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New (to me!) '77 CB400F - US model
mattsz:
--- Quote from: Bryanj on October 26, 2018, 04:00:28 PM ---I will try a basic "how it works"
The piston seal is a square cross section O ring whilst the groove it fits into has a slightly angled base, this means that when the seal is fitted it turns into a "diamond" shape so that only one corner is rubbing on the piston surface.
When the brake is applied the seal "twists" slightly and it is this twist which retracts the piston from the pad. Thus any crap in the groove or on the seal, or tighteness on the piston stops the piston retracting and the brake sticks.
Secondly look at the bracket bolted to the fork with two small bolts at the muguard stay and one big one lower down. The big one has a steel pinthat goes through the swinging part and locates in the top bracket held by the two small bolts, this pivot also gets corroded and the pin pluss hole in the swinging bracket need thourough cleaning and copperslipingso they move very freely. The two bolts you ringed are the ones that split the caliper(no fluid will be lost) the 750 started with bolts you have to undo through the wheel spokes but 550/500/400 do not.
Hope that helps, if in doubt of assembly look at parts book
--- End quote ---
Thanks for the detailed explaination, Bryanj! I do understand how the piston interacts with the seals, and why the condition you describe could cause trouble. I'll study the brackets alongside your explanation, as I'm still not sure why the floating caliper should require manual adjustment. I'll get there, though...
mattsz:
--- Quote from: Oddjob on October 26, 2018, 04:18:01 PM ---One of the first things you should buy if you haven't already got some are these.
http://ruggedroads.co.uk/JIS-Screwdriver-Set-Vessel-Megadora-P1-P2-and-P3
A good set of JIS screwdrivers will pay for itself very quickly by not chewing up all those screws on the bike so that you have to buy new ones.
When splitting the caliper be prepared for some real gross looking fluid coming out, I suspect the fluid hasn't been changed since it left Japan.
As for the speedo drive screw, it's clear someone has already attempted to remove it by using a punch, they may have succeeded and just reused the screw, try lightly tapping the screw with a punch and hammer counter clockwise using the existing punch mark and see if it starts to spin out, if your lucky it will.
--- End quote ---
Thanks, I'll look for some. Does anyone know if the two "cross-head" screw driver shanks in the OEM tool kit are JIS-friendly?
K2-K6:
These calipers are a bit of a hybrid between manual and hydraulic.
The hydraulic, obvious as indicated. The back side hasn't a hydraulic retraction, just done by the little spring until the caliper swing hits the stop screw. So you set stop screw to give clearance required, but as the back pad wears you have to "chase " it with adjustment else the pad ends up with too much clearance, and so increases brake lever travel just to bring pads into contact with disc.
That back part is in essence the same as any cable operated brake.
mattsz:
--- Quote from: K2-K6 on October 26, 2018, 05:14:07 PM ---These calipers are a bit of a hybrid between manual and hydraulic.
The hydraulic, obvious as indicated. The back side hasn't a hydraulic retraction, just done by the little spring until the caliper swing hits the stop screw. So you set stop screw to give clearance required, but as the back pad wears you have to "chase " it with adjustment else the pad ends up with too much clearance, and so increases brake lever travel just to bring pads into contact with disc.
That back part is in essence the same as any cable operated brake.
--- End quote ---
So... if everything is working correctly, the adjustment doesn't change how the pads wear relative to each other, just brake lever travel? I suppose so, but doesn't the piston's movement relative to the seal affect this, too? Why not just have no spring and no adjustment - let the caliper slide freely and the piston, on one side only, will take up any adjustment needed, like my "modern" bike's caliper?
K2-K6:
Yes, as you think, it doesn't affect the wear as that is only the hydraulic force clamping it. And also same forces as the modern ""sliding " single piston type.
It is a bit cock-eyed though (in purist engineering principles) as they've started with a swing geometry so the pads will ultimately wear in a taper, then felt the need to give some sort of assistance plus limit to the assembly. Compared to the straight up design within the engine it does appear to be an odd compromise.
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