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]

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]

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]

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]

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.

 

[StuJohnson]

I am working on this dammmn thing...

Now I am racking my brain. Is it possible I got these mixed up and is causing the problem?
See Photo
Right now when I took apart the longer bolt with larger orifice was at the rear caliper and the shorter bolt with the small orifice was at the master cylinder.
Any chance someone take a look at their bike? You can easily tell by just looking as the head of bolt for the:
Longer bolt = small head as in height
Shorter bolt = larger head as in height
THANKS!!!!

 

[twowheels]

I am working on this dammmn thing...

Now I am racking my brain. Is it possible I got these mixed up and is causing the problem?
See Photo
Right now when I took apart the longer bolt with larger orifice was at the rear caliper and the shorter bolt with the small orifice was at the master cylinder.
Any chance someone take a look at their bike? You can easily tell by just looking as the head of bolt for the:
Longer bolt = small head as in height
Shorter bolt = larger head as in height
THANKS!!!!

Ah hah! I think I see the problem. Someone has removed the brake light switch from your master cylinder and installed a regular, although likely not quite correct, banjo bolt there. If I had to guess I'd say new crush washers were not used and air has likely found its way into the system. Either re-install the brakelight switch and accompanying banjo or get one that's similar and install with new washers. Bleed, bleed, bleed, and bleed. Oh, and de-glaze your pads and rotor.

 

[GMP]

Yes, but the integrated resevoir masters do not back bleed well. Wrap the caliper bleed fitting with teflon tape and repeatedly open/close it with pressure on the pedal. Keep the resivoir full. Mine was full of air and spongy when I got it as well.

The pedal does not have much travel before it hits the frame. Might seem OK on the stand but in race conditions when your stomping on it things might be different. Extra slop from elongation of the hole aggrevates this. I modified mine to use a heim joint like a KTM, no slop.

I had a lot of trouble with the stock pads overheating/grabbing/squealing in aggressive tight woods racing. Switched to the same organic pads I use with my solid rotors and they solved the problem. Faster wear with the wave rotor but its worth it, plus I don't always run that wheel anyaway.

 

[StuJohnson]

Ah hah! I think I see the problem. Someone has removed the brake light switch from your master cylinder and installed a regular, although likely not quite correct, banjo bolt there. If I had to guess I'd say new crush washers were not used and air has likely found its way into the system. Either re-install the brakelight switch and accompanying banjo or get one that's similar and install with new washers. Bleed, bleed, bleed, and bleed. Oh, and de-glaze your pads and rotor.

Steve
Great catch.

So the second question then.
Which one of these bolts goes to the rear caliper?

 

[StuJohnson]

Yes, but the integrated resevoir masters do not back bleed well. Wrap the caliper bleed fitting with teflon tape and repeatedly open/close it with pressure on the pedal. Keep the resivoir full. Mine was full of air and spongy when I got it as well.

The pedal does not have much travel before it hits the frame. Might seem OK on the stand but in race conditions when your stomping on it things might be different. Extra slop from elongation of the hole aggrevates this. I modified mine to use a heim joint like a KTM, no slop.

I had a lot of trouble with the stock pads overheating/grabbing/squealing in aggressive tight woods racing. Switched to the same organic pads I use with my solid rotors and they solved the problem. Faster wear with the wave rotor but its worth it, plus I don't always run that wheel anyaway.

Glenn
Great feedback - thanks.
I was hoping someone would bring up the "extra slop" issue as well. Wanted too, but did not want to complain any more....
In regards to your KTM mod - Can you provide a bit more info in detail? Maybe a photo - Please
I actually took another clevis off a 2005 CRF250x (with slight modification) and installed in place of the GG one. The Clevis is about 1/4" longer which helps adjust the pedal higher to keep from hitting frame (that is if I could get my brakes to work.... and got rid of that "extra slop".

As in for the pads your referring to. What brand did you buy / part # ?

Thanks again for advice. Hope to have this resolved soon.

 

[GMP]

I run the EBC red pads or the Galfer organic pads, both work well for me. As far as the pedal mod I may have posted a pic here somewhere, if not I'll try to do it tonight.
Edit:

Here it is.