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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Filmcamera on January 16, 2018, 01:18:30 PM
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I recently replaced my very old worn front brake discs with new EBC ones, I also fitted new brake pads.
Since then I have noticed my front wheel was binding because the brakes were remaining on slightly.
I have cleaned everything and checked the pads move freely etc - the wheel also spins freely when the calipers are off so the wheel bearing is not the issue.
Today I finally bit the bullet and took the calipers apart and removed the pistons. That showed me the issue, I think. The very last mm or two of the pistons are slightly scuffed and scratched, so I am thinking they do not recess all the way back and since the discs and the pads are new they remain touching when the brakes are off.
So now, finally, my question, is it worth trying to sand the pistons with very fine paper, 400 or 600 grit wet and dry, or should I just accept the inevitable and order new pistons from motobins? The 16v kit of pistons and seals are £56.50 each so by the time they are shipped and I have paid the taxes here in CR I am looking at $220 to put new ones in, which is quite steep, it will also take two or three weeks for them to get here which is a big chunk of the remaining dry season here.
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You need to pull them apart and post pictures of the damage. Until you post pictures it would be hard to recommend sanding without a visual reference.
Regards Martin.
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Here you go
The first pic is the worst damage, I have already had a go at sanding with some success - I think.
(http://www.motobrick.com/gallery/0/3823-160118145220-8771178.jpeg)
(http://www.motobrick.com/gallery/0/3823-160118145220-8771420.jpeg)
(http://www.motobrick.com/gallery/0/3823-160118145225-8822113.jpeg)
That should give you a general idea. I did notice that the pistons in no way all come out at the same time which is also an issue. I am in the middle of cleaning everything to see if it gets better.
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I'd try sanding them, but if you have the original brake lines it may be time to replace them. I've heard of the insides flaking off and blocking flow, could lead to binding.
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Pictures of the bores would also be good. Your first picture shows what looks more like a gouge than a scratch. :dunno
Regards Martin.
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I have replaced the brake lines already. I never had this problem with the old discs and worn pads but there again the pistons were much further out so not right at the edge where the damage is/ It looks like someone grabbed the pistons with a pair of pliers or something to pull them out :musicboohoo:. I have sanded and cleaned everything and will put it all back together and see how things are. Also I had to grind part of the shoulder of the chineses pads I had brought away to make them fit properly, I have ordered some EBC replacements to see if that is part of the issue as well
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perhaps instead of buying "chinese pads" and having to grind them down to fit might be a clue as to why they are not performing correctly. sounds like you are trying to make a part fit your bike that wasn't designed to fit it.
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They were designed for my bike, just the fit was not great. I got them because others on this site have used them successfully. Anyway EBC pads on the way, I am hoping that will help.
https://www.ebay.com/itm/1989-1992-BMW-K100RS-16-valve-Front-Rear-Brake-Pads/161709597631?hash=item25a6a4a3bf:g:A-4AAOSwyGZaRy-e&vxp=mtr (https://www.ebay.com/itm/1989-1992-BMW-K100RS-16-valve-Front-Rear-Brake-Pads/161709597631?hash=item25a6a4a3bf:g:A-4AAOSwyGZaRy-e&vxp=mtr)
Here is a link to the pads - at less than $15 for front and rear pads they were worth a shot, the EBC ones I just brought cost me $63 just for the front.
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i look forward to any updates. good luck
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I have totally stripped and cleaned the brakes and the pistons etc.
They are better than before but still not great.
Here is a video to show how much they are binding still
https://youtu.be/n6bpGJaQ-kM (https://youtu.be/n6bpGJaQ-kM)
Next step is the EBC pads and if that doesn't help then new pistons, seals etc.
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Is it possible that the Chinese pads are a tad too thick............Or is it me :dunno
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No I don't think it is that. When I rebuilt the calipers and first mounted them before bleeding etc when the pistons are all the way in then the wheel spins freely. It is only when I have bled the system and the pistons come out a little to touch the pad that they start to bind, This seems to indicate that the pistons are not retreating far enough when the brake lever is released. I am pretty sure at this point that I am going to have to install new pistons but I will try the EBC brake pads and maybe even just live with it until the pads have worn down enough for the issue to go away, it is not like I ride around scraping knee so having the front brake slightly on all the time, while not ideal, will probably not kill me.
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You will not be doing your rotors any favours, they will wear more and overheat. You could also overheat your brake fluid resulting in reduced or no braking in a critical time. :musicboohoo: :falldown:
will probably not kill me.
It could.
Regards Martin.
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Yes it could but the less lean angle I have the less the brakes being slightly on matters.
I will probably end up biting the bullet and ordering new pistons - sigh
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STOP!
Check the fluid passages in the master cylinder. There are two passages one is a pressure compensation passage for changes in ambient air pressure, if it is plugged the pistons will not retract due to fluid pressure. Hope that is helpful.
Les :bmwsmile
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STOP!
Check the fluid passages in the master cylinder. There are two passages one is a pressure compensation passage for changes in ambient air pressure, if it is plugged the pistons will not retract due to fluid pressure. Hope that is helpful.
Les :bmwsmile
I was thinking the same thing, but if it wasn't happening before the caliper work, it probably isn't.
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Thank you for a great suggestion. I was away this weekend giving back the Triumph Speed Triple I have had for a few months (I will miss that bike :musicboohoo:) but will take a look next week. I actually have a master cylinder rebuild kit so I will use it - I had also ordered the pistons already so between the two and the new EBC pads I really hope to fix the issue once and for all.
Meanwhile I have a new LHS front indicator lens being made, I am very interested to see how it comes out. In theory I get it next week but that does not take into account the famous 'Tico time'. As I was told when I first got here - 'manana doesn't mean tomorrow, it just means not today'...
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Filmcamera see if you can find out how they do it. Is it with a proprietary kit, or are they melting down old lenses with acetone as suggested by a mate of mine.
Regards a curious Martin.
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I will try and find out, they did ask me to provide the housing as well since they cannot do injection molding so cannot make the little lip that goes under the housing and are going to try and find another way to mount the lens
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. . . I actually have a master cylinder rebuild kit so I will use it - . . .
Have you looked at this thread (http://www.motobrick.com/index.php/topic,7738.msg54905.html#msg54905)? It could be relevant.
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It looks very relevant for sure. Thank you
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There are two holes, the smallest one is the compensation passage (outlet side of MC).
Quick fix: 1) Remove all brakefluid from reservoir, use a piece of paper towel to remove last drop of fluid so you can observe the next step. 2) Pass a very fine piece of music wire (0.30 mm) through the smallest passage to unblock it (photo). 3) Pull the brake lever slowly, if you are successful, fluid will pass through the hole into the reservoir. 4) Refill reservoir with new brakefluid and test brakes.
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Thank you for a great suggestion. I was away this weekend giving back the Triumph Speed Triple I have had for a few months (I will miss that bike :musicboohoo:) but will take a look next week. I actually have a master cylinder rebuild kit so I will use it - I had also ordered the pistons already so between the two and the new EBC pads I really hope to fix the issue once and for all.
Meanwhile I have a new LHS front indicator lens being made, I am very interested to see how it comes out. In theory I get it next week but that does not take into account the famous 'Tico time'. As I was told when I first got here - 'manana doesn't mean tomorrow, it just means not today'...
The Speed triple is quite an animal. I always thought when people said that a bike likes to be ridden hard, they were talking complete Bollox until I rode the speed triple. It was difficult to ride sedately. Slight twitch on the wrist and boom.
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Update on the whole pulsing brakes situation
I installed new pistons and cleaned everything very thoroughly, same problem. I took the bike to a BMW mechanic, same problem. I had long talks with EBC and eventually they very kindly sent me two brand new discs and new pads for free (except for the $125 I had to pay in tax when they arrived here :musicboohoo: ). Last week I very very carefully installed it all. The mating surfaces on the wheels are spotless and smooth, everything was torques in two steps using a criss cross pattern etc etc. In other words I took every precaution I could think of.
The good news is the brakes do no pulse The bad news is they drag so badly I cannot spin the front wheel more than 1/4 of a turn by hand. I have now riden about 70 miles and the situtaion is not improving.
I know a certain amount of drag is normally, especially with new discs and pads but how much is too much?
With the pistons all the way out the wheel spins freely, but when I pump the brakes the pistons clearly do no quite retract enough. My theory is because the pads and discs are new the pistons need to be seated very nearly all the way into the calipers when the brakes are released. That means, I imagine, more resistance from more piston in the caliper. Is there a fix or is it just a matter of waiting for the pads to bed in a little more?
I have checked that the return holes in the master cylinder are clear.
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greetings...
ride it till the new disks glow red... spray it off with cold water till cool to the touch... repeat till the disks stop glowing red...
j o
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I took the new pads out this morning to see how they are
(http://www.motobrick.com/gallery/1/3823-150618130508-13681916.jpeg)
It seems both the inside pads are being worn unevenly (they are the top pads in the photo) , like the pistons are not coming out straight or something.
Has anyone seen this before?
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Switch the less worn with the more fully worn in each caliper, then keep riding. Please report back in 1000Km.
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If you have pulsing are you sure you used the proper procedure during install?
My pulsing problem was 99% fixed by this simple advice from in the thread below:
... follow the torque pattern, but not all at once; rather, increase torque values two to three times, i.e. Pattern to initial contact and set, then 25% of rated torque, then 75%, and then final torque.
http://www.motobrick.com/index.php/topic,9679.msg82067.html#msg82067
I'd recommend trying this first before moving on to other, non-installation-related issues.
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Yes I used a the proper procedure and even took the bike to a BMW shop and they reinstalled them and had the same issue, I think that is why in the end EBC gave me new discs under guarantee.
With the new discs installed I have no pulsing but huge amounts of dragging. I put in a new piston and spring in the master cylinder to see if that helps, I will not know though until I get my new clutch cable and can ride again.
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FC with the bike supported with the front wheel of the ground, when you rotate the wheel observe the dragging. With the line to the master cylinder disconnected does it still drag.
Regards Martin.
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FC with the bike supported with the front wheel of the ground, when you rotate the wheel observe the dragging. With the line to the master cylinder disconnected does it still drag.
Regards Martin.
When I reinstall the pads with the pistons all the way back the wheel spins freely. However if I then pump the brakes to get some feel in the brake lever then when the lever is released the wheel drags badly when I try to spin it.
Sent from my SM-G935F using Tapatalk
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FC the problem might not be in the calipers it might be in the master cylinder. It could still be applying slight pressure pushing the pads out.
Regards Martin.
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That is what I thought so I replaced the piston and spring over the weekend.
Sent from my SM-G935F using Tapatalk
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:2thumbup: Hopefully, live in hope die in despair. Due to the way master cylinders work it is sometimes hard to analyse whats going on without putting a pressure gauge in the line. This in itself can be problematic trying to patch a gauge in with various fittings.
Good luck regards Martin.
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When I reinstall the pads with the pistons all the way back the wheel spins freely. However if I then pump the brakes to get some feel in the brake lever then when the lever is released the wheel drags badly when I try to spin it.
Sent from my SM-G935F using Tapatalk
Stupid question, like " did you check if your #@%^ is plugged in, but is the lever returning freely after brake application. ?
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When the brakes are binding does brake fluid release under pressure if the bleeder is cracked open?
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Stokester - no the bleeding process seems normal, pushing the pistons back in all the way does seem very hard either, when I took the pads off I mean.
Beemuker - yes the brake lever itself is fine
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My next move is going to be taking off the old bobbins from the old disc - actually they are brand new stainless steel ones from motobins - and installing them on the first pair of EBC discs that were replaced under warranty. The reason is both sets of new discs from EBC basically float not at all, not even 0.1mm so I am hoping with bobbins that let the discs move more the dragging might go away.
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The reason is both sets of new discs from EBC basically float not at all, not even 0.1mm so I am hoping with bobbins that let the discs move more the dragging might go away.
According to the EBC site, they don't need to move, Filmcamera. Read here (https://ebcbrakes.com/articles/the-facts-about-floating-motorcycle-rotors-or-discs-by-ebc-brakes/) under Two Piece Rotor.
I'd continue exploring the ability of the seals to retract the pistons sufficiently. The pistons were scratched; you smoothed the scratches but they might have already damaged one or more of the seals just enough to impede the ability of the seal to lessen pressure on the piston. If just one seal keeps the pressure on, that might explain the difference in wear on the pads. Pressure on more than one piston might be the cause of the friction in your video.
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... I have checked that the return holes in the master cylinder are clear.
Did you visually check only? Did you try to clean the holes anyways, even though they may have looked clean and in order?
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Laitch. I ended up replacing the pistons and seals so they should be ok
RBM yes I actually cleaned them as well as visually inspecting them.
I am also thinking of taking the brake lines and calipers to a shop with an air line and having them blown through in case there is some junk in there.
Sent from my SM-G935F using Tapatalk
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According to the EBC site, they don't need to move, Filmcamera. Read here (https://ebcbrakes.com/articles/the-facts-about-floating-motorcycle-rotors-or-discs-by-ebc-brakes/) under Two Piece Rotor.
I'd continue exploring the ability of the seals to retract the pistons sufficiently. The pistons were scratched; you smoothed the scratches but they might have already damaged one or more of the seals just enough to impede the ability of the seal to lessen pressure on the piston. If just one seal keeps the pressure on, that might explain the difference in wear on the pads. Pressure on more than one piston might be the cause of the friction in your video.
I was thinking along the same line, many people don't realize that the square cut seals actually retract the pistons after a brake application.
Unless I've missed something here; the brakes are dragging after application and there is no fluid pressure at the bleeder. That to me means the issue is not with the lines and master cylinder because the pressure is releasing with the lever. If the rotors and pads are correct for the installation then the pistons are not retracting properly.
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Yes that is correct, the pistons are not retracting correctly. This was not an issue with the old rotors, I think because they were very worn so thinner and the pads were old as well meaning that even fully retracted after braking the pistons were still a couple of mm proud of the caliper body. So it seems that the pistons retract fine up to a certain point but then stop. To be 100% honest I am actually considering taking a set of pads to a shop and having then mill 2mm off them! I bet that would fix the issue...
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Is the lever firm or spongy? Does the lever if pressure is applied slowly pull back towards the handlebar?
Regards Martin.
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The lever is firm and yes it applies pressure if pulled back slowly towards the bars.
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Second question was, if continuous pressure is applied to the lever does the lever remain firm or does it slowly creep back to the bar?
Regards Martin.
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Ah ok, I just checked and it remains firm, no creeping back to the bar - unlike me on some Friday nights...
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You fitted new pistons and seals, however what condition were the caliper bores in?
Regards Martin.
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THey were ok, nothing great. I did what I could to clean them up using very fine grip sandpaper - 600 I think it was. The issue was that when I took some parts to be powder coated the idiot powder coated the mating sides of the calipers as well so I had to do a lot of cleaning and sanding to get all that rubbish off them. Maybe there is still more work to do. Maybe I need to go back in and do some more, good call.
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If you go back in measure the bores, and also do a check for ovality. Do measurements across the bores all the way around at 45 degree increments. Check for scratches and scoring in both the vertical and horizontal planes.
Regards Martin.
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My thought is that you’re on the right track concerning the powder coating. All evidence points to the calipers themselves and since the coating is a new feature...