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Post by metalforever on Apr 21, 2009 20:36:25 GMT
My front brake wont bleed. I havent tried back bleeding it yet (Which is what im going to try in the morning if i can repair the syringe) but i cant understand why!
I can get some pressure on the lever after a long time bleeding but its not sufficient and the lever still has enough travel to touch the bar.
Whats going on?
I've used new fluid, there are no leaks and im bleeding the brakes as i normally do, they just feel ridiculous. i had 'dry' lines to start with and found it very hard to get fluid even moving through them. any advice?
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Post by Flymo on Apr 21, 2009 20:56:43 GMT
When i first had my D6 i had this problem too, in the end i left it overnight with the brake lever tied against the bar, then it bled easily the next day.
Flymo
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Post by bobh on Apr 21, 2009 21:12:42 GMT
There are two other ways to speed up the process:
One is to bleed air by just cracking open the banjo bolt at the master cylinder, which is the highest point in the system. Make sure you have plenty of rag to catch the spillage.
The other is to take the calipers off one by one and hold them as high as they will go, and bleed them in that position. You need a packer between the brake pads of the same thickness as the disc.
But however much air you get out by bleeding, it still pays to finish the job off by doing the rubber band trick as mentioned by Flymo.
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Post by CD on Apr 21, 2009 21:40:18 GMT
The factories fill the brakes under vacuum - no air - no bubbles.
I reckon tiny air bubbles get trapped in the fluid so no matter how much bleeding we do, the only option is to tie the lever back so they can find their way out.
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Post by Padster on Apr 21, 2009 21:43:13 GMT
I got myself a Mityvac and it solved these problems for me. If a brake doesn't bleed straight away using the conventional method the Mityvac sorts it.
There is an alternative method using a piece of tubing from the bleed nipple into the reservoir. You bleed the brake until you have a full circuit and then leave the lever tied back as mentioned.
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Post by metalforever on Apr 22, 2009 6:38:53 GMT
ive been trying again this morning and have discovered my problem. The brake is actually bled.
The problem is the pistons cant compress enough onto the disc because the 'caliper slider' (the bracket which holds the pads and calliper onto the forks) is moving. im guessing this isnt meant to happen but my haynes is showing that ive assembled it all correctly. any suggestions?
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Post by metalforever on Apr 22, 2009 7:41:33 GMT
I think ive found some sort of solution, although im still less than satisfied, Saying that i think i have a similar level of performance to that i did before the strip down which wasnt too bad on the front really.
Anyway, i took the calliper off and placed an old brake pad in between the pads to act as the 'disc' whislt off the bike. i pumped the pistons until the lever went firm, and it was excellent. I reattatched to the bike and the performance at the lever dropped so i took them back off and pumped the pistons out until the pads where touching, keeping the lever pulled with a piece of string i forced the pistons appart just enough to slide it over the disc and voila!
Sorted brakes.
Ive got a band round the lever at the moment to allow any last air to bleed, and its covered by a weighted piece of paper so in theory i SHOULD be doing a test ride tonight!
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Post by teejayexc on Apr 22, 2009 9:13:59 GMT
ive been trying again this morning and have discovered my problem. The brake is actually bled. The problem is the pistons cant compress enough onto the disc because the 'caliper slider' (the bracket which holds the pads and calliper onto the forks) is moving. im guessing this isnt meant to happen but my haynes is showing that ive assembled it all correctly. any suggestions? It's supposed to slide, are you sure it's sliding freely though?, sometimes they slide out but not back again  |
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Post by CD on Apr 22, 2009 12:13:37 GMT
The D600 brake has two pistons on one side with a sliding mechanism allowing them to clamp the disc.
As TJ say's, if its not sliding properly the brake will feel spongy as it tries to bend the disc.
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Post by amorti on Apr 22, 2009 13:28:18 GMT
I don't know your level of experience, but it is worth remembering that you are not after a lever that feels like an on/off switch. Try the lever on any brand new bike in a showroom and you will see what I mean. Could be your expectations are too high? Problem is, a well-bled XJ600S brake with a metal hose does feel like an on/off switch, that's down to the over-sized master cylinder. But that thread's been done  |
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Post by amorti on Apr 22, 2009 13:32:05 GMT
... I reattatched to the bike and the performance at the lever dropped so i took them back off and pumped the pistons out until the pads where touching, keeping the lever pulled with a piece of string i forced the pistons appart just enough to slide it over the disc and voila!Sorted brakes. This means the seal in your master cylinder is no good. You should not be able to retract the pistons while the lever is pulled (think about it!!) I would put money on the first (deepest inside) seal on your master cylinder being no good. If/when the second seal goes, it will then start leaking fluid from the plunger end. If/when this first seal goes, it also makes it hard to bleed the brake, as you have found. I could try and explain, but looking at how a m/c works should, with a bit of thought, explain it better than I can. Two seals, one pin hole to let extra fluid in/out, first seal works the brakes, but when not applied slides back allowing extra fluid in/out. Second seal is to seal the system from leaking fluid over your tank, but if first fails will partly pick up the slack, but it won't work properly. Take the m/c off, open it up, and check out those seals. By happy coincidence, I happen to have a VGC standard XJ600S front master cylinder going spare  Please please please: either tell us what bike you mean in your posts, or fill out your signature. We don't know if you mean single or dual disc, 600 or 900. Also, you didn't mention why you were bleeding the brakes. or why the lines were dry. Internet diagnosis is already tricky, help us to help you, yeh? |
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Post by CD on Apr 22, 2009 15:24:57 GMT
He does say the lever will touch the handlebar. But why not invest in a Honda NVT 600 mater cyl, as discussed elsewhere and maybe a braided hose.
Also, check the lever span adjustment. When it's set short, there is less space for "slack" in the lever travel.
To give some perspective, my D900 has R6 blue spot brakes with braided hoses and R6 master cyl (sadly they wont fit the 600). The lever can be heaved back a heck of a way but in real use that would lock the wheel. On the road, it behaves normally and it breezed the MOT. Bleeding the brakes has never reduced the "slack" lever travel, and I'm more than happy with the brake performance so assume the hydraulics are good enough.
Every time I have bled the brakes (on any of my bikes), I have had to tie the lever back overnight to remove the fine air bubbles. It's certainly easier to back fill with a syringe, but in my experience the lever tie-back stage can't be avoided.
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Post by Deleted on Apr 22, 2009 15:39:50 GMT
He does say the lever will touch the handlebar. But if the seals are gone why not invest the cost in a Honda NVT 600 mater cyl, as discussed elsewhere and maybe a braided hose. Oh no, it's catching. ;D |
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Post by CD on Apr 22, 2009 15:51:07 GMT
I think the NVT master cylinder idea is well worth doing.
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Post by amorti on Apr 22, 2009 16:20:29 GMT
I think the NVT* master cylinder idea is well worth doing. I think that's a terrible idea, what he needs is a nice XJ600S master cylinder. Oh look, I've got a spare one, isn't that funny?? *NTV650 or any similar 1/2" master. |
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Post by Deleted on Apr 22, 2009 16:22:54 GMT
Since he was happy with the brakes before he lost them I think you should offload the D6 cylinder on him before he reads your NTV thread.
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Post by metalforever on Apr 22, 2009 18:58:56 GMT
Right lads, i reassembled said bike and had it running, tested the brake sin my garden and the front was appauling. whats happening (And i have NO idea why) is the pistons move freely but due to the claiper slider thing move too much, and the calliper is pushed away fron the disc instead of the pistons pushing the pad against the disc. i dont know how to explain this really.
Its as if the pistons need an extra couple of MM length because the full travel of the MC piston isnt providing enough hydraulic pressure to make pads bite disc.
Like i say, they work perfectly when not on the bike and the pads grip the disc perfectly, its only when theyre mounted on the bike and on the carrier/slider that they turn into rubbish.
Its almost as if somethings missing to prevent the movement of the caliper, but theres not...
*checking haynes manual now*
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Post by metalforever on Apr 22, 2009 19:03:02 GMT
By the way its a single disc 600 diversion.
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Post by amorti on Apr 22, 2009 19:14:03 GMT
You're not paying attention are you mate. Once again, for the hard of reading:
the caliper is meant to slide. That's why it's called a sliding caliper.
your problem is probably the master cylinder.
tell us why you had it opened up and what you've done / fixed / changed.
Till that's done, I suggest everyone leave this thread alone as it can only be guess work.
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Post by metalforever on Apr 22, 2009 19:47:44 GMT
Amorti, i mean you no disrespect but i know its meant to slide, what im saying however is it is this sliding motion which is removing the force from the pistons. This same sliding motion hasnt been a problem until the caliper was removed from the slider, the only reason it was removed was to replace the seals etc whilst front tyre was off.
Removing the caliper from the bike and inserting a piece of metal the same width of the disc i get a very firm hold when the brake is pulled. and it leaves about .3 of an inch to the bar, perfect.
As soon as i tighten it all back upto the bike this isnt the case as the sliding motion changes things.
There are no air leaks, the lever doesnt creep or move.
I dont believe its the MC for a moment, as like i say when its not attached to the slider the pistons operate perfectly and clamp the pads tight.
Ive only had the MC cap off to fill with fluid and ive rebuild the brakes with fresh seals and cleaned them. Ive had the frotn brake calliper completely stripped down.
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Post by metalforever on Apr 22, 2009 19:57:19 GMT
Exactly what's happening from my POV:
Bleed brakes as per usual, pressure slowly builds but nothing significant, full lever travel still there, although there is no more visible air being removed.
Notice movement of caliper when brake is applied.
remove caliper and insert piece of metal between pads loosely (with no carrier/slider installed)
Brake operates 100% normally with very good pressure/bite and lever travel is spot on.
Reinstall pads/caliper/slider onto bike.
Notice the movement of the slider is there again, pressure at lever is gone.
Look upto pads from beneath, notice the left (when sitting on bike) is making contact with disc when lever is pulled, right doesnt. Piston movement simply pushes the caliper to the side, but not far enough to bring the other pad into contact with the brake disc.
In my head all i can think is there should either be:
A) something inside of the pistons to add some length to them (As per normal brakes that ive worked on, they have carbon/ceramic inserts in the pistons which the divvy hasnt)
B) there isn't actually enough fluid in the system to be compressed enough to drive the pistons out
Thats the lot!
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Post by teejayexc on Apr 22, 2009 19:59:57 GMT
Take the caliper off again and check the slide pins, sometimes they can get an 'hydraulic lock' if you've put too much lubricant in there when reassembling, they only need a smidgeon of lubricant.
See if that works.
trev
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Post by metalforever on Apr 22, 2009 20:19:38 GMT
Hold the press! Im sitting here studying my haynes, over and over. i reckon i know what amorti means, roughly. Although this problem shouldnt arrise so suddenly, it should have arrisen before or after my rebuild.
My problem is the system isnt building enough pressure to hold the pistons still, pressure(or fluid) is being lost from the hose/caliper somewhere. as you compress the lever the system effectively 'closes' to new fluid entering and what is in, stays in.
However, when you open the lever, new fluid can enter, but already contained fluid SHOULDNT (In theory, my theory at that) be able to escape the hose.
If fluid from the hose reenters the MC then the hydraulic pressure is lost and there is no pressure held to build upon for the next pull of the lever.
This means there isnt enough pressure to make the pads grip.
If a MC seal has gone fluid will return to the MC, but also the brakes will be very hard to bleed (I imagine) and the fluid level in the mc shouldnt barely shange when the brakes are 'being bled' and a similar affect to osmosis isnt able to occur.
That new MC may very well be the solution!
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Post by CD on Apr 22, 2009 21:47:01 GMT
The MC may well be the solution but it was working before you started so its probably not too bad now (Presume you didn't strip it down). Its also only done 25K or so. The grease idea in the sliding pins is a good option as the sliding pins can bottom in the grease and stop dead. Assembling the brake wrong is another. The pistons have to create a clamp action so check the sliding part was put back the right way around. See the parts fische on diversionclub.proboards.com/index.cgi?board=600&action=display&thread=2621Then choose - XJ600SJ-1997.PDF and look at page 44 (shown top left of Adobe Reader) |
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Post by Padster on Apr 22, 2009 21:51:08 GMT
TJ's suggestion sounds very likely as everything works when not used on a fixed disc. It sounds like it isn't sliding enough. Not unusual given the design of the caliper and setting up a hydraulic lock is very easy to do.
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Post by metalforever on Apr 23, 2009 6:11:40 GMT
it's certainly been aseembled properly and its all the correct way around etc... as for hydraulic lock ive questioned this possibility but i can access full movement of the slider easily with just gentle pressure form my hand.
To be honest the only other variable in this lot is the MC now, how would i check the seals in the MC having not had one appart before? I'd rather not have to buy a new one but if its going to cost much to replace/restore i might as well upgrade the whole front brake.
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Post by amorti on Apr 23, 2009 7:19:49 GMT
The m/c seals can go while you are bleeding, because when bleeding you are sliding the seals along the full length of the bore. this isn't usually the case, so there could be a piece of dirt or grit in there that tears the seal. Also, you are at that point running the seal dry until you beat the air lock, which it also won't thank you for.
To get in there, you will need circlip pliers. Open it up, strip it apart and visually inspect the seals, it's very obvious once you have it open.
I'm confused by all the information in the post so not entirely certain that's your problem. But as you say it is a very simple system where there isn't much to go wrong, and it seems to me you have eliminated the bottom cylinder.
The seals set will be about £25+vat+post off Yamaha (guessing based on Honda prices). I wouldn't suggest using pattern seals on brakes as it never seems to be as well made. You can have my XJ600S assembly complete with switch and lever for £20 posted, or you can see what 1/2" Nissin master cylinders you can find. That is an upgrade and will improve both feel and power, but if you like a rock-hard lever feel, and were happy with the brakes before, then it may not be for you.
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Post by metalforever on Apr 23, 2009 14:38:07 GMT
Amorit, im going to take you up on your lever etc. Pm mate.
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