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Rear Brake 'Crunch'


Guest Dhoadley

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Guest Dhoadley

Hi all,

(NC750X Manual, 2014)

So I have had this happen a few times and thought nothing of it. On occasion when applying the rear brake I have felt a strong crunch. This morning this happened and the only way I can describe it is that it felt like I was dropping a gear, that kind of crunch. Now, i've never had ABS on a bike before but I was under the impression that ABS feels more like a juddering than a crunch or click? Anybody else experience this or have any idea what it is. Is it normal?!

Thanks

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Guest dentonlad

It doesn't sound normal.

 

ABS being activated is probably best described as being a 'rhythmic pulsing' or vibration in the lever or foot pedal. I've never had a crunch. It usually only happens under strong braking or on ropy surfaces.

 

I'm assuming that the pad thickness is OK and nothing's loose on the caliper or stuck between pad and disc. 

 

Of course under Sod's Law when you ask someone to check it, it won't happen........but nevertheless it would be worth having it looked at. It's still under warranty! 

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Guest Dhoadley

Thanks for confirming Keith, I have booked the bike in for its starter relay inspection anyway so asked them to look over the brakes whilst its in. Hope its nothing too major!

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Has the rear wheel been removed recently for any reason?

It sounds like the calliper carrier isn't located correctly!

Does the calliper and carrier move any more than a tiny amount if you try to rotate it anti-clockwise?

If so then that is the cause. DO NOT ride the bike.

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Guest Dhoadley

Clive, the rear hasnt been touched as far as I am aware! - I bought it second hand so if it was touched before hand I have no idea. The calliper has got quite a bit of wiggle room, I have tried to move the front one and its solid in place. Should the rear one not move at all? I will try and get a short video up in a moment.

Thanks

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your youtube is set to private,,,,, cant see anything.

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The rhythmic pulsing and vibration interests me -can I have it in the seat  of my  DCT please?

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That movement looks completely normal to me, if it's tight on the pins it would be more of a concern, it's done so the pads can align to the disc and the caliper can float to release the pads when the brake is off.

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Guest Dhoadley

Right, well I just quickly visited the Honda shop down the road and they think its completely fine, its still going in on Monday for the recall and a test ride to see if they can replicate it.

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trisaki

I wonder if the pads arnt fitted correctly in the locating slots in the caliper

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just checked my calliper.

it has vertical movement like your video, but not as much as yours.

it will slide laterally to take account of wear on the pads as it should.

I'm certain that yours is not right.

yours has had new pads fitted. they have blue mountings. 

did you push the calliper back before taking the video, or is that as it was with the clunking noise?

if it is, then I suggest that the pad spring is missing or the pads have not been fitted properly.

if you're not sure how to remove and check, ask the dealer to take the calliper off and double check all is as it should be.

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Will be good to hear what's wrong - I had awful screeching on the KTM which was a fault with the cast iron discs -absolutely fine operation just really noisy.but anything to do with brakes is worrying!

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Mike5100

hmmmm .... I think it could be the ABS activating.  I know when it does so on mine it doesn't feel like I expected it would.  Can't say thatit feels exactly like a crunch, but I do sometimes just get one or maybe two pulses when I would have expected to get a more regular cycling feeling.  And the ABS on the back triggers amazingly early - which has been the subject of another couple of threads.

Mike

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Guest Dhoadley

Thanks for all the replies. I had a car slam his brakes on for no reason this morning so thought it was a good time to give the rear a good old test. I am reasonably sure that the ABS kicked in, I think that I have been thinking its a crunch or a click as I have never had the ABS properly kick in, just start to and I have then bricked it and taken my foot off the brake slightly. The shop are going to have a proper look at the bike on Monday so that will be the clincher. I am not sure if this is just down to the fact that I have never ridden an ABS bike before and had no idea how odd it feels!

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Rev Ken

ABS should only kick in when braking beyond the ability of your tyre to stick to the road. On the very rare occasions that my ABS has kicked in it is more of a 'graunching' sound similar to when there are no brake pads left in the caliper (don't ask! :blush:) . Early systems 'cycled' slowly enough to feel the pulsing through the brake pedal, but modern systems cycle much faster so you are less likely to be able to feel the pulses. 

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Guest Thwaitie

Sounds like the ABS working to me.

It felt unusually different to other machines, without much bike judder it just felt and sounded a bit like the rear brake level had broken.

Done a few practice stops since so it doesn't take me by surprise in another emergency.

 

Which reminds, I've not yet really tested out the front being activated.

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i cant get my abs to activate in the dry  on a gravel free good road as my arms are not strong enough to stop me flying off the handlebars ! It does make a funny graunch though when activated . Its saved me twice in 44000 miles so far.  What this bike lacks in acceleration it certainly makes up for it in stopping power.

 Are there any tests anyones aware of of the different stopping distances between different bikes ? I couldn't find anything on a quick net search.

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I noticed last time I was fiddling with my brakes the pins the caliper slides on were corroded with gunk. When I say corroded i don't mean corroded. I mean they were covered in a type of goo that didn't allow smooth operation which resulted in some odd pedal feel.

 

Pulled the pins, debrided the goo with some scothbrite pads and smoothed the pins.

 

Presto! A more natural feeling brake.

 

Worked for the front and rear. I'm going to guess some of the places I've been allowed for grime to build up, and perhaps get baked on with the heat of the brakes. I'm guessing here.

 

Anyway, ABS activation is more like a buzz….one can sense the rhythmic and rapid pulses.

 

I can tell you for a certainty, the Honda ABS activation I've experienced is far and away more sophisticated than the 90's BMW ABS which would have the motorcycle rocking like a hobby horse!

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Rev Ken

Except on a slippery or gravel surface it is unlikely you can get the front brake to activate ABS unless you 'grab' the front brake which is not recommended. However if you brake hard , but progressively, with the front brake while jamming on the back brake, you will find out what ABS sounds and feels like!

I can confirm the early Maxaret mechanical ABS systems on BMWs were indeed a world apart from modern systems! I tried an early version at was then called TRRL on a BMW with outriggers while riding across wet cobbles. I took three attempts as I found it almost impossible to brake hard as all my experience said no. I managed eventually, and to my surprise it worked. But it had a much slower cycle rate than modern versions so I was capable of beating it over the wet cobble course I was riding. Some say it is still possible to beat ABS systems, but not for 99% of us when faced with a real emergency braking on the publc roads.

Edited by Rev Ken
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