New to CB400 four and new here! Front brake improvement?

[Mikep328]

Thank You!  With the caliper removed (or just loosened), the spring easily moves the arm/pad back on its own.  The piston/pad is not noticeably retracting back into the caliper when brake pressure is released.  I'm now wondering if a new seal is needed.  Sounds like caliper disassembly/inspection would be a good thing...

[Oddjob]

The groove the seal is fitted into is notorious for getting hardened crud inside it, clean that really well and fit a new seal, inspect the piston for rust spots and chrome flaking as well, if any present replace that as well.

Stainless steel pistons are available to cure the rusting problem

[Mikep328]

Will do, thanks!  Any preferred source for CB400 brake caliper seals and pistons?

[Bryanj]

Classichonda spares do a stainless piston and seal kit, cheaper to buy direct than ebay

[Oddjob]

Yeah, good shout Bryan, used them myself.

[TrickyMicky]

Thank You!  With the caliper removed (or just loosened), the spring easily moves the arm/pad back on its own.  The piston/pad is not noticeably retracting back into the caliper when brake pressure is released.  I'm now wondering if a new seal is needed.  Sounds like caliper disassembly/inspection would be a good thing...

. Just be aware that, as somebody else said, when releasing the brake pressure the only returning movement is the seal regaining its original position, which is negligible. Once the whole ensemble is assembled, and on the bike,  the movement of the pad/calliper is barely visible to the naked eye. Can't remember the clearance, it's in the workshop manual which is out on the garage at present, but I'm sure somebody with a better memory than me can help!!

[Nurse Julie]

0.15mm

[Mikep328]

I checked it both with excessive clearance and the workshop manual clearance.  In both cases, after applying the brake/releasing it, there was zero clearance between the rotor and either pad.  Even the smallest blade (.05mm) of a feeler gauge set could not be inserted.

[Bryanj]

Thats Honda-classics.co.uk near daventry, he does lots of stainless bits and special tools, even decent price sets of tappets caps

[K2-K6]

If you take the caliper hydraulic side off then hold it in your hand so your fingers are on the bare piston, now squeeze the brake just a tiny bit, you should feel the piston move back in when released, like a tiny heartbeat 

This shows the seal is soft and chewy, with enough clear geometry in the groove to operate correctly. If it just moves out only, then the groove at least is not clean.

If you've not got this characteristic on any caliper really, the pads will always rub too much, possibly glaze too.

It's imperative the groove is fully cleaned to produce best operation. Lubricate with silicone grease  (it's in the original Honda manuals) that groove and seal to keep it this way as long as possible. This largely stops water (road salt etc) getting into there and causing galvanic corrosion again, it is the only real weather sealing strategy of many caliper with single seal and no boot to protect them from water.

[Mikep328]

I have ordered: braided lines, a new seal and piston for the caliper, and two sets of pads to try, Brembo and Versah.  The Master cylinder seems to operate perfectly so I wasn't planning to rebuild it but wonder if it might be a good idea?  OTOH, "If it ain't broke don't fix it" is always something to consider...

I was going to start disassembling the brake system today but decided to wait until all the parts get here so the bike isn't "out of service" any longer than it has to be.

[K2-K6]

I do a final check with any hand mastercylinder when it's all set up.

Crude but effective, squeeze it with both hands as far as it'll possibly go a few times, until it feels like everything is bending, really severe    then hold a hand behind the twist grip and hit the ball end of the lever in multiple times to pulse the whole system in a controlled violence 

During this the lever should repeatedly give the same travel, neither lengthening or pumping outward. All the seals working properly should give absolute consistency under this routine. Any real variables and you'd have to examine why that's the case.

Sounds severe, but properly puts far more elevated pressure through it than any normal use, and always verifying if there's any likely problem.

Final check, after that, roll the wheel to assess release, it should not bind at all after the above. Then ride it to see what ya got.

I do this with every front brake I work on.

[taysidedragon]

I do a final check with any hand mastercylinder when it's all set up.

Crude but effective, squeeze it with both hands as far as it'll possibly go a few times, until it feels like everything is bending, really severe    then hold a hand behind the twist grip and hit the ball end of the lever in multiple times to pulse the whole system in a controlled violence 

During this the lever should repeatedly give the same travel, neither lengthening or pumping outward. All the seals working properly should give absolute consistency under this routine. Any real variables and you'd have to examine why that's the case.

Sounds severe, but properly puts far more elevated pressure through it than any normal use, and always verifying if there's any likely problem.

Final check, after that, roll the wheel to assess release, it should not bind at all after the above. Then ride it to see what ya got.

I do this with every front brake I work on.

Sounds like recipe for breaking levers!

[K2-K6]

"Sounds like recipe for breaking levers!"

And when would be a good time to find out if there's a failure point in a brake system ?

I'm reasonably confident that any lever I could get to fail with my hands alone I'd not want to be riding with 

I work on many MTB hydraulic system too, would never want someone else to ride something I couldn't place absolute confidence in.

In all honesty I've never broken one like this. Leaking banjo, bleed closure etc detected that had given owners previous problems but couldn't be found by someone else working on them.

[McCabe-Thiele (Ted)]

If you are using a nice soft rubber headed mallet that should not break the lever - I guess it depends how hard you strike the ball end.