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