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Pretty much every master cylinder made has a return hole.
Try googling "airhead master cylinder return hole" if you want to see exactly where it is.

I'm pretty sure your bike has the composite (plastic?) type pistons in its calipers.
These types of pistons very rarely (like almost never) seize in their bore.

Kurt in S.A. wrote: ↑Tue Apr 13, 2021 6:36 am The distortion of the square-oring seal between the piston and the caliper housing is what pulls the piston back after brake application. To a smaller degree, the eccentricities of the disk might "slap" at the pads to push the stack farther into the caliper.

Kurt in S.A.

HI Kurt,

I stand by what I say. Yes, the square seal does move the piston back very slightly, enough to take any pressure off the pads but there is no guarantee that this moves the pads completely out of contact. Consider the ATE caliper as fitted to early bikes. The caliper itself is free to move without restriction... the limit to that movement is in fact contact between the pads and the disc. Consider, also, the later Brembo caliper (and indeed, many, if not most other calipers). There is no rigid connection between the piston and the pad. Once the pressure is off, the pad can move independently. Once again, the limit of pad movement is contact with the disc. Finally, consider disc systems with floating discs. In this case, it's the disc that can move in relation to the pads. Slight contact between pad and disc is quite normal and should not be considered a fault... any residual retardation is, however, a problem.

Rob

I certainly think it's a combination of things. I don't routinely test my front brake on the /7 while on the center stand...I have the Reynolds Rideoff so I can't really check it easily. But I seem to recall that when say having the tire off the ground and then apply the front brake and release, the front tire will turn...it's certainly not still clamped. Sure there was problem some audio hint of rubbing, but the o-ring was enough to pull it partially back. Further rotation is bound to push at the piston/pad to fully clear the disk. All of this together keeps the disk running fairly clear.

As for the OP, I do agree that doing the easy things first makes sense. Definitely check the master cylinder return hole. I've never had a bike with the handlebar master cylinder but I imagine you can look into the bottom of the reservoir and see the hole and/or see little bubbles of fluid every time the lever is squeezed and released.

Kurt in S.A.

Thanks again guys!!
What made me notice this situation was, after a hundred or so mile ride, I had a lot of resistance pushing the bike back into a parking spot. Also a light coating of brake dust on the rim.

Here is the latest development... Master is making a creaking sound and shows signs of leakage around the plunger. I guess all the bleeding and working it has made this issue show up. I have the exact same Magura master on my 94 K bike and it is completely silent. I guess I am going to need to bite the bullet and rebuild the master. I will replace the rubber line as well while I have it apart.

I would at least open up the caliper to see what it's condition is like.

Go ahead, ask me how I know.

and change your brake lines. Manufacturers often require new lines a 4 years.

When you have the master apart pay close attention to the bore way down there in the area when the fluid is compressed, if you see any pitting then having the unit resleeved is a good option. I have used 2 different sources for this process, one in brass and the other in stainless. Cost is around $100.00.

gg

This'll cause drag...

Ok Thanks again to all you guys!! Master off, torn down and ready for rebuild. Parts on order with new braided brake line.
For those looking for the "return hole" on the handlebar mounted Magura master: It is to the left in line with the other hole. It is in a half circle indent just under the lip of the reservoir. Very hard to see with reservoir in place. Easier to take this off to get to it. This is literally a tiny pin hole.
This was filled with a clay colored mud. I think when this is the case... time to rebuild it!
What happened with mine was the rubber seals had simply gone bad (cracked).
The cylinder bore had no pitting, so a bit of clean up is all that was needed.
I got the rebuild kit from Euromoto for 100 bucks.
I think I got lucky because I do change the brake fluid periodically.

I hope this helps anyone who may have similar issue.
You guys are the best!!...keep you posted, Thanks again!!!

Hi
I went through loads of this on a R100R. I stripped the calipers, multiple times, rebuild with new seals, new hoses, new discs, new pads, fresh tin of fluid, red rubber grease everything!

I took it to a garage for help who found that the paint on the pads had gone gloopy and make them cock over on the return. Money well spent, I just wish I had not wasted my time with all the work I did!

George