Front brakes locking up

[CBord]

I've got an issue on my 2000 Roadstar I'm trying to sort out.
I've been rebuilding/ modifying my bike for the past year. In December, I had taken the bike out twice since putting it all back together. The second time I had been riding for about 2 hours and front brake started dragging, brake started smoking, and lever was rock hard. Before I could get pulled off the road it locked up completely causing me to lay the bike down. Right front caliper totally locked. On the side of the road I cracked open the bleeder screw and it immediately released. I got the bike home. Replaced both front brake pads, rebuilt both calipers, replaced lines with stainless lines, and of course new fluid and bled lines well.
Few weeks passes, haven't ridden a lot since it was cold (and fixing cosmetic issues from laying it down). I road for an hour or so, then felt front brake starting to get firm again. This time I was able to get off the road. By time I was stopped front was seized up again. This time I had to open both bleeder screwed to get it freed up. All that was left in the system was master cylinder, so I rebuilt it. New fluid.
Now, I've ridden it a few times and it hasn't locked up, but the lever does seem to get more firm after I've been riding an hour or longer.
I'm not sure where to go next. My other Roadstar that I ride daily the brakes don't seem to change in feel the longer I ride. It has me nervous that it's going to lock again and I don't feel like I can trust it, much less take it on road trip.
Thought?

[Shores]

You are either overfilling the master cylinder reservoir or a fluid line is touching something and getting hot and expanding.

[Doc_V]

Are you using fresh fluid from a brand new bottle or do you have a bottle that's been sitting in the garage for a long time? Brake fluid will suck moisture out of the air like a sponge, then as you ride, that moisture will heat up and expand more quickly than the brake fluid, causing problems. If it's not the fluid, check the spliter under the lower tripletree and make sure there's nothing in there that's clogging up. If you're running HH sintered pads, they're much harder than the stock organic pads, though they shouldn't get harder over time..

[CBord]

I was wondering about over-filling. The first time around there is a good chance, but this most recent time I tried to make sure it wasn't too full. I'll double check and make sure its at a good level.

The fluid is from a new bottle I opened when I did the rebuild in December, so not brand new, but not really old. I used a DOT 3 and DOT 4 fluid; could that cause an issue? I know DOT 3 has lower boiling point, but figured one rated for 3 or 4 would have higher boiling point.
I checked the splitter for any blockage, and actually switched it out for good measure since I had an extra one on hand.
The brake pads are Yamaha brand, so I don't think they are HH pads.

So try a new bottle of DOT4, and make sure it's not too full? Any other thoughts/ ideas?

[Shores]

Try filling the master cylinder to the minimum line, not the maximum line. If this works then you probably have some sort of heat going on which is making the fluid expand inside the system. You don't happen to live in hell do you?

[davej]

have you done anything with the master cylinder?

[Smokescreens]

yes, try dot4 fluid and make sure to bleed all the old stuff out of the system as well. i have heard of rubber brake lines collapsing on themselves (inner lining seoprates and acts like plaque build up in your arteries. and locking up brake calipers as well. not sure if that would cause a hard lever or not but i can see it if the brakes wont let go and things get real hot and expand.

[MikeyC]

I had that same thing happen to my rear brake, it was an ever so small touch spot where the exhaust pipe was heating the tip of a stud on the rear lever linkage. One and a half turns on the adjustment nut and all better.

[Duke]

You said that you rebuilt the calipers, and not the master cylinder? As what Dave was asking on the master cylinder, I would rebuild the master cylinder, and all of the fluid thru out the system. JMO.
Dot 3 boiling point is 401 F., Dot 4 boiling point is 446F., and Dot 5.1 boiling point is 500 F. Are bikes should be using at least Dot 4.
Dot 5.1 has the highest boiling point but is very expensive. Don't even think that you can use Dot 5, as it is a silicon type and not compatible with Dot 3,4, or 5.1.

[davej]

Duke I was also thinking that if he made an adjustment up by the lever that he could have the MC piston partially push and not allowing the fluid to return properly. Or if he didn't make an adjustment by the lever, that could mean the MC piston is just stuck in the bore and not returning.

[Aussie John]

There is a master cylinder kit on ebay, I put one in mine

[Doc_V]

Hey guys, check his first post again... "All that was left in the system was master cylinder, so I rebuilt it."

[davej]

I don't know how I missed that when I first read it. My guess is the the MC piston is sticking in the bore or is adjusted at the leverso the is is not allowing the fluid to return.. and not allowing the fluid to return properly.

[Duke]

Thanks Doc?
Seems like something is acting like a check valve, (one way), in the system.

[davej]

Duke a flap in the line would do just that but he said he has new lines, that don't mean there isn't an issue with them. Maybe throw the old lines back on just to verify.I've seen hydraulic lines crimped wrong and squeeze the hose almost completely closed. I still thick it is the master cylinder piston blocking the holes and not allowing fluid to return.

[Duke]

I'm with you Dave, and like you said, doesn't mean the hoses aren't blocked.

[Pauli466]

If it frees up opening the bleeder there's a blockage in the line from the splitter to that caliper, rubber line is collapsing on the inside.