Topic: Front brake pad seems angled, not retracting ('74 CB750K)

[Yoshimitsuu]

I recently did an overhaul of my brake system and noticed a few things. Upon putting everything back, I noticed that my front brake was dragging as my bike was a good bit harder to move than before. I am confused though because going through some of the threads that speak of this issue, they mention to do things I have already done. One of the things that I noticed was that the brake pad in the caliper seems angled a bit. I can fit a .006 feeler gauge under the bottom but it gets tighter as I move it up and eventually it won't fit anymore. Things that I heard to do:

1) Clean out MC feed hole: I just replaced the old MC with a new Nissin one so I doubt it's plugged but I fed a high E guitar string in there anyway. I don't really see it making bubbles when I press the lever but the brake fluid is moving as it's reaching the caliper.

2) Adjust the swingarm screw: I did this but I don't think it adjust the problem brake pad. My problem is with the pad on the piston side not retracting, not the other.

3) Check brake pad fit: I looked at the new brake pads that I bought and noticed the thick coating of paint on them. I took this layer of paint off until they could wiggle in their slots.

4) Cleaned caliper: There really wasn't much gunk in there but I did lightly steel brush and sand the inside to polish it up a bit. Rubber seal seated well.

Now, I replaced the old piston with a new phenolic one but I'm curious. It was taller than the old piston and about the height of the old piston with the metal cap that was attached to it. I didn't put that cap back on the phenolic when I reinstalled everything since it looked like it would be too tall. Was that a bad choice? I checked online but most pictures of the phenolic piston don't show that cap so I wasn't sure if I needed it.

TL;DR: Front brake pad not retracting and pressing against rotor at an angle. Tried a lot of things but still kind of locked up. Help welcomed. Thank you in advance!

[754]

 Did you clean out the groove the brake seal goes in ?
This is crucial, any debris or corrosion in there will cause your seal to be tighter than it should be..then It will likely drag.
 If you left the rounded metal cap out the brake pad cannot align itself, its a swivel, allows it to tilt. Remember your brake mount is a hinge, it swings in an arc.. Not slide in and out ..parallel to your rotor.

[strynboen]

" steel brush and sand the inside to polish it up a bit. "


hope just a bit..is just a bit..
...it just need to be klean for dirt and korosion and old rubber..not sandet dovn.
.or the piston can be locked if it not do move, absolut paralell.
.and a bit caliber lube need to be moved dovn at the sides..to hold it from Lock.(.dont use any normal grease dovn there)

[rotortiller]

Did you clean out the groove the brake seal goes in ?

+1

[Phinn]

You can't un-bind a dragging front brake pad by adjusting the swingarm screw. You have to adjust the swingarm properly before you get to this point. Once it binds, you have to remove the caliper and press the piston back into the socket.

The swingarm adjusts both pads. You adjust the position of the swingarm using the rear (fixed) pad as a point of reference. It must be adjusted so that the rear pad comes to rest very close to the rear side of the rotor but without binding it.

Remember, the total range of motion of the front (movable) pad & piston is very small, because its forward movement is accomplished by the deformation of the seal. Likewise, the piston's retraction movement is accomplished not by negative fluid pressure, but rather by the seal merely returning to normal shape. As you can imagine, that's not a lot of movement.

As a result, the swingarm needs to be adjusted so that both pads need to travel as little as possible before making contact with the rotor. If adjusted properly, the front pad (when activated by pressure) will travel half of the distance necessary to engage the rotor, and the rear pad will swivel on the swingarm to travel the other half of the distance.

If your rear pad is too far away from the rotor, and the front pad has already been extruded too far out, there's no way to get the piston to retract more than the re-forming seal will allow. At that point, you have to remove the caliper and push the piston back in (open the valve to relieve pressure).

So, I recommend starting over. Remove the caliper from the bike, open the valve, press the caliper piston all the way in (which will eject fluid), and reassemble onto the bike. Replace any lost fluid. At this point, you should have a nice wide gap between the pads. Once it's all back on the bike, adjust the swingarm screw until the REAR fixed pad grabs the rotor, then back the screw off just enough so that the wheel turns freely, then maybe another 1/8th turn. Lock the screw in place. Then, pull the brake handle to move the front piston/pad into position. It should bind the rotor then release.

If not, then your front pad is not retracting, and you probably have a bad seal. That can be due to the seat of the seal inside the caliper, contamination, or just a bad piece of seal material.

[my name is nobody]

As a last resort, I used genuine Honda brake pads to clear up this scenario with my bike. No muss, no fuss, went right in and
worked without any more issues. Expensive, yes. Worth it? yes. The bike stops as intended now, and hasn't
stuck on for over a year. Also used a stainless steel piston to resist rust. The system design is old, but will
perform pretty good when it's working properly. Hope you can get it sorted.

[evinrude7]

this doesn't seem to be your issue however it was part of mine and could be helpful to some.  the cotter pin on my static pad seems a bit thin for the job it's doing.  will replace soon however the quick fix i did was to take the static pad housing off and with it laying flat on a work bench push the cotter pin down with two flat heads against the back of the static pad's housing to make sure it was fully seated and would stay that way.  my static pad was not staying put but flopping ever so slightly inside it's home.

did you put a little brake fluid on the piston's sides?  maybe some brake fluid on the seal where it contacts the piston before inserting?  i would also grease the side and back of the pad before inserting.   

[Yoshimitsuu]

Thanks for all of the responses guys! A few things that I want to check when I take another look at it based on your responses:

1) I'm definitley going to check that seal slot for gunk that might be preventing it from expanding and contracting correctly. I have a new seal so I'll just put that in while I'm at it.

2) I need to refit that metal cap that goes between the piston. I thought because the phenolic piston looked a bit larger that I didn't need it but I should have researched that a bit more.

3) I should probably check on that cotter pin as well. It seemed to be held alright but with a bit of a wiggle. Probably not good for brakes.

When I say that I sanded and steel brushed, I did so very lightly. The goal was not to remove material from the caliper but to clean it out. It is still the same size!

Thanks again guys! It's the last fix I have to make for the bike to be on the road. Just in time for the slowly approaching North Eastern winter

[Yoshimitsuu]

So I pulled the caliper, brake pad and piston out but I've run into another problem. Like I said above the phenolic piston is taller than the stock one but the cap that goes over the stock piston doesn't fit. This seems like an issue. I can't really find anything about how to run the phenolic piston and whether it needs this cap or not. I did replace the seal and took a wire brush to that crevice to make sure it was clear of grime and muck.

In addition, I am not sure how much the brake caliper swingarm should move (or even if it should) but mine is very tight and won't move with the brakes off. I tried Phinn's suggestions but when I reassembled everything as soon as I tightened the two hex bolts on that caliper the pad is touching and I've backed up the adjustment screw quite a bit but still nothing.

Thanks in advance guys. I'll post pictures below:

[Phinn]

I have no cap, and it brakes normally. The length of the piston doesn't matter (assuming it's not so long that the front pad contacts the rotor when the piston pushed all the way in). The piston will be extruded until its pad reaches the rotor.

The fixed pad typically has a rounded bump on its reverse side, which causes it to wobble and thus pivot a bit, so it can accommodate the variable arc of the swingarm.

You might also want to check the edges of the front pad. Many have paint that makes it difficult to move to and fro in the caliper. The pad should go in and out of the caliper freely, with no binding. I had to sand down the sides of the pad to make this happen, and then add silicone grease (being careful to keep it out of the piston & seal area).

[BazF]

I went thru this on my 74 750.
If you slacken the fixing bolts on the swing arm slightly, the arm will now swing. I fitted a thin washer here and retightened. No more problem, did it for me.

[madmtnmotors]

Are you mounting the fender bracket between the caliper and the fork lower (wrong) or are you mounting the fender bracket with the caliper bracket between the fender brace and the fork lower (correct)?

[754]

If the swinging arm does not swing freely   take it off clean and lube it.

[evinrude7]

i futzed with this a bunch over the last 10 months.  i mostly ignored it because the bike stopped great by pulling the brake lever, rolled easily with the brake off but squeaked a bit.  it was not terribly bothersome to me but once i rebuilt the master cylinder i figured i should fix the entire system because rebuilding the mc didn't fix the pad not retracting.  it took me about 10 minutes to get it working properly.  pushed the pad out and cleaned, sanded off the gunk and whatnot.  lubed it up and popped it back in.  bleed the brake and all good.  if the swing arm doesn't move a little bit it seems to me the caliper pad is not retracting.  i'm not even sure what the oem piston is but i have a stainless one.  after cleaning, lube and install it works great.  i also made sure to sand the edges of the pad heavily and lubing the edges and back of the pad with lithium grease.  probably not the right stuff but works for now. 

[ofreen]

If the swinging arm does not swing freely   take it off clean and lube it.

I'll quote this because it bears repeating.

[PeWe]

I have heard about cars with binding brakes due to a bad brake hose, old rubber type that does not allow fluid to retract. Replaced the old rotten hose and fixed the brake.

Important to not lube the caliper piston seal with silicone grease, it WILL leak. Do not ask me how I know

[Yoshimitsuu]

Removed the caliper arm and I noticed two things of concern:

1) The fender is mounted between the caliper (wrong way) and not behind it as it should.

2) The pivot pin is pretty seized and does not move.

Currently soaking it in penetrating fluid to see if that'll loosen it up but it's frozen pretty solid. Any tips on how to remove a seized caliper pivot pin?

[madmtnmotors]

Removed the caliper arm and I noticed two things of concern:

1) The fender is mounted between the caliper (wrong way) and not behind it as it should.

2) The pivot pin is pretty seized and does not move.

Currently soaking it in penetrating fluid to see if that'll loosen it up but it's frozen pretty solid. Any tips on how to remove a seized caliper pivot pin?

I've attached a pic of the correct placement. Mounting the fender towards the tire provides the proper clearance for the steel brake line from the caliper to fit between the fender bracket and the fork lower.





As for the caliper pivot, keep soaking it and working to try and free it up. It should eventually start to release. A little heat might help too. I'm pretty sure there are no clips nor cotter pins to hold the pivot in place, just a couple small o-rings to serve as a rudimentary dust barrier. Once the bracket is bolted in place the pin can't come out. Maybe clamp the head of the pin in a vise (there are two flats on the bottom of the pin where it bolts to the fork) and try to turn the top part of the bracket. Take care to not use too much force at first, it will finally move.

[Phinn]

Any tips on how to remove a seized caliper pivot pin?

1. Remove the swingarm assembly from the bike.
2. Clamp the swingarm sturdily.
3. Drive out the pin with a punch. It has a divot on the top that you can use.
4. Clean it out.
5. Lube it with grease, not an oil.

[RAFster122s]

Use a good penetrating oil.  I like PB Blaster as it works well for me.  Kroil is premium penetrant and worth every cent....works extremely well.
After heating you can spray and cool the joint with the penetrant and it will draw it in as it cools.  It may take several heat and penetrant cycles, so be patient and give it time.  Hit it daily with penetrant for 3-4 days.  Don't force it.
Just like cutting threads or loosening rusted bolts sometimes you loosen a bit and then tighten it and it clears the threads and slowly works its way out.

Once it is apart you will need to polish off any corrosion in the hole as well as on the pivot pin shaft.

[robvangulik]

Important to not lube the caliper piston seal with silicone grease, it WILL leak. Do not ask me how I know

Right, but even more important, the squarefaced o-ring won't have enough grip on the piston and therefore woill not pull the piston back as the brake is released! Resulting in a clean and supple moving piston that still hangs....

[evinrude7]

Important to not lube the caliper piston seal with silicone grease, it WILL leak. Do not ask me how I know

Right, but even more important, the squarefaced o-ring won't have enough grip on the piston and therefore woill not pull the piston back as the brake is released! Resulting in a clean and supple moving piston that still hangs....

rob, square faced o-ring?

[madmtnmotors]

Important to not lube the caliper piston seal with silicone grease, it WILL leak. Do not ask me how I know

Right, but even more important, the squarefaced o-ring won't have enough grip on the piston and therefore woill not pull the piston back as the brake is released! Resulting in a clean and supple moving piston that still hangs....

rob, square faced o-ring?

The piston seal inside the caliper body has a square cross section as opposed to the round cross section of a typical o-ring. 

[evinrude7]

Important to not lube the caliper piston seal with silicone grease, it WILL leak. Do not ask me how I know

Right, but even more important, the squarefaced o-ring won't have enough grip on the piston and therefore woill not pull the piston back as the brake is released! Resulting in a clean and supple moving piston that still hangs....

rob, square faced o-ring?

The piston seal inside the caliper body has a square cross section as opposed to the round cross section of a typical o-ring. 

ah gotcha.  so was i mistaken to apply brake fluid to the sides of the piston before inserting? 

[TwoTired]

ah gotcha.  so was i mistaken to apply brake fluid to the sides of the piston before inserting?

The problem with brake fluid is that it attracts moisture.  The seal straddles the brake fluid containment vessel and the open air.  So, corrosion ensues on the air exposed side.

But, you don't want silicone inside the pressure vessel.  So, what I have been using is "Brake Parts Assembly Lube".  The assembly lube doesn't attract moisture and coexists happily with brake fluid.  All other metal surfaces exposed to the air and water splash, get a coating of Dow Corning Silicone grease, which will not wash away with water or migrate with heat, and blocks oxygen from corroding the metal.

Cheers,