Brake woes

[Alexander Finger]

thanks for the insight :)
I'll keep you guys posted about the progress, we're down to the south of
France next week with the Africa Twin and the GS750,. first..

Jeff Walker <walkerjl at charter.net> schrieb am Mi., 3. Juli 2019, 00:17:

>    Brake temperatures at the pads routinely get past 200C, or 394F. During
>    hard continuous braking, like going down a long hill at speed they can
>    get to 1000F. 200C is easily hot enough to vaporize condensed water in
>    brake fluid after heat transfer through the pad material and caliper
>    pistons. All it would take is for a micro drop of water to vaporize to
>    make the hydraulics feel spongy. Further, I've seen it happen on a
>    poorly maintained car before. The water always condenses at the lowest
>    point in the system, and that's also the hottest part of the
>    hydraulics, at the piston calipers.
>    Unless they've overheated routinely, it's far more likely for the seals
>    in a master cylinder to fail than a caliper piston seals. The
>    degradation mechanism comes from sliding wear, and the piston calipers
>    hardly move at all. The good news is that the master cylinder also has
>    the least contaminated fluid at it's seals, as the corrosion products
>    migrate down to the calipers. The counterpoint is that the heat at the
>    calipers causes hardening of the elastomers in the seals.
>    However, that being said, sticking calipers almost always stick in the
>    applied direction and fail to retract, vs sticking such that they
>    prevent the hydraulic force from squeezing the pads on the rotor. Or if
>    the seals are failing, brake fluid leakage is evident.
>    Otherwise a master cylinder seals can leak by and fail to produce
>    hydraulic pressure with no evidence of leakage. That's what happened to
>    my rear master two years ago. Very minimal brake force applied at full
>    stomp, then it would fail to retract when I took my foot off, and no
>    leakage. Rebuilt it and it's back to perfect.
>    In the last 130K+ miles on my GPz I've gone through several sets of
>    pads, but I'm still on the original calipers. I always bleed them
>    before and after pad replacement, as pressing the pistons back in to
>    install the new pads always frees up more gunk to be flushed out.
>    New brake lines are always challenging to bleed the first time. My
>    metal braided lines both connect at the master cylinder, each having a
>    straight run to their respective caliper and eliminating that "Y"
>    cylinder above the fender. Much easier to bleed that way.
>    Just goes to show the importance of preventative maintenance. I flush
>    and bleed the brakes on all my vehicles every two years regardless of
>    how often they're used. As a result I very rarely have any issues with
>    the brakes outside of normal pad wear. The rate of degradation of the
>    brake fluid is mostly time dependent, not mile dependent.
>    Sorry for the long winded response, but as a mechanical engineer that
>    specialized in maintenance, troubleshooting, and failure analysis of
>    far more complex systems I get interested in topics like this.
> ______________________________________________________________________
> GENERAL GPZList MAILING LIST INFORMATION:
> This is from the GPZList mailing list. GPZList at lists.micapeak.com
> http://lists.micapeak.com/mailman/listinfo/gpzlist
> You subscribed to this mailing list. Therefore, you solicited all
> mail that you receive from this list. Therefore, ANY mail that you
> receive from this list is, by definition, NOT Spam, and if you report
> it as such, you are violating the lists.micapeak.com terms of service.
>
> To unsubscribe, you may send email to
> gpzlist-unsubscribe at lists.micapeak.com
> ______________________________________________________________________
> YOUR PERSONAL SUBSCRIBER OPTIONS:
> Unsubscribe or choose new options at
> http://lists.micapeak.com/mailman/options/gpzlist/af%40genevainformation.ch
> You are subscribed at the email address AF at genevainformation.ch
> ______________________________________________________________________
>