 You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
Morning all
Here's the situation.
XTR lever with an SLX 4 pot caliper, seals failed on the original caliper and I fancied a bit more stopping power.
I've been running the above for a few years with no issues and now when I hop on the bike when its cold there is minimal stopping power and the brake squeels.
However, after some vigorous braking it works OK again.Â
Could this be down to a micro leak in the caliper mildly contaminating the pads and then getting burned off with the braking?
Or am I barking up the wrong tree.
That's my experience.
Have a look on the back of the pads for fluid, if you're unsure clean the pistons and pad backings well and have another look in a day or two
This is most likely related to the friction material attached to your pads - it's probably nothing to do with the mechanics of the caliper/lever/master cylinder.
You would be amazed to see the friction value change that can occur in some friction materials. It can literally double with temperature increase, atmospheric humidity, hydraulic pressure or even wheel rotation speed.
I do work on vehicle dynamometers, we measure and record loads of values and the pad friction value goes up and down all the time. Different blends of friction material behave differently and disc/pad temperature is one of the major causes for friction variation :o)
Your "vigorous braking" is simply warming up the pads and that is increasing the friction value which reduces the lever force required to slow the bike and that feels better.
I had this issue with SLX 4-pots within a few days of fitting them from new. Horrible squealing & could squeeze the lever and push the bike along the garage floor with the wheels turning. Then within the first hour of a ride they'd suddenly start working as normal as they heated up. Changed the pads & fully cleaned the rotors and same thing happened.Â
I eventually changed the pads (again) & rotors at the same time and it never happened again. Not sure what could have gone wrong but I must have contaminated the rotors incredibly deeply somehow whilst fitting them. Couldn't see any residue around the pads, pistons or anything upon many inspections but hey ho. Â
I have had similar issues with a set of 2-pot Shimano brakes on my hardtail, as well as the original Shimano brakes that came with my bike. I am certain there is something in my workflow that is causing this.Â
"I have had similar issues with a set of 2-pot Shimano brakes on my hardtail, as well as the original Shimano brakes that came with my bike. I am certain there is something in my workflow that is causing this."
I feel seen. Always seem to have more brake issues than my riding mates, regardless of the brand or model of brake. I try to be really careful fitting and bleeding brakes but they too often seem to go squishy and/or weak. Sanding, cleaning, new pads and bleeding might see an improvement but it generally doesn't last...
Can only assume it's either something I'm not doing right when working on them (but I'm a pretty decent spanner wielder in all other areas of the bike), or something in the way I use my brakes (I can get a bit draggy, but not sure what impact that would have?).
Since I bought a blow torch, I have not had any contam issues with pads or rotors. I clean the rotors with cloth and isopropanol, then clean again with cloth and water, then blow torch them. Obviously, the cloths themselves need to be clean and contamination free. Lightly blow torch the pads, can't remember if sanded them or not, just lightly I think.
Bleeding the brakes, I make sure the rotors and pads are nowhere near the area as I tend to make a mess. Isopropanol soaked cloth again, maybe a toothbrush, for cleaning the caliper. Also lever and hose. Just want to completely reduce any chance of contam from the bleed process.
Before I started using a blow torch, the brakes would initially be okay right after cleaning, but over the course of a ride they'd bit crap again.
I would tend toward saying if they get better during the ride, it's not contamination.
New pad compound? New disc and proper bedding in, that is plenty of hard braking without actually stopping. Use a hill, don’t try and do it in the stand.
My experience of this in the past with Shimano brakes was due to a micro leaking caliper
Cheers all.
I might give that blowtorch technique a try, because it involves a blowtorch.
I'd bet a significant number of brake pads that it's a leaky caliper. You've got all the classic symptoms. It goes away during a ride as some of the fluid burns off.
Transfer port microleak has symptoms like this. Could be that, could be your systems.