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Front Brake Issue


Rik398
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Morning All,


After rebuilding my front calipers, I now have a odd lever feel.


The seals are square for this particular bike and fit in an angled groove, so they are installed right. There is no air in the system, which was my initial concern, as the local bike shop bled the system for me to confirm. And the master cylinder feels right, as in the lever doesn't sink to the bar. The pistons move freely, moving forward and back, and will push in happily by hand. I cant see that there are any fluid leaks anywhere while applying pressure.


What is happening, is the first pull of the lever has much more travel than the second. The brakes are strong and working, its just that the first pull has more travel.


The garage have speculated that, if the pads have gone back in the calipers in a different configuration to what they were before, then because the pads are not mated to the surface of the disk, they will sit further out until they are bedded in, and that is why the lever travels more on the first pull, because it is moving the piston more, and on the second pull, the piston hasn't had chance to move back, so less travel.


At the moment, to me, that explanation sort of makes sense and i am happy to do a few miles to bed pads in (brakes are operable). However, if this is not the case, what else could this be? Anything else likely to cause excessive piston retraction or the above lever symptoms?

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That to me suggests that their is still air in the system!


It could well be trapped in the master cylinder

 

That would be my thought as well. Brakes that harden up with the second pump is usually down to air in the system. I gather the discs and pads are the originals?

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Thanks for the replies.


Hoping it is not air, as the garage charged 60 quid to bleed the system and swore blind there was no air in there. I did think it was air when I originally took it to them.


Will get some more fluid and maybe crack the banjo at the master cylinder. I don't believe it to be in the calipers or lines, partly due to the pure volume of fluid I put though and did the tie break lever down, tapping lines, calipers off the bike etc.


Pads are the ones that were in there before the rebuild, just possibly in different caliper / position than they were when they were taken out. Seals are OEM suzuki from Fowlers. Seal kit included the one that links the caliper halves.

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Ok , I get what you mean by square seals in an angled groove but is the groove absolutely clean ? Did you fit these new seals and see for yourself or did this garage do it ? If we work on the assumption that there is no air in the system then debris behind the seals is the only other circumstance that I know of that would produce similar symptoms.

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Was considering that as a possibility. The pistons could be pushing in ok because of the angle of the seal, but then be being retracted to much because of a tight fit caused by some dirt. Looked fairly clean at the point of doing it, but pulling the pistons shouldn't be too tricky now as they move a lot easier so no harm in a double check.


Before that though, I was thinking of putting a square bit of wood in there and seeing if problem persists. If it stops, then it would point to some oddly worn pads which may knock pistons back unevenly. Don't look bad enough to do that at first glance though.

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Was considering that as a possibility. The pistons could be pushing in ok because of the angle of the seal, but then be being retracted to much because of a tight fit caused by some dirt. Looked fairly clean at the point of doing it, but pulling the pistons shouldn't be too tricky now as they move a lot easier so no harm in a double check.


Before that though, I was thinking of putting a square bit of wood in there and seeing if problem persists. If it stops, then it would point to some oddly worn pads which may knock pistons back unevenly. Don't look bad enough to do that at first glance though.

It's worth a look . All I know is that the difference between clean grooves and ones with crap ( mineralization ) in them is like night and day . For years I could never figure out why I had such long lever travel and such poor braking even when I had bled the air out and thoroughly cleaned everything visible from the outside. Things got so bad that I was having to position the adjuster between settings and even then I was almost trapping my fingers with the lever.Then I started to completely dismantle my calipers and I was shocked by the amount of shit that had built up in the seal grooves . Of course you have to be very careful not to do damage when you remove it which is why I make up various scraping tools from bamboo kebab skewers . Now the brakes on both my bikes are amazing with rock hard lever movement that only requires the gentle use of two fingers instead of grab and hope .

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Thanks FastBob,


At this point, I am half considering just taking it to a garage and saying "sort it". May cost but then at least it is done and I can sip coffee while waiting.


Moved from somewhere with a garage to somewhere without recently (big mistake!) think I am done with standing in a driveway in the rain trying to sort stuff out (it was dry when I bled the system, no water!) At least with stuff like chain and sprockets its on and done, but this could turn into a bottomless pit of testing.


Will give it a crack on the weekend but after that, I shall have to succumb. Saved enough other the years to give a garage a shot!


Will report back should anything odd be the cause. May save some people some pain.

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Before you take it in anywhere have you tried cable tying your brake lever overnight? If there is any stubborn air bubbles in there it gives them the chance to raise up through system and out of master cylinder.


May not do anything but for the cost of a cable tie (or anything else you have to the brake lever to bar) and minimal effort it is worth a go.

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