Rear Brakes

[dr nick]

Here`s my story on bleeding the back brake on my Techno about 14mths ago -

I (naively) took my back brake caliper apart to thoroughly clean it (previous owner didnt know what cleaning was by the look of the bike)

Anyway - I put it all back together ,thinking all I have to do is bleed it and hey presto.

Days and days went by which turned into weeks and still no back brake.

I tried all sorts, apart from the back bleed method,small ball bearing on the inside of the bleed nipple on my bike ,which allows fluid out and stops air going back in apparently,anyway the problem seemed as if air was getting trapped somewhere,but god knows where or how.

Eventually ,I took the system off the bike and decided to check everything individually.

Starting with the caliper ,I filled it with brake fluid using the syringe,then holding it in both hands and having the threaded holes uppermost,I gently shook it .The fluid level dropped 2/3 times then It stopped.

BTW - the garage was full of brake fluid splashes and empty bottles of the stuff by now

I then sealed up the end of the brake pipe that connects to the caliper with a `G` clamp and the copper washers and syringed fluid into it.

I then filled the M/C with fluid and put the brake pipe on.I undid the `G` clamp slightly and pumped the M/C with a screwdriver till I thought all the air was out the pipe(always checking and filling the resevoir).When all the air was out I tightened the `G` clamp up and pumped the M/C to check for leaks and pressure.I found I couldnt pump it at all by hand,the `G` clamp was sealed perfectly so it was solid so I knew all that worked .

Holding the caliper in a vice I attached the brake pipe carefully so as not to let to much air in.

I thought `now` there is the smallest amount of air in the system...real easy to get out.So connected everything back and bled the system again ,and pressed the brake lever by hand...nothing,then again....nothing....3,4,5 times nothing...then on the 6th time I felt resistence ...`great` I`m getting somewhere I thought.

Took the bike for a run and kept pumping the peddle ...I eventually got a brake of some sort ,it would slow me down eventually.

I had to take it to a dealers for some work done a few days later anyway ,so I thought I`d ask him what the problem was.

Turned out that the joint that pushes the little rod up in the M/C at the back of the brake lever was very worn( after me bleeding it vigourously no doubt) so he put a newbush in it ,and also there was a bolt stopper to adjust the height of the lever that he took out .He said that I wasnt getting enough lever movement when bleeding and that everything was now fine.

And so it was...worked perfectly ....that`ll teach me for thinking it was easy and I`ll not to touch it again

Hope some of this helps

and to let you know you are not alone in your problem.

Regards

N

[windlestone]

i still have no rear brake.

I have blown everything out with compressed air. filled caliper before assembly then filled hoses from caliper to master cylinder.With a syringe i cannot "backfill" system past master cylinder. i've had bike hanging from front wheel and bled system and i've hung bike by rear wheel and bled system. still nowt. Had a small amount of movement at caliper pistons today but then it disappeared. One minute the hoses are bleeding fluid and air then they stop. Sometimes i can backfill the hose from the caliper bleed nipple to master cylinder then the next minute i can't. i'm becoming obsessed with fixing it. i should just take it to my dealer but it's getting right under my skin now.Haven't took swing arm off but had bike hanging by front wheel with master cylinder, header tank and caliper all diconnected from frame and still no joy!

[alan bechard]

If you are trying to back bleed the brakes, and it is not going back, up into the resovoir, check to make sure that your bleeder does not use a check ball under the bleed screw, (I do not believe that it does) Then I suspect that you have the pedal push rod adjusted out too far and it is blocking the return port in the master. Screw it in, or just pull it off too bleed.

Sounds too me as though the master is hanging a little high sometimes and not dropping all the way down to the circlip. (based on you saying that sometimes it would and sometimes it would not work.)

It may be high treason, but there is an article on brake bleeding on the front page of this site, as well as a different article with pictures etc. on www.rypusa.com

[charliechitlins]

BUMMER!

Try bleeding the master by itself.

This is done by disconnecting the hose at the master, and pumping the master with your finger pushed firmly over the hole where the hose goes in. Sometimes it's the only way to get that little bit of air out.

Keep the piston in while you re-connect the line.

I sure would like to know how they do it at the factory!

[bigfoot]

I think your missing the point of JTT's answer. It sounds liek your trying to use a syringe to draw air out of the system buy pulling it back. What you need to do and I've never seen it fail is to fill the syringe and push the fluid the othr way. i.e. push fluid all the way back to the master cylinder from the bleed nipple. If your syringe is big one shot should do but if not push a few shots through closing the bleed nipple each time before you take the syringe off.

Good Luck

[ndrordr]

Another thing to try...

You may be introducing air around the bleed nipple. I completely unscrew the bleed nipple and then seal the threads with teflon tape. This helps to eliminate one more place that air can enter.

Also, I second Alan's suggestion about the master cylinder push-rod. If you don't have enough slop adjusted in there, the rod cannot fully extend. It's only at the fully extended position that fluid can pass the piston.

Hope this helps.

Rob

[brucej]

" Sometimes I can backfill the hose from the caliper bleed nipple to the master cyl. and the next minute I can't"

I had a similar problem when bleeding my clutch a while back. I checked the master cyl. piston return, lever adjustment, completely diassembled the master to clean it, nothing seemed to work. Eventually I tried to see if I could push fluid back up the hose with the master off. It wouldn't go. I took the hose off, blew it out, made absolutely sure it was clear, put it back on and tried again. Still nothing! And yet once in a while it would work for little bit before stopping again. After spilling about a gallon of DOT 4 all over the bike and floor I realized that it worked when I was pressing the hose firmly down onto the bleed nipple, and didn't work otherwise. The fluid was leaking out past the nipple threads instead of going up the hose.

When I kept steady pressure on the nipple, I was able to pump fluid up the hose and into the master to my hearts content, and when I was done the clutch worked better than it had since I first got the bike.

The next time I try bleeding one of these things I will use teflon around the threads like Rob suggested. BTW, I found that a small oil pump can is a good alternative to a syringe - it's easier to work one-handed, but you have to clean it out carefully before and after using it. Good luck!

[windlestone]

Thanks for all the suggestions and offers of help lads. it was much appreciated and needed.

Now i have tried pushing fluid into system with the syringe and i have tried drawing fluid out with the syringe.

I took the bleed screw out completely and modified an extended bleed screw on the lathe. this meant the bleed screw was open at all times but threads were perfectly sealed. i still could not push/pull fluid past master cylinder. I ordered a new master cylinder and banjo bolt washers and a new bleed screw oh and a new adjusting rod for base of master. by the way a lot of the time master has been disconnected from frame and rear brake rod so i presumed master was in a position to let fluid leave/enter.

I hung bike from garage roof by the front wheel and removed rear wheel. I stripped rear caliper and took pistons out. then filled caliper and put pistons back only half way. Reassembled caliper blew out hose from master cylinder to rear caliper with an air line then connected rear caliper but left it to hang. Put wooden wedges in against pistons to stop them extending too far. Connected rear hose to master cylinder then connected master cyl to brake fluid reservoir. By the way i blew out reservoir nad hose. Connected syinge to caliper bleed screw and back filled system up to reservoir. Lots and lots of air coming through to reservoir. refilled syringe 4 times then no more air bubbles. However if i closed bleed screw off and drew back into syringe i was getting air coming in through hose/bleeder connection to syringe even whith wire on connection so i presumed i was still pushing some air into system. However i kept bleeding system first at bleed screw then caliper hose then highest point master cylinder. after probably 20 times of this process i started to get a pedal. No air at bleed nipple slight air at caliper and slight air at master cylinder. Kept bleeding in same order and topping up reservoir and eventually got rear wheel to lock up. Still have lots of pedal travel which i can't seem to cure. I have new pads and the more i bleed now i get no air and still no difference to pedal travel. So at least i'm fixed.

Now i can't sleep trying to figure out how the master cylinder could have become damaged whilst i was bleeding or forcing fluid into systeem. Changing the master did the trick but the old system was working perfectly apart from one sticking caliper piston.

Thanks again lads.

[alan bechard]

It may or may not be relevant, but something to look for. I had one that drove me nuts, and several other mechanics as well. It was a mid 90's Montesa, but most are pretty much the same. I took the seat / fender off for something, and wiggling, jiggling things I obviously should not have, I ended up killing the brake.

I danced, waved chicken bones and had a seance trying to figure out what had happened, and why I could not get it going.

Finally figured out that the little plastic elbow, that feeds fluid into the master, really was not truly round. The rubber piece that it sits into had taken its slightly oval shape from it being there 5 years or so untouched, and when I wiggled it, it did not ever, seat back itno the hole.

The other real complication is that these things move so little volume of fluid, that the tiniest problem just gets magnified.

Good that you got it going. Be careful as you adjust up your rod, that you do not put it up too far, and block the return port of the master.