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'76 850 T3 front brake master cylinder seal issue?

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T3Chris View Drop Down
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    Posted: 03 Apr 2017 at 19:39
Hi, I've just rebuilt the caliper & master cylinder on my bike & replaced the brake hoses with Venhill diy ones. I've fitted lower & narrower 'bars & had an excessive amount of old Goodridge hose. After bleeding the air from the system & checking for leaks I was just feeling pleased with myself when I noticed a metal ring dangling from where the lever pushes against the piston! This is the metal part of the outer seal that is supposed to hold everything in place I think - so not so cocky now.Angry
Does anyone know if this seal is "just" a dust seal? I fitted an overhaul kit & must have damaged the metal ring when I fitted it - or maybe I fitted the seal the wrong way round.
Is there a right way (& wrong way) round? 
The seal & ring have parted company, so I am thinking of re-using the old one.
Any advice on this would be gratefully accepted.
Thanks, Chris.
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italianmotor View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote italianmotor Quote  Post ReplyReply Direct Link To This Post Posted: 03 Apr 2017 at 20:03
It should clip in inside the master cylinder. Try using a deep socket to get it into place. If it doesn't stay in one way, spin it round and try the other way - but it is needed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ed.bremner Quote  Post ReplyReply Direct Link To This Post Posted: 04 Apr 2017 at 09:49
I have had exactly this problem with a rear master cylinder.  

Seems to me that if you have any problems getting it into the groove, then the chances are that you will bugger it up and have to use the old one or get a complete new kit.

I persevered with mine, which luckily was not damaged and finally did manage to get it to stick in place.

I made up a tool out of a bit of 15mm copper pipe, which I think I needed to cut a section out of to get to fit.   Mmmmmm, I think I also made another one which I could use in situ without removing the actuating arm, with a bit missing so it could go around the arm and push all sides.

I kept trying and it kept falling out, till finally I managed to get it in place and it stayed put.  Have to say, I didn't notice any difference in braking capability when it was not in place as the piston is kept in place by the arm anyway, but I wouldn't try to live without it.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote theoneandonly Quote  Post ReplyReply Direct Link To This Post Posted: 04 Apr 2017 at 16:45
13mm deep socket should fit just perfect 
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T3Chris View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T3Chris Quote  Post ReplyReply Direct Link To This Post Posted: 04 Apr 2017 at 19:42
Hi everyone & thanks for your advice.
I'd like to try & fit the seal & clip without taking the master cylinder off the 'bars - having just reassembled everything & bled the air out. I used a piece of 15mm copper pipe to push the old metal washer against the new seal & clip to assemble it - but that was with just the master cylinder on the bench. I realise it will be awkward to re-fit the seal & clip with the brake lever still attached on the 'bars, so I may try making a better tool for the job. From what I can see on the internet the metal clip should be facing the lever end of the cylinder.  Is the metal clip/ring supposed to flatten-out to fit in the groove, or is it meant to fit as it is?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ed.bremner Quote  Post ReplyReply Direct Link To This Post Posted: 05 Apr 2017 at 08:55
I think it fits as it is.  I certainly have never done anything to them other than tap into place.  The problem that I find is simply knowing how hard to tap to get it into the groove.  The front (hand) brake-cylinder I have not had too much problems with, the foot brake master cylinder has at times been a bit of a challenge.

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T3Chris View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T3Chris Quote  Post ReplyReply Direct Link To This Post Posted: 14 May 2017 at 11:47
I tapped the seal back into place - a bit harder this time - and it has been working well for some time now. There were problems at the caliper end too, as the seat for one of the bleed nipples was too worn to seal anymore. I got round that by using a banjo bolt with built-in bleed nipple on the brake pipe & filling the two old bleed nipple holes with araldite - sounds bad, but it seems to work. Just got a new MoT & the brakes have bedded-in nicely.




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T3Chris View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T3Chris Quote  Post ReplyReply Direct Link To This Post Posted: 16 Nov 2017 at 20:42
Now I have worked out how to upload pictures, this is my mod for leaking bleed nipple seats -

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T3Chris View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T3Chris Quote  Post ReplyReply Direct Link To This Post Posted: 16 Nov 2017 at 20:44
and this is the side view with a new brake hose -

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Post Options Post Options   Thanks (0) Thanks(0)   Quote nab301 Quote  Post ReplyReply Direct Link To This Post Posted: 21 Nov 2017 at 20:41
Originally posted by T3Chris T3Chris wrote:

& filling the two old bleed nipple holes with araldite - sounds bad, but it seems to work. Just got a new MoT & the brakes have bedded-in nicely.


I not sure about subjecting araldite to brake pressure ? Surely a bolt with a copper washer sealing on the caliper body would be better?
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T3Chris View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T3Chris Quote  Post ReplyReply Direct Link To This Post Posted: 21 Nov 2017 at 23:20
Hi Nigel, I'm keeping an eye on it & it seems okay - for quite a time now. There is only a tiny passageway from the caliper bore to the bleed nipple threaded hole & that is now full of araldite, so I think it should do the job. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 22 Nov 2017 at 10:56
Would it not have been better to use an M5 (or whatever it is) bolt with a copper washer?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dukedesmo Quote  Post ReplyReply Direct Link To This Post Posted: 22 Nov 2017 at 15:02
Originally posted by iansoady iansoady wrote:

Would it not have been better to use an M5 (or whatever it is) bolt with a copper washer?

I did this after one of the M6 bleed nipples broke off on my rear brake caliper.

I drilled it out but damaged the taper at the bottom of the hole and so couldn't get a new bleeder to seal, so I used an M6 bolt with copper washer and fitted a combined banjo bolt/bleeder to the hose fitting.

I did consider filling the bleed hole with weld but I'm not sure I'd be happy with any kind of glue to hold against the pressure?    
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