ZEPHYR550/400 Caliper Overhaul. Aluminum Piston Conversion (Partially)

13 June 2023

It’s the rainy season, isn’t it? Damp and drizzly… it’s been raining constantly (；∀；)

Now, I’m overhauling the original Tokico single-piston caliper and want to convert to aluminum pistons as much as possible! (wishful thinking)

I did various research and it’s partially possible (*´ω｀*)

Zephyr 400/550 Original Rear 38.08φ×28.40MM (with resin anchor)
*Please note that specifications may vary depending on model year.

Zephyr 400/550 Original Front (Large) 33.83φ×31.16MM (with resin anchor)

Zephyr 400/550 Original Front (Small) 26.86φ×30.85MM (with resin anchor)

The front (small) can be done with Honda’s resin piston only. The (large) doesn’t exist in that length.
The rear has options available.

Now let me check the rear dimensions by arranging them in images.

Kawasaki 43048-0003

The aluminum piston is about 0.9MM longer.
Please note. I’ll use this difference.

Honda 45107-ML0-016

I’ll use this for the front (small).
The resin piston is about 1.3MM longer.
Well, I don’t think anyone would copy this, but here’s a reference.

The culmination of pad grease enthusiasts gets stuck through the gaps in the resin anchor.
Often you can’t remove it without heating.

I wish old stuff would be removed and fresh grease applied.

I’ll proceed with seals for the Zephyr.
Be sure to pass them through the piston for inspection.

The key to a single-piston caliper is making the slide as smooth as possible.
I think it’s better to remove the old grease without adding more, and apply only the minimum amount.

The cylinder inner wall is also clean, and assembly becomes even more enjoyable ♪

The rear caliper is now converted to aluminum pistons.

I couldn’t find a close match for the front caliper piston (large), so
I decided to use a mix of steel and resin.

Single-piston calipers can become stiff if the boot condition is poor.
Replacing it along with pad changes makes operation smoother.

The rear bracket shape is so maniacal I had to check the parts list.
Once you see it, it makes sense, but… yeah.

DuPont Molykote SH-44M Silicone Grease
Well, anything works really“The design looks cool”

As expected from DuPont, it has an expiration date (；∀；)

RK’s sintered pads seem to be discontinued.
There are quite a few discontinued items…

I decided to use Daytona’s Golden Pad X instead.
Front NO056
Rear NO058

I wonder if axial caliper pads will become harder to find in the future.

I’m sourcing titanium bleeder nipples.
They don’t rust, which is nice (*´ω｀*)

For now, front and rear caliper overhaul and pad installation are complete.
I’m torn between replacing or overhauling the brake master (*´ω｀*)

When brake caliper seals deteriorate,
“the push and pull become heavy.”

Brake input is“pressure”
return is“seal deflection”
When seals wear out and harden, return becomes poor and push-pull becomes heavy.

When it goes “suuu~” and you think “Oh! It’s light!” – that’s when you can really enjoy your bike.