NC750x rear brake no pressure

[Guest eifionglyn]

Hi,

 

Just gave the brakes on my 2016 NC750x a clean today before going back to work and now I have no pressure on the rear brake. Front is fine. I commute year round so need to be able to keep the calipers clean, never had this issue with other bikes I've done. I took the caliper off, didn't disconnect any lines, took the pads out then pressed the pedal gently to get the piston to protrude out a bit. Cleaned it with an old toothbrush followed by some brake cleaner, then pushed the piston back into the caliper - only by hand, no clamps or screwdrivers!. Pads back on, remount the caliper and I have no pressure building up on the rear brake pedal, no matter how much I pump the pedal. Tried bleeding the brakes, doesn't seem to have made any difference. Took the caliper off and back on again, to make sure it's mounted correctly, it is as far as I can tell. I did notice though the forward caliper mounting bolt is very hard to screw back in, despite application of copper grease, much tougher than it was to undo. Haven't cross threaded it (I'm pretty sure, when that happens it's tough then get suddenly very easy and turns forever - the bolt screws home alright, just a big effort to get it to do).

 

Things I've read on other forums - not NC specific - but not tried yet:

1. Take off the cap of the brake fluid reservoir, rubber cap might seal too well and stop pressure building up. 

2. Undo caliper mounting bolts, pump up brakes, tighten up caliper mounting bolts with brakes applied.

 

Any of that makes sense? Any other ideas? I'm on the bus till I get this sorted, which doesn't get me home before it gets dark, making it harder to actually do anything on the bike!

 

Thanks,

Eifion

 

 

[Spindizzy 7,109]

Not sure if this will help, but I have had brake pistons return in after applied pressure as they were so free to move with the dust seals. Might try stopping the piston returning after applied pressure.

 

Also had a stuck piston in the brake pedal/lever so after one pump it was just moving against spring tension.

 

 

[ontwowheels 19]

Is it possible that you've twisted the flexy on reassembly? This would pinch the brake line, stopping fluid getting to the caliper.

[Andy m 23,473]

Is the pedal hard (feels like you are pushing against a jammed piston) or soft (feels like the fluid is going somewhere but not doing anything)?

 

Andy

[Dunnster 1,650]

Without sounding patronising, have you tried pumping the pedal whilst the calliper is off, just to make sure the pistons are moving? Obviously not too much pumping that the Pistons pop out the calliper! Just so you can check the Pistons are not stuck. 

Hope you manage to get it sorted. 

[Grumpy old man 4,670]

Hi

In reference to the front bolt, will the calliper slide, by hand,? Ie; is it free? It must slide to create pressure on the disc. 

Hope this makes sense I've had a whisky or two 😊

[Guest machinman]

What happened next?

[Guest eifionglyn]

Thanks for the responses,

 

I've just had a mate over who does a lot more mechanichy things with bikes than me and he's as stumped as I am.

 

We've had the caliper off again, checked everything goes together fine, bled the system properly with a vacuum bleeder.

 

The piston moves in and out when you operate the pedal, so fluid is getting to it.

 

The caliper is free to slide on its pins. The pedal feels soft when you operate it. The entire caliper looks like it's rotating or twisting a bit when I apply the break pedal, which is probably taking up some of my piston movement instead of it applying pressure on the pads and disc. I will take a video to show you what I mean.

 

Cheers,

Eifion

[Guest machinman]

100% sure the mounting bolts not cross threaded and pulling the caliper diagonally, resulting in the pad not hitting the disc square. That would give you excessive travel.

[Guest eifionglyn]

47 minutes ago, machinman said:

100% sure the mounting bolts not cross threaded and pulling the caliper diagonally, resulting in the pad not hitting the disc square. That would give you excessive travel.

 

Not 100% sure no. I don't think they're cross threaded, they look OK, however it does take a lot more effort than I would expect to get the front bolt home, so maybe? How that happened I don't know, as it came out easily enough first time, and I always do things up by hand first, I'd got a a good few turns in by hand before I needed the spanner to refit.

 

Here's what it looks like:

 

 

Cheers,

Eifion

 

[Spindizzy 7,109]

Something looks a bit wonky, shouldn't be moving that much. Its an incremental movement to apply brakes usually.

[Guest machinman]

There is something wrong with the foreward most slider, it seems trapped somehow, hence the twisting motion.

Id pull it apart again, 

[Guest eifionglyn]

8 minutes ago, machinman said:

There is something wrong with the foreward most slider, it seems trapped somehow, hence the twisting motion.

Id pull it apart again, 

 

I will.

 

How much hassle is it to take the exhaust off? Thinking it might make it easier to make sure everything's lined up right.

[Guest machinman]

Also, just noticed that the inboard pad seems a long way from the disc. Is it trapped at the front where it locates in to the clip/body

[Guest machinman]

1 minute ago, eifionglyn said:

 

I will.

 

How much hassle is it to take the exhaust off? Thinking it might make it easier to make sure everything's lined up right.

Very easy, 12mm clamp and nut and bolt through footrest hanger and gently twist off while supporting its weight. As long as your gentle the gasket will be good to reuse.

 

[Trumpet 215]

Agreed. Somehow you have got the caliper out of alignment, or the pads have been worn with the caliper out of alignment, and now its back to where it should be. . Machineman is right. Well done, I've never seen anything like it.. Either that, or the pads or they are not in properly. The pads are not parallel to the disk right now, or they have been worn previously at an angle. My money is on a crossed front bolt.

Edited January 2, 2018 by Trumpet

[Dunnster 1,650]

Undo the rear calliper bolt and the whole assembly swings upwards and pivots on the front bolt,  check the pad alignment and make sure the metal spacer/clip is in there too. The forward calliper bolt doesn't look as though it's in straight. Could be camera angle though. 

[Andy m 23,473]

Are there a load of washers under the rear bolt? The front one doesn't seem to be screwed into anything or the pin is undersize?

 

Andy

Edited January 3, 2018 by Andy m

[Slowboy 20,359]

Be careful if you manage to get it apart, check the thread very carefully, it sounds like it's cross threaded and will have lost significant strength. Either that or it's been reassembled incorrectly.

Please don't take this the wrong way, it is well meant, but it would be handy to have someone who knows what their doing to be there when you start. Brakes are the most important part of the bike and must be right (I know, statement of the blooming obvious). I feel you might end up needing a new caliper or carrier if it's too badly damaged. 

[Trumpet 215]

Come on, come clean and tell us what you found.

[Guest machinman]

8 hours ago, Trumpet said:

Come on, come clean and tell us what you found.

Yep, curious here too!!

[Bart Stilgo 428]

Very curious

there seem to be quite a few of these technical issues raised that we don't hear the final report on.

[Tex 36,816]

11 hours ago, Bart Stilgo said:

Very curious

there seem to be quite a few of these technical issues raised that we don't hear the final report on.

 

One of the facts of forum life, that. 

[MikeBike 5,005]

I'm guessing he took the exhaust off in the end and sorted it. Noticed that a year ago his first post was saying it was difficult to do the job with the exhaust on.

 

[Simeon 30]

It appears this is the very same problem I have

 

https://www.nc700.co.uk/index.php?/topic/29409-rear-brake-not-very-effective

 

When I get to it again over the weekend i'll let you know what my problem was hopefully