My friend...Brake Fluid

roymichaeldean · Post by **roymichaeldean** » Sat Dec 30, 2006 10:16 pm

Hi

I have reassembled the rear brake.....with replacement s/h Rear Master Cylinder etc...everything is in the right place,,...but..I am having problem getting the brake fluid to pump through...is there a suggestion...to get it to travel through the system.......I have put it in the reservoir...and thats as far as it wants to travel........
Any ideas ?

roy

PS...and Happy New Year

trixynut · Post by **trixynut** » Sat Dec 30, 2006 11:12 pm

Mate,
You need to 'pump' it through, or bleed the system as it's called..

1.Put a piece of plastic pipe on the bleed nipple on the back caliper and put the other end into a clean bottle (milk bottle?) so you can reuse the fluid thats pumped out.

2.Put a spanner (8mm I think) on the bleed nipple on the caliper and turn it a half turn just to open it.

3.Press down on the brake pedal and KEEP IT PRESSED DOWN. Fluid, with air bubbles in it should come out into the pipe.

4.With the pedal pressed down, tighten the bleed nipple back up.

5.Release the brake pedal.

6.Open the bleed nipple and repeat from step 2 above, and keep going until the fluid being pumped out the bleed nipple has no bubbles in it at al.

The aim is to get all the bubbles out of the fluid so the brake doesn't feel 'spongey'.

Remember to keep an eye on the reservoir as the fluid is being pumped out of it, so it needs to be kept topped up.

..or buy a 'speed bleeder' which sucks the fluid through and the air bubbles that are in it.

Dave.

Post by **dicky** » Sun Dec 31, 2006 12:08 am

In theory what trixy says is correct.
In practice the rear brake on the TRX requires a little more work.
I have had the same experience as yourself.
Any air in the line will rise to the highest point given time. Looking at the way the line bends around, and also the position of the master cylinder, this can be a problem as air will remain trapped in the line. Even worse, there is so much air in the line to begin with that no fluid will pump through past the piston.
To overcome this I had to unbolt the master cylinder and the reservoir from the frame to straighten out the lines a bit. Once it starts to pump properly you should be able to bolt everything back up.

I don't do it exactly as trixy says, but that may just be me being pedantic.

1. Fit a clear hose over the bleed nipple on the rear caliper
2. Pull the brake lever, or press the brake pedal.
3. Open the bleed nipple so that fluid flows out under pressure.
4. Close the bleed nipple, make sure that you do this before step 5.
5. Release the lever (or pedal).
6. Check the fluid level in the reservoir, make sure it does not run empty.
Repeat from step 2.

I don't reuse the fluid that comes out, this may be wasteful but it doesn't cost that much.
If you release the pressure before you tighten the bleed nipple, air may get sucked back into the line, making all your effort to that point wasted.
If the reservoir runs empty you make have to start the whole process over again to get the system to pump fluid past the piston.

You may find that it takes a lot of patience to get the lever (or pedal) to be firm again. If so, give up, go and have a beer, watch telly, be extra nice to your missus, just stop working on the bike.
Try it again the next day, any air in the lines will have settled to one point and it may be much easier to finish the job.

If you find that you've been through three bottles of brake fluid, 15 dozen bears and a box of durex, it may be time to buy a reverse bleeder (speed bleeder).

Maybe someone else has a nifty trick to make this all easy, I for one think that the rear brake circuit is a prick to bleed.

Hope this helps.

dicky.

roymichaeldean · Post by **roymichaeldean** » Sun Dec 31, 2006 12:10 am

Hi Trixynut

I just pumped like mad with the screw undone.....and nothing happened....I thought the Master Cylinder might not be working properly...so I will try your method tomorrow........and report back !!!

regards

roy

Post by **dicky** » Sun Dec 31, 2006 12:13 am

One more thing, but you probably already know this.
Brake fluid is nasty stuff, it attacks paint work and most plastics and is not at all nice to get on your skin.
Wear gloves, the latex ones from the supermarket are good for this work.

dicky.

Post by **Kevtrx849** » Sun Dec 31, 2006 2:01 am

One thing not mentioned above guys is that the rear brake has 2 bleed nipples. I might be stating the obvious but it caught me out the first time i bled the mongrel

The inside one is where the air seems to get trapped in my experience.
CYA, Kev.

Kirk · Post by **Kirk** » Sun Dec 31, 2006 7:06 am

I'm with Kev, spent about 45 minutes scratching my head till i found the second bleed nipple! Hopefully its that simple for you too.

WickedTRX · Post by **WickedTRX** » Sun Dec 31, 2006 6:41 pm

I usuallly use a big seringe,

Fill it with brake fluid, use a clear tube connecting the open caliper nipple and the seringe, pump the fluid from the caliper to the master.
It is very effective on a empty system, because it pumps the air from the lowest point, forcing it to move up
Keep an eye on the master cylinder bottle it can overfill, and try to fill all the system with only one move of the seringe.
After you have filled the system, and if you feel it's necessary, you can bleed it.
On the front brakes i didn't find necessary to bleed it after i changed hoses.

hope this helps end your odissey

burty · Post by **burty** » Sun Dec 31, 2006 6:43 pm

Use a big long length of windscreen washer tube attached to the bleed nipple. Open the nipple and suck on the end of the tube. A big syringe on the open end of the tube is best for this.

I have filled brake callipers with fluid before fitting them before now, that often works to 'prime' the system, but you still need to bleed it of course.

roymichaeldean · Post by **roymichaeldean** » Sun Dec 31, 2006 7:41 pm

Hi Wicked

It's funny you mention a syringe...as I tried the ...basic method and could see I was getting nowhere...so I had a large plastic syringe, got some clear tube...and have spend some time sucking air out of the system..pedal down, open valve...suck...close valve, release pedal....
All I have sucked out so far has been some horrible liquid...but I think I am getting somewhere....it's gone dark...so will try again over the next few days....the brake fluid is just too reluctant to flow through the system at the moment.
If no success ( after 2 hours more)...I will try using the syringe as a pump, to pump in the brake fluid from the caliper end...........then see if I can connect up the dots...in this case, get rid of the air by normal brake bleeding method

Thanks for all the advice...just what I needed

Happy New Year again

roy

PhatVR6 · Post by **PhatVR6** » Sun Dec 31, 2006 10:17 pm

I find that you have to press the brake lever really sharply, so as to blast the air out. just merely pumping it doesn't get the bubbles out.

Greg · Post by **Greg** » Mon Jan 01, 2007 1:01 am

Hiya ...

I was just going to suggest using a syringe to push fluid up the system via the bleed nipple, although it's not much use if you've got dirty fluid in there to flush out though..

The other trick for helping the bleeding process is to tape or zip-tie the lever down - the bubbles in the system will rise to the top and self-bleed on the next lever actuatiopn... might be a pain doing the rear though, you'd have to drop the caliper to straighten the hose...

G

roymichaeldean · Post by **roymichaeldean** » Mon Jan 01, 2007 7:55 am

Hi

Am I right in thinking that with the Brake Pedal ' down '....the brake fluid can flow past the seals in the brake master cylinder....and with the Brake Pedal not pressed down, the brake fluid is unable to pass by the brake master cylinder seals...hence the necessity of keeping the brake pedal ' down ' when trying to bleed the system......
I will have another try Wednesday.....to suck out the air...and get it flowing...it's been a bit of a mongrel

regards

roy

burty · Post by **burty** » Mon Jan 01, 2007 10:22 pm

Another trick might be to remove and suspend the caliper at a point above the master cylinder with the bleed nipples uppermost and bleed with it like that (remembering to fit some device between the pads to stop them moving out).

A common problem with some bikes is that air gets trapped and doesn't come out because it naturally wants to flow to the highest point.

That said, I've only ever bled the TRX rear system once or twice and not had a problem.

Yamaha TRX850 Enthusiasts Forum

My friend...Brake Fluid

My friend...Brake Fluid

Pumped like mad

Many uses of a Syringe

With Brake pedal down