Brakes lock up while parked.

The OP's problem is not the sun, but the heat generated by the brakes, because it only set for 15 minutes. My problem was the sun, because the bike had been parked for nine hours in the sun on a hot summer day outside the hanger I worked in at Rhein Main Airbase Germany,
I had the same problem with a 750 twin I assembled last year but with the rear brakes. In that case it was the heat generated by riding that caused the air to expand and caused the brakes to start dragging.

There are only two things that could be present in the brake system that will cause this, air or water.

www.afcoracing.com/tech_pages/fluid.shtml

Unless the brake rotor is glowing red hot

I think I have experienced every possible brake problem :woohoo:

Based on above post I will lose the silicone fluid, after the M/Cyl RE-Rebuild.
I will also disassemble the caliper and check everything.
The only problem with this approach is I may never know for sure what the cause is.

Post edited by: FloridaBiker, at: 2008/02/06 12:53

steell wrote:

There are only two things that could be present in the brake system that will cause this, air or water.

www.afcoracing.com/tech_pages/fluid.shtml

Unless the brake rotor is glowing red hot

I think I have experienced every possible brake problem :woohoo:

Interesting link; good read. Thanks Steell.

the dot 5 fluid is way better than dot , it does not absorb water, and has a higher heat range than 3,if the 5 is affecting the rubber seals for some reason, then it could cause a problem, but I dont think so.

Maybe a review is needed. what was the reason for the rebuild, what parts were changed, most of the time with brakes there is something simple to fix the problem

BSKZ650 wrote:

Maybe a review is needed. what was the reason for the rebuild, what parts were changed, .......

This was a winter project on a "garage find" bike.
The bike did not run when I got it, and no braking function was present.
I just wanted to do everything right.
I rebuilt the M/Cyl and Calipers, put in all new stainless hoses, new pads and used silicone fluid.
In a previous post (older) I dealt with the calipers not sliding smoothly on the mounting bolts.
I got the system working perfectly after all that work.
The bike has gone over 600 miles since the rebuild, without a problem.
It has locked up twice. Both times it was parked in the sun (not common for me). Both times the brake lever was rigid and unmoveable. When parked no problems were noted. I am an agressive rider, and use the brakes a lot. I assume there was a lot of stored heat in the discs to dissipate.
The only repair I have done to date is to just open the bleeder, relieve pressure, and ride away normally.

Of all the suggestions that were made, air (or water) getting heated and causing expansion in the lines make the most sense to me.

Post edited by: FloridaBiker, at: 2008/02/07 08:28

When I say the brakes worked normally that is an understatement.
The brakes were SUPERB!!
I could easily have done a "stoppie" (not my style), THE BRAKES WERE THAT GOOD!

Post edited by: FloridaBiker, at: 2008/02/07 08:31

There is a member here who has the same problem on his 900, on our rides he has to crack the bleeder before resuming ride (no sun) He says (he's a mech) that his return port is plugged but is almost impossible to get to with various tools. He may have to ebay another nicer M/C.

Bluemeanie wrote:

There is a member here who has the same problem on his 900, .........He says ........ that his return port is plugged.............

Unfortunately, that may well be the problem. I will try agressive (chemical and ultrasonic) purging of the return port.

PROGRESS REPORT:
1) I used a pressure bleeder to replace the silicone fluid with regular. I did find a few air bubbles in the system.
This may have been the cause.
2) I had my lab test the fluid removed for water, and small quantities were present.
This may have been the cause..
3) I disassembled the master cylinder and found it in perfect condition. The little ports were open and NO debris was present.
4) I checked both calipers and found them to be free of debris, and the pistons moved easily. The caliper mounting bolts allowed the caliper to slide freely.
5) I replaced the brake lever with the correct Kawasaki part. I had an after-market lever that was slightly different in measurements where the lever contacted the M/Cyl piston.
This may have been the cause.
6) Reassembled everything and bled the system excessively.

The brakes work great, still.

So far No lockup has occurred.
If it is going to happen it may take a few days for the right conditions to be present.

Perhaps relevant: My brake 'feel' is a little softer now. Before doing the above my brake lever had virtually no free play and required a fair amount of effort to apply brakes. Now the effort required is significantly lower.

Post edited by: FloridaBiker, at: 2008/02/08 13:57

is it possible something is going on with the piston causing it to lock, ifthe return port was plugged seems to me you should be able to apply some pressure to the system

You said when you rode the brakes worked great, but I'll bet if you pulled over and were able to get front wheel off ground and spin it you would have found it to be dragging. This explains why there was no freeplay, freeplay is the slight distance the caliper moves to contact the rotor. Plus with pads already very hot from constant contact with rotor they may have expanded slightly when parked which could cause a lock up. This is just my theory... Changing fluid, lever and having some freeplay may have fixed your problem. Hope so, let us know.

Update, after more riding.
The brakes work without any problems..
I am now convinced that the problem was related to my silicone fluid, (and possibly how it related to contamination of water and air).
In any event, since going back to conventional fluid it has worked great.

Post edited by: FloridaBiker, at: 2008/02/17 20:03