Topic: Help rebuilding brake caliper

[BradyN]

Hey guys, I'm about half way finished rebuilding my front brake caliper ('78 cb550k). I just have a couple questions, and a bunch of pictures in case that helps other people doing this for the first time too.

Here it is all taken apart:

Brake pads are very smooth, except for a groove in one of them. Looks like there's plenty of life left in them though:

Piston looks clean, but has a narrow bad around it with little pits;


Here's everything all cleaned up. I coated the caliper bolts in naval jelly, but decided not to clean anything else with it because I don't know what the bolts are made of or plated with. The rest of the bolts I just scrubbed with a wire brush and wd40:


Is the groove clean enough? It's smooth to the touch, but the discoloration doesn't seem to be going anywhere:


And finally, here are the new brake pads:


Questions:
Do you think the inside caliper looks clean enough? I've been scrubbing with a wire brush and simple green.

Should I prep the new pads at all? Do I need to sand the paint off the sides, or bevel the edges of the brake pad? Maybe I should just use the original brake pads?

Can I reuse the cotter pin for the right side brake pad, or should I get a new one?

I was surprised the piston didn't look worse, but I got a phenolic piston to replace it with. Thanks for your help with this, I just want to make sure I don't royally screw up one of the most important safety mechanisms on the bike...

[540nova]

Definitely lightly sand the black paint on the pad side, they are known to bind up. A little grease on the side would not hurt, either.


1974 CB450, 2006 CBR1000RR

[BradyN]

Okay, will do. I have silicone high vacuum grease to use as well.

I also took apart the swinging arm that the brake hinges on. What kind of grease should I use on the hinge? There are two O-rings on both ends of the hinge. Should I use silicone grease like on the brake pads or some kind of more traditional engine grease? Thanks

[flybox1]

There are multiple threads about this same topic:

http://forums.sohc4.net/index.php?topic=56544.msg610718#msg610718
  Lets' review.
There are four products needed to restore a caliper.
1. Brake cleaner
2. Brake parts assembly lube for the caliper seal only.
3. Dow corning High vacuum grease.
4. Brake fluid

Each has it own specific application and needs for the task to be performed.

#1 is used to get everything clean.  (given the confusion, it had to be said)
#2 is used ONLY on the seal and must be compatible with #4, as some of it will invade the brake fluid chamber.
#3 is NOT used on the seal, as that would put silicone inside the brake fluid chamber.  This is a bad thing as the compounds are incompatible.  It is used behind the brake pads and a thin coat is used on the parts of the calipers and piston that are exposed to the elements and subject to water ingression.  The Dow Grease will not mix with ANYTHING.  It is a simple barrier with the very important property that it will NOT melt when the parts get hot and then run/creep into the brake pad friction material and provide lubrication between pad and disk rotor.
#4 is what makes the hydraulic part of the brake function. (I hope that part is clear.)

Cheers,

[flybox1]

A light coating of general use blue grease on the pivot is all you need.  new orings there too, of you have some thatll fit.
Dow corning vacuum grease only as it has the comp to withstand high brake temps before it runs.

[Bailgang]

If it were mine I'd toss the piston and get a new one, all it takes is one little nick from those pits while installing it and you may ruin your new seals and I'd go ahead and put new pads in while I was at it. Yes I know you may be on a tight budget and you may be able to get away just fine with the piston and pads you have but I'm just sayin that's how I would do it "IF" it were mine. I rebuilt the caliper on my kids 73 750 years ago with it's piston in similar shape as yours and it did actually work OK but it worked even better when my kid finally spent the $ for a new piston and another rebuild kit.

[Phinn]

Definitely replace the pads and that piston.  Those pits are right where the seal sat for who knows how long, with moisture trapped under it. 

The groove looks fine from what is visible in the photo.  Clean and smooth is good.  I don't think "discoloration" matters too much. 

My pad looked like that, and I had to sand it to the point that it removed all the black paint around the edges.  The pad needs to be free-moving, but not loose.   Very important: when dry-fitting the pad, do not press the pad into the caliper while the piston is out.  The pad can get stuck, and with no piston behind it, it would be very hard to extract it out without damaging it.  Ask me how I know. 

Be sure to clean both the caliper arm pivot pin and the holes of the brackets.  I think general use grease is fine, as far as I know.

Also, if you've ordered the phenolic, they usually are designed to work without the white spacer ring.  You can leave that out.

[BradyN]

Thanks for the info/ links.

I have Dow Corning vacuum grease to seal around the brake pad/piston (it's a new phenolic resin piston). I'm going to use just brake fluid on the seal itself, couldn't find brake assembly lube. The new brake pads seem to fit in without rubbing too much, so maybe I won't have to sand them.

I will buy some "general use blue grease" for the pivot. Can I reuse the O-rings? I didn't order any new ones.

I would also like to remove the front wheel while I'm taking things apart, so I can clean it. I noticed with all the brake parts off the wheel moves side to side a couple of millimeters on the axel. Is this normal?

wheel pushed to the right:

wheel pushed to the left:


Thanks for the help, sorry about all the beginner questions.

[Phinn]

I'm going to use just brake fluid on the seal itself, couldn't find brake assembly lube.

Maybe someone with more experience can answer, but when using a steel piston, I don't understand why you'd want to use brake fluid to lube the seal, since brake fluid retains moisture ... which then eats rusty pits into the piston.  It seems like the piston-seal connection should either be (a) dry or (b) lubricated with something that's waterproof. 

But, since your piston is made of resin, it's a non-issue. 

The new brake pads seem to fit in without rubbing too much, so maybe I won't have to sand them.

As long as they move in and out freely, they're fine.  I manage to get brake fluid all over everything no matter what I do, which causes the paint to bubble and flake, so sanding the paint off of brake parts seems like a safe bet, but if yours fit while painted, then roll with them. 

Can I reuse the O-rings? I didn't order any new ones.

If they're intact, I guess so.  They appear to me to be almost 100% ineffective anyway.  My plan is to just disassemble and re-grease the caliper arm's pivot pin once a year no matter what. 

[flybox1]

the lateral play along that front axle...not safe.
Check everything for tightness.  might be an issue with your bearing, internal bearing spacer(or lack thereof) or axle spacer stack .

[BradyN]

the lateral play along that front axle...not safe.
Check everything for tightness.  might be an issue with your bearing, internal bearing spacer(or lack thereof) or axle spacer stack .

Okay, I didn't notice this until I took the brake caliper off. I think I'll drop the front wheel off and try to see what might be wrong.

Thanks again for all the help everyone.

[Stev-o]

the lateral play along that front axle...not safe.

+1...something is not right

[BradyN]

the lateral play along that front axle...not safe.

+1...something is not right

I'm surprised I didn't notice it while riding or when I checked the play of the wheels before. Could it be because the fender is not bolted on because I removed the brake? How should I troubleshoot this? I have to take the wheel off anyway to put the brake caliper back on.

[DaveBarbier]

Maybe someone with more experience can answer, but when using a steel piston, I don't understand why you'd want to use brake fluid to lube the seal, since brake fluid retains moisture ... which then eats rusty pits into the piston.  It seems like the piston-seal connection should either be (a) dry or (b) lubricated with something that's waterproof. 

That's what the brake assembly fluid is for. It won't contaminate the brake fluid on the inside of the caliper and it won't absorb water from the air on the outside because it's not hygroscopic.

[Stev-o]

the lateral play along that front axle...not safe.

+1...something is not right

I'm surprised I didn't notice it while riding or when I checked the play of the wheels before. Could it be because the fender is not bolted on because I removed the brake? How should I troubleshoot this? I have to take the wheel off anyway to put the brake caliper back on.

No, would not have anything to do with fender.  First thing I would check is the axle nut. Is is screwed on all the way?

[BradyN]

the lateral play along that front axle...not safe.

+1...something is not right

I'm surprised I didn't notice it while riding or when I checked the play of the wheels before. Could it be because the fender is not bolted on because I removed the brake? How should I troubleshoot this? I have to take the wheel off anyway to put the brake caliper back on.

No, would not have anything to do with fender.  First thing I would check is the axle nut. Is is screwed on all the way?

I think that was it. I tightened the axle nut and that space went away.Couldnt get the speedo cable off so I installed the brake with the wheel on... what a pain in the ass. I got a little discouraged because this is one of the easier things to do on the bike I'm sure. But I got it on there. Bled the brakes a bit, seems to work better already.