Topic: 1975 Honda 750F Front Brake Drag

[RodSOHC750]

I'm having a problem with my front brakes dragging and can't seem to resolve it. I rebuilt the front brakes totally. New disc pads, new piston seal, new piston, new master cylinder kit. I adjusted the inner disc pad to 0.006" clearance from the rotor disc. I installed a new master cylinder kit again. I made sure the wider part of the two rubber cups went into the master cylinder bore first. I pulled the disc pads and filed around the pad's steel edges and verified there is no binding of the disc pad or piston. It was virtually impossible to get fluid to the brake caliper.  It was finally accomplished using a vacuum pump attached to the air bleed valve. I discovered the brake drag goes away when I open the air bleed valve. I verified the hoses/tubing was clear from the caliper to the master cylinder. I now took the master cylinder apart (again) to see if there is a return port that may be blocked. Looking at the pictures of the master cylinder, one of the two ports in the bowl bottom appears plugged. Is this normal? How does the fluid return back to the fluid bowl when the brake is released?

[robvangulik]

Open the blocked hole...
Did you clean the o-ring groove in the caliper very meticulously?

[BenelliSEI]

Rod..... you have been very thorough. As previously mentioned, did you really clean out the groove the caliper seal sits in? A dental pick and then a small brass wire wheel on a Dremel works wonders..... Anything behind the seal will cause the piston to drag. Did it slide in easily when installed?

The other thing that caught me out on my K1, last Spring: my MityVac wasn’t pulling brake fluid from the Master Cyl. What I discovered was the top and bottom rubber hoses (originals) were so collapsed inside, fluid wouldn’t pass. Once I did get it bled (by using the master to pump the fluid), the hoses acted as a check valve. They would not release line pressure and the brakes stayed on. Changed them both, problem gone.

[przjohn]

You state that you couldn’t get fluid to the caliper until you used a vacuum pump to pull the fluid. If you have properly rebuilt the master it sounds like a clogged line. With the brake bleeder valve open fluid should flow out of the fitting freely without doing anything to the master. If not it is likely your line is clogged. Remove the line on both ends and check it. It is not uncommon for them to clog up from corrosion and crap.

[RodSOHC750]

Problem solved. I opened the very small blocked hole in the bottom of the reservoir. I didn't know there was suppose to be a small hole there until robvangulik mentioned it and I found a picture. Works likes a charm now. No problem at all with bleeding the system. No squealing, no brake drag. Test drove it. Nice smooth braking. Rotor only slightly warm. Thanks Forum!

[BigJimG]

Problem solved. I opened the very small blocked hole in the bottom of the reservoir. I didn't know there was suppose to be a small hole there until robvangulik mentioned it and I found a picture. Works likes a charm now. No problem at all with bleeding the system. No squealing, no brake drag. Test drove it. Nice smooth braking. Rotor only slightly warm. Thanks Forum!

You're not the first or will be the last to miss that hole.  It clogs up so nicely on an older system that sometimes you don't even realize they are there. 

From your avatar pic, looks like we are working on the same bike, color and all.  Good luck!  I'm in the middle of a brake rebuild as well.

[ekpent]

 Yes that hole is very tiny. I find that using one single strand from a wire snipped from a wire brush works well.

[Bankerdanny]

Yes that hole is very tiny. I find that using one single strand from a wire snipped from a wire brush works well.

I have several lengths of guitar string I keep in a zip lock bag for things like this and carb jets.

[WhyNot2]

Well, learn something everyday................

Thanks guys for posting and answering issues that we the people have.

I too, have had serious issues with my front brakes on both of my SOHCs.

I will go home 2nite after work (actually, nap) and play with mine.

I tell people all the time at work, "I don't come here to work, I just come here to catch up on the sleep I miss at the house last night".

Once again, thanks for the info.