Do rim brake pads actually expire?

[Jere_h]

I'm currently struggling with my V-brake setup. I'm using a pair of approx. 3 year old TNN black pads with CNC v-brake packings and those were absolutely mental when they were new. Silent, tacky, locking up effortlessly. They were better than Cousts in my opinion that I loved too. The up to rears on a steep rock surface that I didn't quite make, I was still able to stick to the rock with ease and not sliding backwards. I was blown away how well the V-brake works compared to HS33 at that time.

Currently I can't get the brake to stick anymore, until squeezing very hard, but then it's also hard to release quickly when needed. There's barely any initial bite and it takes way too many cm for the rear wheel to stop completely when rolling to a ledge before drop, so I can't trust the brake in these situations. Just did a fresh grind and it helped only marginally, and I remember the grind quality never being an issue when the pads were new. It just worked no matter how bad the grind was. I've completely replaced my entire V-brake system and there's no issues, no loose that would affect etc. It's just not gripping anymore like it used to.

Could it be, that the solvents of the pad material have been slowly escaped, so that the rubber has hardened a bit and lost it's elasticity over time? The pads are barely halfway from new, they don't seem to wear much although I ride a lot.. But the time and temperature changes must have something to do with it. I sometimes ride in a freezing temperatures too before the season is officially over.

Have you guys noticed this being an issue with old pads? With tires it is very noticeable, when you swap to a new rubber it's so smooth and tacky compared to the old one that has seen some UV rays etc.
Also what pads would you recommend for cold weather, meaning I'd like something softer to compensate when they turn wooden in almost freezing temps. Jitsie blue? I also prefer a subtle grind so the brake is not too grabby when it's time to release it quickly. Probably going to give another go for a new set of Cousts because those I remember being very good even with a worn grind. But is there something now that is even better?

[basstrials]

Try to clean rim with IPA(isopropyl alcohol)or acetone after grinding,using some proper rag or towel.Give the pads a little bit of sandpaper work,just to remove old surfaces.Make sure that the pads are in a proper angle to the rims. Check out if the cable is ok and it is not loose,maybe it is needed some set up again.Where do you store your bike?Maybe sun or cold weather probably damaged the pads.Try Heatsink yellow or white with light grind with alloy backings(it is possible to put them in TNN backings with some little modification or wait until they will be released again from Heatsink site).It would be set up issue or pads or in worse scenario both.

Edited 10 hours ago by basstrials

[Jere_h]

As said in my original post, the setup is 100% dialed and not to blame. I know these brakes inside out, have designed and built my own adapters and ridden them many years now.

Rim brake contamination I have a hard time believing, but I guess that can be a real thing? With disc brakes I get it, the surfaces are very smooth and critical there. But with grinded trials rims I find it weird that any significant contamination would be left after grinding, and the pads will pretty effectively "sand" themselves after some hard braking. At least the surface looks like it now. But yeah I'm going to wash the braking surface with a brake cleaner just to see if it helps.

Just ordered some Jitsie and Coust pads to see if those would help too. I'm keeping my bikes inside mostly but at some point they have been on a sunny balcony so it's totally possible that the pads have seen too much UV radiation in their life. Still not 100% buying this theory but will see when the new pads arrive.

Another one would be, that the pads character has just changed because they are a bit thinner now than brand new. Less material, less squish would mean stiffer pad = less initial bite. At least this could be one of many reasons.




 

[La Bourde]

Difficult to know

Everyone warmly recommends the Coust brake pads but the ones I got with an used bike are OK, but I prefer the Crewkerz ones or the cheap Jitsie (but the last ones broke...)

I also assume they somehow expire.

 

Cleaning the rim may have a negative effect first.

I read that, the rim requires a first thin layer of rubber to deliver the best result.

According to my experience, that is the case (and in different applications the same applies)