[Maintenance Log] SR400 (FI) Statutory Inspection! Elevating Braking Feel with Sunstar Brake Discs

During inspections, I propose replacing various wear items.
There are surprisingly many parts that technically work but are in less-than-ideal condition.

I’m currently based in Chiba too, and I want to keep bikes in a condition where you can “ride carefree for two years without worry.”
You get both comfort and peace of mind, so riding becomes genuinely fun.

Day in and day out, I live by the motto “no complaining, no criticizing.” (*´ω｀*)

Chiba Relocation 1st Anniversary Inspection Certificate Holder—Limited Stock Available! (*´ω｀*)

After four years of use, the battery performance is quietly impressive

Lately I’ve been recommending this AGM-GEL battery for its reasonable price and high durability.
Rather than running a battery until it’s completely dead, replacing it after a certain period is best practice.

Startup performance improves dramatically, and interestingly, the overall feel seems to improve slightly too.
You might think it doesn’t matter since the alternator is charging, but it actually does.

I check the maximum output voltage at various RPMs.
A little extra effort makes a huge difference in reliability.

Fuses are definitely worth checking during maintenance.

Fuses are cheap—if they look dirty, I just replace them.
This is basically a good-luck ritual (*´ω｀*)

Always give a new battery an initial charge.
Sometimes they arrive partially depleted. You want that full punch when you hit the starter button.

Brake disc is Sunstar & Daytona Sintered

Large center bore with a modern design.
Excellent compatibility—I’m amazed at how many bikes it fits.

The brake caliper was reasonably clean.
Piston operation is fine.

Single-piston caliper enthusiast here.
Fine deburring makes movement about 1% smoother.

I clean the bolt threads to eliminate vagueness in tightness.
It’s subtle but makes a real difference in feel.
If thread-locker residue remains, torque can reach spec too quickly.
The question isn’t whether a bolt stays loose with thread-locker—it’s whether it’s properly clamped and stays tight as it should be.

Also, replace dust boots generously.
They cover the slide pins, and stiffness is bad news.
Always lubricate slide pins with silicone grease.

I also use silicone spray to keep movement as smooth as possible during assembly.

As I’ve gotten older, I’ve come to appreciate single-piston calipers. And seeing cracks in aged dual-piston calipers (especially from Brand B),
I realize manufacturers really understand cost-benefit balance.
Braking performance has improved so dramatically with modern discs and pads…

that’s my impression anyway.
Heat-treatable stainless is limited, but…

Oddly-shaped wheel hub

Unique to Yamaha? I’ve only seen it on the SR400 in our shop.

The hub has no bearing—it’s a free-floating design.
Pretty innovative!

The hub damper is still in good shape, so I reused it.
But I wanted to tighten clearance a bit, so I added POM shims.
This time I used six shims for 6mm of preload (*´ω｀*)

Turned out great and feels solid.

Replaced the drum shoes while we’re at it.
After vacuuming, I wet-blasted them to this shine ☆
It’s not a visible area, but it should help a bit.

Assembled with Yamaha OEM parts—perfect fit.

Axle shaft and wheel bearing check

Axle shafts rarely bend, but it’s good to check anyway.
I also inspect and adjust wheel bearings— knowing the bearing number makes ordering easier later.
Most people don’t order OEM wheel bearings, but…
it’s handy to know (*´ω｀*)

I also lubricated the speedometer cable.
Honestly, I’ve never seen anyone break a cable.

Replaced fluid, air filter, and spark plug too.
The SR400’s simplicity and serviceability are why it’s so beloved.

Test ride before the rain—chop chop! ♪

Thin tires like this are genuinely wonderful.
There’s real feedback and it’s incredibly fun.

Going wider for looks is totally valid, but
“wait, something feels off?” —I bet many people have felt that.
Manufacturers really nail the balance.

The FI version starts so easily—nothing like the old SR!
It fires up almost instantly, so even people who hated old SRs can come back to this.
Light, punchy, comfortable seating, and it feels like you could ride forever.
Braking and cornering feel refined now.