1974 CB 750 front brake sticking.

[rm56]

I have a 74 CB 750. I just put it back together as I had some parts re-cromed. After bleeding my front
brake and adjusting the caliper the front brake sticks. The master cylinder pumped up fine and since there was no fluid in it for a few months I had to bleed off the air. The front wheel would turn fine, and when I
applied the brake it would grab. But when I released the lever the front brake was dragging. I am only the second owner of this bike which has just over 20K on it. In the past I replaced the caliper piston and seal along with rebuilding the master which had started to leak. The bore in the caliper had looked good, but the original piston was pitted so I bought a new one. They are not cheap $105.00. Since I did that I have put about 5,000 on the bike. When I turned out the adjustment screw (The large flat tip one) I noticed after
applying the brake that the mount for the caliper seems to not pivot out against the screw? I sprayed some dry lube on the pivot point but that did not cure the sticking brake. Any ideas? Thanks muck

Rick in Lincoln, CA USA

[Re-run]

Probably a couple of things.
First, you might need to pull the caliper off and make sure the arm pivots freely. If it does not, it will have to be cleaned and then lubed. It also needs to be adjusted so there is about .008 gap between the stationary pad and the rotor.

If you still have binding, then you will probably need to pull the caliper apart again provided that the lever action is firm.
What happens is corrosion builds up from the dot3 fluid attracting moisture. This occurs throughout the housing and especially in the groove where the rubber seal sits. A good brass brush will help you clean this out. If you got a dremel withe brass brush, go to town!. The corrosion comes out looking white.

[rm56]

Yesterday I removed the pivot, cleaned it, lubed it, and put new o-rings on the shaft. I reassembled the brake but it still sticks. I even checked for .008 clearence which I don't have. When I back out the adjusting screw it backs out but the brake ancor arm does not move towards the wheel. I noticed in the MC fluid cup that the hole closest to the cylinder explelled bubbles when I worked the brake lever. That tells me there seems to be a small amount of air in the system at the MC. With air in there the cylinder would have trouble returning an drawing the caliper piston back away from the disc. I also plan to remove the caliper and check the condition of the piston and seal as well as the caliper bore for corrosion. I will pick up a small brass dremel brush to clean it. Very frustrating since this is all that is keeping me from gettng back on the road. Again thanks for the help.

Rick

[EHondaWins]

I'm getting a very similar problem, different outcome, still no solution. Not very surprising though. I'm very novice at being a mechanic, but I still try. :)

Front brake was sticking and making an increasingly horrendous squealing noise and making it pretty tough to walk the bike around.

I applied some bluing on the disc (not the brightest idea in retrospect), and find that the pad was in fact contacting the disc.

I attempted a brake adjustment, but after loosening the adjustment screw so it turned freely, the pad was still in contact with the disc. Same as OP.

So I do what I always do with stubborn brake cylinders and I wedged a screwdriver between the pad and the disc. It's not giving particularly well, so I threw on a janky bleeder kit and opened the bleeder valve.

Eureka! The piston retracted. Then I bled the brakes lines (poorly because of my janky kit and inexperience), and I completed the adjustment.

I mount the bike and don't even pull out of the driveway before I find that the front brakes are soft, but weirdly the lever is still pretty stiff.

So I bought a better bleeder kit and all new brake fluid, then flushed the system and bled the brakes the right way: open the valve, squeeze and hold the brake, check the bleeder line: no bubbles, close the valve, release the brake. Repeated several times over for confidence. Also, no bubbles coming from the master cylinder. (I didn't check the brake fluid pressure with the vacuum pump, but I can confirm later.)

Still no dice. Front brakes were soft, even though lever was firm.

I attempted another brake adjustment. Same deal. Wheel didn't want to rotate freely unless I manually retracted the piston (even then it sounds like it's contacting). I cleaned the disc with contact cleaner and engine degreaser, thinking maybe the bluing I used early on was affecting the pad/disc interaction. Still no change.

Here is what I think my next steps should be:
1) Verify the brake fluid pressure (not quite sure what it should be), and attempt to bleed brakes again.
2) Inspect pads for gunk (like bluing). Replace if necessary.
3) Inspect piston for gunk that could be impeding extension/retraction. Clean per post above.
4) Check pivot arm per post above.

---or---
1) Call a real frickin' mechanic already!

Anyone got any other suggestions, or am I the right track?

[Re-run]

Ahh brakes, so much fun. How far can you pull back the lever? Do you still have the original brake line?

First, remove the caliper from the mount. Now pull the bolt out for the arm. Clean it well and put grease on it. Put the bolt back in and make sure the arm moves freely. Once you got that, it is time to check the caliper. Did you clean it? If not, then you will need to. DOT3 fluid attracts moisture and builds up crud that makes the piston stick. Also, the brake pad my now be contaminated by the blue stuff. That may explain the soft brake with hard lever. You will probably want to replace them but try spraying them with brake cleaner spray and see if that helps.

[EHondaWins]

How far does the lever move as in mm? Haven't measured... But I'm pretty sure it's not loose.

The lever action seems pretty "firm" like it's pushing back with the same amount of force as it did before it was got worked on, and not limp like when the bleeder valve is open.

However, the brakes are "soft" because they don't seem to grip the wheel tightly. It's like the lever is acting properly with the right amount of force but the brakes aren't biting as hard.

For example, even at low speeds, pulling the brake lever with same force/action, the wheel can still rotate some despite the grip from the brakes, making for crazy slow stops. The right force, but the wrong friction. (not the same with the back brake)

I believe most people's first reaction would be air in the brake lines. However, because there are no bubbles in the fluid, I'm guessing it's probably a gunked-up pad or cylinder (or, worse yet, both...).

As for "original" brake lines, the upper part towards the cylinder is likely new. The PO laid it down on the right side, and I think the line had to be replaced. From the looks of it, the lower portion into the caliper is likely to be original, but there's no knowing for sure because there's been at least 2 POs. If you're curious, I'll post some pics.

The whole brake assembly pivots pretty easily while inspecting it up close, but it never hurts to clean up and re-grease that puppy up, does it? :)

Guess it's time to go buy a grease gun...

tl;dr seemingly same force, but less bite; partially original lines; pivots ok, but never hurts to grease

[Re-run]

It is possible that the return holes are clogged up. The master could probably use a good cleaning too. For now, try inserting a small strand of wire into each of the holes and see if anything changes. I am betting the blue though has contaminated the pads too.
When you release the brake, does the front wheel spin now?

[EHondaWins]

I can check the master cylinder. FYI, when pressing the brake, the return hole spits up a little bit of brake fluid. I'm pretty sure that's normal.

After braking the wheel sticks a little by hand until I either pull it around about two dozen times, or retract the piston manually with a screwdriver wedge. Even then it's not completely free, but it can spin a good 5-10 rotations without stopping. The sticking is imperceptible when I'm actually rolling around on the bike unless I turn fully left or fully right.

Too much info? :)

[Re-run]

The pad will usually touch to a very small amount. If you can spin the tire after releasing the brake, then that should be ok. As for the return hole, it should shoot about 10-20 feet up with a firm pull of the lever!

Just make sure to have the inside pad set with a .008 clearance when the outside pad is retracted.

[vern401]

With front brakes if your caliper piston goes back in EASILY with the bleed valve open you eather have a bad brake line or your master cylinder is at fault. I have seen brake lines allow flow of fluid one way but not allow it the other way. I would loosen the brake line conection on the master cylinder and slowly try compressing the caliper. Make sure you dont get brake fluid on your paint it will ruin the paint job. if you have good flow here, clean your master cylinder or rebuild it.

[dkruzan]

OK. I did everything you did. Soaked, scrubbed, soaked, scrubbed. Still dragged. Finally spoke with a retired 77 YO mechanic who helped me. The metal groove that the o ring sits in on the piston side of the caliber required scraping with a nail or toothpick. I did not believe the old guy but I tried it (since I was out of ideas). I had soaked it and scrubbed it but the inside of the groove had just enough corrision to keep the piston from completely retracting. Worked great for 2 or 3 years and just had to do it again this year. Good for several more years I hope. Ride Safe.

[TOOLS1]

I always clean the grove with a small wire wheel on my Dremel Tool.
TOOLS