Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Integra99 on February 07, 2018, 10:31:27 AM
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Hi all,
Has anyone had issues bleeding up the front brake.. I have rebuilt the caliper, new pads, new M/C so all good. I have brake pressure but not much.. unfortunately I dont have use of a compressor to assist as feel it might need a little help. All the lines are tight but I keep getting bubbles in the line so I have no idea how its getting air in.. I assume the brake switch is an area for air to get trapped. The switch works as its operating the rear light I'm just struggling to get a firm lever.
Any tips.. its off for an MOT soon so my friend can do it on his system but would be nice to turn up a little more prepared.
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All I can suggest is fill the reservoir slowly so you don't introduce bubbles there. Keep pushing the fluid through and make sure you close the bleed valve while still squeezing the brake lever each time.
It should work once enough has gone through. Patience required.
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Thanks yes I probably haven't been patient enough.. one thing I am getting is bubbles out of the reservoir when releasing the brake lever.. not a lot but seem odd"!
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Is that after closing the bleed nipple then releasing the lever?
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Persistence pays off, I ended up cracking open all the banjo bolts on the lines on my 500, lots of air came out there, bloody messy though.
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Yes I bled the bolts.. really messy and panicking with all my nice paint ha!
the bubbles come when I pump the lever a few times to build up some pressure after a bleed and tightening of the nipple.. in the mechanical sense ha!
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It sounds like there is either air bubbles still in the fluid and need to keep bleeding through - or you may have a leak somewhere in a joint or in the m/c.
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Thanks I will keep persisting.. I have a brake but must just be lots of air.. the M/C is new and worked perfectly before the strip down. Will bleed the banjos again top to bottom, then leave a strap around the leave and the cap off over night maybe to force air up.
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Yep, keep at it. Those pesky air bubbles are a pain! You'll get there. :)
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Put a couple of wraps of ptfe tape around the thread of the bleed nipple this will stop air getting in there, I always draw fluid through using a 50ml syringe and it only ever takes about half an hour.
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Thanks all, do you draw fluid out of the bleed nipple with the syringe once slackend off..?
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Thanks all, do you draw fluid out of the bleed nipple with the syringe once slackend off..?
Yes, its awkward but it works for me, squeeze the lever while drawing syringe then keep drawing while shutting nipple you almost need three hands.
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I'll have a go this evening! ;)
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It is possible that you are pulling the lever too far, past its normal travel when you are trying to bleed it. if this is the case, particularly if you are pulling the lever all the way to the grip, you'll never do it, ask me how I know.
I'm pretty sure there is a service bulletin that advises you to tape a suitable object to the grip, to stop the lever from travelling further than it should.
The rear disc on my Sportster can only be bled using 'baby steps' - if you push the pedal to far, even just once, the piston sticks in a part of the bore it never normally sees, and you are fecked until you take it to bits again. I learned this the hard way, too :(
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Interesting.. yes I guess I am pulling all the way in.. its how I've always bled brakes same on a car.. foot to the floor and up. I didnt get a chance last night so will try again.
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Do the ptfe tape bit this will stop air getting in around the nipple, and keep the reservoir topped up whilst bleeding, pull the lever slow nipping up the nipple just before the lever reaches the bars, this will work, i have never used an auto bleeder and don't see the need to ever use one.
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+1 on using PTFE tape. It also prevents bimetallic corrosion.
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Thanks guys will pick some up tomorrow!
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It is possible that you are pulling the lever too far, past its normal travel when you are trying to bleed it. if this is the case, particularly if you are pulling the lever all the way to the grip, you'll never do it, ask me how I know.
I'm pretty sure there is a service bulletin that advises you to tape a suitable object to the grip, to stop the lever from travelling further than it should.
The rear disc on my Sportster can only be bled using 'baby steps' - if you push the pedal to far, even just once, the piston sticks in a part of the bore it never normally sees, and you are fecked until you take it to bits again. I learned this the hard way, too :(
I have a copy of the service bulletin and it basically tells you to tape a 15mm spacer between the lever and the grip to prevent the seal on the piston in the master cylinder travelling too far and uncovering a port which can allow fluid into the wrong side of the seal.
How big are the bubbles you are seeing in the fluid coming through?
Air in the system shows up as large bubbles in the fluid. If you are getting lots of tiny bubbles then that is more likely to be cavitation of the fluid as it is squeezed through the small apertures at high pressure.
You can prevent air entering the system around the bleed nipple simply by closing the nipple at the end of each pressure stroke.
When I rebuilt the system on my 350F it didn't seem to bleed all that effectively leaving me with a soft feel to the lever and too much free movement but a couple of days later the free travel had disappeared and the lever feel was solid.
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Is this the Service Bulletin you are looking for?
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I didn't know any of that. Thanks for sharing. I'm now older and wiser than I was yesterday.
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I bought a gunson easybleed like what you used to use in the 70s and I have drilled a few spare caps to fit various bikes. It works all the time with no mess, its just a bottle with fluid it is pressured with a hose which has a toggle the same as a foot pumpthat you put on the valve of a spare wheel with about 20 psi in it, another hose which goes to the bottom of the bottle so it is in the fluid with the other end fitted to your cap which you have drilled. you just pressurise the system put a bit of tube over the bleed nipple and crack it open it forces all the air and dirty fluid out, close the nipple, disconnect the pipe from the spare wheel or whatever you used and refit your original cap. It is also good for replacing old fluid .
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Very interesting ... yes big bubbles in the resevoir that push fluid out of the res , I think I was pulling the lever too much!
Its getting much better now.. almost a hard lever.
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try putting a cable tie round the lever with it pulled tight and leave it overnight sometimes this lets the bubbles find their way up the pipe.
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Actually Ogri I ended up doing that and was much better... thanks all we got there in the end, just some persistence and I learned something thanks!
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I always back bleed them, especially on the Honda V4 cluches that are a real PITA. Plus, as mentioned before,cracking the banjo bolt on the master cylinder can help a lot.
I use a large syringe with a pipe securely fastened around it and the caliper bleed nipple and gently push the fluid up into the m/c.
Cheap enough on the bay of eezz.
(https://farm3.staticflickr.com/2816/34230375131_f9cd51b9b9_b.jpg) (https://flic.kr/p/U9PBXz)Honda special tool number 876954365489 (https://flic.kr/p/U9PBXz) by Adrian Lee (https://www.flickr.com/photos/fracster/), on Flickr