumulate, the boiling point drops down even further which allows for a greater possibility of fluid boiling. Not good.

So, 3 % a year? Let's think about this. If your system absorbes that amount, and you don't change it for 6 years (not unusual I would suggest), then that's about a 20% increase in volume. Does anyone see this, ever? Of course not.
On top of this, your Yamaha designers (well the m/c designers actually), were very clever in designing a system sealed to ambient air, without sealing the top of the m/c. So any moisture has to get through the lines, As well as the rubbers at both ends. 3%? Yeah right.
In Europe, car manufacturers specify 3 or 4 year intervals, much more reasonable. Even then, many cars are riding around at 10years plus on original fluid - and have the reservoirs overflowed? Unsuprisingly, no.
Yes change the fluid regularly, but every year?

 

I'll refer to my personal experience, every factory service manual that I'm aware of, and SAE standards for brake systems.
Glycol brake fluid does absorb water, which does lower the boiling point, which can cause that water to flash to steam, which does lead to a sudden lack of braking when brake fluid is not changed on a regular basis (how often will depend on local humidity). Excessive water in teh fluid also causes corrosion, and the formation of that gooey-gunk that we all end up cleaning out of the system when we rebuild the calipers and master cylinders.
The science behind the practice of regular fluid changes is well established, and such changes are standard in all industries that use glycol hydraulic fluid systems.

Besides, brake fluid is cheap. There's no sense in skipping a critical maintainance item when it's nearly the least costly thing you have to do to a machine.

I agree that in most locations a once-per-year change is excessive, but it's not unwarranted in some conditions (such as those areas of the U.S. that regularly see 60-80% humidity through the summer months), or of the machine is not ridden regularly enough for the brake fluid to heat up and drive off accumulated moisture.

 

Lets agree that it does absorb water. So we agree on the first paragraph.
Then, from simple and undesputed fact you jump to "besides its cheap" . Again, I'm not aruing with you.
So how does this (and bear in mind you haven't disagreed that 3 percent absorbsion is nonsense, if this were true I might agree with changing every year), then transorm to change it one a year?
I ask you, even in the high rh you might have in some parts of the US, if you left the cap off a bottle of the stuff, would you see plus 3%? Absobsion ?
Fine, change it once a year, give yourself a hug, feel better, but don't advise peple that this is a requirement - unless of course you can be certain it is?
Please don't take this as personal in any way, I just don't want someone with little experience to be mislead and miss an important fault while assuming the issue was "old" brake fluid.

 

Actually, almost all m/c covers have an air-bleed (atmospheric vent) in them, and I suppose that this is the manner in which most moisture penetrates into the system.

Yamaha recommend that various components within the brake system be rebuilt or replaced every 2 years........and this would also involved a brake fluid change.

 

Where brakes are concerned I err on the side of caution. They are one of the few parts of a vehicle that cannot be allowed to fail. This is one area where the liberal application of preventative maintianance has no downside.

A previously opened conatiner of glycol brake fluid should be recycled after 12 months. This is the standard recommendation from all manufacturers of brake fluid. Brake systems aren't closed, and the fluid within gets its additional useful life from the addition of heat from the braking system, which helps to drive off absorbed moisture.

I won't dispute or confirm the previously cited 3%/ year absorption rate, except to refrence the industry standard regarding shelf life of an opened container, and the fact that glycol brake fluid becomes unsafe to use once it contains ~3% moisture. It is reasonable to deduce that is where the 3%/ year rate comes from.

Brake-Fluid-FAQs.pdf


There's also the matter of moisture sequestration. As glycol absorbs moisture it also forms a gooey jell, which eventually solidifies. That's the translucent crud we've all seen inside of the calipers and master cylinders that we've rebuilt. That's the same (but not only) crud that can block the return passage in the master cylinder and cause the brakes to lock up once they get warm.

 

Now.
Can we get back to helping this fella make his brakes work correctly?

That is, if they still need to be fixed. The thread is not exactly new.

 

Another interesting difference of opinion that goes nowhere then. You are right kmoe, the op hasn't been back to confirm the outcome, shame.

 

That's often how opinions work.
Just the nature of being human I guess.

 

start a thread and debate all you want