Author Topic: Brakes sticking  (Read 14263 times)

Offline Filmcamera

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Re: Brakes sticking
« Reply #25 on: June 15, 2018, 01:07:17 PM »
I took the new pads out this morning to see how they are





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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Offline Laitch

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Re: Brakes sticking
« Reply #26 on: June 15, 2018, 01:48:56 PM »
Switch the less worn with the more fully worn in each caliper, then keep riding. Please report back in 1000Km.
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Offline Motorhobo

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Re: Brakes sticking
« Reply #27 on: June 18, 2018, 11:02:35 AM »
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.
1994/1995 K75 ABS Frankenbike: original engine 136k miles, frame from Gary Weaver (RIP), 173k miles -- Current Odometer: 193k miles
1994 K75 since 2013, 76,000 mi (11k mine) w/California Sidecar Friendship II Sidecar & Black Lab 'Miss B'

Past: 1974 Honda 550/4 (first bike), 1994 K75 (sold), 1995 K75 ABS (parts bike), Sidecar Dog & Best Bud 'Bo' - RIP

Offline Filmcamera

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Re: Brakes sticking
« Reply #28 on: June 18, 2018, 11:18:02 AM »
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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Offline Martin

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Re: Brakes sticking
« Reply #29 on: June 18, 2018, 03:31:53 PM »
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.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Filmcamera

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Re: Brakes sticking
« Reply #30 on: June 18, 2018, 03:35:30 PM »
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. 

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Offline Martin

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Re: Brakes sticking
« Reply #31 on: June 18, 2018, 03:51:05 PM »
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.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Filmcamera

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Re: Brakes sticking
« Reply #32 on: June 18, 2018, 03:52:53 PM »
That is what I thought so I replaced the piston and spring over the weekend.

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Offline Martin

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Re: Brakes sticking
« Reply #33 on: June 18, 2018, 04:02:43 PM »
 :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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Offline beemuker

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Re: Brakes sticking
« Reply #34 on: June 18, 2018, 07:04:06 PM »
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. 

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Stupid question, like " did you check if  your #@%^ is plugged in, but is the lever returning freely after brake application. ?
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Offline stokester

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Re: Brakes sticking
« Reply #35 on: June 18, 2018, 07:36:33 PM »
When the brakes are binding does brake fluid release under pressure if the bleeder is cracked open?
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Offline Filmcamera

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Re: Brakes sticking
« Reply #36 on: June 18, 2018, 07:41:52 PM »
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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Offline Filmcamera

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Re: Brakes sticking
« Reply #37 on: June 18, 2018, 07:57:21 PM »
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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Offline Laitch

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Re: Brakes sticking
« Reply #38 on: June 18, 2018, 08:53:59 PM »
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 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.
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles
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Offline rbm

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Re: Brakes sticking
« Reply #39 on: June 18, 2018, 08:57:29 PM »
... 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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Offline Filmcamera

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Re: Brakes sticking
« Reply #40 on: June 18, 2018, 09:13:36 PM »
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.



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Offline stokester

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Re: Brakes sticking
« Reply #41 on: June 19, 2018, 09:57:13 AM »
According to the EBC site, they don't need to move, Filmcamera. Read here 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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Offline Filmcamera

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Re: Brakes sticking
« Reply #42 on: June 19, 2018, 11:28:07 AM »
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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Offline Martin

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Re: Brakes sticking
« Reply #43 on: June 19, 2018, 02:55:02 PM »
Is the lever firm or spongy? Does the lever if pressure is applied slowly pull back towards the handlebar?
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Filmcamera

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Re: Brakes sticking
« Reply #44 on: June 19, 2018, 03:15:12 PM »
The lever is firm and yes it applies pressure if pulled back slowly towards the bars.



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Offline Martin

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Re: Brakes sticking
« Reply #45 on: June 19, 2018, 03:19:21 PM »
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.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Filmcamera

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Re: Brakes sticking
« Reply #46 on: June 19, 2018, 03:31:03 PM »
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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Offline Martin

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Re: Brakes sticking
« Reply #47 on: June 19, 2018, 03:58:51 PM »
You fitted new pistons and seals, however what condition were the caliper bores in?
Regards Martin.
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  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Filmcamera

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Re: Brakes sticking
« Reply #48 on: June 19, 2018, 04:28:19 PM »
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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Offline Martin

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Re: Brakes sticking
« Reply #49 on: June 19, 2018, 05:27:57 PM »
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.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

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