I need to replace the front brake cylinder ( piece up by the bars and brake fluid container) - I've got the pieces from gas gas ( its for a txt pro 250) - i've been told i'll have to bleed the front brakes after its all done - any guidance on how to do that please, I dont have a clue !

many thanks

Loosen the brake hose from the master cylinder whilst its still fixed to the handlebars, then remove the master cylinder and unscrew it from the hose making sure the hose remains upright and full of brake fluid. Reverse the process to install the new master cylinder onto the hose and then the handlebars, and tighten the hose. Remove the cap from the master cylinder and fill with Dot 4 brake fluid. Turn handlebars to full left hand lock so brake master cylinder is at highest point of the brake hose and make yourself a cup of tea. Return to the bike and gently and slowly squeeze the brake lever several times, just a small amount (it doesn't have to go back to the bars) and if you look at the bottom of the reservoir you should see tiny bubbles appear. Repeat until the bubbles cease and the lever is firm. Top up reservoir if necessary, replace cap and go ride!

dont look too closely or wear goggles as brake fluid in the eyes is worse than petrol and it will spit back

Wait, bleed the master before you attach the brake hose

Put your finger over the banjo bolt hole and bleed up the master first, the less air the better

After connecting the banjo, gently squeeze the lever as you loosen the banjo and burp the air there a few times

After that you may not even need to push air all the way downhill through the caliper

Trying to push a master cylinder full of air all the way down through the hose is a big pain in the butt

Nobody's trying to push air downhill; the fluid finds it's way down the hose and any air comes to the top given a little time - hence the cup of tea! I've never found it necessary to prime the master cylinder, but I guess if you're in a hurry it could be a good idea.

Edited January 26, 201412 yr by lowbrow

Nobody's trying to push air downhill; the fluid finds it's way down the hose and any air comes to the top given a little time - hence the cup of tea! I've never found it necessary to prime the master cylinder, but I guess if you're in a hurry it could be a good idea.

sure, a cup of tea

Nobody's trying to push air downhill; the fluid finds it's way down the hose and any air comes to the top given a little time - hence the cup of tea! I've never found it necessary to prime the master cylinder, but I guess if you're in a hurry it could be a good idea.

The bleeder is at the bottom and most people bleed the air out of a brake there (can I get a witness )

The only other way to get air out of the banjo and brake hose is to push the pistons back in

It returns the fluid to the master and often the air that is at the top of the hose

Loosen the brake hose from the master cylinder whilst its still fixed to the handlebars, then remove the master cylinder and unscrew it from the hose making sure the hose remains upright and full of brake fluid. Reverse the process to install the new master cylinder onto the hose and then the handlebars, and tighten the hose. Remove the cap from the master cylinder and fill with Dot 4 brake fluid. Turn handlebars to full left hand lock so brake master cylinder is at highest point of the brake hose and make yourself a cup of tea. Return to the bike and gently and slowly squeeze the brake lever several times, just a small amount (it doesn't have to go back to the bars) and if you look at the bottom of the reservoir you should see tiny bubbles appear. Repeat until the bubbles cease and the lever is firm. Top up reservoir if necessary, replace cap and go ride!

agreed as long as there is fluid in the caliper and the pipe the master will be a doddle to bleed ive also just found just moving the lever a few mill will release a few tiny bubbles

Hi

As you know the air will be introduced to the system at the top, it makes sense to push new fluid up from the bottom. Best way is with a loaded syringe fitted to bleed nipple.

If you push down from the top you may trap the air in the calliper.

This is a job that will either be incredibly easy or incredibly hard. If you do it with a syringe, fit it to nipple with a short piece of clear pipe, slacken nipple and draw some fluid out before slowly pushing fluid into the system. You need to do this with the reservoir cap off, so beware it may spray into the air at first. I now just drape a rag over it to stop it spraying. Keep pushing till you see no bubbles, then re-fit reservoir lid, hopefully job done.

Another thing to be careful of is squeezing brake lever with the cap off as this can cause fluid to squirt upwards too.

Good luck.

I assume you know brake fluid is a great paint stripper so be careful.

TLTEL

dont look too closely or wear goggles as brake fluid in the eyes is worse than petrol and it will spit back

I would say wearing goggles was a good idea.

TLTEL

Well - i now know how to do it ! I did have to cheat in the end and get some supervised help as reading all your info made sense but made me realise i would probably just mess it up and make things worse. Too ashamed to admit I had no idea what a banjo was ( other than an annoying guitar type thing) but now I do. Rag and glasses definitely recommended, just a little squeeze on the lever got an inch high jet ! its nasty stuff..

thank you all for the help, at least I can get out again and practice now, just keeping an eye out for the next local easy trial for my first one

Hi Snobbly.

Our trial that was cancelled in December has been resceduled for the16th feb, same place, we are going to make it on the easy side so come along and have a go.

you can enter on the day, no problem.

TLTEL