Rear brake bleeding problem, ?
 

Hi, I am bleeding the brakes on my XTZ660 and am having a problem with the rear brake, the front bled fine.
Firstly i should say the rear brake has been siting for a few months removed from the bike with caliper end hose disconnected. (I have been rebuilding the bike and had to disconnect the hose to remove it from the swingarm).

Ok so the problem is, i have it all back together and on the bike, I've re-filled the reservoir, hose it connected to the nipple on caliper.
I start pumping and cannot get any pressure build up, the pedal will press after press go straight to the bottom, and the fluid in the reservoir does not lower, whats the problem?

There are no leaks
There are no blockages in the hose from the reservoir to the master cylinder.
The rear brake was working fine before i took it off.

What do you think?

thanks
Brad

If you get fed up I can get you all the bits to convert to drum at the back:rofl:

You'll NEVER have to bleed it again!!!

you could get in contact with Kev off the www.xt660.com web site.

On the reservoir check to see if it has a rubber dish, this has to be removed, seems obvious but I missed it as it looks like part of the reservoir and I was pouring fluid into the rubber.
I was doing the brakes on my TTR and could not figure out why the fluid was not going down.

you need to bleed the master first at the banjo bolt on the master, then bleed the hose to the banjo on the caliper then you should be able to bleed it normally :thumbup1:

I've never had a problem bleeding the brakes on a bike, but if it was a car I would say that a seal has gone in the master cylinder. If it's been left dry for a while, perhaps the seals have perished.

hi there ive had this problem in the past when the hose is disconected , the first thing to do is make sure the bleed nipple is not blocked ,it can happen . the main problem i think you have is there is no fluid in the hose to build up pressure what you can try is to get 2 hose clamps ,sqweeze 1 clamp as close to the outlet from the master cylinder , slave cylinder the other 1 a few inchs down the line, plyers and a rag will do if you have no clamps. pump the pedel if all go,s well you will get resistance on the pedel if so take the first clamp off and keep pumping, the fluid should now reach the second clamp , keep putting the clamps on until you are at the caliper and the hose is full ,then bleed as normal. oh by the way if you have goodridge this will not work ,if you have try unbolting the hose from the caliper put the hose in a jar of fluid and pump away this may bleed the hose enough ,then reconect . if you can borrow a syfone gadget that conects to the bleed nipple even better. just keep at it and you will get it to go. good luck zigzag

zigzag if your still using rubber hoses and they are over 5yrs old bin them and fit braided lines

Bleenin!
 

Zigzags technique is a good trick and works well on standard rubber hoses. Steel braided can be damaged though.
Be carefull to pad out the jaws if using pliers (long nose pliers with insulstion tape padded jaws work well).
You could also try back filling the line from the slave cyl (caliper) bleed nipple.
There are specific pumps you can buy for this but a large syringe does it well.
Once the line is full is should bleed ok.
Dave.

I agree with Wolfzero's first reply, but first remove & check the bleed nipple isn't blocked.
When bleeding it you should pump the pedal quite fast to ensure the air bubbles don't remain at the highest point in the hose.
Bob

I had this problem as well.

Eventually I solved it by sucking the brake fluid from the resevoir into the cylinder by attaching a vacuum pump (the kind used to drain car sumps via the dipstick ) to the bleed nipple and going through almost an entire bottle of brake fluid. It seems that no matter how much I pumped the brake peddle there was always a trapped air bubble in the line causing a vapour lock.

there is another way of getting the air out of the line its a bit slow but does work well
take the hose off the caliper and cable tie it to the resevoir or at the same height top the res up to the brim and use something to wedge the brake pedal down leave it over night and the air rises through the system and presto the line is full of fluid

:clap: :D:mchappy:

That system works really well on the front brake even with everything attached and in situ. It's still a bugger on the back brake tho as when the air bubbles have gone you still got to get the hose back down to the rear brake calipers without getting any air in. Not so easy. Unlike the front brake lines, the back brake line has "elevation" changes both sides of the median that preclude the rise of air bubbles back into the resevoir.

:oops2:maybe i should have added the following info to that post

once the line is full allow the brake pedal to return to its normal position and give it a couple of presses to fill the line fully and using some tape or a rubber bung block the eyelet of the banjo union to keep as much fluid in the line as posible whilst you route the line back to the caliper try and get as much fluid into the caliper as posible prior to ataching the line this wil help prevent air going back up the line if done carefully any air in the line will not be sufficiant to prevent the brake being bled as normal
:thumbup1:

:clap: I should have realised that. I'm having a stupid day:oops2::stupid:. All the same. The back brake has always proved a nuisance for me what ever way you look at it. Traditional bleeding has always given me a PIA. Sucking the air and fluid through the system albeit with wastage has saved me an endless amount of faffing about. At £20 for the vacuum pump I now consider it an essential part of my mechanics toolbox.

when i get a chance i'll be making a 12v vac pump for doing things like bleeding brakes, i have a spare vac pump off my rangrover that should do the trick. :cool4:

Im struggling with my back brake too, quite possibly just me being a newb tho.

I managed to sort the front brake out no problem by filling the cylinder and bleeding,several times and iv tried to do the same with the back but i dont seem to be getting any pressure from the rear master cylinder. The pin which pushes into the cylinder seems very loose and I can wiggle it in all directions. Is this normal or do i need a new cylinder?

they all wear out at that pin and adjuster, if its really bad you wont be getting the full stroke of the piston so its prob not pumping as much as it should.

try winding it out to its max adjustment or take the pin out and pumping it direct.
:thumbup1:

Two ways I have resorted to in the past, just to save my self some headache.

1. If you are just changing the hoses, take the caliper off the swingarm/fork and pump the pistons out, but not so far that they start to come out of the caliper: 1 cm per piston is plenty. Connect the new hose, nip up the banjos by hand and then, push the pistons back in. Fluid will go up the hoses and into the master cylinder. Then just reconnect to the swing arm/fork, torque up the bolts, open the bleed nipple and start pumping out old fluid, whilst topping up with new till the stuff coming out is clear and new...

2. If you have dismantled everything and you cannot pump out the pistons with the existing fluid, get a 20cc sysringe from a pharmacy, connect some clear PVC tubing, fill the syringe with brake fluid, connect to an open bleed nipple and plunge the syringe. Go easy and you get the same result as above. Once you have 1-2 cm of fluid in the master cylinder, nip everything up to the correct torque settings and top up the reservoir.

Either way done: 20-30 mins. When brakes have been bled/rebuilt, I always bungee the lever at the bar, so that the system is under pressure overnight. Not too tight, but enough to highlight any leaks and to squeeze air bubbles from the system....

If the lever is not tight in the morning then you have a problem. Wrap cloth around the joins and seals just in case as brake fluid kills paint work

Iv found the problem, the piston inside the master cylinder has seized in what should be the full on position. The only way I can think of moving it is to attach the front brake hose to the cylinder and using the front lever to try and force it out. But of course this will mean id hve to bleed the front again.

does anyone have any other suggestions please?

Rob

hi there it sounds like the cylinder needs dismantaling and inspecting carefuly ,an air line would be the best way to get the piston out if it is stuck , but it should just pull out once any circlip etc is removed you may just have forced it up in the bore if you were pressing too hard trying to bleed the brake. if things look at all IFFY get a replacement cylinder DONT TAKE ANY chancers take care zigzag.

Just to let you know, I managed to free the piston in the end.... I tried an airline but didnt budge, also tried a heat gun but the piston must have been getting just as hot as the cylinder so that didnt work either.

Freezer! I put it in the freezer for an hour then it just tapped out. Iv cleaned it up and now its working just fine.

cheers for your advice though,

Rob