Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: mattsz on August 09, 2020, 01:22:23 AM
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I have a brake master cylinder kit from 4 into 1:
https://4into1.com/reproduction-brake-master-cylinder-rebuild-kit-45530-377-305-cb360-cb400f-cb450-cb500t-cb550-cb750/ (https://4into1.com/reproduction-brake-master-cylinder-rebuild-kit-45530-377-305-cb360-cb400f-cb450-cb500t-cb550-cb750/))
I know not everyone has had success with these rebuilds, but what the heck...
Regarding lubricating the reassembling bits: the Honda manual says to use brake fluid. The 4 into 1 kit includes a tiny tub of pinkish grease, but doesn't say what kind it is or exactly where/how to use it (I've got silicone grease for use in the caliper, as recommended in the manual). I've seen a Youtube tutorial in which Marvel Mystery Oil is used. I'm tempted to forego the grease and oil and just use the brake fluid as the manual recommends - anyone have better ideas?
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Brake fluid on the seals WEAR GLOVES use the greasin the area above the circlip to try and stop corrosion like there was when you took it apart.
When rebuilt these masters frequently need bleeding to banjo fitting.
With gloves on put a finger over the outlet hole and pull in lever, release and re apply finger, release lever. Repeat until you get pressure on finger then whilst holding lever in quickly fit pipe with banjo bolt and washers----oh should have said have them handy before starting!!
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Thanks for the tips Bryan! I have some big syringes, one of which I was going to use to try to fill the system from the bottom through the bleeder, but if that doesn't work out, I'll remember your suggestion...
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It wont is the easy answer, i find well over 95% of the masters need to be bled the way i said, also forgot to mention make sure both the holes from reservoir to bore are clear one is tiny
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It wont is the easy answer, i find well over 95% of the masters need to be bled the way i said, also forgot to mention make sure both the holes from reservoir to bore are clear one is tiny
I would say the same Bryan.
You have to bleed the M/C first as Bryan has explained or fit a banjo with a bleed nipple on the M/C ;)
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I attached a syringe to the bleed nipple on the caliper and sucked the fluid down whilst pumping the leaver, once fluid was in the system I just bled as normal, must add that was a 500 m/cyl
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Regardless, I have a project ahead. I watched a Youtube "video" (mostly a narrated slide show) which shows the master cylinder rebuilder inserting the spring with end caps, piston (with rubber seal installed) and flat washer, then getting the circlip just into the cavity and pushing the whole works down into place with a deep socket, which pushes on the clip evenly until it snaps into its groove and everything is in place in one go.
My reality: even with lots of brake fluid lubrication, the rubber seal on the piston doesn't insert without getting caught and folding up backwards on its way into the cavity. I have to hold the piston in just the right spot against the spring pressure and use something small and gentle to push the lip of the seal into place (I used a red "wd-40" spray-type applicator straw). But then I can't let up on the pressure holding the piston in place to install the washer and circiip or the rubber seal pops back out again - and I can't reinsert it with the washer and circlip in position. I need four hands...
I removed the spring, re-inserted the piston and left it overnight - maybe sitting at rest, compressed into its working position will help make the seal easier to insert tomorrow... where I'll have some extra hands at work to assist me if need be...
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I find assembly of brake seals etc easier with rubber grease or silicone grease, the parts just offer less "snagging" and resistance in the situation you describe.
Prefer to leave it assembled with grease present on the outside rather than remaining brake fluid.
Deal with the bleeding through as already described above.
Have a close, very close, look at the bore where the seal catches to make sure any previous corrosion has not left it effectively undersized.
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I find assembly of brake seals etc easier with rubber grease or silicone grease, the parts just offer less "snagging" and resistance in the situation you describe.
Thanks - I assumed that having grease on parts that are exposed to brake fluid was something to be avoided. I don't have any "rubber" grease, but I do have silicone grease.
Prefer to leave it assembled with grease present on the outside rather than remaining brake fluid.
Not sure what you mean by this - I was planning on putting some grease on the washer and circlips to help prevent them from rusting up down the road...
Have a close, very close, look at the bore where the seal catches to make sure any previous corrosion has not left it effectively undersized.
I have done this to the best of my ability. I cleaned everything I could reach, then "honed" the cylinder with a small bit of cleaner-soaked 3M green scrubbing pad "trapped" on the end of a drill bit. When inserting the working end of the piston into the cylinder, it fits perfectly and moves freely as long as the piston is perfectly centered and in line with the cylinder - if it's at all crooked, the piston drags and binds if I try to insert it...
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"Thanks - I assumed that having grease on parts that are exposed to brake fluid was something to be avoided. I don't have any "rubber" grease, but I do have silicone grease."
It's fine to use either red rubber grease ( most systems would be assembled with this in production) it'll just dissipate when the system is filled with fluid, it's not a risk.
Silicone grease also is compatible with dot 4 brake fluid and won't compromise the integrity. Most of these system will run dot4 or dot5 which is silicone brake fluid.
The bore originally would have have a very small chamfer on the approach side of the clip rebate to facilitate the seal passing into the bore. It will often get left really sharpened and angular after corrosion takes place. It's safe to re establish this as the seal will never need to operate on this area once it's passed through.
To "scrape" it by hand you'd need to grind a tool out of an old hand file or similar to recut it. Or usea proprietary deburr tool to get in there. It's only a small amount but stops the seal peeling back as you are getting.
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By deburring tool, I mean this
https://www.amazon.co.uk/Silverline-248844-Deburring-Tool-145/dp/B00NVPMV5I/ref=asc_df_B00NVPMV5I/?tag=googshopuk-21&linkCode=df0&hvadid=256196245361&hvpos=&hvnetw=g&hvrand=11784786374201878300&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9045909&hvtargid=pla-351907783351&psc=1&th=1&psc=1
Used in engineering to do this type of work.
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I got it done today. I don't have much confidence in the job - it feels like I think it should, but it was such a hassle to get everything together, and I really feel like I abused the rubber bits trying to get everything in place, which I eventually did after a number of attempts. We'll see what happens...
The only circlip tool I have is one of these cheap kit jobs:
[attach=1]
They are the devil's own - what horrible junk! Never again...
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It wont is the easy answer, i find well over 95% of the masters need to be bled the way i said, also forgot to mention make sure both the holes from reservoir to bore are clear one is tiny
Any hints or tips on unblocking the tiny hole in the reservoir?
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Two strands of multicore flex twisted together, usualy with piston out
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Gently push a very, very fine piece of wire down the return hole. Don't make the hole any bigger than it is, as the system won't work properly.
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Gently push a very, very fine piece of wire down the return hole. Don't make the hole any bigger than it is, as the system won't work properly.
Are we talking a guitar E string thickness or something finer Julie?
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Whats a guitar?
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Gently push a very, very fine piece of wire down the return hole. Don't make the hole any bigger than it is, as the system won't work properly.
Are we talking a guitar E string thickness or something finer Julie?
E will be just perfect 🤣🤣🤣
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Are we talking a guitar E string thickness or something finer Julie?
E will be just perfect 🤣🤣🤣
Light, medium, or heavy gauge? ;D
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Oh dear, my poor master cylinder thread...
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I'm reassembling my brake system - I'm having a difficult time getting the brake switch junction back in place. It's really fighting me. This is the only way it seems to fit, slightly crooked and the tab on the right (of the photo) in contact with the fork clamp (see arrow). Is this right?
[attach=1]
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Never mind... I don't know what happened, but when I went back to check it again, the junction/bracket turned freely when I loosened the mounting bolt... (https://advrider.com/f/styles/advrider_smilies/ne_nau.gif)
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You probably forced it on its place by screwing it on the first time ;)
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So, going to try bleeding the system tomorrow, keeping in mind all the advice above.
But: when doing this, do I need to have the rubber MC diaphragm in place at all? Or is that just to keep the fluid under control when the bike is in use?
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It does the same while bleeding the system, fluid can spritz out and ruin your paint, always wise to cover the tank with a cloth...
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Well, I think I managed bleeding the system. Filled the system with fluit, got the MC working and bled until no more air came out, either from the bleed nipple or from the return hole inside the MC reservoir. Not sure exactly how it's supposed to feel, or what the "correct" lever travel should be, as the brakes were frozen when I got the bike. But the lever works, it stops the wheel spinning and allows it to spin again when I release the lever. The brake light switch works.
Anyone care to comment on lever travel? How far before the brake light comes on? How far from the grip does the lever really harden up? I'm sure there must be variations from bike to bike, but nice to have an idea.
I've got the lever pulled back to within about 1/2 inch of the grip and tied overnight, just in case it helps draw more air out...