Lost another brake pad last night!

[Gattopardo]

Anyway... , whatever the backing, or pad, is made of, they shouldn't part company should they. How about a poll of those that have come adrift, so we can see of there is a trend. So , that'll be 

Clarkes semi-metallic  (front)
Clarkes semi metallic  (front)

Pour moi.

We need to know the backing material....as it seems to be important.  We also need to know the materia lthe frame is made of and the pedal of the side of the brake pad material.

[Blodwyn Pig]

Colour of socks worn might also be a factor,  . Come on chaps 

[mrcharly-YHT]

Anyway... , whatever the backing, or pad, is made of, they shouldn't part company should they. How about a poll of those that have come adrift, so we can see of there is a trend. So , that'll be 

Clarkes semi-metallic  (front)
Clarkes semi metallic  (front)

Pour moi.

OEM BB7  (whatever they are)

[Gattopardo]

Colour of socks worn might also be a factor,  . Come on chaps 

And sock and insole material

[cameronp]

Tyre pressures! And brand of knicks...

[Torslanda]

Oddly enough a chap brought a Trek 3500 in at the weekend. Cheap SNG or Zoom calipers, the ones with the tiny pads about the size of a 5p coin. Pad hadn't separated but gone altogether AWOL. This is the second time it has happened, once at each end. I service the bike twice a year (he's a regular customer) and replaced the pads around 12 months ago.

To avoid any more scary incidents (both times the pad came out while riding) I took the executive decision to file the calipers under B1N and fitted a pair of Tektro Io with Oxford 'Full Stop' organic pads. I've used them for 5 years and haven't had a failure.

[Brucey]

the Clarkes pads that I have seen have had steel backings.

Re outright pad loss from some calipers;  disc thicknesses and caliper gaps vary plus both are subject to wear (yes I know the caliper gap shouldn't wear but for some users an amount of wear should be considered 'normal'... ).

The brake manufacturers also say (in the small print) that you should replace the brake pads at a certain wear state. A typical brake pad is ~4mm thickness of which about 2.4mm is friction material; most manufacturers recommend that (effectively) you don't wear much more than half the friction material away.

Some brake pads are retained in the caliper with pins and so forth and some are not; some use springs to hold the pads back (which can wear through when the pads are worn past a certain point) and some don't. Those that don't use springs use magnets instead, and magnets vary in quality; none are entirely resistant to the effects of heat (which quickly weakens them) but some are worse than others. IIRC the ones with the '5p pads' (they probably cost less than that to manufacture.... )  have feeble magnets that quickly degrade.

 The net result of all this is that if
- the friction material is more than half worn and/or
- the pads wear unevenly and/or
- the disc and/or caliper are worn and/or
- the disc is off-centre in the caliper gap (eg through lack of fixed pad adjustment) and/or
- the magnets are weakened or the springs are broken (eg worn)

then a whole pad can slip its moorings and be off on its own journey, with predictable 'look Ma, no brakes!' consequences.

If you look at it from another perspective, i.e. worst possible setup condition, it is normal to find that; 
caliper gap  - disc thickness ~= (or >)  pad backing thickness   
with  many brake designs.

 Also whilst I have not yet seen it happen in a bicycle disc brake, it is possible that (under similar conditions) even a properly retained pad could move and then jam in the caliper gap.

There's a lot badly designed calipers out there and even some pretty good ones are not immune to problems of this sort once the pads wear.  Unlike rim brakes, (unless you know exactly what you are doing), it isn't obvious at a glance what is going on, either.

cheers

[mrcharly-YHT]

It is a definite that corrosion was a factor in my losing a brake pad. The rust was very obvious on the area of the backing plate behind where the pad would sit.

That suggests that the pad is/was oxygen-permeable.

[Blodwyn Pig]

Oky doky!! swapped front pads and I thought I would compare them all!!!!!!!!!!!!!!!!!!

WP_20170802_17_33_58_Pro by mark tilley, on Flickr

firstly this is the other half of the offending Clarkes pad.   Notice 2 things....firstly how shiny the surface is, it is like this on both sides, and secondly, the tiny indentations, presumably to help bond to the braking material.


WP_20170802_17_34_35_Pro by mark tilley, on Flickr


I'm pretty sure this is an old Shimano one, notice the rough surface and the larger indentations. (these have not failed btw)


WP_20170802_17_35_20_Pro by mark tilley, on Flickr


Lastly the Nukeproof ones I have just fitted, with a painted? surface and instead of indentations, there appear to be holes, so the braking material actually oozes thro to get hold of something. Only time will tell.

[Brucey]

It is a definite that corrosion was a factor in my losing a brake pad. The rust was very obvious on the area of the backing plate behind where the pad would sit.

That suggests that the pad is/was oxygen-permeable.

Not necessarily; corrosion in a small crevice between a coating and a steel substrate causes swelling and this can 'lever up' the coating, enlarging the crevice and then creating a new surface to corrode. And so on....  All kinds of coatings (e.g. Powder coating) corrode like this. Note that whilst corrosion is implicated in the failure process, the coating does not need to be in any way permeable for this to occur.

cheers

[rogerzilla]

EBC Greenstuff friction material had a reputation for falling off the pad backplate on bikes, motorbikes and cars.  I think they've solved that now.

I've avoided Clarks since some of their V-brake pads ate my rim; they embed chips of aluminium and grit, whereas Kool-Stop don't.  I wouldn't expect their disc pads to be great either.

[Brucey]

WP_20170802_17_33_58_Pro by mark tilley, on Flickr

firstly this is the other half of the offending Clarkes pad.   Notice 2 things....firstly how shiny the surface is, it is like this on both sides, and secondly, the tiny indentations, presumably to help bond to the braking material.

re the indentations/holes; these help with the shear strength of the pad.  In some manufacturing processes, the amount by which the friction material oozes through the holes may be part of the QA process because it tells you if the material did see enough consolidation pressure or not.

BTW one cannot be sure from a photo but that backing plate looks like it might be made of a stainless steel.  It is (by and large) more difficult to make certain adhesives work with stainless steels, because the chemical reaction with the metal surface is inhibited; this may perhaps outweigh any benefit arising from its corrosion resistance in this application.

cheers
 

[rogerzilla]

I tend to agree with the late Jobst Brandt's favourite rant: the bike industry keeps re-inventing the wheel (sometimes quite literally) and re-creating problems that were solved decades before, and then forgotten again, in the drive for constant progress.  It wouldn't be surprising if they chose a totally unsuitable material for the backplate.

I'd like to say that the car industry has better engineers but we still see basic specification errors like stretched or broken timing chains having to be replaced by duplex chains in later model years, something Mercedes were having to do 30 years ago.  Nikasil, diesel swirl flaps, plastic timing belt tensioners - the list is endless.  You'd think that after 100 years everyone could make a car engine that would run for 100,000 miles without destroying itself, but only those clever Japanese seem to consistently stay just behind the bleeding edge.

[frankly frankie]

pretty sure both sets were Clarkes semi sintered (50-50)

Point of order, Clarkes make footwear.  Clarks make brake pads.

WP_20170802_17_33_58_Pro by mark tilley, on Flickr
firstly this is the other half of the offending Clarkes pad.   Notice 2 things....firstly how shiny the surface is, it is like this on both sides, and secondly, the tiny indentations, presumably to help bond to the braking material.

re the indentations/holes; these help with the shear strength of the pad.  In some manufacturing processes, the amount by which the friction material oozes through the holes may be part of the QA process because it tells you if the material did see enough consolidation pressure or not.

This is the back side of the backing plate is it not?  It appears to have circular piston marks on it.

[Brucey]

This is the back side of the backing plate is it not?  It appears to have circular piston marks on it.

yes, but because of the way they are made, there are (if there are indentations like this rather than holes all the way through the backing) corresponding protrusions on the other side of the backing which are meant to increase the shear strength of the bond to the friction material.

cheers