Brake bleeding help
 

Okies, after weeks of on/off working on my brakes, I'm just past the point of being stupidly annoyed.

Original hoses were knackered beyond belief, so replaced them with a set of braided hoses. This improved the feel dramatically, and made them a bit less spongy, but I could still pull the lever back to the bar on all but the number 1 adjustment level.

The brakes have now been bled for the last hour, going through almost 250ml of brake fluid. They've been bled from the master cylinder, the banjo on the caliper and the bleed nipple, but there's absolutely no change. In frustration, I took the double banjo-bolt off the master cylinder and connected each line to the MC individually, in turn, using a single banjo. As soon as I did this and bled from the bolt a little bit, I barely had to pull the lever and it was rock solid.

Thinking that maybe there'd been air at the top of the lines that I couldn't displace previously and that it was gone now, I put both lines back on with the double-banjo and bled till no more air was coming out. The lever's now back to where it started originally.

I've now only got 2 assumptions left:
1) MC is buggered and can't push enough fluid for both lines.
2) There's air right at the top of the banjos on the line closest to the MC. The crush washers on either side of the banjo form too complete a seal for any air to be pushed out at the top on anything but the other banjo, so I can get air from one line at the top but not the other.

So! Has anyone got any ideas on what to do with this, or a pressure bleeder to try to whack on it to force the air out?

Re: Brake bleeding help
 

Leave it open a few hours without fiddling and gravity will sort it out.

Works for me.

Re: Brake bleeding help
 

Leave what open? The reservoir cap? Master cylinder banjo bolt? Unsure how this would help

Re: Brake bleeding help
 

have you tired tapping the caliper, lines etc with a bit of wood to displace any trapped bubbles?
Also you are doiing this with the bike on a paddoc stand i assume?

Re: Brake bleeding help
 

Yep, tapped all over, no joy.. As mentioned above, if there's air in the lines, it's definitely at the top, since changing the banjo bolt over to a single-line setup (to pump just one caliper) then bleeding out the air that the changeover puts into the system instantly makes the lever rock-hard - you can barely pull it back more than 2cm. It's been bled on a paddock stand in the past, but the most recent bout was done on the side-stand, turning the bars side-to-side to keep the MC bolt as the highest point in the system.

Re: Brake bleeding help
 

well thats my helpfull hints locker empty now sadly mate.
i'm sure someone who knows better of these things will come along with some better advice soon tho.
I'd bled my brakes quite well i thought then went in to have tryes put on. They bled them during fitting but didnt mention it and i was really suprised at how much better they made them feel, so there must be some devious trick or slight of hand you need to perform somewhere along the line to get it right.

Re: Brake bleeding help
 

See, I'm pretty sure I'm doing things right based on how rock-solid the lever gets with just one line on. I'm pretty sure that on one disc it'd stop just fine at the moment for me to get the feel I want...but I'd like the second caliper working ideally ;)

Re: Brake bleeding help
 

hhmmm, are you sure that you dont have a sticky piston on one of the callipers... i have at the moment and my brakes are the same'ish.. nowt then spongy then rock hard..

Re: Brake bleeding help
 

Pretty sure, based on a) Cleaning them up a bit when switching the lines over and b) the switch to single-line setup. As soon as I'm only running the system as MC->single hose->single caliper they're both rock-hard. Change back to MC-> dual hoses->both calipers and sponge comes back.

Re: Brake bleeding help
 

yup.. mine are the same, but i know for a fact then 3 of the pistons on one of the 6 pots are sticky.. connect the callipers with a single line and both are spot on.. connect both lines and crap brakes (well not so much as crap but just a lot of play before they work) where before i serviced them they were rock hard... (yes i forgot to grease 3 of the piston seals)

Re: Brake bleeding help
 

Aha, interesting.

I shall have a proper gander at the pistons tomorrow and report back!

Re: Brake bleeding help
 

Did you over haul calipers? are you using dot 4 fluid (dont know if this makes a difference if you use different dot fluid but its just a suggestion/question) calipers moving freely on sliders? (if that actually affects it), MC seals ok?

Hope this helps you in some way :)

Re: Brake bleeding help
 

Umm, i didnt grease any of my seals... *worries* but i did soak them in fluid.

Neeja i found this pretty helpful when i done mine was linked to me by some one else

http://forum.svrider.com/showthread....hlight=caliper

Re: Brake bleeding help
 

Last caliper overhaul was in...November-ish last year, so coming up on a year now (tends to be an annual affair for me with intermittent cleaning). Definitely Dot 4, calipers definitely moving freely on the sliders because I had an issue with one being stuck when I changed the lines over, and cleaned+regreased then, still working. MC seals I'm assuming are ok because on a single-line setup the lever's rock-hard and doesn't sink back to the bar, so no fluid seems to be getting past them.

Re: Brake bleeding help
 

I found when i did my seals my lh caliper slider had siezed up as well and my seals lookd pretty decent when i replaced but even then my lever barely moved, and then when replaced moved even less! Good luck to you my mech knowledge on brakes stops there. You may want to ignore my prev post then as you have done seals before xD

Re: Brake bleeding help
 

i used to do exactly the same, but once i started using red rubber grease between my fingers and very lightly smearing the seals with the grease has made a huge difference.. its the 3 pistons that i haven't greased that are sticking.. i also soak the seals in brake fluid overnight first, then use kitchen roll to remove off the excess fluid before greasing..

Re: Brake bleeding help
 

Meh, 10 mins in a pot, stick em in the caliper, job done.

You learn from your mistakes, and learn even more from others mistakes, ah well have to remember next time i ever do an overhaul, was my first time and it took me a good 5 hrs as well :D

Re: Brake bleeding help
 

Are you vacuum bleeding ?

Re: Brake bleeding help
 

I'm glad this has come up as I have the same problem. There's loads of freeplay since I switched over to braided lines (well even before then to be fair). The brakes still work really well, they just don't activate as soon as I'd hoped they would. It's not so bad as I have the lever in position 1 anyway, I'd just prefer to get that rock solid feel again.

I'll look into greasing up the seals first, but I overhauled the calipers March/April time, so it's not been too long for me.

Re: Brake bleeding help
 

Yeh agree, you really wanna grease those seals as the brake fluid dries between the seals and the pistons and can case them to stick.

I had a very hard time finding any red rubber grease so called Castrols helpline, the nice man there advised i could use anything that is vegetable based. I flipantly said "what like oile oil?" and he laughed and said "yeh if you wanna be posh about it, i was gonna say chip fat myself" so there is an easy solution if you dont have the red rubber grease :)

Re: Brake bleeding help
 

One question. Are you sure the double banjo bolt is lining up properly with the hose ends? I swapped to braided lines on a previous bike that had a double banjo and had to pack out the hoses with washers, as the connectors were thinner than the standard ones. Worth a check.

Re: Brake bleeding help
 

is that a common change? at the caliper end?
Ironically I seem be the 3rd person with a similar problem this thread couldnt be better timed. :)

I get no braking power over the first inch of travel but then get from 0-full braking power over the 2nd inch. Ive gone for the leaving the top off the MC and zip tieing the lever to the handle bar approach. So tonight I'll put the lid back on the MC and then release the lever and hope for the best :D

Re: Brake bleeding help
 

You, sir, are a freakin' genius :D

Have just pulled the calipers off and popped the pistons out. RHS was fine, so cleaned pistons+reassembled. Was a bit of a nightmare on the LHS because both calipers stuck a bit. When they came out, they pulled the dust-seals with them. My god, the amount of crap under them was shocking! Spent ages cleaning the bores+pistons, and the dust-seals seem to be ok so they've gone back in now until I can get a full seal set and some red rubber grease. The difference is phenomenal; I know for a fact that there's still some air in the system because I ran out of brake fluid before I could finish bleeding, but even so I can't pull the lever closer than an inch and a half away from the bar on number 1 adjustment now. Number 5 just touches the bar if pulled hard.

Pint for you if you're ever in the area ;)

Re: Brake bleeding help
 

I'm so going to try this at the weekend, cheers.

Re: Brake bleeding help
 

anyone got a good (photo) description of caliper cleaning?
cheers

Re: Brake bleeding help
 

I'm just about to do a service on my front calipers, I can take some snaps as I go along if you wish.

Re: Brake bleeding help
 

As i mentioned before if you cant find red rubber grease ( i could only find 5ltr tubs on ebay) then you can use any vegetable based oil. The Castrol helpline will confirm this if you think i'm pulling your leg. ive strppied and cleaned my brakes many times and used Olive Oil and d never had any problems at all.

Re: Brake bleeding help
 

or here for a fiver http://www.mgocaccessories.co.uk/aca...rease_176.html

or here for £4.50 :-) http://morrisminorspares.co.uk/shop/...2471b8153d49bc