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Bleeding monza brakes

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MGGGG View Drop Down
Guzzino
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    Posted: 24 May 2018 at 22:49
I have been weeks off and on, trying to bleed the linked brakes on my monza. The seal kit came with the seals already fitted to the piston so seemed fairly straight forward, but it has been impossible to get any sort of brake. For the umpteenth time I have dismantled the master cylinder, and what I have found is that when the piston is installed it actually seals the inlet that gravity feeds fluid from the reservoir! So when assembled no fluid is getting into the system. What am I doing wrong, and has anyone got the solution? I just had a John Cleese moment and had to walk away. New to Moto Guzzi so any help gratefully appreciated.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2018 at 23:03
A lot of people reverse fill the system, from the calliper back to the master cylinder using one of those larger plastic syringes.

However, your problem with the seals covering the bleed hole soen't seem right. Have you punched that little sealing ring on fully which holds the piston in properly?
Brian.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote MGGGG Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2018 at 08:37
thank you Brian. I have tried the reverse fill method, but realise now that it didn’t work because the piston was sealing the hole back to the reesvoir so there was nowhere for air or water to go!
Later today will get a bigger hammer to make sure the seal is right in and try again. Thanks for the info, will let you know how I get on.
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iansoady View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2018 at 10:16
Is the brake lever over-adjusted so that it's partially applying the brake (ie pushing the piston in far enough to cover the hole)? Obviously when the brake is applied the hole needs to be sealed.
Ian
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MGGGG Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2018 at 13:11
yes got the brake leaver sorted. Thanks for the suggestion.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2018 at 16:01
Silly question but you're sure the little hole isn't just bunged up?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote MGGGG Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2018 at 07:49
spent a few hours at it yesterday. The hole is clear, thanks for suggestion though. I blow into the hole with the piston in placeand as I push the piston slowly back out eventually I can blow through it, but by now the piston protrudes about 4mm, out of the cylinder, and the securing washers are out of the cylinder. So cannot be secured. When it is secured the piston is just inside the cylinder. Seems to me the only way to bleed the brakes is to leave the piston protrude until the brakes are bled, then tap it home and secure it. Which doesn’t seem right somehow. A Guzzi owner locally tells me he had the same problem trying to fit new seals, gave up, then bought complete cylinder, and it worked immediately. So that is probably the answer. But still puzzling. Thanks for all your help though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2018 at 09:29
No, that's not right. I fitted a new piston in mine and didn't have that problem.

Have you compared the old and new?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 28 May 2018 at 19:22
Yep sounds like wrong piston. Doesn't fit.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote MGGGG Quote  Post ReplyReply Direct Link To This Post Posted: 28 May 2018 at 22:15
tried again got nowhere, trying again tomorrow! This bike stood in a collection for 20 years apparently, but ridden to mot station annually. When it came the brake was working then the piston began sticking in the cylinder. On inspection one of the seals had split and causing it to foul in the cylinder. I explain this because I have the piston that came out, and the replacement seals came fitted to a new piston, and the new piston is identical to the onei  that came out! When the piston is properly located it seals the hole that gravity feeds fluid from the reservoir so for the life of me I can’t see how it is possible to bleed the brakes with the piston located! In fact how does fluid feed into the system at all! I did see an old post on this forum suggesting that there was another very small hole further in the cylinder that allows fluid in when everything is in place, but I had a very good look and it’s not in my cylinder,
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Post Options Post Options   Thanks (0) Thanks(0)   Quote red leader one Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2018 at 16:57
Just Because it's the same as the one that came out doen't mean it was right one the first place.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MGGGG Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2018 at 17:31
your right, but it was working OK when I first had it. And Gutzibits are adamant it is the correct one. Had some more info earlier from a friend of a friend whose had the same problem, and he is a wizard with anything mechanical. The fluid feeds into the cylinder behind the front seal then when the brake is applied  and released, the seal is shaped to allow the fluid to pass the seal into the brake system, he believes the material in the seal in these replacement kits is to hard and won’t allow this to happen. Which certainly makes sense to me, his remedy was to put the old seal onto the new piston and hey presto! So that’s my next move, but he is to let me have a seal as mine was split.
 




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Post Options Post Options   Thanks (0) Thanks(0)   Quote MGGGG Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jun 2018 at 20:50
thought that I would just round this off, having finally managed to bleed the brakes. Had to buy a new master cylinder to achieve it! This is what I discovered, the front seal on the piston is chamfered to allow fluid to pass when it retracts. So the fluid gravity feeds from the reservoir behind the seal. When the foot brake pressed it compresses the fluid in the system, when the footbrake comes up the piston retracts and the fluid that has gravity fed down behind the seal is then passed into the system. This means that there is no way that fluid can be forced back through the  system, unless of course the seal is shot. A theory I share with a knowledgable friend is that the new seal in the kit you buy to refurb the master cylinder is to hard and won’t allow the fluid to pass when the piston retracts. The new MC worked fine. Also of note is the £11.95 vacuum pump I bought on eBay = awesome, sucked the fluid through to the calipers in an instant! Thanks for all th help, 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jun 2018 at 10:05
I have one of those vacuum pumps as well - makes bleeding very straightforward.
Ian
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