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Leaking nipples... Brake nipples

8K views 18 replies 8 participants last post by  Billy10 
#1 · (Edited)
After cleaning up my calipers I replaced my brake hoses with new HEL braided ones, but had a nightmare bleeding my front brakes...

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I bought a vacuum pump and it just consistently sucked air into the system. I eventually found that the air was coming from between the threads of the bleed screws. I ended up doing it the old fashioned way and it worked fine. My brakes were great and super sensitive.

However, after the first ride I noticed fluid on the calipers. It turns out the nipples were leaking. I had torqued them up to 7nm as per the manual.

I decided to replace them but could only get mild steel ones at short notice...

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After swapping them out and going for a ride... The problem persists.

I did have to "break" the old nipples out when I did the first bleed. They were in very tight so I guess whoever did the brakes last has overdone it.

I've now tightened them up way more than recommended but still leaking around the threads.

Any suggestions? As I understand it it's not the thread that seals them so don't see how retapping will help...
 
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#4 ·
... As I understand it it's not the thread that seals them so don't see how retapping will help...
That is correct - it is the tapered seat at the bottom that is the 'seal' - it leaks past the threads because it is first leaking past the actual seal.

Looking at your new nipples, it appears the taper is not exactly the same (well at least originals look more pointed and replacements rounded)
- I would get some 'better' nipples, or even re-try the originals
 
#6 ·
After installing nipples and re-torquing to spec, give them a good spray of brake cleaner, wipe down, and re-check.

I had nipples that didn’t want to stop leaking. Thought I wasn’t tightening enough even though it was set to spec. Turns out it was residual, as previously mentioned. Brake cleaner saved the day!


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#8 ·
... As I understand it it's not the thread that seals them so don't see how retapping will help...
That is correct - it is the tapered seat at the bottom that is the 'seal' - it leaks past the threads because it is first leaking past the actual seal.

Looking at your new nipples, it appears the taper is not exactly the same (well at least originals look more pointed and replacements rounded)
- I would get some 'better' nipples, or even re-try the originals
Agreed. I noticed the angles and diameter was different so I replaced with the old... No luck and the problem was still there (on all three brakes!)
 
#10 ·
I think I fixed the problem tonight. I drained the system, cleaned the bleed holes and took a look inside. Each of the calipers had a slightly misshapen bleed hole under the screw. It didn't make sense to me that the cone of the nipple could sit in a hole that was oval or had ridges... I should have taken a photo really.

So I got the drill out with a bit just the right size and rounded off the holes in the calipers. I've cleaned the filings out, filled and bled the system and it doesn't appear to be leaking now. ?

I went back to using the new nipples again because my "FT" attempt ruined them ?
 
#13 ·
Brake fluid dissolves PTFE tape over time so when I have tried this in the past I ended up with disappearing tape.

I have had bleed screws that were over tightened and deformed as the base is hollow to allow fluid through - thus not strong. I fitted Stahlbus speed bleeders that have the hole in the base so you seat them once and then open/close via a second screw in the top of the nipple. They work brilliantly and make bleeding super easy. Only concern is corrosion to caliper so worth backing them out slightly every so often.

Failing that, you probably have to seat the valves by hand rather than torque spec. If you cable tie the lever to bar overnight to allow air out then you can put a rag around the nipple and check in the morning if there is a leak. Saves finding out when riding
 
#14 ·
Never had this problem as such before but I did have a leak many years back on a GPz550. Turns out I wasn't as good a mechanic as I thought I was and managed to trap a bit of grit in between the bleed nipple and the caliper that allowed a littel fluid to leak out over time… It was in this way that I learned "cleanliness is next to godliness"!
 
#16 ·
personnally i'd stay far far away from messing around with teflon tape on brake systems; i consider my brakes more important than my life insurance. i prefer reliable brakes over cast and bandages :ride
i used to fit my race bikes with bleed nipples from Stahlbus. these are perfect: once they're in place you only loosen the top screw to bleed your brakes. they have a built-in valve so you can't mess it up. on top of that they look really nice too.
i also use their filling/draining tools which make things even easier.
you can check them out here: http://www.stahlbus.com/info/en/products/operation
i stil have a couple of these nipples lying around but unfortunately they're M7x1 thread and don't fit my S3.
 
#17 ·
personnally i'd stay far far away from messing around with teflon tape on brake systems; i consider my brakes more important than my life insurance. i prefer reliable brakes over cast and bandages <img src="http://www.triumphrat.net/images/smilies/ride.gif" border="0" alt="" title="Ride" class="inlineimg" />
i used to fit my race bikes with bleed nipples from Stahlbus. these are perfect: once they're in place you only loosen the top screw to bleed your brakes. they have a built-in valve so you can't mess it up. on top of that they look really nice too.
i also use their filling/draining tools which make things even easier.
you can check them out here: http://www.stahlbus.com/info/en/products/operation
i stil have a couple of these nipples lying around but unfortunately they're M7x1 thread and don't fit my S3.
This is the path I'm persuing. As much as I've been told "just wrap some ptfe tape around the threads" it didn't make sense to me after all I've read.
 
#18 ·
So to give you a little update, I got some Sealey brake sealant and one of those Stahlbus speed bleeders. I drained the brake and removed the caliper. Then removed the old nipple and cleaned and dryed the threads. A little bit of sealant on the thread of the new valve and screwed in to 10Nm. Lovely job. I think this is going to be a dream...

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#19 ·
Only issue is the possibility of steel to ally corrosion I mentioned previously. I have these on a bike I ride all year round so I back base out slightly and retorque to stop thread corroding, although I have had steel bleed screws before with no problem. I also put an o-ring around the base to reduce amount of water that can get at top of thread. For what it's worth... prob not much!
 
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