School me on brakes

Merlin MR29 around 2008-2009 from what we know.

What is this knurled knob used for? Best I can tell, it takes up the gap between the pads and the rotor since the calipers have springs that keep pressure off the pads to reduce friction?

My problem is that I don’t have enough brake pressure. The pads look plenty thick, but maybe I need new pads?

I want to put new fluid in and drain the old gray yuck. How do I bleed these, I see no classic looking bleeders.

I’m sure I’ll have more questions. Thanks in advance for your kind help.

’ What’s the knurled knob for?’ Well its specifically not for adjusting the pad to disc clearance. That adjustment is done at the caliper by either inserting shims between the pad and the caliper piston or removing shims from between the caliper halves. Required clearance about 1 mm. per side.So set that up first.

Slacken off the knurled knob and check that the master cylinder piston is returning fully. You are now ready to bleed the system.
Fluid is likely to be DOT 4 (glycol based) but could be DOT 5 silicon. DOT 4 dissolves in water is normally yellowish and smells of brake fluid. DOT 5 doesn’t.Take a sample from your system and use the same spec.fluid to bleed. Remove the filler plug from the m/cyl and screw in your bleed tower or improvised alternative. Remove the bleed screw from one side of the caliper ( small allan cap head screw )and run fluid through the system until clear and free from air bubbles. Replace bleed screw and repeat for other side. Remove tower and replace filler plug.Take up slack in m/cyl operating rod with knurled knob.

Recommended refinements .Remove pads and correct any taper wear. Strip caliper remove pistons and seals clean out thoroughly and replace. You have a spring return caliper as distinct from a self adjuster.Glycol fluid will attack your paintwork. And the best of luck!

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Thank you for your time, that was very helpful.

Figured I’d report back as a courtesy for your help. The MC was nearly empty, fluid dirty, and the knurled knob and return-stop misadjusted.

I flushed with clean fluid and bled using this home-made contraption (go ahead and laugh). It turns out that you can use 1/8” pipe thread in the MC plug threads if you just barely go finger-tight, and that’s enough to keep gravity pressure from leaking fluid all over (and presumably air getting in).

Firm pedal, short stroke, plenty of room to modulate pressure.