Brakes sticking

[Filmcamera]

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.

[Martin]

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.

[Filmcamera]

Here you go

The first pic is the worst damage, I have already had a go at sanding with some success - I think.







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.

[Chaos]

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. 

[Martin]

Pictures of the bores would also be good. Your first picture shows what looks more like a gouge than a scratch. :dunno
Regards Martin.

[Filmcamera]

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

[blackie1]

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.

[Filmcamera]

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

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.

[blackie1]

i look forward to any updates. good luck

[Filmcamera]

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



Next step is the EBC pads and if that doesn't help then new pistons, seals etc.

[Skunky]

Is it possible that the Chinese pads are a tad too thick............Or is it me   :dunno

[Filmcamera]

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.

[Martin]

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.

[Filmcamera]

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

[lmiklosy]

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 

[beemuker]

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 

I was thinking the same thing, but if it wasn't happening before the caliper work, it probably isn't.

[Filmcamera]

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'...

[Martin]

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.

[Filmcamera]

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

[Laitch]

. . .  I actually have a master cylinder rebuild kit so I will use it - . . .

Have you looked at this thread? It could be relevant.

[Filmcamera]

It looks very relevant for sure.  Thank you

[lmiklosy]

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.

[Skunky]

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.

[Filmcamera]

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.

[johnny]

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