Re: Disc Compatibility?

On 3/5/25 8:36 AM, cyclintom wrote:

On Tue Mar 4 15:49:26 2025 Joerg  wrote:

On 3/4/25 2:29 PM, Mark J cleary wrote:

On 3/4/2025 2:16 PM, cyclintom wrote:

Andrew, I have GRX levers and Ultegra actuators. It acts as if these
are not compatible. The levers on both front and rear will not "pump"
the brake pades close enough to the discs so that they actuate with
almost no pull. Instead they pull almost all of the way to the bar.
>
The pads are hardly worn and there are no leaks from the connections.

This is a common problem if I understand it correct from you. The travel
of the brake levers hits the bars before the pads fully engage or stop.
The first thing to do is take of the bleed nipple in the shifter and
pump it lightly with the wheel in lace. You likely have air in the
system that is not fully out. Just pump a little at a time no all the
way down to allow air to come up out of the top. Might need to do it
twice. It can be that you need to even add bit of fluid to the brakes
but see how this goes and report back.
>

>
Tom, look at the brake pads closely while pulling the handle very
slowly. If they travel the whole time while pulling they might be
incompatible. But that would be really odd.
>
If they engage the rotor and stop there but you can pull the handle
farther without the pads moving, that indicates air in the system like
Mark said. Very dangerous and it needs to be bled off.
>
When the pads hit the rotor there should instantly be a hard-stop
feeling in the brake lever. There should also never be a need to "pump"
bike disc brakes except during the bleeding process.
>
-- Regards, Joerg
>
http://www.analogconsultants.com/

    Good to see you around Joerg. My suspicion is that there is still air in the system, rather than the GRX levers not having sufficient capacity for the Ultegra actuators. The Shimano manual and video showed bleeding the brakes from the bottom up but the video of a mechanic swhowed him bleeding the brakes from to to bottom. When I tried that method I extracted a LOT of air and the levers began working. I seemed to be drawing pure fluid but I expect that there is still air in the system to the back discs. I am a little surprised that the front brake which is all up has the same lever pull though. That is why I questioned the compatibility. I began wondering if the 10 speed GRX levers have the capacity to drive the 11 speed Ultegra actuators.
 

Both front and back should have the same lever pull, assuming similar pad and rotor wear. If you got a lot of air out the question is, how did that much get in there in the first place? That doesn't sound healthy.
In a well-designed brake system air tends to bubble up towards the handles. Maybe ride around a little, get the brakes good and warm, and bleed again. I always vent at the top when bleeding my MTB brakes. Only very little air comes out, if any. The brakes always feel firm but I do it as a preventative maintenance to prevent a surpsise brake fade. I have seen that happen with a rider in front of me on a long downhill. His front faded but since he was a good dirt bike rider he saved the situation with a nice sideways slide, stopping in a massive plume of dust. And some expletives.
--
Regards, Joerg
http://www.analogconsultants.com/