Rear brake not building pressure

[yz_mik3]

I have a 2005 yz250 and I am still having problems with the rear brakes even after putting a new caliper and master cylinder. Before and after I changed these parts, the brake has a little pressure to stop the wheel when I spin it on the stand but no where near enough to stop in motion. I bled the brake with a brake bleeder kit. The fluid is clean. I lifted the caliper above the master cylinder and that didn’t work either. I’m thinking that it could be the line because I heard that sometimes the line goes bad and expands. Or maybe there is still somehow air in there. I’m just tired of looking like a sorry rider because I can’t wheelie.

[yz_mik3]

Also, how would could I find out if the brake line is bad?

[freeride250r]

1 hour ago, yz_mik3 said:

Also, how would could I find out if the brake line is bad?

On my KTM Freeride 250R, I blew compressed air into the banjo terminal and checked for hisses though I doubt this is a good way to check. If your brake line is hosed I'd expect fluid to leak out. If any seals around the brake line are hosed I'd also expect fluid to leak out.

I think you have air in the system. I don't know what bleeding kit you used, but on my Freeride 250R, I used a home made reverse bleeding kit that I thought was going to fill up the system properly, but wound up getting air into the system. I took it to the KTM dealer and for about half an hour of labour they filled up the system with the aid of an vacuum tool used for automotive calipers. I wasted about 2 hours and a can of DOT fluid pumping, filling, and bleeding. They determined air was stuck in the looping part of my brake line.

May I make a suggestion, take your bike to a Yamaha dealer and ask them how they do it and tell them to fill up your rear brake system and check it over. I strongly suspect for 1/2 hour of their labour you will be riding at the end of the day with working brakes and will be able to wheelie safely.

[8675309]

I fought this same issue on my yz front brake and after rebuilding the master cylinder, replacing the brake line and waiting for a slave cylinder rebuild kit I pulled the caliper off the mounting plate and cleaned the dried on grease off the sliding pins then reassembled with brake grease and it now works like new. I wasted a bunch of money and worse was the time I spent dicking with it.

[yz_mik3]

I just bought a galfer rear brake line, hopefully this works.

[freeride250r]

1 hour ago, yz_mik3 said:

I just bought a galfer rear brake line, hopefully this works.

Best brake lines money can get imo

[fixitandy]

Best brake lines money can get imo

Mate, you’ve got air in the line, if it’ll stop the wheel spinning on the stand but not while riding, it’s due to lack of pressure. As your bleeding the system tap the whole line with the handle of a screw driver to release the tiny air bubbles attached to the inside of the line.

[nuity5]

Is your brake pedal bent so it’s hitting the clutch cover? If so it might not be letting the pedal / master return fully to allow it to refill from the reservoir. Might not be the answer but something else to look at. Clay

[YZDOC]

Only way to do it is bleed.

Make sure the rear caliper is higher than the master. Remove the filler cap and pump brake, hold peddle down, release front banjo/tighten front banjo, release brake peddle. Do this about 4 or 5 times and make sure you are continually adding fluid to the top of master.

Now move to rear banjo and do the same...

Now move to actual bleeder on caliper and bleed it into a tube and into a clear bottle submerged in brake fluid until no bubble come out. "OR" use a clear bleeder line attached to the bleeder valve and run it into a loop upwards. Bubbles will be seen at the top of the loop so you know when they are all out of the system. 

You should have brakes again. If this doesn't work fully: Put the front of the bike high so the master cylinder is higher than the caliper, tie/strap/attache a 25-50lb weight to the peddle forcing it down and leave it for 24 hours. During this 24 hours tap the caliper, brake line, and master with the handle of a screw driver, or equal. This will leave the system "open" and any air will travel to the highest point and out into the master reservoir. You can leave the cap on tightened. 

 

Edited July 7, 2019 by 2 STROKE YZ DOC

[yz_mik3]

What about reverse bleeding like this guy did? I'll try your way too 

 

[YZDOC]

Way more work than needs to be done. But yet, another way to get the job done.

[StillSmoking]

Get a mityvac. I drove myself crazy trying to get my front brake caliper to pressurize. I tried every trick in the book and nothing. After spending $35.00 on the mityvac and it was problem solved in 10 minutes.

[freeride250r]

On 7/7/2019 at 9:28 PM, StillSmoking said:

Get a mityvac. I drove myself crazy trying to get my front brake caliper to pressurize. I tried every trick in the book and nothing. After spending $35.00 on the mityvac and it was problem solved in 10 minutes.

If I use a Mityvac, I connect the hose from the vac to the bleeder screw on the caliper and fill fluid into the master's reservoir? The idea being to fill the system by sucking in fluid from the master's reservoir?

Sorry if this is such an inane question. I've sometimes found that things are not as they would have initially seemed.

[freeride250r]

On 7/7/2019 at 9:05 AM, yz_mik3 said:

What about reverse bleeding like this guy did? I'll try your way too 

 

Referring to what he's doing at 5:12...... I did something similar but what would happen is that when I loosened up the bleeder screw when it came time to pump in fluid, fluid would slightly leak from around where the bleeder screw and the caliper meet (not where the rubber hose and the screw meet).

[fixitandy]

I have a 2005 yz250 and I am still having problems with the rear brakes even after putting a new caliper and master cylinder. Before and after I changed these parts, the brake has a little pressure to stop the wheel when I spin it on the stand but no where near enough to stop in motion. I bled the brake with a brake bleeder kit. The fluid is clean. I lifted the caliper above the master cylinder and that didn’t work either. I’m thinking that it could be the line because I heard that sometimes the line goes bad and expands. Or maybe there is still somehow air in there. I’m just tired of looking like a sorry rider because I can’t wheelie.

Hey, I noticed that the clevis pivot pin is facing the wrong way, the split pin should be on the inside, so it can’t get jagged on something, & get ripped out & lost at the track or trail, which leads me to the next line, at the risk of being hacked, are you absolutely sure the calliper rebuild is done correctly? Cheers Andy.

[yz_mik3]

its a new caliper so it should be fine. I just got the galfer brake line yesterday so i'll work on this on the weekend

[yz_mik3]

I talked to a guy that lives near me. He talked to his friend that is a mechanic for me. He said that the brake isn’t working because my linkage is bad. I know my linkage is bad but I’m not sure if linkage has anything to do with brakes. What you guys think?

[YZDOC]

As long as seals are good and the master is getting full stroke of piston, it should build pressure. What linkage is bad, is the piston getting a full stroke, are the seals on both ends good, do the pistons move at all or is the caliper frozen? 

[yz_mik3]

The rear shock linkage. The master cylinder moves and gets pressure but not enough.