What bonds pad lining to backing plates?

[supton]

It's just regular glue, right? Am trying to figure out why I have yet another pad showing it is missing glue. Maybe this pad was never glued in this corner?



Note, the pad has about 6mm of lining left. Obviously, it's about due to be replaced, due to rust anyhow (136kmiles, so it's aging out). I can probe around under the pad using a dental pick.

This is the rotor side of things.


Other side of the car isn't fairing much better on rust, but at least the linings are staying bonded:

 

[Trav]

I read the pads are bonded to the metal with phenolic resin glue, the problem is rust from the metal around the pad begins to creep under it and pushes it off the metal, the loose hardened glue just falls away. A few pads are riveted and tend to hold up a lot better. Its a typical salt belt problem.

 

[supton]

Yeah, it's about the fourth time for me, in about 10 years, over two vehicles. Crazy. I accept it as a fact of life, just wanted to know the failure mechanism better. Rust causing glue cracking, that makes sense.

 

[Chris142]

Hmmmm. Never seen that out here.

 

[Michael_P]

As someone who commutes 7000+ miles a year by bicycle, its darned near a daily occurrence I see brake pad linings laying in the road.

 

[BigD1]

Many years ago the good premium pads were riveted, and the cheaper pads were bonded. Seems most of it is bonded now.

 

[mk378]

Yes it's phenolic resin glue, which is not commonly found in the consumer market. The resin is also used to bind the fibrous stuff in the pad itself. The resin must be heated to cure. Phenolic resin withstands high temperatures. When it does start to burn it has the distinctive smell of overheated brake pads.

 

[nthach]

Originally Posted By: Michael_P
As someone who commutes 7000+ miles a year by bicycle, its darned near a daily occurrence I see brake pad linings laying in the road.

I see them all the time on my casual rides, mostly molded pads too. I also saw the older riveted Bendix design on the roads too.

There's a Canadian firm that makes "hooked" backing plates for friction, most integrally-molded pads will use phenolic or epoxy-based adhesive. It's probably cheaper pads that use a friction "puck" that's glued onto the backing plate. Wagner ThermoQuiets are the exception to the rule, they mold in both the friction and insulator on most of those, and it looks like the backing plate in that case is more of a "frame".

 

[HerrStig]

Originally Posted By: Trav
I read the pads are bonded to the metal with phenolic resin glue, the problem is rust from the metal around the pad begins to creep under it and pushes it off the metal, the loose hardened glue just falls away. A few pads are riveted and tend to hold up a lot better. Its a typical salt belt problem.



What a nice job those rivets would do on the rotor.

 

[supton]

Yeah but I bet there wasn't much pad left by the time you got there. Meaning, it wasn't far from being backing plate on rotor.

Besides, at least up here, by the time I'd run through that much pad, the rotor would have been long gone anyhow.

 

[SwampSurvivor]

Originally Posted By: Michael_P
As someone who commutes 7000+ miles a year by bicycle, its darned near a daily occurrence I see brake pad linings laying in the road.


I do highway cleanups (volunteering, not a legal thing) and we see a lot of brake pad linings on the side of the road too. And pieces of catalytic converters

 

[CR94]

Originally Posted By: BigD1
Many years ago the good premium pads were riveted, and the cheaper pads were bonded. ...
Bonded pads and shoes were advertised as superior, because no rivet would score your disk or drum (per HerrStig's comment).

 

[CR94]

Originally Posted By: Miller88
... I do highway cleanups ... and we see a lot of brake pad linings on the side of the road too. And pieces of catalytic converters
... and v-belts and, strangely, spark plugs.

 

[nthach]

Originally Posted By: CR94
... and v-belts and, strangely, spark plugs.

I actually hit an oil filter on the ground, a Fram orange can or Delco blue can, it was a while back but I did recall seeing the filter spin behind me. It was on my bike - I was able to retain control and not eat it.

 

[Kestas]

There is new technology to prevent debonding. Tiny metal hooks are plowed up from the base metal backing before the pad material is sintered onto the surface..

I'm not sure where you could buy such pads. A quick search shows this technology seems to be aimed for the motorcycle market.

 

[BigD1]

Originally Posted By: CR94
Originally Posted By: BigD1
Many years ago the good premium pads were riveted, and the cheaper pads were bonded. ...
Bonded pads and shoes were advertised as superior, because no rivet would score your disk or drum (per HerrStig's comment).


I just made all that up because I did not see premium riveted pads in the 80's that cost more than cheap bonded pads.

Have seen plenty of bonded pads that did not have any brake material left, and they were braking metal to metal scoring the rotor. Bonded or riveted once the pad is gone it's time to change, or the rotor is going to be damaged.

 

[aquartlow]

Originally Posted By: Trav
I read the pads are bonded to the metal with phenolic resin glue, the problem is rust from the metal around the pad begins to creep under it and pushes it off the metal, the loose hardened glue just falls away. A few pads are riveted and tend to hold up a lot better. Its a typical salt belt problem.





The early riveted pads were like todays drilled rotors, had holes to vent the outgassing of the pads.

 

[Trav]

Originally Posted By: CR94
Originally Posted By: BigD1
Many years ago the good premium pads were riveted, and the cheaper pads were bonded. ...
Bonded pads and shoes were advertised as superior, because no rivet would score your disk or drum (per HerrStig's comment).


Many brake rivets are brass and should not score a decent iron rotor the ones that use steel will tear the rotor up if you let them get too far. This is still important as many brake shoes are still riveted. Most car and light truck clutch disc use brass rivets.

 

[jhellwig]

By the time you get down to the rivets the pads are shot anyways.

Most bonded pads I have seen have dimples pressed in the backing plate to lock into the material.