Safety is a top tier priority on your vintage Honda motorcycle. The Honda CB350G / CB360 / CB450 / CB500 / CB550 / CB750 series of bikes were some of the first mass produced motorcycles using a hydraulic brake system and when you throw the age of these components into the mix you have a disaster waiting to happen. Being that we make everything you need to get your hydraulic brake system in tip top shape we thought it was time we gave you a full guide on how to put it all together. Be sure to watch both part 1 and part 2 to learn how to disassemble, inspect, rebuild, replace and properly install all of the pieces in your hydraulic brake system.

Part 1

Honda used a very similar single-disc hydraulic front brake layout across many mid-to-large displacement motorcycles from the late 1960s through the late 1970s. The example shown here is a Honda CB550K3, but the same basic master cylinder / rubber hose / junction block / hard line / caliper arrangement commonly appears on many of the twins and four cylinder motorcycles of this era.

Compatibility

CB350G

CB360 / CB360T / CB250

CB450 / CB500T

CB500K / CB550K / CB550F

CB750K / CB750F / CB750A

Safety Notes

Brake fluid damages paint. Cover the fuel tank, fender, and any painted surfaces before opening the system.
Work clean. Brake components do not tolerate dirt. Keep rags handy and cap open lines when possible.
Do not reuse contaminated friction parts. If brake fluid has soaked into the pads, replace the pads.
Verify for leaks before riding. A hydraulic brake rebuild is only as good as the sealing surfaces and final tightening.
First ride = gentle test. Use light brake pressure and confirm the motorcycle stops predictably before riding normally.

System Overview

Start at the handlebars and work down:

Master cylinder
Upper rubber brake hose (master cylinder to junction block)
Junction block (splits/joins the line routing; usually includes a brake light pressure switch)
Lower rubber brake hose (junction block to hard line)
Lower hard line (hard line down to the caliper)
Brake caliper assembly, typically including:
- Bleeder screw
- Caliper body (active/piston side)
- Pad holder (passive/static side)
- Caliper swing arm (mounting/pivot mechanism)

Tools and supplies

Penetrating oil
Sockets & Wrenches
Catch pan / dish for fluid
Rags and paint protection
DOT 3 brake fluid
Caliper grease (high-temp brake grease)
Anti-seize compound
Fine abrasive/sandpaper (for cleaning corrosion in the pad pocket if the caliper body is being reused)
A vise can help on stubborn parts

Parts planning: What typically gets replaced?

On a neglected/locked-up system, plan for a “replace-first” approach on wear items and rubber.

Common “replace without debate” parts (as shown in this rebuild):

Component	Replace reason	Notes
Rubber brake hoses (upper and lower)	Aging, cracking, internal breakdown	Replace even if they look acceptable; age alone is enough.
Brake pads	Wear and contamination risk	If fluid touched the pads, replace.
Caliper piston	Pitting/corrosion causes leaks	Pitting is a strong indicator the piston will not seal reliably.
Caliper piston seal	Hardening/swelling/age	Replace whenever the caliper is rebuilt.
Bleeder screw	Damaged or seized	Replace if head of threads are worn
Master cylinder diaphragm (and often the master cylinder)	Old rubber and internal corrosion risk	If the master cylinder is questionable, replacement can be the faster, safer path.
Crush washers	One-time seal	Use new crush washers at banjo fittings during final assembly.

Parts often reused after cleaning/inspection (if in good condition):

Hard line
Banjo bolts
Junction block and brake light pressure switch (if functional)
Caliper body and passive pad holder (if corrosion is removed and sealing surfaces are good)
Caliper swing arm and pivot pin (after cleaning and regreasing)

Disassembly: How to tear down a locked-up front brake safely

Break fasteners loose while mounted

Apply penetrating oil to brake line fittings and caliper fasteners.
While the brake system is still mounted to the motorcycle, crack loose each fitting/bolt without fully removing it.
Use the motorcycle’s stability to your advantage—mounted parts give you something solid to “fight against” instead of twisting parts in your hands on the bench.

Remove caliper, lines, and junction block

Remove the caliper from the motorcycle.
Remove/route the caliper swing arm as needed (it may be tied into the fender area).
Remove the hoses and junction block components as the system comes apart.

Note: If the system is crystallized and “dry,” it may not gush fluid—but still assume brake fluid can drip at any point and protect paint accordingly.

Bench technique: How to push the caliper piston out hydraulically

A stuck piston is easiest to remove using hydraulic pressure rather than pliers or brute force.

What you’re doing: Using a master cylinder and brake line filled with fluid to push the piston and pad out of the caliper.

Connect a master cylinder to a brake line and hard line (any functioning master cylinder can work for this purpose).
Add old brake fluid to the master cylinder reservoir (fresh fluid is not required for piston removal).
Submerge the open end of the line in fluid in the reservoir.
Slowly squeeze the lever to purge air until bubbles stop.
Connect the line to the caliper.
Place the caliper in a catch dish.
Pump the lever to push the brake pad outward and then continue until the piston pops free.

Inspection: Deciding what to reuse vs replace

Caliper piston

Wipe the piston clean and inspect the surface.

If the piston has pits, treat it as a replace item. Pitting commonly allows fluid to bypass the seal, leading to leaks and pad contamination.

Caliper body and pad pocket

The caliper body can sometimes be reused if it cleans up well.

Clean the caliper thoroughly.
Remove corrosion from the pad pocket and piston area (the pad needs to move freely).
Test fit a new pad:
- The pad should drop in cleanly.
- The pad should remove easily.
- If the pad binds, corrosion is still present and needs more cleaning.

Hard line, banjo bolts, and junction block

Hard lines can be reused if they clean up well and show no damage.
Banjo bolts can often be reused if threads and sealing surfaces are good.
Junction blocks are commonly reusable; the factory paint mark can be an indicator it has not been disturbed, but condition and function matter more than paint.

Reassembly: Caliper rebuild steps

Caliper seal and piston

Lightly stretch the new seal just enough to help it seat correctly (do not overstretch).
Install the seal into the caliper groove.
Confirm the seal is not twisted in the groove.
Lubricate the seal and the piston’s leading/tapered edge with DOT 3 brake fluid.
Insert the piston squarely into the caliper bore.
- It should go in with firm, controlled resistance.
- If it requires excessive force, stop and re-check seal placement and lubrication.

Brake pads

Apply caliper grease to metal-to-metal contact areas only, such as:
- The back of the brake pad
- Metal edges where the pad slides (do not get grease of the friction surface edges)
- The pad’s outer metal diameter contact points
Do not apply grease to the friction surface.
Drop the pad into the caliper body and confirm it seats cleanly.
If grease squeezes out near the friction surface, wipe it away immediately.
Install the pad retention hardware (including the cotter pin).
- Spread the cotter pin ends securely; trim if needed so it doesn’t interfere.

Install bleeder screw with anti-seize

Apply a small amount of anti-seize to bleeder screw threads only.
Keep anti-seize off the bleeder tip and away from fluid passages.
Thread the bleeder in smoothly.

Reassembly: Caliper swing arm rebuild steps

A caliper that does not pivot freely can bind and make noise.

Clean the swing arm pivot pin.
Reuse the original O-rings if they are in good shape (they function primarily as dust seals in this design).
Apply caliper grease to the pivot pin, including the groove that acts as a grease reservoir.
Assemble the pin and confirm the swing arm pivots smoothly and freely.

Final assembly notes (lines, crush washers, and bleeding)

Replace upper and lower rubber hoses during final assembly.
Use new crush washers at banjo bolt connections.
Once assembled, the system must be filled and bled properly before riding.

This draft focuses on tear-down, inspection, and caliper/swing arm rebuild steps shown in the video segment provided. If you want, share the remainder of the transcript and we can add the exact bleed sequence and final checks used on-camera.

Troubleshooting

The piston will not move with hydraulic pressure

The caliper may be heavily corroded internally.
Confirm the line is fully purged of air before connecting to the caliper.
Confirm the master cylinder is generating pressure and the lever feel firms up as fluid moves.

New pad feels stuck in the caliper body

Corrosion is still present in the pad pocket.
Remove the pad and continue cleaning until the pad drops in/out easily.

The piston is extremely hard to install

The seal may be twisted in its groove.
The piston may not be entering squarely.
The seal and piston may be too dry—lubricate with DOT 3 brake fluid and try again.

Bleeder screw feels like it wants to seize

Stop and clean the threads.
Apply a small amount of anti-seize to the threads only and reinstall carefully (steel bleeder screw + aluminum caliper body is a common seizure combo).

FAQ

What brake fluid should I use for assembly?

DOT 3 brake fluid works well as an assembly lubricant for the caliper seal and piston during installation.

Should I replace rubber brake hoses even if they look okay?

Yes. Old rubber brake hoses are a high-risk failure point on a vintage hydraulic brake system. Age alone is reason to replace.

Can I reuse the caliper body?

Often yes, if it cleans up well and the pad pocket and seal areas are in good condition. A clean pad test-fit is a simple, effective check.

How do I know if the caliper piston is reusable?

If the piston has visible pitting/corrosion on its sealing surface area, replacement is the safer move to prevent leaks and repeat failures.

Where should caliper grease go?

Only on metal contact points (pad backing plate, pad edges/slide surfaces, and other metal-to-metal interfaces). Never on the friction material.

Part 2

Assembly

Mount master cylinder and upper line

Clamp the new master cylinder to the handlebar.
Apply anti-seize to the master cylinder clamp bolts.
Start the bolts and snug the master cylinder enough to hold it in place.
- Do not worry about perfect lever angle yet; final positioning comes later.
Remove the rubber plug from the master cylinder outlet (if present).
Install the upper brake line, including the protective boot.
- Common mistake: forgetting the boot until the line is already installed.

Mount junction block and lower line

Mount the junction block and snug its mounting bolt.
Apply a small amount of anti-seize to the junction block mounting bolt.
Install the lower hose to the junction block using the banjo bolt and crush washers (details below).
Keep the banjo bolt slightly loose until the hose routing is confirmed.

Important fitment note: The junction block has a locating groove/notch. Make sure the fitting sits correctly in the groove so the line cannot rotate out of alignment.

Mount caliper, swing arm, and hard line

Rough-mount the caliper and caliper swing arm.
Leave selected fender/swing arm bolts out initially if needed so you can flex the fender slightly and snake the hard line into position.
Thread hard line fittings by hand for alignment first.
Once routing is correct, tighten the hard line flare nut while holding the opposing fitting so you do not twist the rubber hose.
- The goal is to tighten the flare nut without rotating the hose.

Note: Brendan intentionally loosens and redoes certain fittings during this phase to avoid committing to a final torque before the line routing is correct.

Banjo bolts and crush washers: correct stack-up and best practices

Crush washers are one-time use. Once crushed, they should not be reused.

Typical banjo stack-up (per banjo connection):

Banjo bolt
Crush washer (one side of the banjo fitting)
Banjo fitting (hose end)
Crush washer (other side of the banjo fitting)
Thread into master cylinder or junction block

Best practice from the video:

Start the banjo bolt assembly and thread it in.
Leave it slightly loose until the hose angle is correct.
Final tighten once you’re confident the routing is where it needs to be.

Two-stage bleeding method (no special tools)

Brendan bleeds the system in two stages to make the job easier without vacuum bleeders or specialty tools. The reason is simple: the master cylinder does not move a large volume of fluid each lever pull, and trapped air in long lines acts like a spring.

Stage 1: Purge the master cylinder and line(s)

This stage purges air from the master cylinder and the upper line routing before you try to bleed at the caliper.

Remove the junction block temporarily (after the lines are installed up top).
Open the master cylinder reservoir and confirm it is clean.
Fill the reservoir with clean DOT 3 brake fluid (synthetic DOT 3 is also mentioned as a preferred option).
Submerge the hard line end (or line end) in the fluid inside the reservoir.
Slowly pump the lever and watch for bubbles.
Tap the master cylinder body to help stubborn air bubbles rise.
Continue until bubbles stop and the flow looks consistent.

Purge test used in the video:

With the lever released, pull the line end out briefly.
Squeeze the lever and confirm you get a strong squirt.
Hold the lever, then resubmerge the line end before releasing the lever so you don’t suck air back in.

Once purged, top off the reservoir and move to Stage 2.

Stage 2: Bleed the caliper with a catch bottle

This stage finishes by bleeding remaining air at the caliper.

Simple tool setup:

A catch bottle (Brendan uses a plastic bottle)
Clear hose to the bleeder screw (implied by the bottle method)
An 8 mm box wrench on the bleeder screw

Bleeding sequence (repeat until clean fluid and no bubbles):

Squeeze and hold the master cylinder lever.
Open the bleeder screw.
Watch fluid and bubbles exit.
Close the bleeder screw.
Release the lever.
Repeat.

Critical check during bleeding:

Keep the master cylinder reservoir topped off. Do not let it run dry or you will pull air back into the system.

Expected result:

Fluid runs clean with minimal/no bubbles.
The lever feel becomes firm.

Video note: Brendan had an initial drip because the bleeder screw was not fully closed—worth double-checking before you start pushing fluid.

Adjust caliper swing arm drag (pad-to-rotor position)

After bleeding, Brendan adjusts the caliper swing arm drag to set caliper position relative to the rotor.

Loosen the jam nut.
Back the adjuster screw out until it is loose (turn counterclockwise).
Turn the adjuster screw in slowly until it just becomes lightly snug by feel.
Add only a tiny amount more if needed (“a hair more”), then stop.
Hold the adjuster screw steady and tighten the jam nut.

Target setting from the video:

The inner pad should be just lightly touching on the inside of the rotor.
Do not force the adjustment. If it feels like the adjuster is binding or stripping, back it off slightly.

Verify the brake light pressure switch

If your junction block includes a pressure switch, confirm it works before calling the job finished.

Apply light lever pressure and verify the brake light turns on.
If it does, the pressure switch is functioning.

Final checks before riding

Verify every banjo connection and hard line fitting is tight and dry.
Wipe the caliper, junction block, and master cylinder clean so leaks are easy to spot.
Confirm lever feel is firm.
Confirm the front brake applies and releases correctly with the front wheel off the ground (if safely possible in your setup).
Perform a cautious first ride:
- Use gentle braking.
- Confirm the motorcycle stops cleanly.
- Re-check for leaks immediately after.

Troubleshooting

The brake lever still feels spongy

Air is still in the system. Repeat Stage 1 purge and Stage 2 caliper bleeding.
Confirm the reservoir never ran dry during bleeding.

No fluid movement during bleeding

Too much air in the line can act like a spring and “bounce back.” Purge the master cylinder and lines first (Stage 1).
Confirm the bleeder screw is actually opening and closing correctly.

Brake fluid drips during assembly

Confirm the bleeder screw is fully closed before pushing fluid.
Re-check crush washer stack-up on banjo fittings.
Re-check flare nut seating at the hard line connection.

The brake drags after reassembly

Re-check caliper swing arm drag adjustment; back off slightly if over-tightened.
Confirm the caliper swing arm pivots freely and the pad can move in the caliper body.

FAQ

Do I need special tools to bleed this brake system?

No. The method shown uses a two-stage process and a simple catch bottle setup to make bleeding effective without specialty equipment.

Why purge the lines before bleeding at the caliper?

Because a vintage Honda master cylinder moves a limited amount of fluid per lever pull, and trapped air compresses like a spring. Purging the lines first makes caliper bleeding much faster.