ADVrider

Go Back   ADVrider > Bikes > Old's Cool > Airheads
User Name
Password
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 09-28-2013, 04:10 PM   #1
LandLeftBehind OP
Gnarly Adventurer
 
Joined: Feb 2012
Location: Maryland, 'merica
Oddometer: 138
dual front disc caliper rebuild

Im about to attempt rebuilding both of my front brake calipers on my 91' R100rt.

One disc is partially corroded where, Ive been told, the piston isnt making full contact with the disc. The rotor is a little out of true (0.007" - still within spec per Clymer), and this might be causing the problem, but I would like to rule out cheaper repairs prior to more expensive repairs. I figured I would do both calipers while Im at it, even though the other isnt showing signs of malfunction.

The Clymer manual mentions nothing of the cross-over brake line connecting the calipers (the solid one that runs under the fender). Are there any precautions I should be aware of before detaching these lines from the calipers?
__________________
We have left the land, and have embarked...
LandLeftBehind is offline   Reply With Quote
Old 09-28-2013, 04:18 PM   #2
Plaka
Brevis illi vita est
 
Joined: Jun 2010
Oddometer: 4,587
Wicked

Quote:
Originally Posted by LandLeftBehind View Post
Im about to attempt rebuilding both of my front brake calipers on my 91' R100rt.

One disc is partially corroded where, Ive been told, the piston isnt making full contact with the disc. The rotor is a little out of true (0.007" - still within spec per Clymer), and this might be causing the problem, but I would like to rule out cheaper repairs prior to more expensive repairs. I figured I would do both calipers while Im at it, even though the other isnt showing signs of malfunction.

The Clymer manual mentions nothing of the cross-over brake line connecting the calipers (the solid one that runs under the fender). Are there any precautions I should be aware of before detaching these lines from the calipers?
Corrosion. brake fluid Id hygroscopic. The water it attracts and dissolves corrodes the daylight out of things. As long as you are rebuilding the caliper, I would get generous with the heat when braking the lines loose. maybe start with a penetrant if you aren't going to get to it for a couple days.

Cleanliness is critical. Hose out the hard line with brake cleaner then shoot some WD 40 in it and put in a clean plastic bag. Spray with brake cleaner again on re-assembly, dry with compresses air, anti-sieze on the threads and don't over tighten. Better it leaks and you snug it a bit more then you strip it and things get....unpleasant.

A bent rotor can be straitened.

Pistons don't contact disks, brake pads do.

Corrosion is a chemical process. Do you mean erosion?

You are not attempting anything. You have succeeded. Work backwards from there..

P.S. Brake fluid is a fine paint stripper.

Plaka screwed with this post 09-28-2013 at 04:24 PM
Plaka is offline   Reply With Quote
Old 09-28-2013, 04:37 PM   #3
LandLeftBehind OP
Gnarly Adventurer
 
Joined: Feb 2012
Location: Maryland, 'merica
Oddometer: 138
Quote:
Originally Posted by Plaka View Post
Pistons don't contact disks, brake pads do.

Corrosion is a chemical process. Do you mean erosion?
Thanks for the tips. I was thinking of just leaving the lines in place, but I realize it might be better to remove them so they can be thorougly cleaned and protected from moisture.

This is what I mean by corrosion:



Several folks have told me this could be the result of a sticky piston.
__________________
We have left the land, and have embarked...
LandLeftBehind is offline   Reply With Quote
Old 09-28-2013, 04:47 PM   #4
Plaka
Brevis illi vita est
 
Joined: Jun 2010
Oddometer: 4,587
Quote:
Originally Posted by LandLeftBehind View Post
Thanks for the tips. I was thinking of just leaving the lines in place, but I realize it might be better to remove them so they can be thorougly cleaned and protected from moisture.

This is what I mean by corrosion:



Several folks have told me this could be the result of a sticky piston.
What do the faces of the pads look like for that wheel? You may have some stuff imbedded in them. Pics please.

What does the other side of the disk look like? More pics.

Is the shiny wear area deep or very shallow? Can you feel an edge with your fingernail between the shiny and dull areas? No pics of feeling disk. imagination will suffice.

Look at the back of that pad. See the thick steel plate? it rides on two guide rods. What condition are those in? Pics.
Plaka is offline   Reply With Quote
Old 09-28-2013, 04:59 PM   #5
disston
ShadeTreeExpert
 
disston's Avatar
 
Joined: Mar 2011
Location: Silver Spring, Md
Oddometer: 8,798
I would remove the caliper on the side that is showing the uneven wear pattern and clean it out. Take the piston out and clean it. Examine the insides for dirt and rust, pitting. And put it back together. Do the same thing on the other side. Install with new pads.

If there is any leaking of fluids or the pistons are badly pitted then get the rebuild kits.

The kits should be available with or with out pistons. Do not buy the kits until you know which kits are needed. If you buy the kits with out pistons you can not later add pistons. Pistons are available only in kits with seals.

edit; What I have posted above is the story on Ate brakes. I think you have Brembo's? The story about parts and what is available may be different. You can still do the cleaning before you buy a bunch of parts.
__________________
.
Never memorize something you can look up.
---Albert Einstein

Pay your debt, piratejohn.http://www.advrider.com/forums/showthread.php?t=949341
disston is online now   Reply With Quote
Old 09-29-2013, 02:58 PM   #6
LandLeftBehind OP
Gnarly Adventurer
 
Joined: Feb 2012
Location: Maryland, 'merica
Oddometer: 138
This is the other side of the rotor (taken from the left side of the bike).



Notice how the wear is on the opposite side of the rotor relative to the other side.



The corrosion doesnt catch my finger nail, but it sounds rougher as I scrape my finger nail across it.

Here are the pads:





They appear to be worn at a slight angle, if I get the rotor straightened should i not reinstall these?

The lockpins seem to be in fair condition, with only a bit of rust. They came out easily enough.
__________________
We have left the land, and have embarked...
LandLeftBehind is offline   Reply With Quote
Old 09-29-2013, 05:28 PM   #7
kaput13
Gnarly Adventurer
 
kaput13's Avatar
 
Joined: Nov 2010
Location: South Florida
Oddometer: 458
Quote:
Originally Posted by LandLeftBehind View Post
Are there any precautions I should be aware of before detaching these lines from the calipers?

The only precaution that you need to be aware of is - as already mentioned - the corrosive properties of brake fluid. Just take precautions in not allowing fluid to mar paint etc.

You really need to rebuild these calipers. It would be foolish not to. Easy to do. Just buy the right kit. Seals are easy to remove and install. The only difficulty is in removing the piston. Don't settle for vice grips or some other makeshift solution to dislodge it but use air with a towel or piece of wood to catch the bullet.
kaput13 is offline   Reply With Quote
Old 09-29-2013, 05:59 PM   #8
Plaka
Brevis illi vita est
 
Joined: Jun 2010
Oddometer: 4,587
Quote:
Originally Posted by LandLeftBehind View Post
This is the other side of the rotor (taken from the left side of the bike).



Notice how the wear is on the opposite side of the rotor relative to the other side.



The corrosion doesnt catch my finger nail, but it sounds rougher as I scrape my finger nail across it.

Here are the pads:





They appear to be worn at a slight angle, if I get the rotor straightened should i not reinstall these?

The lockpins seem to be in fair condition, with only a bit of rust. They came out easily enough.
I'm seeing full contact across the pad, but not full contact across the rotor. Suggests they are the wrong pads. In fact, I'd bet a chocolate bar on it.

if they are worn at an angle you can't re-use them any way. So you need new pads. I would get those and make very,very sure they are the correct pads for that bike. Put them in and begin the break in per the manufacturer. But just ride 25 miles or so. Then look at the contact pattern on the disk. You can put some radial lines on the disk with a sharpie, and rust ride around the block, braking as hard as possible. You will see how the lines wear off.

Do clean the disk well first with a scotchbrite pad and some alcohol. Scrub so all dirt is off.

When buying pads remember you have stainless disks. I would check out EBC pads. Decent price.


The pistons have tremendous pressure behind them. They won't stick going out. if there is a real problem, they will stick on the retract. They only move a very small amount---they should be riding the disk lightly. But they should not be dragging and a piston problem will cause that.

Things like rusty and pitted piston bores will chew up the seals. The pistons will leak.




if your new pads don't give a good contact pattern, you can use them (because they are still flat) to check for alignment issues. if the entire caliper were tipped, the contact would be at the inside on one side and the out side on the other. not what you have. if the caliper was twisted (or the entire fork lower) then you would see a heel/toe wear pattern on the pads.

You can also rotate the pistons. leave that check for after you do the new pads check.

You can also check for caliper distortion (although I would expect leaking at the seam between the caliper halves)

If you have a micrometer, I would check the disc thickness at the center and at the rim.
Plaka is offline   Reply With Quote
Old 09-29-2013, 08:49 PM   #9
LandLeftBehind OP
Gnarly Adventurer
 
Joined: Feb 2012
Location: Maryland, 'merica
Oddometer: 138
I really doubt they are the wrong pads because I never changed them, and this wasnt an issue until an accident I had last summer.

Because im almost positive the bent rotor is the source of my problems, Im considering just waiting to send the wheel/rotors for straightening prior to working on the brakes. That way I can also rebuild the forks when I take the brakes apart (I was having some fluid leakage the previous summer).
__________________
We have left the land, and have embarked...
LandLeftBehind is offline   Reply With Quote
Old 09-29-2013, 09:42 PM   #10
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 8,665
Something is seriously not right. What would take more and better pictures of the rotors, forks, calipers, ALL the parts holding in the pads and a description of how they were holding the pads in, wheel spacers and whatever else might not be right. I suspect the pads were not in place correctly for some reason?

Straighten the rotor? Who? I would just get a new one unless the picture unfolds somehow a lot better than it looks now.

There is no reason to flush the lines with anything other than brake fluid. There are GOOD reasons not to. Good brake practice is to not let anything but brake fluid and brake cleaner close to your setup. No need for anti-sieze or anything else. It contaminates the brake fluid. The thing you really need is the right tool which no one has mentioned: Line wrenches! Regular open end wrenches will distort the line nut and then it will leak no matter how much more you tighten it and distort it! I am hoping you are keeping your waders on around here!

Once again, the condition of the piston bores does not matter. The piston seal is stationary. It does not move in the bore and the pistons themselves do not even come close to touching the bore. Corrosion on the pistons matters little too unless it is where the seal rides on the piston during the life of a pad.

Pistons can and do stick in place and won't come out but retracting is a much more common problem.
supershaft is offline   Reply With Quote
Old 09-29-2013, 10:00 PM   #11
Plaka
Brevis illi vita est
 
Joined: Jun 2010
Oddometer: 4,587
Quote:
Originally Posted by LandLeftBehind View Post
I really doubt they are the wrong pads because I never changed them, and this wasnt an issue until an accident I had last summer.

Because im almost positive the bent rotor is the source of my problems, Im considering just waiting to send the wheel/rotors for straightening prior to working on the brakes. That way I can also rebuild the forks when I take the brakes apart (I was having some fluid leakage the previous summer).
sounds like a good plan. Except rebuilding the brakes. Do everything else first. You don't want to go into them unless you know positively they are bad. I never go into a brake cylinder before it dies. That means badly cracked rubber on the outside or leekage from around the piston seal. You see it (loss of fluid) before you are in brake failure land. but fix it as soon as you see it. With the pads out, very gently squeeze the lever to extrude the pistons slightly. Go too far and you can trash the seals. Then try squeezing the pistons back by hand. Two hands. See how they feel. it's not unusual to use a c-clamp to compress pistons and you can try that if they don't move by hand. but just see if they are smooth,.

you still need to replace the pads tho'. Don't try grinding them flat to milk more life out of them. Spend the fat insurance check from the crash on nice new pads. if you want more serious brakes fit iron rotors. but those brakes should be plenty if they are anything like my old K bike. Wish I had a set.


The typical symptom of a warped rotor is chattering or pulsing. You will see a wear paterns that's unever around the disk, not from the inside to the outside.


possibly the calipers are spreading? They would spread more on the outside than the inside so less braking at the rim. But they would have to be permanently distorted to get what you are seeing. Check with the new pads. put them in, squeeze lightly and see if they are touching towards the inside of the disk but not near the rim. Then rotate the pistons 180 (both) and check again.

Plaka screwed with this post 09-29-2013 at 10:09 PM
Plaka is offline   Reply With Quote
Old 10-02-2013, 07:59 AM   #12
LandLeftBehind OP
Gnarly Adventurer
 
Joined: Feb 2012
Location: Maryland, 'merica
Oddometer: 138
I cleaned up the pins yesterday, brushing all the dust off of them, and geeze - they are chewed up - one more than the other. They are still straight, and fit into the calipers like they should, they are just really pitted. Not with rust either - just looks like a surgeon in the civil war gave them to his patients to bite down on while he amputated limbs.

I wonder if that is a symptom or a cause. Eitherway they are going to be replaced.
__________________
We have left the land, and have embarked...
LandLeftBehind is offline   Reply With Quote
Old 10-02-2013, 08:28 AM   #13
H96669
A proud pragmatist.
 
H96669's Avatar
 
Joined: Nov 2009
Location: Hiding off Hwy 6, B.C.
Oddometer: 4,462
Are you checking the rotors "as found" on the wheel??? I had one on a GS that showed really close to the max deflection allowed. Removed it and carefully cleaned the mounting surfaces, back on the wheel and then well within specs. Had to check it carefully as I sold it later, did not want a new owner to experience pulsing.
__________________
Have tools, will travel!
H96669 is online now   Reply With Quote
Old 10-02-2013, 09:50 AM   #14
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 8,665
Quote:
Originally Posted by LandLeftBehind View Post
I cleaned up the pins yesterday, brushing all the dust off of them, and geeze - they are chewed up - one more than the other. They are still straight, and fit into the calipers like they should, they are just really pitted. Not with rust either - just looks like a surgeon in the civil war gave them to his patients to bite down on while he amputated limbs.

I wonder if that is a symptom or a cause. Eitherway they are going to be replaced.
Something is not right. I hope you have someone with experience look at that. Or at least more pictures here so we can figure out what is going on. That stuff can hurt you!
supershaft is offline   Reply With Quote
Old 10-02-2013, 07:28 PM   #15
LandLeftBehind OP
Gnarly Adventurer
 
Joined: Feb 2012
Location: Maryland, 'merica
Oddometer: 138
Quote:
Originally Posted by supershaft View Post
Something is not right. I hope you have someone with experience look at that. Or at least more pictures here so we can figure out what is going on. That stuff can hurt you!
Thanks for your help SS. My hunch is that this all is due to a warped rotor that could have happened last summer when I met a deer on the highway. The brake pulsing is quite evident, especially during moderate/hard braking. Your opinion is very much appreciated though.

Here are the pins:





Want to see anything else specifically?

H96669 - Im not sure I catch you - are you saying a dirty rotor can cause pulsing? I havent cleaned mine thorougly ever...
__________________
We have left the land, and have embarked...
LandLeftBehind is offline   Reply With Quote
Reply

Share

Thread Tools Search this Thread
Search this Thread:

.
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


Times are GMT -7.   It's 07:35 PM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014