Topic: Front brake woes ad infinitum

[scottly]

It doesn't look like a mismatched rotor/caliper in those pics, but I think I see the cause of the caliper misalignment; I'm guessing that rotor "fender" is mounted underneath the head of the  bracket pin, spacing it inward and cocking the rotor.
 

[Saperlipopet]

It doesn't look like a mismatched rotor/caliper in those pics, but I think I see the cause of the caliper misalignment; I'm guessing that rotor "fender" is mounted underneath the head of the  bracket pin, spacing it inward and cocking the rotor.

I think you might have it, can I just remove it?

[scottly]

Yes, remove it, and also remove the adjuster screw and spring, at least until your brake problems are corrected.

[Saperlipopet]

No time to wrench it off tonight, unfortunately. Here are some more pictures though

https://imgur.com/a/Q11sWx8

Attached below is the only sort of exploded view I've been able to find, and it's not much help to figuring out the right order for the dust cover / rotor "fender" thing.

[RAFster122s]

It is possible that the arm needs shimmed.  It should not, but the fork lower not orienting the pads square to the face would yield a twisting force....similar to how you describe.  The cb550 brake arm is different as is the rotor, so I do not know what impact that could have on your disc setup. Is the brake pad completely covered by the disc surface? It should be.

Pulled this up earlier today before so many replies...mine above is redundant as I had not seen the questions and responses....


If the disc fender is not cocking the caliper arm pin as was suggested you need new pads as those are causing issues from bad wear unless they are just looking uneven in wear.


You could pull the disc rain shield and assemble without it or even the fender itself until sorted out.


SohRon has a cb550 assembly/restore thread that will clearly show the correct sequence of assembly...even for the 750 disc.
David

[RAFster122s]

It doesn't look like a mismatched rotor/caliper in those pics, but I think I see the cause of the caliper misalignment; I'm guessing that rotor "fender" is mounted underneath the head of the  bracket pin, spacing it inward and cocking the rotor.
 

Correct me if I am wrong but I believe Scott said rotor when he meant to say caliper is cocked by the rotor's dust/rain shield/fender (black plastic fender covering rotor behind the fork.

[thep1pe]

The pad on the piston side is perfectly aligned with the rotor. It's the swing arm pad causing the problem. Have you even taken off the caliper to see the pads instead of guessing it's the MC. Also you say you've fitted new pads, those are not new pads, unless you messed up fitting them. Never seen a pad that badly worn/ fitted.

[calj737]

It doesn't look like a mismatched rotor/caliper in those pics, but I think I see the cause of the caliper misalignment; I'm guessing that rotor "fender" is mounted underneath the head of the  bracket pin, spacing it inward and cocking the rotor.
 

Correct me if I am wrong but I believe Scott said rotor when he meant to say caliper is cocked by the rotor's dust/rain shield/fender (black plastic fender covering rotor behind the fork.

It’s the dust shield for the rotor.

[Saperlipopet]

SohRon has a cb550 assembly/restore thread that will clearly show the correct sequence of assembly...even for the 750 disc.
David

If the 550 assembly thread is this one http://forums.sohc4.net/index.php/topic,86697.0.html then sadly it's of no use since all the pictures are gone 

[RAFster122s]

Photo bucket fix available for Chrome and another browser that gets around Photo_bucket. Then images are viewable.

[Saperlipopet]

Photo bucket fix available for Chrome and another browser that gets around Photo_bucket. Then images are viewable.

Thank you sir!

[ef9tuning]

After seeing the new pictures, its looks like the caliper on the swing arm side is square to the rotor. The piston side being crooked might be a suspect of the piston was never properly seated. Someone correct me if I am wrong but I believe there is a white plastic ring that sits between the piston & pad? Do you remember installing that when you rebuilt the caliper?

[Saperlipopet]

After seeing the new pictures, its looks like the caliper on the swing arm side is square to the rotor. The piston side being crooked might be a suspect of the piston was never properly seated. Someone correct me if I am wrong but I believe there is a white plastic ring that sits between the piston & pad? Do you remember installing that when you rebuilt the caliper?

Yes I installed this ring and put it all together according to the exploded view I posted earlier. The piston is seated correctly, it's brand new and the dust seal is new as well.

I'm planning on taking the front wheel and pivot arm off completely because there seems to be a washer or shim between the pivot arm and the left fork, may be the culprit. I also want to clean and grease it, anyways stay tuned.

[HondaMan]

And, have you confirmed the small return hole in the MC reservoir is clear? If the fluid can’t cycle, it won’t build pressure.

I took the master cylinder apart and used 110psi compressed air through it.

Here's a question, with the reservoir cap off, if you yank the brake lever back quickly should it shoot brake fluid up into the air? I've heard some people say this means there's still air in the system namely the small return hole mentioned above might not be clear, so maybe my next course of action is to empty the master cylinder of fluid and make extra sure that little hole is clear with a piece of guitar string or something...

This indicates air in the system somewhere. It will usually raise the fluid ("bump" the surface) if the air is gone.

Several things: those who hate these brakes usually don't understand them (like the opposite sex?) very well. Here's the best way to de-air it:

Turn the handlebars fully right, with the bike on the centerstand. This tilts the front of the master downward. Connect a (clear) bleed hose to the caliper, route the open end upward higher than the master cylinder (I tie it to the throttle grip) and crack the bleeder a tiny bit, enough to see fluid reach into the hose. Then put a piece of wire on the lever to hold it in about 1/3 to 1/2 the travel distance (to the handlegrip) and go to bed, and loosen the reservoir cap. Next day, close the bleeder screw and then slowly operate the brake in the "high" position until the tiny bubble streams that appear after each release will quit flowing. If the lines or old or the caliper was emptied (opened), this will take a while, much like bleeding a car's master cylinder without power tools.

When the tiny bubbles finally stop (some will simply vent themselves while the lever is released), swing the bars fully right and repeat to remove the air in the master cylinder itself.

ABOVE ALL - do NOT operate the lever quickly while doing this, as this causes the air to dissolve into the brake fluid and increases the time for it to separate out into bubbles that can float upward. This slow-move bleed method takes a little while, but always works.


Also: do you have the little nylon washers between the pucks and the caliper/piston? All of the post-1976 brakes had these...

[754]

It doesn't look like a mismatched rotor/caliper in those pics, but I think I see the cause of the caliper misalignment; I'm guessing that rotor "fender" is mounted underneath the head of the  bracket pin, spacing it inward and cocking the rotor.
 
 

Correct me if I am wrong but I believe Scott said rotor when he meant to say caliper is cocked by the rotor's dust/rain shield/fender (black plastic fender covering rotor behind the fork.

It’s the dust shield for the rotor.

As far as I know it's for water spray..

[ef9tuning]

After seeing the new pictures, its looks like the caliper on the swing arm side is square to the rotor. The piston side being crooked might be a suspect of the piston was never properly seated. Someone correct me if I am wrong but I believe there is a white plastic ring that sits between the piston & pad? Do you remember installing that when you rebuilt the caliper?

Yes I installed this ring and put it all together according to the exploded view I posted earlier. The piston is seated correctly, it's brand new and the dust seal is new as well.

I'm planning on taking the front wheel and pivot arm off completely because there seems to be a washer or shim between the pivot arm and the left fork, may be the culprit. I also want to clean and grease it, anyways stay tuned.

Yesterday I started to disassemble to the front end to change the stem steering bearings. I can confirm for you there was no shim on the swing arm for the brake caliper on my 78K

[754]

Was the spray fender between the swing mount and the fork leg ? Or not ?

[HondaMan]

It doesn't look like a mismatched rotor/caliper in those pics, but I think I see the cause of the caliper misalignment; I'm guessing that rotor "fender" is mounted underneath the head of the  bracket pin, spacing it inward and cocking the rotor.
 
 

Correct me if I am wrong but I believe Scott said rotor when he meant to say caliper is cocked by the rotor's dust/rain shield/fender (black plastic fender covering rotor behind the fork.

It’s the dust shield for the rotor.

As far as I know it's for water spray..

At that time, Honda was touting it for helping to keep the front of the bike cleaner in the wet (it actually works, just in a small area...).

[Saperlipopet]

Well my friends... the ordeal is over. Big thanks to all of you, especially scottly for getting me thinking in the right direction.

I took the caliper off, took the front wheel off and took the pivot arm assembly off completely, cleaned everything up nicely, greased up the shaft and before re-installing it I noticed what I think was the problem. I'll be using the picture attached below as a reference.

There was a washer in between the fork and the pivot arm pin (#9) that shouldn't have been there, just imagine another washer (#22) wedged between the pin and the fork and that's what the setup was on my bike. Seems like just that extra few millimeters was enough to throw the whole thing off. Either that or the pivot arm needed to be re-greased (it was pretty dry) in order to function properly; I don't know but as soon as I put the caliper back on, it felt like the pad was making good contact with the rotor and after a short test run it was pretty clear that this is how the brake is meant to feel.

Now to try HondaMan's bleed method for that last little bit of sponginess...

Ride on fellas 

[AwesomeCB]

This issue really puzzled me and it's great you solved it. I learned something.  For bleeding, either a Mity-Vac or a Speedbleeder makes life easy.