Topic: CB550f Master Cylinder - Is this normal?

[Itineo]

Hello, I'm new on here and this is my first post.
I just got it back from the workshop where it got a lot of TLC including a master cylinder and caliper rebuild.
The brake lever is a bit soggy and I could hear a squishing noise from the master cyinder when I pull the lever.   I unscrewed the cap to see if I could find out what was going on. I pulled the lever and a jet of brake fluid shot out of the reservoir and over the front of the bike. I've never seen this happen before. After some frantic cleaning of paintwork I'm now trying to work out the probable cause.  The workshop I used has a very good reputation and specialise in old bikes. Could they have made a mistake?
Any Ideas or suggestions?

Thanks

Itineo.

[MauiK3]

I think I remember doing that years ago as a newbie.
The squish is from incomplete bleeding, many threads here on how to do it, some shops don't have the patience, it takes  some time.

[Itineo]

Thanks, I think I'll just buy a few bottles of brake fluid and bleed it myself. I've done it before on other bikes. I never saw anything as spectacular as this though. I've read around it since posting and what you say seems to be the consensus.
In fact I think I'll get some fuel line and try to vacuum bleed it using a syringe I have lying around since priming the scottoiler on my other bike.

[jlh3rd]

remember, if you bleed these bikes by using the brake handle, you don't pull it all the way back to the grip. I think it's like 15 mm or so gap measured from the tip of the lever to the grip...

[carnivorous chicken]

To answer the question, yes, that's normal to have brake fluid squirt like that when you have the cap off and use the lever. Regarding it feeling soggy -- how does it work? If you're not used to an old Honda disc brake you might think something is off with 50-year-old technology.

[The Sovereign Man]

A soggy brake lever is, as already mentioned, due to the brakes not being bled properly. I found success on my 550F from bleeding from the bottom i.e. pushing fluid up the line from the nipple.

As for the squirt when the MC cap is off, that's perfectly normal.

[Itineo]

Thanks for all the helpful suggestions.
Itineo.

[Bodi]

Pretty much all covered.
The master cylinder has a pressure relief passage that lets brake fluid flow back into the reservoir. Without one the brake will lock up while riding as the caliper warms up. The passage is a quite small hole visible in the bottom of the reservoir, a few mm closer to the lever end from the larger feed hole. Pulling the lever quickly will shoot a stream out (just as the m/c piston starts moving) right through the fluid and out of the reservoir, as you discovered. You can still pump the lever for bleeding with cap off, just go slowly at first.
Complete bleeding is not easy.
Bottom up pressure bleeding is my personal choice. I use the caliper as a pump, with it dismounted. I pump the piston out pretty far via the lever very slowly, then press the piston back in with a C clamp. With the cap on loosely to catch the jet from the relief hole (except when checking for air bubbles) - and careful not to add much fluid with the piston extended as the reservoir can overflow when pushing the piston in. A few cycles of this with the caliper held so air will go up and out the brake line, plus some tapping and turning the switch tee, has been the most successful way I've found to bleed.
You should not hear squishing noises, air bubbles coming through the relief hole makes a sound but if you hear that your shed must be super quiet!
Vacuum bleeding where you put suction on the caliper bleeder and keep adding fluid so the reservoir doesn't empty is an option. But special equipment is needed. Using my method does not, and after trying both I got a better lever feel after the upflow pressure bleeding.

And it's true these disc brakes are not the same as on modern bikes. They are about as effective as double leading shoe drum brakes but without the heat fading but you won't be doing stoppies. They are scary when wet with almost no friction for a sphincter loosening second while water is squeezed out.

[Itineo]

Pretty much all covered.
The master cylinder has a pressure relief passage that lets brake fluid flow back into the reservoir. Without one the brake will lock up while riding as the caliper warms up. The passage is a quite small hole visible in the bottom of the reservoir, a few mm closer to the lever end from the larger feed hole. Pulling the lever quickly will shoot a stream out (just as the m/c piston starts moving) right through the fluid and out of the reservoir, as you discovered. You can still pump the lever for bleeding with cap off, just go slowly at first.
Complete bleeding is not easy.
Bottom up pressure bleeding is my personal choice. I use the caliper as a pump, with it dismounted. I pump the piston out pretty far via the lever very slowly, then press the piston back in with a C clamp. With the cap on loosely to catch the jet from the relief hole (except when checking for air bubbles) - and careful not to add much fluid with the piston extended as the reservoir can overflow when pushing the piston in. A few cycles of this with the caliper held so air will go up and out the brake line, plus some tapping and turning the switch tee, has been the most successful way I've found to bleed.
You should not hear squishing noises, air bubbles coming through the relief hole makes a sound but if you hear that your shed must be super quiet!
Vacuum bleeding where you put suction on the caliper bleeder and keep adding fluid so the reservoir doesn't empty is an option. But special equipment is needed. Using my method does not, and after trying both I got a better lever feel after the upflow pressure bleeding.

And it's true these disc brakes are not the same as on modern bikes. They are about as effective as double leading shoe drum brakes but without the heat fading but you won't be doing stoppies. They are scary when wet with almost no friction for a sphincter loosening second while water is squeezed out.

Thanks - That's really helpful and I'll give it a try. I've had the bike for a good while so I'm used to it even though I hadn't ridden it for a while. I took it to the repair shop to get it sorted and back on the road after being parked up for a few years. I got a lot of work done to it.  One of the jobs was to sort the front brake which had become poor.  The squishing noise is quite audible - I reckon it's the jet of fluid hitting the cap of the reservoir. It can be heard from six feet away.  And yes I remember that first half second in the rain .  On the topic of performance, I'm surprised on how planted the bike feels on its new Avon tyres - really stable and solid. As much so as my modern bike.

[Itineo]

After four years I finally sorted the problem and thought I'd share the experience in case it's useful.   Apologies for digging up an old thread.
Remember I said after getting the bike refurbished at a repair shop the brakes were soggy and the apologetic mechanic said he had done his best.  ( They were fine before I gave him the bike but that's another story). I bled the system upwards, downwards and at all points going on the good advice given here. Still no good.  As I would pump the lever it seemed to emulsify the fluid with air bubbles and there was an audible squishing sound.  Reluctant to dismantle the MC as it is a pig of a job,  I dismantled the caliper, got the pivot machined and bushed in case it was mechanical play or something flexing or misaligned. Sorted out an issue where the mechanic had mis-assembled the pivot with the mudgaurd/fender bracket in the wrong place. Checked the pads were contacting the rotor evenly and the pivot bracket was aligned perfectly with the rotor. Then I replaced the brake lines with good quality new ones. Still no change. Then I got an OEM master cylinder kit. Still no good even though the old one seemed to have been been nicked on assembly.  I was starting to doubt my sanity at this stage.  So I decided to start methodically and work in a logical manner until I found the problem. It's not a complicated system after all and this was what was killing me. Removed and clamped the caliper and bled again.  Wasn't that. Fairly sure there was no air in the lines. Was suspecting the brake light switch ( yes desperate at this stage ) and then came across the post by  jonda500 on thi sforum http://forums.sohc4.net/index.php?topic=165094.0 and decided to have a go at modifying the brake lever. I drilled and tapped and fitted an M4 screw at the point of contact between the lever and plunger on the MC and immediately the problem was solved. I don't know how the lever got changed or what the mechanic did but I'm a happy biker at the moment. This and the UK forum are great places. Safe riding all

[wolf550]

glad you got it figured out. was the aluminum lever just worn down or was it a lever that just was too short that contacted the plunger

[Itineo]

There wasn't any sign of wear on the lever - you can still see the parting line of the casting with a bit of polishing at the point of contact.  I don't doubt the mechanic put in the correct kit when doing the refurb in 2020 as it was identical to the OEM one I got last week.  Even if he did nick the rubber... So either he picked up the wrong lever when putting it all back together (unlikely) or, possibly, the previous owner did something that needed the other style lever to work properly. It's twenty years since I bought the bike so I guess I'll never know for sure. The extension in reach is about 6mm at the point of contact to the MC so a fair difference. What I don't understand is how the old setup worked fine - any ideas on what combination of MC / parts would have added up to this?

[Itineo]

To clarify, I imagine the previous owner used some combination of  MC/Brake lever that worked for him but didn't work when my mechanic replaced with OEM  Master Cylinder parts. In any case it isn't that important but wanted to flag it as a potential cause.  I wasted a lot of time on it but learned a lot as well

[Stev-o]

Good to hear you got it sorted, hope it didnt take 4 years!

[jonda500]

It took me years to find a correct brake lever for my 500 -(#53170-369-003).
Any one know how to reverse part# look up? I would love to know what these dud levers fit (#53175-369-003)?

edit: the lever on the right is the one I eventually found. It is an aftermarket version of the correct 53170-369-003 honda lever.
John

[bryanj]

Go to cmsnl and create an account(free) log in and look up the number then you can look at models it fits

[jonda500]

Thanks Brian!
Well #53170-369-003 (LEVER, R.STEERING) has been superseded by #53175-369-003 which fits all the models that #53170-369-003 fits, plus 81 more... wtf? - well technically it fits, but will result in unacceptable excessive lever travel.
The early one is available at cmsnl but they have a picture of the later one with the smaller nub so I would be very leary about buying that one!
John

[pekingduck]

I love a good mystery.  Yours is a very strange situation, and I'm glad it's resolved.

The original part number was 53170-300-000, followed by 53170-333-000, which superceded to 53170-369-003, and finally to the current 53175-369-003 with the plastic dipped ball end.

All of these would have fit every round Honda master cylinder that had a hydraulic brake switch, which is a lot of bikes, and give identical function.  So the "dud" levers would have been on a lot of bikes, but I never heard of it before. 

I looked at the picture, and 3 of the levers had "333" stamped in them, and 2 had "369".  I couldn't make out 1, and expect that the 53170-369-003 would have a stamping also.  Do you know what number it is?  I also see the more pronounced shape of the "nub", and it is different from any OEM lever I've seen.   

 

[newday777]

Any one know how to reverse part# look up? I would love to know what these dud levers fit (#53175-369-003)?

edit: the lever on the right is the one I eventually found. It is an aftermarket version of the correct 53170-369-003 honda lever.
John

To find the models the part number fits....

Go to online parts lookup, "quick search" the part number,  hit the "where used", scroll down through the list of models, hit "show more" until you get all the models

To do a quick search

https://www.southsoundhonda.com/--xpartsstream#

(Sorry, the screenshot are the 53170 lever)

[jonda500]

My 1st 500 came to me with black dog leg levers so that's no help (but the brake lever has the bigger nub and does have the circle with the line through it!).
My 2nd 500's lever has the bigger nub and the circle with the line through it but no 333 or 369 so maybe it is aftermarket like the black one.
Some of the levers also have a small circle with a letter in it (D,F,G, etc).
Aside from the 333&369 none have any matching numbers or letters (above and below the line in the circle).
I am currently unable to locate my broken lever collection, still looking...

I thought of super gluing little washers to the end of the plunger in the master, and then wondered if there are variations in the rebuild kits plunger lengths just to add in another variable to the mystery!
John

[jonda500]

By the way the hard to find new aftermarket one in my picture has no markings at all on it. John