Topic: Having Fun with a Honda CB550 Master Cylinder

[kyle750]

Finally getting around to assembling the CB550 brakes. Bike sat unused for many years and brake pads were rusted in the caliper.  Master cylinder actually still worked when I got the bike and was full of clean brake fluid.  After carefully rebuilding the master cylinder with all NOS Honda parts the master cylinder would generate pressure but I could not get any fluid through the lines. Removed all the brake lines and no leaks.  Took apart the MC again and bore was clean without any rust.  Cleaned the bore out with steel wool wrapped around a drill bit.  Bore is shiny and very smooth.

[kyle750]

Carefully cleaned the holes from the brake fluid reservoir.  No gunk clogging up the holes.

[kyle750]

MC reservoir is clean.  All new NOS rebuild parts installed corrrectly (maybe or maybe not )  I watched 3 different videos so I am fairly certain I got it right? Will assemble it again, fill with fluid, and try again!

[kyle750]

Here are the parts that were originally in the master cylinder and were removed.  I believe only the C-Clip is original. Now replaced with original NOS Honda master cylinder rebuild parts.

[kyle750]

You know you might be becoming a Honda nerd when rather than order and wait for specialized tools to arrive you grind down your tools so you can start on rebuild work.

[kyle750]

Late Edit:  My handmade C-clip remover did not work so well.  Too big to get inside the cylinder.  My future as a custom tool fabricator is not very bright.

Slightly off topic:  I bought a CB550 tool tray top for my air filter compartment a long time ago but it was missing the air box screen/lid.  I tried to make one and it was laughable. Really bad.   My future as a custom part fabricator is not very bright.

This one showed up on Ebay today so I bought it

https://www.ebay.com/itm/297842276730

[kyle750]

Here is how the NOS rebuild parts were installed.  I put some silicone grease on the rubber parts and it gunked up.  I will clean the grease off the rubber, clean all the parts, and apply a little brake fluid only to the rubber and reinstall.

In this photo the final dust cover is pictured upside down but was installed correctly with the final C clip locking it in at the base.

[newday777]

Master cylinder actually still worked when I got the bike and was full of clean brake fluid.  After carefully rebuilding the master cylinder with all NOS Honda parts the master cylinder would generate pressure

 but I could not get any fluid through the lines.

Did you bleed the master cylinder at the banjo bolt first? (WARNING! Protect all painted surfaces!)
Then you bleed the caliper.
That is known to "bench bleed any master cylinder that was dry".
Without doing that you get very little pressure to the caliper.

[BenelliSEI]

Looks all correctly installed. I’m a big fan of Mity-Vac brake bleeding tool, but you can also bleed just using a hose on the bleed nipples. Assume you know the sequence?
Pump, pump, pump, hold. Open bleed screw, close bleed screw. Release lever. Wait a few seconds, and repeat, over and over.

[kyle750]

Did you bleed the master cylinder at the banjo bolt first? (WARNING! Protect all painted surfaces!)
Then you bleed the caliper.
That is known to "bench bleed any master cylinder that was dry".
Without doing that you get very little pressure to the caliper.

Thanks Mate.  I believe I primed it correctly. Filled the reservoir full of new brake fluid. Removed the banjo bolt and held the opening tightly closed with my thumb.  Pumped the brake lever and there was decent pressure.  Then removed my thumb and a little trickle of fluid spurted out.  Then  let out the brake lever.  Then reattached the banjo bolt and tried to pump fluid into the lines.  For an hour bleeding and only a trickle of fluid reaching the bleeder valve at the caliper. Clear hose and container on the bleeder valve. I even had one of the guys at the local motorcycle shop try bleeding the brakes and he got nothing through the brake lines.

[MauiK3]

Maybe the brake lines are collapsing?

[BenelliSEI]

Maybe the brake lines are collapsing?

+1.

[newday777]

Did you bleed the master cylinder at the banjo bolt first? (WARNING! Protect all painted surfaces!)
Then you bleed the caliper.
That is known to "bench bleed any master cylinder that was dry".
Without doing that you get very little pressure to the caliper.

Thanks Mate.  I believe I primed it correctly. Filled the reservoir full of new brake fluid. Removed the banjo bolt and held the opening tightly closed with my thumb.  Pumped the brake lever and there was decent pressure.  Then removed my thumb and a little trickle of fluid spurted out.  Then  let out the brake lever.  Then reattached the banjo bolt and tried to pump fluid into the lines.  For an hour bleeding and only a trickle of fluid reaching the bleeder value at the caliper. Clear hose and container on the bleeder valve. I even had one of the guys at the local motorcycle shop try bleeding the brakes and he got nothing through the brake lines.

Do it with the hose and banjo bolt and lower parts attached to correctly bleed out the air at the banjo bolt.

[kyle750]

Thank You Gentlemen. I am going to clean all the parts and try again in the morning.  Here is an old photo of the brake caliper.  I had to use a hammer and chisel to remove the brake pad. Caliper was totally cleaned and sanded and new piston, new piston seal, and  EBC semi sintered brake pads installed.

[rosewood]

Are you sure the replacement/rebuild parts for the MC were the same and what you took out? There are a couple of variations to the 550 MC depending on what model/year etc. I got got caught out and ordered the wrong one which wouldn't work. (the oil lines weren't lined up in the bore I think).

I had to re order the correct one and it sorted the problem out...

From your images some parts look different which is the reason I ask..

[kyle750]

Are you sure the replacement/rebuild parts for the MC were the same and what you took out? There are a couple of variations to the 550 MC depending on what model/year etc. I got got caught out and ordered the wrong one which wouldn't work. (the oil lines weren't lined up in the bore I think).

I had to re order the correct one and it sorted the problem out...

From your images some parts look different which is the reason I ask..

It is my understanding that the early CB750 and early CB550 use the exact same master cylinder and exact same rebuild kit/master cylinder parts. Maybe this is not correct?

Late Edit:  The CB550 does use a piston and piston seal different from the CB750 as it is a different brake caliper

As a quick side note.  The local motorcycle shop guys have been very helpful.  The boss has been very patient and removes and installs the C-clip for me as I can't manage it.  He came out with 2 helpers and tried to bleed the brakes and got nothing through the lines.  He says "50 year old master cylinder - no good" and shows me modern master cylinder replacements that are cheaper than what I paid for the rebuild kit alone. The new replacement master cylinders might look OK on modern bikes but just don't look right on a 50 year old vintage Honda CB550 or CB750. I will keep trying.

[rosewood]

Are you sure the replacement/rebuild parts for the MC were the same and what you took out? There are a couple of variations to the 550 MC depending on what model/year etc. I got got caught out and ordered the wrong one which wouldn't work. (the oil lines weren't lined up in the bore I think).

I had to re order the correct one and it sorted the problem out...

From your images some parts look different which is the reason I ask..

It is my understanding that the early CB750 and early CB550 use the exact same master cylinder and exact same rebuild kit/master cylinder parts. Maybe this is not correct?

As a quick side note.  The local motorcycle shop guys have been very helpful.  The boss has been very patient and removes and installs the C-clip for me as I can't manage it.  He came out with 2 helpers and tried to bleed the brakes and got nothing through the lines.  He says "50 year old master cylinder - no good" and shows me modern master cylinder replacements that are cheaper than what I paid for the rebuild kit alone. The new replacement master cylinders might look OK on modern bikes but just don't look right on a 50 year old vintage Honda CB750. I will keep trying.

Hopefully you are correct...I have a later 550f and the MC changed between the 76-77 year which caught me out...

Here are the images which made me think they may be the wrong parts...hopefully im wrong, I rebuilt mine years ago so my memory is a bit foggy..

[kyle750]

Thank you for the side by side comparison.  Probably the most frustrating part is that the CB550 master cylinder was WORKING with the old parts in the bottom photo.  Excellent pressure and after unbolting the caliper I was able to  push out the piston entirely (with a pop and small puddle of fluid).

With the new parts installed in the top photo it no longer works.

[kyle750]

CB550 brake caliper cleaned and sanded.  New stainless steel piston and new piston ring installed.

In hindsight I should have bought another caliper in better condition. Too much work and time was spent with this part.

[carnivorous chicken]

As a quick side note.  The local motorcycle shop guys have been very helpful.  The boss has been very patient and removes and installs the C-clip for me as I can't manage it.  He came out with 2 helpers and tried to bleed the brakes and got nothing through the lines.  He says "50 year old master cylinder - no good" and shows me modern master cylinder replacements that are cheaper than what I paid for the rebuild kit alone. The new replacement master cylinders might look OK on modern bikes but just don't look right on a 50 year old vintage Honda CB750. I will keep trying.

David silver Spares makes a replica MC (for about the cost of a rebuild kit) that is pretty close to the original (especially if you put an oem cap on it). I've used two of them so far, and they work well.

[kyle750]

David silver Spares makes a replica MC (for about the cost of a rebuild kit) that is pretty close to the original (especially if you put an oem cap on it). I've used two of them so far, and they work well.

Thanks Mate.  Looking into it now!

From an AI search:   The primary concern with a 50-year-old part is the potential for internal corrosion and bore wear that a rebuild kit cannot fix.

[kyle750]

(especially if you put an oem cap on it)

OEM caps from the CB750 and CB550 

[slyguy]

As I recall, an old timer Honda mechanic I worked for use to always pump the brake fluid up from the caliper to m/c with a hand pump. I’ll ask him, we’ll be doing mine in the future since I’ve been restoring a 70’ 750. Btw here’s the type of tool for that clip- https://www.amazon.com/MFBJXC-Internal-Cylinder-Retaining-Motorcycles/dp/B0D1YBHZ43/ref=mp_s_a_1_9?crid=WQO136RKD3N2&dib=eyJ2IjoiMSJ9.y90965Pe_Pq2RsJdtmdaHGQLUz9YNPEtdKJ0FPKeFFeFgUJ0AXBxBBUdfy-jZQFJo0sIVxL850v79F7UpNUNPnkK86vkHGdl0hcNkIicbPvcqjFON1HaxeIEll5pXA-q9meiD9zwcTVGENo5xJgpXlts3-gDhaujSYdJkAf39E_CY44dQGGmm2TDSbcA5TWI_bGd4w6YQZECLyk1Xm8T6g.vFsZD9QoRbyVGmfH3_VqhZtca4TaIhV29sa0mWB3K6E&dib_tag=se&keywords=long+barrow+circlip+pliers&qid=1765774365&sprefix=long+barrow+circlip+pliers%2Caps%2C142&sr=8-9

[kyle750]

Another go at it.  I'm too stupid to quit

[kyle750]

We have PRESSURE  

When intially priming much more brake fluid squirted out than earlier attempts.  Brake lines filled up with fluid quickly with no leaks anywhere in the system.   Rapidly built up good solid pressure and bled the line of air.   Not spongy at all but very hard when pressing the brake lever. Lever engages at about 1/4 of the way down and at 1/2 depressed it is at full pressure. It feels just like new brakes - solid and firm.    I will check the brake again in the morning after leaving it for 24 hours to make sure the system has not lost any pressure overnight.

I'm not sure why this time was different but I am thrilled    Thank You Gentlemen for all the helpful advice and encouragement.