Bleedin Brakes!!!

JohnnyCrash

Hi guys,only recently back to bikes. Bought a 97 Fazer 400,so set about doing little bits n bobs to it. One was replacing the rear brake pads,no probs,but discovered one of the pistons was seized. Got a seal kit,dismantled caliper,cleaned it up,new seals,re-assembled,eezy peezy. When it came to bleeding the system
A. took an age to do it
B. when I did eventually get a pedal back,couldnt get to a stage where I only had fluid in the bleed tube i.e. there would only be fluid in the bottom half of tube at all times

Ideas???

Note: brakes work, but am puzzled as to why I cant get to the stage where I only have fluid in the tube

jayok

Not sure of the angles you are working at. But is it possible to move the tube around so the bubble can float to the top?

I had this bleeding the brakes on a burgman, I couldn't get a bubble to shift. I removed the caliper and twisted the unit around (carefully don't damage the hoses) so that the tube and bubble floated out.

JohnnyCrash

jayok wrote: »

Not sure of the angles you are working at. But is it possible to move the tube around so the bubble can float to the top?

I had this bleeding the brakes on a burgman, I couldn't get a bubble to shift. I removed the caliper and twisted the unit around (carefully don't damage the hoses) so that the tube and bubble floated out.

I dont think angles etc are relevant in this case. The pressure from the master cylinder should be enough to push it out. I mean,the rear brake system is only a couple of feet long,so should be relatively easy to bleed (one would have thought)

jayok

JohnnyCrash wrote: »

I dont think angles etc are relevant in this case. The pressure from the master cylinder should be enough to push it out. I mean,the rear brake system is only a couple of feet long,so should be relatively easy to bleed (one would have thought)

Is the problem, even with the master cylinder pushing the bubble out, is that it's not pushing far enough? If so, that's why I was suggesting that if the hose could be moved to assist the bubble to move.

Alternatively, you could get a brake bleed pump. It pumps the brake fluid from the caliper back to the master cylinder.

jayok

Thinking about this some more, could you flush it out by keeping the master cylinder topped up?

That is

1. Open the master cylinder cover, fill it with brake fluid (it should be full to start)
2. Open the bleed nipple and connect say 50cm of clear tubing to it.
3. Start pumping brake lever, the fluid will start to move from the master to slave and out the bleed nipple.
4. Ensure the master cylinder is permanently filled with brake fluid
5. Keep pumping, the bubble should flush into the 50cm of tubing on the hose
6. Close the bleed nipple

All done.

I've done this with success a few times.

furerer

It is definately trapped air. Have a close inspection of the caliper, on some calipers, such as mine, there is another allen bolt sitting at the side of the caliper, it is not for the standard bleeding process but rather for the renovation process you have undertaken. Air will probably be trapped at the far side of the bleed nipple behind the piston, I'm assuming your calipers are at least 2 pot. Releasing this bolt will allow the air to pass, once fluid is coming out without air do it up fully and continue with the normal bleeding process using the standard bleed nipple. When you believe all air is out leave the bike to stand for an hour, and gently tap the master with a soft faced malet, this should bring any air left to the top. If you haven't got it sorted yet, hope this helps.

If you have no extra bolt.
Release the bleed nipple, push piston/s in as far as they go, chock the piston/s in that position, do the bleeding process. Make sure the master is topped up, remove piston/s chock, bleed again. This should prevent air building up at the back of the piston/s.

galwaytt

...I feel your pain. And my GasGas is similarly a nightmare to bleed.

Part of the reason, imho, is the tiny volume's of fluid involved.

Here's my way of doing it:

1. Get a cheap big syringe from chemist/vet, and some suitable tubing, to fit on OVER the bleed nipple. Remove master cylinder cover.

2. Fill syringe, put tube over nipple, and crack open bleed nipple........

3. Then, drive fluid back through the system, up to master cylinder, slowly.

If think about it: this is how they're filled in the factory - they don't go naffing about with the master cylinder and bleeding, etc, on a production line. By filling from the bottom up, you are filling whilst automatically excluding air (it rises, ahead of the fluid..), whereas by filling from top, you're working against physics the whole time.

JohnnyCrash

Cheers for all replies guys,have enough there to try out:D Where ye all mention Master Cylinder,take cover off,keep it topped up,im sure ye mean the Fluid Reservoir,right.
The suggestions with the pump and syringe look like they could work!!!

JohnnyCrash

furerer wrote: »

It is definately trapped air. Have a close inspection of the caliper, on some calipers, such as mine, there is another allen bolt sitting at the side of the caliper, it is not for the standard bleeding process but rather for the renovation process you have undertaken. Air will probably be trapped at the far side of the bleed nipple behind the piston, I'm assuming your calipers are at least 2 pot. Releasing this bolt will allow the air to pass, once fluid is coming out without air do it up fully and continue with the normal bleeding process using the standard bleed nipple. When you believe all air is out leave the bike to stand for an hour, and gently tap the master with a soft faced malet, this should bring any air left to the top. If you haven't got it sorted yet, hope this helps.

If you have no extra bolt.
Release the bleed nipple, push piston/s in as far as they go, chock the piston/s in that position, do the bleeding process. Make sure the master is topped up, remove piston/s chock, bleed again. This should prevent air building up at the back of the piston/s.

The caliper has 2 opposing pistons and has 2 bleed nipples,one on each side,but ive tried bleeding thro both

furerer

JohnnyCrash wrote: »

Hi guys,only recently back to bikes. Bought a 97 Fazer 400,so set about doing little bits n bobs to it. One was replacing the rear brake pads,no probs,but discovered one of the pistons was seized. Got a seal kit,dismantled caliper,cleaned it up,new seals,re-assembled,eezy peezy. When it came to bleeding the system
A. took an age to do it
B. when I did eventually get a pedal back,couldnt get to a stage where I only had fluid in the bleed tube i.e. there would only be fluid in the bottom half of tube at all times

Ideas???

Note: brakes work, but am puzzled as to why I cant get to the stage where I only have fluid in the tube

OK Mr.Crash........if I read this correctly, your brakes are fine, yes? You are just inquiring as to why the bleed tube you use is always half full at the end of bleeding. If this is the real question then you need no assistance with bleeding your brakes........am I right in stating that?
So, if you want to know why the bleed tube is half full that is because as you pull the lever in it forces the fluid out of the "one-way" tube. You are using a one-way tube? if you are then as you release the lever the fluid in the tube is drawn back into the caliper, but not all of it. You then tighten the bleed nipple. If you want the tube to be full, depress lever, while nipple is open, tighten nipple, release lever. If your tube is half fluid, half empty after doing that, I would suggest that air is being drawn into the system, and you need to inspect all of the braking system for imperfections, but, as you state the brakes are fine, this cannot be the case. I do not know your level of experience with the "bleeding" problem so I'm not going to assume it, but I have included a link to bleeding bike brakes with pictures. If it helps, fine, if I'm totally wrong........someone is bound to point it out.
http://www.therevcounter.com/motorbike-articles/34369-motorbike-brakes-beginners-information-bleeding-guide.html

JohnnyCrash

Cheers for the tips Furerer,but ive tried all of these.When i say the brakes are working,im sure they could be better,or could it be just the case that im being over critical?? It there was air being drawn into the system,this would mean a leak,no??? if there was a leak,surely fluid would be lost?

furerer

Air being drawn in does not mean a leak. Have you checked the master? Because the piston was seized perhaps the master needs a rebuild. If you have access to a compressor blow out the lines also, but at a low pressure. When you reconnected everything did you use new banjo bolt washers?
To test the master just disconnect the line from the calipers and stick it in a half full jar of fluid and depress the lever, checking for air bubbles, do this a few times and you'll see if it is in the master area. I have known of masters to allow air in as the lever is depressed but with no fluid loss, sometimes just opening the lid and depressing the lever while looking in the master will show bubbles appearing in severe cases. I know it means using fluid but if the jar is spotless the fluid can be reused. Then reconnect 1 line at a time going through the same process. If all is ok and you're still getting air try the backward fill as galwaytt suggested.

Added:
Scoring. If the master is suspect check the bore for scoring when doing a rebuild, this would allow air in, in which case try to get a new master or a good second hand one........dont bother with trying to repair it.

JohnnyCrash

Cheers for all the help guys.Bought a 50 ml syringe from chemist,yoked it up to some clear tube with rubber tubing on both ends. Flushed the system,put PTFE tape on the bleed screw threads,filled the syring and tube with fluid,bled the syringe(like you'd see doctors doing,ha ha)to make sure no air in syringe,attached tube to bleed nipple,put slight pressure on syringe whilst cracking the bleed nipple and when the fluid started moving,kept steady pressure on until the reservoir filled up,closed nipple,hey presto,instant brakes!!! Now,in saying all this,the pedal doesnt seem any harder than before,but im assured now that theres only fluid where its supposd to be. All this took a max of 20 mins,so its gonna be back bleeding for me now for evermore:D:D:D