twin front brakes wont bleed

[rattytcb]

hello all im giving my bike a ovehall and i cant get the front brakes to bleed, im getting oil out and everything is happening as it should but i cant get the brakes to bite up or the pressure to build up, have given up for the night now but could this be becouse of the oil need deaireating if so will it clear if i try again tommorrow.
many thanks
tony

[taint]

Hi Rattytcb,

It sounds a lot like an airlock in the system. Do you have two separate lines running from the master cylinder or one that splits further down the line? Also did you back bleed, or are you starting from the top?

With twin brakes, you need to clamp off one of the lines while you bleed the other; otherwise you're trying to bleed both callipers at the same time. You can do this by clamping the line, or by fitting clamps to the pistons. I apologise, if I'm trying to teach you to suck eggs, but it's always worth checking .

When bleeding my brakes recently, I found it easiest to back bleed; i.e. fill the fluid via the bleed nipple using a syringe. While it doesn't eliminate all the air in the calliper, it does clear it out of the line; which will make bleeding twin lines a lot simpler. Once you're no longer getting bubbles in the master cylinder, you can then bleed normally; to eliminate the bubbles in the calliper.

Once that's done, leave the system to settle, possibly with the brake handle tied back (or weighted in the case of the rear brake). Then bleed the system again; to clear any remaining air that has collected. Top up the master cylinder and the jobs done.

I hope this helps

T.

[General Gman]

Clamp the lines ?
Never done that, I must admit - the pistons can only go so far if the calipers are fitted to the bike, so not really an issue AFAIC.
Ratty - you need to bleed the caliper furthest from the master cyl. first - bleed fluid through until you see no air bubbles, then swith to the other caliper.Once you see no air coming through there, close off the bleed nipple and tap the brake lines gently to help dislodge any bubbles.I do agree that back bleeding makes it a quicker job - like taint says, once you stop getting bubbles in the master cylinder, bleed normally.
It is useful to tie the brake lever to the bar and leave for a few hours (or overnight) - this keeps the sytem under pressure and helps to force air bubbles out.
The most important thing, though, is to do it slowly - if you're pumping the lever like mad and there's air in the system then you'll never get it out.

[taint]

I only have a single disk model; so I only suggested the clamp because that's what Reaper says on the DVD ;D

Personally; I'd be wary of crushing a braided line, so I'd probably do it without clamping as well; but it's always better to defer to an expert when giving advice ;D

T.

[General Gman]

Ah.
Not seen the DVD (although Jools has a copy...)
Divvy brakes are buggers to bleed, though - must be summat to do with the design of the caliper.
The nissin calipers on my ZX9 (which are ageing gsxr items) take about 2 mins to bleed through from a totally empty systemto good pressure.
The Tokico 6 pots on Jools's bike are worse than the divvy calipers for bleeding...

[billywhizz]

twin disks and bleeding, yep real pain...
But i did mine, and I clamped one side off first, bleed the other in the normal manner, pump lever, undo bleed nipple, nip back up and re pump lever etc.., then clamped the line and did other side.
seemed to take hours, but actual did it all in about an hour,

Done the same to the Fazer last october, as popped a piston when i was cleaning them..

To clamp I used two screwdrivers laid flat across the pipe and a 'g' clamp!!,
only have to close the tube, not crush um though!!

[nobby]

I hav e had this problem on bikes with twin discs and only the other week on my single disc divi.

in the end I took the bike to a local bike shop who bled the system with their pressure beelder.took about 5 secs on their machine but took me 2 weeks to get nowhere

[suzukikidontheloose53]

I've bled my front brakes twice(twin discs and braided lines)and it took me 3 days each time

[rattytcb]

thank you for all you help so far im gonna give it another go tommorrow night as been working late this week. will post how i get on

[rattytcb]

oh sorry and its two hoses splits from the master cylinder.
ta
tony

[taint]

Hi Rattytcb,

It's definitely worth back bleeding if you have two separate lines; should make the job a lot simpler. If you get yourself a 25/30/50ml syringe and a short length of pipe (available from many eBay sellers), you can fit over the bleed nipple. Use an open ended spanner to open and close the bleed nipple with the hose attached. Fill the syringe and hose with brake fluid and fill via the bleed nipple. It helps to use a clean or new bleed nipple as you're less likely to get crud in the system.

Be gentle when pushing the fluid in, don't force it if you meet resistance; the brake fluid will leak up around the edges of the nipple, so be ready with a cloth. If you push too hard, the hose can come loose from the syringe and you'll end up spraying the bike with brake fluid (I speak from experience ). Keep an eye on the master cylinder; just in case it overflows.

If you find that the bleed nipple leaks after tightening, you can use some plumbers PTFE tape in the threads to cure this; just don't cover the hole at the bottom.

I hope this helps

T.

[General Gman]

May 21, 2008 9:41:30 GMT @taint said:

Hi Rattytcb,


Be gentle when pushing the fluid in, don't force it if you meet resistance; the brake fluid will leak up around the edges of the nipple, so be ready with a cloth. If you push too hard, the hose can come loose from the syringe and you'll end up spraying the bike with brake fluid (I speak from experience ).

T.

Glad it's not just me, then

[rattytcb]

hello all and thank you for your advise got the brakes bleed last night in the end i clamped one bleed the other then clamped the other and so on took me about 10 minutes which is sods law,
and doesnt seem to have damaged the new hoses at all. so got up the ace cafe on it last night.oh and also wifes uncle turned up as im finishing and says he has got a vacuum pump at home.
grrrr but he did heliciol my caliper for me so good man, guess where im going next time i need to bleed the brakes though.
altogether im much greyer due to this experiance but happier now its back on the road again.
ta tony

[darren]

theres always someone that has something to make the job easier after you jave done the job

[CD]

I didnt fancy clamping the braided hoses, so used the syringe method when I fitted twin braided lines. I used a ring spanner on the bleed nipple so needed only one hand to open/close it. I also slipped a smaller ring spanner up the neoprene tube and pressed it over the top of the bleed nipple. This stopped the neoprene from pushing off the bleed nipple.

A second syringe is handy for sucking excess fluid out of the master cylinder.

When done, the brake was mushy, so I tied back the lever with a rag and went for a break. 2 hours later there was no mushyness.

[bobh]

You're right, Dave, I don't know exactly how it works, but pulling in the brake lever with a rubber band or similar and leaving it for a while (e.g. overnight) seems to get rid of a lot of the sponginess.

Bob

[CD]

Makes no sense to me but it works so hey...