Help! Front Brake Locking Up.

[BeerFriendly]

Hello Everyone. I rebuilt the front brake caliper, master cylinder and installed a new brake line a couple years ago. I rode maybe 100 miles with no problems at all. I did not ride it for a year or so. Now, as soon as the front brake gets hot, it locks up. After some time to cool, it unlocks. What could the problem be? Could the pads have gone bad and are swelling under heat? I have bled the brakes to make sure there is nothing in the system other than brake fluid.

Thanks.

[JanM]

Check the return port in the master, it must be functional when the brake lever is released - lots of potential issues, wrong clearance for the lever, dirt in the hole etc...

[BeerFriendly]

Check the return port in the master, it must be functional when the brake lever is released - lots of potential issues, wrong clearance for the lever, dirt in the hole etc...

Would these be problems that only arise when hot and go away when cooled down?

[JanM]

Would these be problems that only arise when hot and go away when cooled down?

Can't say for sure if a non-functional return port will only give the problem you describe when hot - but it is a very common failure mode for brakes and it usually just means that the brake initially drags, then gets hotter and locks. Normal remedy is to service the brakes and check the port.

But maybe excessive dirt in the seals can be a cause, maybe the brake lever gives a little actuation all the time...

[bitzz]

The symptoms you describe could be water or air in the brake fluid.
When water turns to steam at 100 C it expands by a factor of 11, so one CC of water makes 11 CC of steam... so a tenth of a gram of water is enough to lock your brake.
Air expands by a factor of 4 (IIRC).
Bleed the brakes and flush with new fluid

[rpcraft]

Water in the brake fluid is not just about steam. Once contaminated to a certain level your brake fluid can turn to a gel and if it does when you apply the brake it expands and will not retract. That is probably more likely the reason it is locking up if it has not ever really been properly services. The solution is the same as mentioned on the previous posts though. Plan on taking it all apart, clean it all out with brake cleaner. if there is some scum on the caliper pistons use some scotch brite and brake cleaner to get them clean and if you can't then replace them. Plan on replacing the seals and it also might be a good time to get a new brake line and time to rebuild the master cylinder as well. If your bike still has the original rubber lines over time the rubber lines become porous and can also be brittle in areas or swollen inside and can stop proper flow of brake fluid. Goodridge makes a great OEM replacement that has a stainless protective shell and will probably last the rest of the life of your hawk (compared to the OEM cables). Hord has all the parts you need to rebuild a front or rear at his site and that is money well spent. They're close to the bottom of the first page there as I have linked below. Once you get everything cleaned lubricate the seals with some brake fluid while you reassemble, then fill the system with some fresh DOT 4 brake fluid and bleed properly. After that top it off and then your brake's should be operating properly.

https://www.hordpower.com/index.php?main_page=index&cPath=1_44&zenid=9dgf3rcvcs8n67380c1uv89g57

[6]

Last time that happened to me it was because i had the wrong lever for the master, It was close, but wrong. swapped it out and all was good.

Id start by doing anything Jan says..

if it where mine id be checking the lever is fine, correct, clean, service the master cylinder, flush/blead the brakes with FRESH (new, as in just broke the seal, not sitting in a garage half full for two years) fluid, and while you are at it, it cant hurt to service the caliper.

As always follow any and all advice from JanM

[rpcraft]

Last time that happened to me it was because i had the wrong lever for the master, It was close, but wrong. swapped it out and all was good.

Id start by doing anything Jan says..

if it where mine id be checking the lever is fine, correct, clean, service the master cylinder, flush/blead the brakes with FRESH (new, as in just broke the seal, not sitting in a garage half full for two years) fluid, and while you are at it, it cant hurt to service the caliper.

As always follow any and all advice from JanM

Good point 6. Contamination issues aside a mechanical issue won't be resolved with just cleaning and reassmbly!

[squirrelman]

........also, it's important not to over-fill the mc, leaving.air space above the fluid.