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Discussion Starter · #1 ·
Just got back from a 2 week off road ride through the Italian alps. Was a fantastic ride but for a nagging problem with the front brakes.
It started on the first days when the trail was taking us between 500m and 2500m elevation a few times a day. All of this on dirt roads ranging from mild to wild. Looong uphills and looong downhills. Too many hairpins to count!

The first time I noticed this, I grabbed the front brake in a reasonably steep decent going into an off road hairpin and suddenly the brake felt “stiff”. Harder than normal to compress the lever, and a sluggish reaction from the brake on the wheel. I released the brake lever and grabbed it again and it felt good again. I would get to know this gremlin very well over the next few weeks. It would always vanish with 1 pump of the brake.

First days it happened only rarely. A few times in the day. I did not even mention it to my riding buddy. Then he noticed my riding change and asked what was going on. I was becoming less and less confident and he could see it. As the ride progressed, this gremlin was appearing more and more often.

I got my friend to try to ride my bike to see what he thought, but he was coming off a RD-07 (for those that do not know what this is, its the old Africa twin from the 1990’s) and had never ridden a modern AT, he was not quite sure of what to look out for. At the very least we did some hard braking tests on a quiet section of tarmac, and the brakes worked, and the ABS seemed to be operating properly.

As the ride went on, this problem was becoming a old uninvited friend to my trip. I used to be able to do an emergency stop on my bike using just the middle finger. This is now difficult even with 2 fingers.
I screwed around with the lever adjustment but this did not help.

In Italy, as in the rest of Europe, there is never much off road without meeting tar somewhere, and with off road tyres, this braking was quite disconcerting on tight narrow country roads, especially on dewy mornings.

I had a 1000km road stretch to get home at the end of the trip (back with more road biased tyres) and I noticed this gremlin had taken up almost permanent residence in my front brake.

I have some theories, and because today is my first day back, I have not started to fiddle with anything yet, so I thought I would write the whole thing down here (also for my own benefit. Memory is a slippery thing, especially in advancing years) and put it to the collective wisdom of the awesome Honda Africa Twin forum!
I have avoided sharing my theories here in order to get some unvarnished opinions from you guys.



Just to give some stats here:
  • The bike is a CRF1000L 2017
  • Its got 29000km on it at the moment
  • The bike has Karoo Street tyres but for the 2500km of this trip I had more aggressive off road tyres installed. (Heheheee, pretty much destroyed these off road tyres in 2500km, but part of the reason was the street sections which the tyres really did not like. It was fun destroying them!)
  • The front brakes are about 8000km old and by the looks of them, they are about half way through their life. The current pads are SBS Street Excel Sinter HH Front Brake Pads. These are the first replacements since stock. When I changed to pads, I did not change the caliper bolts as the workshop manual suggests. I figured I will do this every second change and my mech gave me the nod that this is no big deal. (In fact Honda seem to suggest that every time you take the calipers off the forks, new bolts should be used! So since you need to take one of the calipers off to do a tyre change or to fix a flat, a new set of bolts are specified by Honda!)
  • The system has never been bled. I was contemplating bleeding them before this trip, but thought not to screw with a working system before this trip, and I had no indication at all to suggest it was required.
  • Just in case it makes a difference to someone, I replaced the rear spring for a stiffer one for this trip, BUT I did nothing to the front end. This “may” result in a little but more rake angle on the front end I think. I mention it because it ‘may’ be significant.


So, has anyone had something like this on their bike?

Has anyone got any ideas on what this could be?

And finally, any ideas on remedies?
 

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I have never experienced it on a bike, but have dramatically in a car.

The root cause was debris in the brake system master cylinder. Specifically, rust particles and water.
 

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@Mastercore , Thanks for taking the time to write that up; that sounds like a great ride, except for the brake issue!

I would also suggest flushing the system thoroughly, it does sound like maybe contamination got in somehow and is causing some "stiction" on a caliper puck or master cylinder.

Regarding changing out the caliper bolts everytime: I think that is a misconception from a poorly worded manual. The calipers come with "shipping bolts" installed from the factory, when the bike is in it's steel crate. The manual and setup sheet warn you profusely to change these bolts out as part of the setup process; this warning can be mistaken to do it every time you unbolt the caliper.

My interpretation at least, is that it would be silly to change them every time the caliper comes off. This would be a first in 40+ years of wrenching on bikes.

Here is another thread that details that whole saga out, complete with videos and manual exerpts. The upshot: Dealers' setup monkeys aren't always so great at reading instructions:

Bolt Thread
 

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Discussion Starter · #5 ·
Hey @Beowulf, Thought so myself. ... But, ya know... can't help pay a slight bias toward checking, just these, particular bolts.

But hey, lets face it. We all gotta be a tad more on the vigilant side when we mess around on our bikes with tools.
 

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Discussion Starter · #6 ·
btw, rode my bike out to get it clean, and tested the brakes out. They seemed fine.
I guess any water in the system had not yet reached boiling point.

A bleed is too easy not to try first. Its probably time as well.
 

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btw, rode my bike out to get it clean, and tested the brakes out. They seemed fine.
I guess any water in the system had not yet reached boiling point.

A bleed is too easy not to try first. Its probably time as well.
Be very, very careful. That is the exact behaviour I experienced before I knew rust and water was in the brake system. Two out of three days were "normal", the other day, hair-raising. The Forum likely does not wish for a hair-raising story from you @Mastercore. :oops:

Bleed it baby, bleed it.
 

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Something else to check - there is a small bleed port inside the fluid reservoir on the bottom of the reservoir. If this port gets blocked or gummed up it can cause this type of problem. You can take a small wire such as a paper clip and clear out this port. I would also suggest that you flush out and bleed with new fluid. Moisture contamination can also cause strange behavior.

Dan
 

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Discussion Starter · #9 ·
I just looked at the workshop manual searching for this bleed port but could not find it. Are you sure there is one on the AT?
57633


57634
 

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The port under discussion is inside the MC. There are two small holes in the bottom of the reservoir, one larger than the other. The tiny one can get blocked and cause issues as bdalameda said.
 

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Discussion Starter · #11 ·
What has confussed me is that true the problem seemed to plague me more when the brakes would be hot - consistent with something reacting to heat in the system.
But if it is water in the system, then as the water boils, it would introduce some compressable element to the system making the brakes "spongy"
This is rather the opposite of what I experienced.
My brakes seemed to develope some "resistance". The braking power did not seem to be diminished, just required more pressure to apply. But this pressure was not "spongy"
It felt more as if there was some mechanical resistance in the lever.

In any case I have bled the system completely now.
But have not yet tested it in heated braking.
Normal test is good.

@bdalameda
Something else to check - there is a small bleed port inside the fluid reservoir on the bottom of the reservoir.
where do these two small holes come out?
If they are for bleeding, should they not have a bleeding nipple outside somewhere?
Further, seems a mystery why they would completely ommit metioning it in the workshop manual!

hang on, do you mean the holes that will feed brake fluid from MC to the Master piston?
 

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What has confussed me is that true the problem seemed to plague me more when the brakes would be hot - consistent with something reacting to heat in the system.
But if it is water in the system, then as the water boils, it would introduce some compressable element to the system making the brakes "spongy"
This is rather the opposite of what I experienced.
My brakes seemed to develope some "resistance". The braking power did not seem to be diminished, just required more pressure to apply. But this pressure was not "spongy"
It felt more as if there was some mechanical resistance in the lever.

In any case I have bled the system completely now.
But have not yet tested it in heated braking.
Normal test is good.

@bdalameda
where do these two small holes come out?
If they are for bleeding, should they not have a bleeding nipple outside somewhere?
Further, seems a mystery why they would completely ommit metioning it in the workshop manual!

hang on, do you mean the holes that will feed brake fluid from MC to the Master piston?
The term bleed may be confusing you. These small ports are on the bottom of the mater cylinder reservoir. The smaller of the two relieves pressure from the piston as it returns. If this is plugged the master cylinder will at times pump up tight and take all the play out of the system. It can even cause the brakes to stay on and not release if it get bad enough.
 

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Discussion Starter · #13 ·
This is the inside of the master cylinder.
The 2 holes you are talking about I am guessing are the dark spots in the green circle in the bottom.
That green circle seems to be a platic disc with a bunch of penetrations, probably acting as some kind of basic filter.
As I was bleeding the brakes, I could see the master piston moving in those 2 dark holes.

57641
 

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Discussion Starter · #14 ·
The smaller of the two relieves pressure from the piston as it returns. If this is plugged the master cylinder will at times pump up tight and take all the play out of the system. It can even cause the brakes to stay on and not release if it get bad enough.
So do you suggest I pop this green cover and poke something into these 2 holes to make sure they are clear?
Visually, everything seems OK to me, but I am a novice at this stuff.
 

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Yes I have seen these with a cover - some are not covered. You will have to pop it off to access the holes. Just take a small wire and gently pass it through the holes and make sure they are clear of debris - that's it.

Dan
 

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If you can see through to the master cylinder in both holes, they are not blocked, and are not likely to be your problem. Do you have ABS on your European bike? Not exactly sure how that system works, but it modulates the pressure to the front wheel when in operation, so it may be possible to make the lever feel hard if it's not functioning properly. Just a guess, though.
 
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