I haven’t heard of someone using the fluid as a cleaner and then following up with alcohol. In that case, it seems fine, if just a bit more complicated.
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Fair comment. I was just following Calvin and to be fair, it didn’t take very long.
Even if it’s not the main cause of my problem, it doesn’t seem bad to clean the caliper thoroughly. I was about to do that as a part of the winter hibernation anyway!
My view is that using mineral fluid to clean pistons essentially introduces a lubricating film around the periphery of the piston, which isn’t ideal. The piston seals act like springs to retract the pistons back to their preset positions** once pressure within the system is released, once you’ve let go of the brake levers. The seals in hydraulic disc brake calipers are carefully designed to do this, but not excessively so, so that the pistons can advance further forward towards the rotors, as compensation for pad wear. Adding mineral fluid into the mix as such, disrupts this fine balance, as well as (now) introducing a coating that’ll attract brake dust and other debris onto it. When the piston retracts, it pulls these contaminants with it (over time), into the hydraulic system, while also possible abrading the seals. it’s worth bearing in mind that brake dust, however minute, are essentially abrasive, especially if they’re coming off metal pads. Youl’ll notice the residues worked into the surface of the white ceramic pistons of Shimano calipers, when no amount of cleaning can remove.
That’s my reason for using IPA to clean pistons, and never mineral fluid.
** advanced, or otherwise, to compensate for pad wear, or in the OP’s case, to reduce brake lever throw.
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Very well explained 
.
In addition, I’ve found on SRAM braking systems ,with oiled pistons, that the piston does not fully retract and after time the brakes constantly rub on the rotor.
Thanks. I’m sure that using a cotton bud with IPA would be just as effective in terms of cleaning (i guess). So can easily do this method, even though i doubt there’s any brake fluid on the caliper by the time it’s moving again.
To be fair, the park tool video was to address sticking calipers / seals, so a specific use case for using brake fluid - not just cleaning.
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Reach ist how far away the lever is away from the handlebar.
Free stroke is how far you have to pull the lever until it does anything.
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I would caution against using brake fluid to lubricate the pistons. I did exactly that after watching the same Park Tool video and thought I had thoroughly cleaned the pistons with IPA. Nope, I ended up contaminating the brake pads.
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I think we have a clear consensus: use IPA for cleaning and only use brake fluid for sticking pads (assuming cleaning hasn’t already solved). If brake fluid is used, use sparingly and clean throughly afterwards.
A little thread drift, but still on brakes.
Contaminating pads.
This seems to be a more common reoccurring preventable problem.
I can’t count how many times I have observed or heard of folks bleeding brakes with the pads installed and accidently pop a hose off and whoops…
Remove the brake pads for any fluid related task. Quick n easy task. Free pad insurance.
Something that has yet to be mentioned in many forums that I believe is causing issue with this generation of lever is Servo-wave technology. Essentially the pistons move more during the early part of the lever movement giving what is described as ‘progressive’ brake feel which then apparently translates to more braking power for less hand effort. Google it for a more succinct description.
As a proficient shop mechanic, I had one particular bike this year that no matter how many bleed procedures and tricks I tried I just could not get these brakes to feel good. Without going to into the weeds I’ll just set a small test for anyone with the st-r8170.
Find a bike with the 105 equivalent brakes (st-r7170) and let me know which brake you prefer the feel of. As mentioned above, the Ultegra brake has servo-wave with progressive braking were as the 105 equivalent is linear. It is my opinion that the gimmick of servo-wave has made the braking worse.
PS @Simon_Lockwood I worked in the Bike Boutique 10 years ago with Steve & Cheryl as mechanic and Wattbike trainer. Pretty sure we met somewhere or maybe I just recognise your CCL kit in the photo.
@Ciaran_O_Hara - Yes!! i used to ride saturday mornings from BB in around 2015/16 
I struggle with the same situation, the free stroke is just too long before it bites and the lever can sometimes hit my finger before fully breaking (especially in winter with think gloves).
I solved this with the free stroke adjustment, I just want to caution you about a couple of things if you do this:
- If you adjust the freestroke you might get a small rattle in your STI. It is is annoying but i have not yet found a real solution.
- The freestroke adjustment works by already inserting the piston partially into the cylinder. This means that the connection between the reservoir and the airbladder is blocked, which has a couple of interesting consequences.
2a. You can no longer bleed the system (this is important, a bike shop that did a bleed for me once told me the STI was blocked and had to be replaced, while it was just the freestroke that had be set back to 0 again)
2b. The automatic adjustment of the brakepads no longer work, so if you ride and the brake pads become thinner your effective freestroke becomes larger again.
The above I find really annoying, so your business card trick might be really a good solution. I heard that in the pro-peleton they use worn rotors for freestroke adjustment for example.
Will keep an eye on this thread to see if anyone has a better solution to this!
Surprised by 2b. I thought the auto adjustment for pad wear was from the caliper moving through the caliper seal a bit more before hitting the rotor, then the seal moving it out a tiny bit but using the new caliper position. But i’m a mechanical clutz!
The free stroke adjustment should NOT close off the reservoir. That said, I have come across a few instances where reducing free stroke to the minimum did exactly that. Frequency of occurrence must be less than one in 200 levers (Shimano).
For the brakes to function properly, the master cylinder must be open to the reservoir when the brake lever is not engaged. It is not only for wear compensation. It is also to handle fluid expansion due to heat. If the system was closed, braking on a long enough descent could expand the fluid enough to lock the pads to the rotor, clearly a huge safety risk.
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