Topic: 350f front brake questions

[dougan]

I have already posted this thread http://forums.sohc4.net/index.php?topic=108774.0 but I kind of missed the mark on what's going on so I am just starting over

Basically, once my front brakes heat up, they tighten up against the rotor. If you're just riding casual on 25mph roads, everything is fine, but once you do some serious braking, the pads rub against the rotor when you're not braking-- if you stop the bike, put it on its centerstand, lean it back, and spin the front wheel there's some pretty good resistance coming from the brake pads.  You can also hear them squealing as you ride.  If you let it sit for a few minutes they'll cool down and everything will be fine again.

I originally thought the problem was a warped rotor because at the right point it will only catch in some spots and not others, but if you continue braking hard on it, it'll heat up enough that it's tight on the rotor for the whole 360 degrees.  So I'm sure there's some kind of warp in that rotor but it's probably not significant and definitely not the cause of my troubles.

I figure the first step is to replace the pads and then go from there.  Maybe after I clean up the caliper everything will magically be OK.  But I'm kind of thinking it may have to do with the master cylinder...  Does anybody have any idea at a diagnosis here?  I'd normally try what I know first, but since this is dealing with the brakes, I figured I'd ask questions before I break something, not after.

Thanks in advance.

[HondanutRider]

There's a lot posted on the topic of dragging/squealing brakes.  The most typical cause on these bikes (and most use the same basic design and type of caliper and pad) is the caliper needing a good cleaning (i.e. the piston, seal and cylinder) and then proper re-assembly and adjustment.  Often its a good idea when doing this cleaning to replace the seal/o-ring with a new one.

[MCRider]

In order of probability:
MC -99%
caliper-1%
rotor-0%

IMO

A good clean caliper is always a good idea. And true it contributes to a squealing brake.

But i think your problem is beyond that. There is a fluid return hole in the MC. It is very small. Only a very small guitar string, or strand of electrical wire will enter it. They get clogged over time from debris of the inside of thelines. You pump the piston to grab the rotor, when you release the lever, some fluid must return to the MC to allow the caliper to withdraw the puck from the rotor.

So, my money is on the MC. Remove, clean, be sure that hole is clear. Some air might help. Watch you don't spray brake fluid all over. Full fluid flush to get out any remaining debris.

[Johnie]

I think MC is on the money here. Been there done that sort of thing. Here is a picture of the hole MC is talking about which is located in the master cylinder on the handlebar. One hole is larger than the other one. The smaller one is plugged (return hole). Get a fine guitar string and push it through. It may take a bit to get it through too. Sometimes they are plugged like concrete. In the lower pic I am using a super small drill bit to get through the gunk. Click the pic to enlarge it.

[dougan]

Thanks guys.  I'll try messing with this after work-- those pictures make me think I can at least determine whether or not this is the cause without bleeding... then wait to bleed it out until I have time to take apart the caliper too.

[MCRider]

Thanks guys.  I'll try messing with this after work-- those pictures make me think I can at least determine whether or not this is the cause without bleeding... then wait to bleed it out until I have time to take apart the caliper too.

here's a test: Get it to where its sticking real good. Release the pressure from the bleed valve, quick open and shut. Put a hose on it or cover it as fluid may come out under force.

If the wheel immediatley turns free, then its the master cylinder return hole. The caliper can be eliminated as it did its job and pulled the puck away from the rotor.

If releasing the pressure does not free up the brake, or only a little, then the caliper is hanging up and needs work.

And it could be some of both.

[dougan]

Okay, went out and did your test.  Not surprising, it didn't happen as bad, now that I *want* it to happen.  But I was able to stick a bit.  I did your test and not a whole lot changed.  When I turned the bleeder screw, a tiny bit of fluid came out but it didn't change the tension at all.  I also took this video (before my experiment) of the master cylinder, where it seems like the hole you guys describe is working.

June 22, 2012 5:41 PM

I know I'm low on fluid, I'll fix that when I bleed it all out.

After this experimenting, I'm starting to lean more towards it being a caliper problem. Would you guys agree?

Also, the thought occurred that I just need to adjust the calipers so the pads rest farther away from the rotor.  But right now, there's a lot of play in my brake handle, and I'm getting pretty close to the handlebar when I squeeze it.  Once I get through the play, it brakes fine, so I don't think there's a problem w/ the brake line.  I'm worried that adjusting the calipers this way will worsen this.  After taking a quick look, I wasn't able to find any way to adjust the handle.  I done any searching on this yet, but is there a way to adjust the brake handle?

[MCRider]

Interesting, a 1%er eh?

I'm not familiar with the 350F does it have a caliper adjuster? If so the dead pad, or Pad B, should have 5 thou of clearance between it and the rotor, not much. You shouldn't try to fix this with the adjuster. The more play you give Pad B, the more the lever must travel to engage pad A and B. Your thoughts on this are correct.

So HondaNut gets a score. The caliper should be disassembled, pads removed, piston removed, Oring replaced as it is the driver to pad retraction, the groove it fits in needs thorough cleaning. Might as well get some new pads.

[dougan]

Interesting, a 1%er eh?

That's how it always goes, isn't it?

[dougan]

Should I be getting the rotor turned if I replace the pads?  The rotor passes the eye test, but I know this isn't enough with a car...

[MCRider]

Should I be getting the rotor turned if I replace the pads?  The rotor passes the eye test, but I know this isn't enough with a car...

Generally not. it's hugely rare that one of those old boat anchors would go out of true. And a standard car brake place couldn't work with it anyway. I wouldn't suspect it unless i felt it in the lever, or knew it had a history of abuse.

There is a forum member that can grind them. But I'd put pads in it and see if you detect any pulse in the lever indicating out of true.

[dougan]

I bled out the brake line and took the caliper apart.  First off, caliper looks like this:


It already fell off by this point, but the piston was covered in rust gunk that must have fallen off the caliper.  I'm probably going to sand this rust down off the caliper.  How do I get the piston out?  My manual doesn't tell me much.  Maybe there's a better manual; I'm looking at the pdf on this site.  Should I re-fill the brake line and pump it out?  When I pushed the piston in, it wasn't smooth at all-- I had to put decent thumb pressure on it to get it to retract, and it wasn't a smooth movement like i've seen when using a C-clamp on car calipers.  No idea if this behavior is normal, but I could see the effort needed to move the piston being what's forcing the pads to rub on the rotor.

By the way, everyone probably already knows this, but I learned today that any time a service manual for a 40 year old vehicle uses the term "light tap" you're probably screwed.

Thanks so much for the help so far, you guys are awesome!

[camelman]

Yep, it's dirty...but you already figured that out.  You can pump the piston out by hooking the master cylinder up to it and pumping the handle until it pushes out.  Clean it up really well, replace the rubber ring if necessary, and reassemble.  If there is rust on the piston, then you might need to replace it.

[tomkimberly]

If you can, hook it back up and push (pump) it out using the master cylinder.

If not, you can use air but be careful as it will shoot out like a rocket unless you cover it up with a heavy rag, or the only way to get the most stuborn out, is to use a grease gun and fill it with grease. Messy, but it works.

Tom

[Johnie]

If you pump it out with the master, put a rag around the whole thing as when the piston pops out brake fluid will spray. You need to keep that off paint and out of your eyes. Plan on replacing the rubber seal which is in a groove on the caliper wall. It is only $4 or so at the Honda dealer and you may as well do it while all the parts are off. Send us a pic of the piston and we can tell you if it needs replacing.

[Bodi]

This is all entirely typical after 30+ years. Nothing major is wrong.
You should rebuild the m/c. The kit is available from Honda, as usual I like to get OEM parts but there are aftermarket kits. Disassembly is a bugger because of the retaining clip way down the hole but it IS possible, there are a lot of posts on this procedure. The kit is difficult to figure out - when you take the old parts out carefully record their order and orientation or take some pictures. You have to snap the rubber piston over the rod, this isn't really explained anywhere in the instructions. Wet the parts with brake fluid before reassembly. The bleed hole does get plugged but is easy to clean out.
The caliper looks to be OK. You won't know about the piston until it is out, if it is pitted then you want a new one, no "fix" is reliable and this is your primary brake - don't take many chances with it. The seal is the key to caliper pull-back. You need a new one. The seal groove is also very important and it gets corroded and full of gunk. This groove has to be completely cleaned out and that's not easy. The best way is with a dremel type tool and a brass circular brush wheel. Don't use steel - bits of steel get impacted into the alloy housing and rust causing more brake problems in a short time. Stainless steel is an option but brass is safest. You don't want to take alloy off, just remove the corrosion and crud build-up. Using a dentist type mirror you can inspect the groove. You want sharp corners and no globs of corrosion.
On reassembly of the caliper use brake system lube on the seal and a bit in the groove, plus a coating on the caliper cylinder past the groove toward the open end. Nothing in the "wet" are of the caliper cylinder. This should be clean but removing all traces of corrosion is not required.
If you need a new piston, there are stainless and phenolic replacements available - these will not corrode and pit like the chromed steel originals.
Using a speed bleeder is a good idea. These are stainless steel and make bleeding much easier than with the rust-prone OEM bleed screw.