Topic: 1978 CB550 K4 Been sitting a while

[BenelliSEI]

That 550K was my first SOHC Honda (my wife had a 400F at the same time). I still have cb750K7 and K8….. sold the 550 10 years ago.

[BigAl]

Finally received my master cylinder rebuild kit.  I paid little attention to the parts I pulled out and have been trying to make sure that I put the rebuild kit back together correctly in the master cylinder.  The parts diagrams are a bit fuzzy, but I did happen to find the old one during in the pile of parts on my workbench. 

Question, is the old one I pulled out correctly configured?  The main rubber plunger?  I think I can figure the rest out, just don't want to put anything on backwards...

That should button up the front brakes.  Reading through the manual, I need to pull the replacement pads and apply some grease around the edges and backs.

[BigAl]

Master cylinder is back together.  I went to install the handle and noticed it was dirty so I gave it a scrubbing and set it out to dry.  With that I can fill with Dot3 and see if everything is tight.

I feel kind of like a dumbass.  As I was looking at the parts exploded view I was thinking that what it showed made no sense at all.  Why would the two rubber pieces be back to back.  Then I found my old piston? plunger? and shook my head a little bit and put it together.  I often find myself doing something, thinking that it just does not make sense, doing it anyway, and then realizing that if I had just listened to that little voice in my head I would have been alright.

Oh well.  It's back together, the snap ring was a pain but not too much of one.

[BigAl]

Well, after no luck with anything of note happening in my rebuilt master cylinder, I read through the threads a bit.  First mistake was to no clean out the little divot forward of the main opening in the reservoir.  I did clean it, just not enough to open the apparently little tiny orifice at the bottom of the divot.  I questioned the feature as I cleaned it and thought that I would be able to spot SOMETHING looking down the shiny barrel of the mc.  So that needs routed out with a guitar string.  I need to restring mine anyway, so I guess that's a sign.  Second mistake was to not really read any advice on priming, filling, etc.  Several methods seem to work, so I'll try a few.  I have some tools that may help floating around in the basement somewhere.

[newday777]

Well, after no luck with anything of note happening in my rebuilt master cylinder, I read through the threads a bit.  First mistake was to no clean out the little divot forward of the main opening in the reservoir.  I did clean it, just not enough to open the apparently little tiny orifice at the bottom of the divot.  I questioned the feature as I cleaned it and thought that I would be able to spot SOMETHING looking down the shiny barrel of the mc.  So that needs routed out with a guitar string.  I need to restring mine anyway, so I guess that's a sign.  Second mistake was to not really read any advice on priming, filling, etc.  Several methods seem to work, so I'll try a few.  I have some tools that may help floating around in the basement somewhere.

If you are talking about the return port in the master cylinder (tiny 2nd hole) use a wire from a wire brush, held with needle nose pliers to poke the hardened gunk clear so the port is open to release the pressure from the caliper so the pad frees up when you release the lever/pedal.
To prime an empty master cylinder, put fresh Dot4 in reservoir, then use the master cylinder banjo bolt as the 1st bleed port(protect all paint below and around the bolt from drips!), then bleed the calipers as usual manually. No special tools required other than a "one man bleeder bottle" with a check valve in it.

[BigAl]

Thanks newday, I will go that route (although I was geared towards a restring on my guitar...). One question on the DOT4.  I had initially refilled with DOT3.  I see you mention DOT4 in your post.  Does it make that much of a difference?

This slight problem with my master cylinder may prompt me to buy that fancy brake bleeding tool I saw the other day.  Looked like a built in wrench / bleeder / tubing combo.  I hate to buy a new tool, but maybe I will be forced to.....

[Stev-o]

This slight problem with my master cylinder may prompt me to buy that fancy brake bleeding tool I saw the other day. 

I have the "fancy brake bleeding tool", have not had the need to use it on my bikes, but worked well when I was having trouble bleeding brakes on my old Chevy.

https://www.amazon.com/MV8000-Automotive-Tune-up-Brake-Bleeding/dp/B00265M9SS/ref=asc_df_B00265M9SS/?tag=hyprod-20&linkCode=df0&hvadid=312174136943&hvpos=&hvnetw=g&hvrand=2757049052309351390&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9028270&hvtargid=pla-316724733774&psc=1&mcid=77d7b33124bb3847828b4a3b56a761e9&tag=&ref=&adgrpid=63790029762&hvpone=&hvptwo=&hvadid=312174136943&hvpos=&hvnetw=g&hvrand=2757049052309351390&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9028270&hvtargid=pla-316724733774&gclid=Cj0KCQiAgqGrBhDtARIsAM5s0_kYEcEtxMbnRni1chN2LfF0wGk0zAKe5ZConvDJzV9dQ9NP_Jt9YOUaAlgjEALw_wcB

PS. I use DOT 3 brake fluid.  DOT 3 and DOT 4 brake fluids are both glycol-based. DOT 4 has a higher boiling point than DOT 3. You can use DOT 4 where DOT 3 is called for, but not the reverse.

[BigAl]

I will admit Stev-o, I have spent too much time under my old Bronco bleeding those cursed rear drums.  It would be nice to have for that....

[BenelliSEI]

Thanks newday, I will go that route (although I was geared towards a restring on my guitar...). One question on the DOT4.  I had initially refilled with DOT3.  I see you mention DOT4 in your post.  Does it make that much of a difference?

This slight problem with my master cylinder may prompt me to buy that fancy brake bleeding tool I saw the other day.  Looked like a built in wrench / bleeder / tubing combo.  I hate to buy a new tool, but maybe I will be forced to.....

I bought a MITY-VAC hand pump kit +10 years ago. Fantastic tool and use it on everything!

[BigAl]

BenelliSEI, I actually have one of those as well.  I have used it for many things, but never for brakes.  So would you fill the reservoir and then apply the vacuum to the caliper with the bleeder screw cracked?  Slowly keeping the fluid level intact as it filled?  It seems like it would be better the other way around; somehow applying the vacuum to the master cylinder and backfilling through the caliper.

Master cylinder comes back apart tomorrow.  I sprung for the 90 degree 2.5" long snap ring pliers.  They will come in handy for more than just the bike I think.  I peeled the old rusted snap ring out with needle nose, at least I'm pulling out a new, clean installation.  It was odd, I took the mc off the bike and it is sitting on my workbench now.  Looking down the barrel I can see through the spring and the little "flower" looking end of the piston where the rubber cap should be.  Evidently, during my first attempt the rubber must have been dislocated.  Maybe it was too dry and it snagged it up as it pumped?  Fluid should be passing around this rubber if I understand the system correctly.

[BenelliSEI]

I use my MityVac hooked up to the bleed nipple and just as you describe. It works great. The only snag is that it pulls air by the threads on the bleed nipple, so you never really see pure brake fluid coming into the container. I often go back the next morning and give it a few extra pulls, just to make sure any air that has “floated up” in the caliper gets drawn off.

You should not be able to see the “flower thing” from the end of the master. Where did it go? The spring should hold the seal up against it……

[newday777]

When you reassembled your master cylinder did you lube the new rubber parts with fresh brake fluid before inserting them??
Never assemble dry.....

[BigAl]

I did reassemble wet, but there was definitely something hanging a bit the first time.  I took it back apart this morning, my wire brush donated a bristle and I cleaned that very very small hole in the mater cylinder.  It is a very small hole.  One bristle would fit, two would not.  I reassembled and everything feels smooth.  I need to hunt down my vac and then fill er up!

I will probably regret filling the brake system.  Front fork rebuild is in my plan at some point, I assume that I will have to strip the brakes off to remove them.

[calj737]

You can remove the brakes without disconnecting caliper so you can service your forks. Just tether it to the triple tree to prevent any undue stress on the line from hanging.

[BigAl]

Hours at work have been long, so I haven't had much time to tinker with the bike.  But, I did manage to initially fill and bleed my front brake system.  I started with my hand pump vac and fairly quickly sucked a couple of full reservoirs through.  I then bled normally.  I realized that there was a small leak at the switch fitting but I think it's tight now.

A couple of observations.  First, the system seems squishy to me.  I bled the brakes per the shop manual, not letting the handle depress all the way to the grip, but holding it off an inch or so.  And I bled, and bled, and bled.  I ended up where there really was nothing but fluid coming out, no air to speak of, but it it still felt squishy.  I topped off the reservoir and put the cap on the mc and all of a sudden it was much tighter.  So secondly, does the cap provide some type of pressure function on these bikes?  I have bled many a vehicle, most notably an on Bronco which I bleed way too much, and I have always left the reservoir cap off during this process so that I could make sure that I am not emptying the reservoir out and sucking air.

At the end of my brake session, with the cap on, the brake does seem to very effectively stop the rotation of the front wheel, although this is all by hand, not moving with me riding on it (carbs are still out, tank is in process).  Anyway, just throwing it out there to the masses that know more than I.

[BenelliSEI]

Diaphragm and cap shouldn’t make any difference. What I find is when I’m done bleeding, let it all sit over night. Next day, with the cap off, just depress the lever a little bit and repeatedly. Watch the two holes in the bottom of the reservoir. I usually see tiny air bubbles escaping from there. Just keep barely pumping the lever until they stop. I then pull a few more ounces of brake fluid out of the caliper (with the Mity-Vac) incase there is any air in the top of that part. This procedure usually takes out that “softness” you are feeling now.

I just use DOT 3.

[Stev-o]

First, the system seems squishy to me. 

Do you still have the rubber brake hose?  If yes, that may explain it.  Stainless braided hose could help

[BigAl]

Stev-O, I replaced all of the rubber with braided line.  Cleaned up and used the original master cylinder but rebuilt the guts.  Rebuilt the caliper.  I am not seeing any leaks other than a little tiny drip out the back side (handle side) of the mc during the bleed process.

BenelliSEI, I have taken your advice and let it sit overnight, bleed a bit, overnight, bleed a bit, rinse and repeat.  It does feel a bit stiffer, but still a bit squishy.  I don't bleed it much, maybe twice and then I leave it alone.  Maybe my mc was pitted and I couldn't really tell?  It looked awfully clean and shiny to me down the bore.

[BigAl]

The ongoing project is a tank rehab.  My 78 stock tank was TRASH.  It leaked out the Honda badge because it was paper thin and basically rusted through.  I came across a 74 tank through a bit of extraordinary generosity and now am letting my slight OCD take me down the path of cleaning it up.  It has a bit of unknown tank sealer that partly came out in chunks, but a lot still remains.  I think I may buy a gallon of MEK and just see what happens with a prolonged soak.  Then a handful of nuts and bolts and rattle it around for a while.  Then resoak?  I'm hoping the MEK will dissolve whatever grey colored coating is there. 

It also has the old style petcock.  I'm thinking that is no big deal.  I can buy a two into one Y-shaped fitting and run a single like to my set of 78 carbs.

I also think I may take a bit of wood and some sandpaper and flatten out the underside of the tank where the petcock seats.  It's not a screw on type, but mechanically seated with a gasket and two screws.  In my mind, the smoother that seat area the better.

Ultimately, once I get it as clean as possible I will re-coat the inside with some degreaser, metal prep, and POR fuel tank coating.  Then, there will be absolutely no excuse not to fire that ole girl up.

[HondaMan]

The ongoing project is a tank rehab.  My 78 stock tank was TRASH.  It leaked out the Honda badge because it was paper thin and basically rusted through.  I came across a 74 tank through a bit of extraordinary generosity and now am letting my slight OCD take me down the path of cleaning it up.  It has a bit of unknown tank sealer that partly came out in chunks, but a lot still remains.  I think I may buy a gallon of MEK and just see what happens with a prolonged soak.  Then a handful of nuts and bolts and rattle it around for a while.  Then resoak?  I'm hoping the MEK will dissolve whatever grey colored coating is there. 

It also has the old style petcock.  I'm thinking that is no big deal.  I can buy a two into one Y-shaped fitting and run a single like to my set of 78 carbs.

I also think I may take a bit of wood and some sandpaper and flatten out the underside of the tank where the petcock seats.  It's not a screw on type, but mechanically seated with a gasket and two screws.  In my mind, the smoother that seat area the better.

Ultimately, once I get it as clean as possible I will re-coat the inside with some degreaser, metal prep, and POR fuel tank coating.  Then, there will be absolutely no excuse not to fire that ole girl up.

When you do the POR15 thing (which I use, it is fantastic in the end!) be sure to do this one little thing first: grease up a couple of long-ish 6mm screws (or bolts) and run them up into the holes for the petcock's mounts, using them to hold a small [handmade] plate of steel or tin (I use roof flashing, have half a roll of it sitting aorund here) over that opening to keep the POR15 inside during the process. The greasing of these bolts will let them unscrew easily after the POR15 does it thing and sets, and this forms a watertight (gas-tight) pair of 'bumps' inside the bottom of the tank at the site. Then when you reinstall the OEM petcock, the screws should be shorter than the bolts you used (more like flush to the inside of the tank) and the threads will be protected from the POR15. If that stuff gets into the threads and sets up, it is impossible to remove it enough to reinstall the screws again (don't ask how I know this...).

[BigAl]

Thanks HondaMan, I have been pondering that exact scenario.  Good to have some real world experience to confirm my thought process.

The bolts that came out with the petcock were fairly long.  I will grab a pic tomorrow.  The thing I had not sorted out yet was whether or not to use the petcock holes to allow for better drainage of excess coating.  This would require that handmade plate and bolts to come back out during the process.  My very limited coating experience involves slowly tumbling the tank for a while by hand and then draining as much out as I can.  What I don't want is a big thick coating on the bottom that could delaminate.  Draining excess out the fuel fill hole does not seem to work as well as the petcock opening.  Neither works well...

Maybe I should get a syringe and some tubing and suck the excess out?

[BigAl]

It's been a bit, but time for an update.  The project went on hold for a bit due to life, but I have done some work in the last couple of months and I just needed to post the results.  After ALL the things I have done to take this bike that had sat for 20 years and make it run again, today was a milestone.  I finally had the new tires put on and took it for a real spin.  I had taken it down the street once or twice slowly, but tonight I got to lay into it a bit.  Wow, takes me back to my youth.  Runs like a champ.

[BenelliSEI]

Congrats! Nothing more satisfying than that first ride! Enjoy.