Front brake question

[Qckslvr]

Need to confirm my beliefs, before I go and drop more cash. This morning I buttoned up my 78 GS750 and was getting ready to go on its first voyage with new tires, carbs etc. When I first rolled it out I noticed it was a little hard to push. Grabbed the front brake a couple times and it then rolled fine. I rode it around for a while, and all was well, then I decided to hit the freeway. As I am going along, all of a sudden I noticed I am slowing down. First thought was crap I lost the engine. As I pulled over and got to about 5 mph the front wheel locks up. And the lever felt real hard. I pumped the lever about 5 times and it freed up, and the bike rolled freely again. I gently rode it home on the rear brake only.

So my thought is that I have a front line collapsing. But I would think that pumping the hand brake would not make it free up? And I know I built the master right, it will only go together one way.

Thoughts please. I don't want to drop $200 on brake lines if I don't have to.

[Qckslvr]

if a mod could move this to the right forum, I stuck it in the wrong place

But I rebled the brakes, and they seem to be much better. Time will tell I guess.

[BassCliff]

Hi,

Air or water in the brake fluid system will expand when heated and cause the brakes to lock. Bleeding is the right thing to do. I hope you got out all the air/water. Be very careful until you are sure. I'm glad the front wheel didn't lock while you were at freeway speeds.


Thank you for your indulgence,

BassCliff

[TacoFeo]

May I also suggest before bleeding the brakes remove the front calipers and using a c-clamp of appropriate size force the pucks fully back into the calipers. This will aid the bleeding process as well as break any 'set' the puck seals may have developed from sitting. Just be certain there is room in the reservoir for the displaced fluid.

[Colin Green]

May I also suggest before bleeding the brakes remove the front calipers and using a c-clamp of appropriate size force the pucks fully back into the calipers. This will aid the bleeding process as well as break any 'set' the puck seals may have developed from sitting. Just be certain there is room in the reservoir for the displaced fluid.

What an excellent idea. Why haven't I thought of that before

[Qckslvr]

I should have mentioned. The front brake system is virtually all new, except for the hoses and hard parts. I installed new caliper seals and boots, brake master cylinder kit, pads, and a new resevoir. I did this all when I rebuilt the front forks, and installed all new wheel bearings and neck bearings.

[Nessism]

First thing is ditch those stock lines. Suzuki calls for replacing them every two years, which obviously is excessive, but retaining them on a system rebuild is pretty crazy. In addition to the rubber degrading the lines develop scale on the inside which will contaminate your new brake fluid.

Regarding the issue at hand, my guess is the master cylinder return hole, the itty bitty one, is plugged up so the fluid can't expand as designed. Should be an easy fix (other than getting rid of those lines that is).

[Big T]

I'm with Ed

Go out and take off the master cylinder cover

Gently pump the brake lever and release (repeat several times)

Do you see a healthy spurt of fluid coming from the bottom of the MC?

If not, that release hole is clogged

You may have missed a small bit of gunk in the MC when you rebuilt it, and it migrated to the release hole.

Since you put new seals in your calipers, you have removed any water, scale, gunk, etc inside the caliper, so it's got to be in the MC