Sheared Bleed Nipples And Adapters

[jim21070 2]

I am currently battling the dreaded sheared-off nipple in a aluminium caliper monster. It's not GTi caliper but a very similar one from our 205 Junior.

 

In the past I have successfully drilled out a sheared nipple with a 6.5mm drill and re-tapped the hole to M8. However I have never been entirely happy with this method as there is not much length in the resulting hole to cut a good, long thread and it is all too easy to damage the nipple seat and end up with a less than perfect seal.

 

I thought about an alternative method and knocked up on the lathe a very rough (test of concept only) adapter that takes a standard M7 bleed nipple in one end and has an M8 thread on the other end to screw tightly into a retapped M8 thread in the caliper.

 

I made it out of brass as I have a bit of round stock lying around.

 

Question is though, as brass and aluminium have very different galvanic potentials I am concerned that in service and in the presence of salty winter water the brass of the reducer might eat into the caliper moreso than a steel bleed nipple does. Also, is it likely that a steel bleed nipple will seize in brass just as much as it does in aluminium.

 

I was thinking that brass jets are used in aluminium bodied carbs without a lot of problems but then they don't get flooded by salty water. I can't think off-hand if brass, steel and aluminium are used anywhere else together like this where they may get wet.

 

Any thoughts?

[chris1986 1]

if i ever sheer one, i can usually drill it down the middle and put an easy out down it and it brings em out. oh and give a hit with a hammer to shock the rust apart. have you tried asking a garage if they have any spare nipples. we keep spares at my work.

[jim21070 2]

if i ever sheer one, i can usually drill it down the middle and put an easy out down it and it brings em out. oh and give a hit with a hammer to shock the rust apart. have you tried asking a garage if they have any spare nipples. we keep spares at my work.

 

You are one very lucky person Chris. In all my work on ally Pug calipers I have never successfully got a sheared nipple out. Once only I broke an easy-out trying. Never again. I've tried all the usual tricks (and a few unusual ones) without any significant success so now I just go straight to drilling them out with a 6.5mm drill, tapping to M8 and putting an M8 nipple in. In my experience, they get so well corroded thay appear to be welded in. Even the flexi hose can be jolly tight too!

 

As I say, I'm not entirly happy with this method, being able to cut only about 7mm of thread and the risk of seat damage. I don't entirely trust it as a good, quality repair. Hence I was looking at an adapter solution to retain the original M7 size nipple in an M8 hole. I'm most worried about dissimilar metals corrosion if I use brass to make the adapter.

[M3Evo 0]

My wilwood calipers have brass nipple ( ) holders into alloy calipers and then steel bleed nipples if that's any help?

 

I'd be more concerned about the extreme lack of material between the M7 and M8 threads, unless you've made the brass bit long enough to space them apart?

[PumaRacing 2]

Brass will be no worse in aluminium than steel so I don't expect you'll find a problem. Brass is pretty soft though so when you try to remove the bleed nipples if there is any corrosion they're just going to round off.

[jim21070 2]

I'd be more concerned about the extreme lack of material between the M7 and M8 threads, unless you've made the brass bit long enough to space them apart?

 

Yes, absolutely. I made my test piece with a 10mm x 10mm boss above the M8 thread so all the M8 part of the thread has is a 1.5mm hole (to let the brake fluid through to the nipple) to weaken it. The M7 nipple thread is up in the boss. There is plenty of clearance available (on a 205 Junior at any rate) for this longer nipple assembly.

 

Thanks Dave for the note about corrosion. I'll go ahead with it now.

 

I've got hold of some M6 nipples today so will make a better example using those. Using a smaller nipple will allow me to reduce the size of the boss. I'll post up some pictures when complete.

[Jrod 7]

If it intrests you I've got a pair of calipers you can have for cheap.

Edited September 28, 2006 by Jrod

[jim21070 2]

If it intrests you I've got a pair of calipers you can have for cheap.

 

Jrod, you have a PM...

[jim21070 2]

This is a poor picture (blame my camera ) of my second prototype bleed nipple reducer using an M6 nipple.

 

 

I shall try this one out for real on a caliper and see how it goes. It might well prompt a redesign.

 

Watch this space...

[Turbo7379 3]

If you're worried about corrosion why don't you make the adaptor from stainless steel . Then put the adaptor into the caliper using high strength loctite & use copper grease on the bleed nipple . That way you'll not have to worry about galvanic corrosion - the loctite will prevent corrosion between the caliper & adaptor .

 

BTW , how did you get the seat cut in the adaptor for the bleed nipple ?

[M3Evo 0]

Aah but the oil in the copperslip might corrode the seals in the caliper!

 

photo of my second prototype bleed nipple reducer using an M6 nipple.

 

Looks very neat, just needs some flats on the adaptor I guess?

[jim21070 2]

BTW , how did you get the seat cut in the adaptor for the bleed nipple ?

 

 

Just by drilling the hole on the lathe with a high quality 5mm drill (M6 tapping size) created a perfect seat It seals perfectly.

 

I'll be using loctite to seal the threads and I've always used a trace of copperslip on nipple threads for years without problems. Once belleding is complete I then cover the nipple and its exposed threads in copperslip.