UK Monster Owners Club Forum » .: Technical :. » Cans, Tyres, Brakes, etc. » Bleeding front brake...spongy no matter what!

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Old 28-06-2020, 04:58 PM   #1
Bitza
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Bleeding front brake...spongy no matter what!

Hi alll, any advice. I have just changed my front brakes a bit I now use four-pad calipers, brake lines are the link type with one line to the master, and the master is a 2003 coffin type. I've been trying to get the bled and have just replaced my old master as it was leaking. My first problem turned out to be getting the air out of the line to master banjo joint, which was simply achieved by taking the master off the handle bars and tilting while shallow pumping it. But I just can't get all the air out of the system. I've tried the conventional technique, i.e. top down with master, reverse pumping through the far bleed screw, I've also tried taking the calipers off moving them around & tapping them to let any air trapped inside to get up to the bleed screws, I've tried just cracking the banjo bolts while depressing the master. I also tried to suck the fluid down through the system via the bleed screw, but I found that I was sucking air in via the thread of the bleed screw. I also tried the tie wrapping the lever back to the bar overnight (micro air bubbles more likely to come out under pressure). I also restarted right from the start again with brand new brake fluid. The best I get is definitely some pressure but you can still can just about pull the lever back to the bar. If anyone has some useful ideas, experience of four-pad calipers, link type brake line set up etc. because I'm right out of ideas of what else I can try. Thanks Bitza.
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Old 28-06-2020, 05:40 PM   #2
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.I also tried to suck the fluid down through the system via the bleed screw, but I found that I was sucking air in via the thread of the bleed screw.
Apply PTFE tape to the thread and try vacuum bleeding them again.

http://www.ukmonster.co.uk/monster/s...d.php?p=577122
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Old 28-06-2020, 05:55 PM   #3
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Apply PTFE tape to the thread and try vacuum bleeding them again.

http://www.ukmonster.co.uk/monster/s...d.php?p=577122
Pedro has been having trouble with a soggy back brake on his M1200R.

He has solved it now though:

‘ stumped up for a new master cylinder and swapped it over and also fitted the Stalhbus nipple, low and behold I have a decent rear brake again, not ridden it yet (prob tomorrow) but the pedal has remained firm for a few days (normally goes a little mushy in a week).

but... omg, how flipping good was the new bleed nipple! System was bone dry, undo bleed nipple 1.5 turns to fully open the ball valve and use a vacuum pump to fill the system, took about two mins, close the nipple fully, pedal felt quite good. Onto “bleeding” it, open it half a turn so the ball valve is in play, pumped through a couple of reservoirs of fluid, close valve, pedal good and firm. Chuffing marvellous!!

I pulled the old cylinder apart to see if there was anything obvious wrong with it but nothing other than some uneven wear in the bore from the naked eye. I still think it was letting air in, perhaps via the reservoir connection but not sure.’
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Old 28-06-2020, 09:51 PM   #4
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Tie wrap the lever back over night or for 24 hrs, cut tie wrap and let lever return. It apparently pressurises the system and the bubbles rise, let the lever go and they enter the master cylinder.
I was skeptical but it worked for me.
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Old 28-06-2020, 10:34 PM   #5
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may I suggest you change the master cylinder to a radial master cylinder, used on ebay.

https://www.ebay.co.uk/itm/DUCATI-11...Condition=3000
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Old 07-07-2020, 06:38 PM   #6
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Well Chris.P I took your advice, on the basis that the four pad caliper's pistons have a larger surface area (approx + 12.5% I recon). Very problematic getting radial masters to fit in with existing switches twist grip ect. but have managed it "just". Once I worked out that the integral reservoirs (749/999 type) have a bleed valve too, all was plain sailing and I finally have brakes again, RESULT!! Thanks for everyones suggestions and emotional support? Bitza.
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Old 07-07-2020, 08:39 PM   #7
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No problem Bitza. I had meant to follow up with a better explanation and some pics, as I had the same problem when I fitted the 4 pad callipers to my 2000 748R, but a few things cropped up & it slipped my mind sorry. I am pleased you got it sorted, I had the same problems as you did fitting the radial master cylinder, but it does go on in the end.
Any way, pleased you have resolved the issue.
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Old 07-07-2020, 09:24 PM   #8
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After the event and now you have solved the problem, the penny has dropped as to what the problem was.

I think that you were most probably getting all the air out and bleeding successfully, but the increased lever movement and light action was due to the larger caliper pistons demanding much more fluid movement. Much more than the 16mm master piston could deliver in the stroke available. So you never got a hard feeling brake lever.

Now that you have converted to probably something like 19mm master? It can move sufficient fluid with less lever movement.

Sorry to be so slow off the mark. I clearly did not register that your caliper pistons were larger than before.

Glad you are sorted now..
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Old 08-07-2020, 07:14 AM   #9
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I believe you can easily convert the 749/999 type radial masters with the triangular reservoirs to use the round type remote reservoirs which may give you more room?
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Old 08-07-2020, 08:06 AM   #10
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yep, my first conversion on my 748r was to 4 pad callipers as I said earlier and I used 749 master cylinders, and removed the reservoirs, they need replacing with inlet connectors as per this pic

https://s61.photobucket.com/user/chr..._0017.jpg.html


If the link works.
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Old 08-07-2020, 11:43 AM   #11
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Yea, the little black plastic elbows are what you need, and some pipe/clips etc.
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Old 08-07-2020, 01:26 PM   #12
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https://www.reactiveparts.com/brakin...-90-inlet.html
https://www.reactiveparts.com/brakin...voir-pipe.html
https://www.reactiveparts.com/brakin...ipe-clips.html

Last edited by slob; 08-07-2020 at 01:28 PM..
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Old 08-07-2020, 02:53 PM   #13
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As slob listed, those are the three parts needed to go from a 749/999 unit to having a separate reservoir. A word of warning, getting the inlet adapter in and housed correctly is a bit of a B***h.
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Old 08-07-2020, 03:35 PM   #14
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Quote:
Originally Posted by chris.p View Post
As slob listed, those are the three parts needed to go from a 749/999 unit to having a separate reservoir. A word of warning, getting the inlet adapter in and housed correctly is a bit of a B***h.
B***h? Is there a specific bracket needed or does the standard goldline one work? Do they even have somewhere to fix the reservoir brackets in the same style as the goldline ones or do you need to use the clamp bolts like they do with the RCS style ones? It's a mod I have in the pipeline as I have some 4 pad calipers but still undecided whether the masters I have will be ok or upgrade to 749/999 type or RCS ones.
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Old 08-07-2020, 04:07 PM   #15
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B***h? Is there a specific bracket needed or does the standard goldline one work? Do they even have somewhere to fix the reservoir brackets in the same style as the goldline ones or do you need to use the clamp bolts like they do with the RCS style ones? It's a mod I have in the pipeline as I have some 4 pad calipers but still undecided whether the masters I have will be ok or upgrade to 749/999 type or RCS ones.
I just made a bracket myself out of piece of annealed aluminium strip.
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