Rebuilding front Master cylinder on my '79

[Rolls]

Based on the wisdom gained from searching the forum and the good suggestions of members here, I'm getting after my front master cylinder. If you recall, upon arrival from Michigan to me in California, the front brakes were locked up so hard the driver had to drag the bike off his rig and leave it in the street at my home. When I arrived home, I was able to loosen the caliper bleeders and get it into the garage. I ordered brake lines from J.R. At CBextras, and found a K&L mc rebuild kit locally.

I got the old mc off and placed it on my workbench, or as my kids call it, "the kitchen table."

First, the return hole is indeed plugged. And plugged good. I'll need a tiny drill bit. It wouldn't yield to the sharper end a tiny sewing needle.

This is after much cleaning, and more to go.




Second, by blind luck I got the circlip released and the parts, after some coaxing sprung out - although I caught all the parts, I didn't catch the assembly order. Can anyone help me with that?

1. Skinny end of the spring goes in first, right?

2. Then the rubber "hat" goes over the wider end of the spring, so its flat top goes against the "propeller" side of the piston, is that right?

3. Last, what is the correct orientation of the sweeper ring that I install on the piston assembly? Should the wider side of the flare go toward the lever or the banjo bolt side of the caliper? The existing one is worn, but it looks like wider side towards the lever. But I can't follow the logic of that. (Parts fiches are a little too blurry to make out, at least from my searching.)



Thanks for any help with this part of the rebuild.





Third, there is seepage where the reservoir meets the mc. it'll need a new reservoir o-ring, and it could benefit from a fresh cup, too. I'll order asap.



Man, that was a bugger to pry off. The o-ring is pliable, but corroded. The o-ring channel was a complete mess before a laborious clean out.

Obviously, which fluid to use won't be a point of controversy Seriously, let's not even discuss that in this thread.

I'm hoping with the freshened mc and new black stainless lines, the brakes will cooperate so I can ride this over to DMV and get it authorized to be ridden on the street. It'll need new front pads, so I'll do the calipers and maybe fresh caliper pistons after I get plates on it. Heavy bike and treacherous mountain roads spells tip-top brakes and tires to my way way of thinking.

[steve murdoch icoa #5322]

Tom from the 1100F site has made a couple informative, easy to follow videos on common repairs for our old bikes.
Parts orientation can be found in the clip. https://www.youtube.com/watch?v=6YSldW85ioI

[Rolls]

Thanks, Steve. Tom's video is great. Super helpful.

J.R., who already has the new lines in the mail to me, also commented, pointing out that the wide end of the spring goes in first, and the wide part of the flare on the rubber sweeper on the plunger assembly should be oriented towards the banjo bolt side of the mc, not like it appears the one on the old part in my photo was done.

Still waiting to get a #78 bit as my return hole is very stubbornly resisting all other efforts and tools so far.

If all goes well, I'll return from my business trip around midnight on Thursday, and put this together such that it'll work in time to get this old beast mobile and blessed and registered by the whimsical state of California on Friday. Everyone please keep your fingers crossed.

I will say after some honing/polishing, the bore is as smooth as well, insert your own metaphor here. A new cup and o-ring are headed my way, too. If everything goes just right, while I won't be done with the front brakes, I'll be able to ride the 55 miles over the Santa Cruz mountains on highway 17 safely to make it to my favorite cars and coffee in Soquel, near Santa Cruz, early on Saturday morning. Again, fingers crossed!

[daves79x]

You are wise to get a new cup, cap and o-ring. The old cups are easy to pry off if you rotate 90 degrees. Then insert a large screwdriver between the open cavity now revealed and the cup. It will pop right off with no left-over marks. Powder coating is the way to go on the m/c body, but someone needs to do it that has done brake parts before. There's a great guy from the 1100F forum that does fantastic work and quick turn-around, but he's in Mass. You need back on the road soon. Alternative is to use satin rattle-can caliper paint. You can get that done while waiting on other parts. Mask off the red dot. A little heat will clear your plugged orifice. You also really need to disassemble the calipers and clean them as well. While you are at it.

Bleeding the whole system is a real pain if you use conventional methods. I've described my way to do it here several times. Get a Mity-Vac. viewtopic.php?f=50&t=8634&p=66090&hilit ... ing#p66090

Dave

[Rolls]

Yeah, I think I'm constrained to paint, so I'll be looking for high heat caliper paint locally, probably VHT, unless anyone has a better suggestion. I might protect the red dot, or possibly paint red first, then mask dot and spray satin black.

Turning the the reservoir cup 90 degrees is a great tip. Why didn't I think of that? Brilliant.

[Rolls]

I was thinking of EBC sintered HH pads, as they work very well on my CB1100, but not available for the CBX. Any suggestions for a high performance street occasional track day type of pad? I've seen the PDF on pads here. Maybe that's up to date and no new options.

[Larry Zimmer]

Two things to comment from the school of been-there-done-that. INDEED do those front brake calipers. Might just take the time now. You don't need a caliper locking on you while going to/from the DMV. Secondly, a tip: Boiling hot water is quite a good thing for cleaning 'stuff' from m/c and caliper bodies. Won't cut grease from the outside; however, does rather well at getting other crud from the insides. If the crud doesn't fall of with the water, it will clean much easier. Obviously, be certain to dry things well before reassembly. (Can't say that if the previous fluid was DOT 5 silicone.)

[Rolls]

Good points. The calipers shouldn't really be that much more work, so maybe I can get them done before the DMV rather than after. And you and Dave have me convinced I haven't been leveraging heat enough in my quest to clear the return orifice. Thanks!

[daves79x]

All I can say is that you don't want to be bleeding the front system twice. And really do take note of my procedure for doing it - it will save you a lot of time and brake fluid and you still won't have good brakes until all the air gets worked out if you don't.

Dave

[Larry Zimmer]

Ditto on that bleed job, Dave!!

[Rolls]

Great progress on the front master cylinder. Was able to use heat, needle poking, and general persuasiveness to open the return hole to accept a #78 drill bit, as spec'd in Barry's post:

I checked that hole diameter on my m/c using some wire drill sizes. Turns out it was #78 drill (0.0160 in.), which actually measured @ 0.01575 in. – 0.01580 in.
I did this to compare the hole before and after I anodized the whole thing.

Barry

Still, that's pretty small. Are we sure that's sufficient? A very thin sewing needle doesn't quite make it through. I'm tempted to try to ream it out a bit to maybe 0.0320 in. to be on the safe side, but the m/c is all reassembled, though still dry. (Listened to the advice of the forum luminaries and I'm working on the front calipers now.)

Is 0.016" the real spec?

Thanks! Hope to someday actually ride my new-to-me CBX.

[Larry Zimmer]

While I don't know the 'soec' size for the hole, .032" sounds far too large. It doesn't require anything to bleed enough fluid to release the caliper pistons. It is a small hole! (Note: it needs to be small to minimize piston/lever travel when applying brakes.)

[Rolls]

Well, it's a relief that the relief hole is indeed supposed to be so tiny. I wasn't keen to mess with it further now that it's back together, the circlip is in place and it's back on the bike. Thanks!









Chugging along.

[cbxfer]

If you got the new reservoir cap with the cup kit, don't forget to remove the metal frame from the old cap and install it on the new one, otherwise it will spill brake fluid all over you fuel tank when you go for a ride (ask me how I know....)
Fernando.

[cross]

I use ATE Type 200 in all my bikes. It's dot4 and has higher temp rating.
It's also good for track days ;)