Rear Brake Problem

[StuJohnson]

Just took the bike (2012 - 300) around the block for a spin.
When I apply pressure on rear brake lever the rear brakes do nothing....
So put the bike on the stand.
Spin the rear wheel and apply rear brake and it locks up.
WTH??

Here are items I have checked:
1) Is the brake pedal hitting the frame = NO
2) Is there enough fluid = YES

Questions I have:
1) When others put pressure on rear lever how much pressure to get brakes to apply?
2) See photos below -- I have about 20mm of thread. But not must left for adjustment if I wanted to raise lever up higher??
3) Could my rear disc be bad or glazed over?
4) Could my pads be bad?
5) Could the rear piston be leaking some fluid -- I don't see any leaks....?
6) Is there air in the line?? -- I say no as I recently put in new fluid and bleed it until no air.

Any input would be greatly appreciated!!

[Jakobi]

So the brakes engage properly and will pull the rear wheel to a halt on the stand, but won't stop the bike when you're riding. Sounds like something on the disk/pads to me that doesnt allow them to bite under load. Overspray of lube/oil etc?

Or...

Did you recently have the back wheel off or caliper spread open and forgot to pump it back up before putting it away? You wouldn't be the first person to do that.

Have you taken it for a test again since?

[StuJohnson]

Originally Posted by Jakobi

So the brakes engage properly and will pull the rear wheel to a halt on the stand, but won't stop the bike when you're riding. Sounds like something on the disk/pads to me that doesnt allow them to bite under load. Overspray of lube/oil etc?

Or...

Did you recently have the back wheel off or caliper spread open and forgot to pump it back up before putting it away? You wouldn't be the first person to do that.

Have you taken it for a test again since?

I will try and clean the pads / disk. Brake cleaner the best thing here?
I did have the rear wheel off and did spread open but after that I did spin wheel and engage brakes/pumped up. Did work on stand. Then took for a spin and that is when I noticed not grabbing....

I will clean and go for another test ride

[Jakobi]

Brake cleaner on the disk. Don't go spraying too much on the pads. Just inspect. If they look glazed you can sand them back a bit on a flat surface.

How far does the pedal depress? Does it feel firm or spongy?

[desertgasser300]

My 12' has more then 20mm exposed on the threads. I can get full lock up with the rear. I like my pedal just above the peg to further avoid rocks. Where is your pedal sitting and relationship to the peg?

[StuJohnson]

Originally Posted by Jakobi

Brake cleaner on the disk. Don't go spraying too much on the pads. Just inspect. If they look glazed you can sand them back a bit on a flat surface.

How far does the pedal depress? Does it feel firm or spongy?

In my opinion it fells spongy....
Does not seem right.?

[jostby]

has the feel of the pedal changed? If it's still solid as before you may have a caliper piston hanging up. Spongy feel will stop the brakes on a stand but not with you and the bikes inertia combined. If spongy feel then it's probable caliper or master cylinder seals have started leaking and allowing air in (doesn't mean there will be a fluid leak) If your brakes are working good you can oil them and it will still stop. Maybe not as good as 100% but it will so I say ignore dirt, ain't the problem.

[Rick]

By the look of the photo it looks like the pistols are exposed too much? Then again, could be the photo.

Soft pedal feel= air....bleed them from the caliper with a syringe , clear tube with a loop, pulling a vacuum works great.

[Jakobi]

Originally Posted by Rick

Soft pedal feel= air....bleed them from the caliper with a syringe , clear tube with a loop, pulling a vacuum works great.

Ahuh. Spongy = Rebleed! Could be either air or moisture in the system.

It also does look a bit strange with a lot of piston exposed for pads that have that much meat on them still. Not sure if thats contributing the issue or not though.

[bowhunter007]

Originally Posted by Rick

By the look of the photo it looks like the pistols are exposed too much? Then again, could be the photo.

Soft pedal feel= air....bleed them from the caliper with a syringe , clear tube with a loop, pulling a vacuum works great.

That appears to be a lot of piston. I'd pull the wheel, and do a thorough inspection. Make sure the pads are installed 100%, especially on the forward side(that you cannot see).
This happened at a recent race. A pad came out, on the foward side(YZ450f). The piston was way too far exposed, and got packed with mud & debris. We were able to disassemble, clean & reassemble before the race.