Rear brake assistance needed

I went to take out my kz yesterday, and when I depress the rear brake pedal I encounter no resistance (and no stopping power!).

I filled the reservoir and bled the brakes... nothing.

I removed the caliper to make sure that the piston still expands ... it does.

What is the problem? Do I need a new master cylinder, or what?

Thanks in advance!

if it was bone dry id start by looking for your leak,if it was just low id check to see how much meat is on brake pads and then check for leaks.when you bleed the brakes do it untill you get all the old brake fluid out of system.if that dont do it then its time to rebuild mastercylinder and or caliper;)

How many miles on the chassis? Has the fluid ever been changed / flushed?

How much fluid was in the resevoir when you added fluid to the resevoir. What color was it?

Could you see any moisture or dirt buildup anywhere on the exterior of the brake parts?

The line could have swelled shut internally. The master cylinder seals might be shot.

If you have a vacuum pump, you can try vacuum bleeding the brake to maybe get it to work.

But if the resevoir was dry when you started, you have a problem that fluid/bleeding alone isn't going to fix.

Post edited by: KaZooCruiser, at: 2007/03/13 13:23

Not sure about your particular case, but I just finished rebuilding the brakes (front & rear) on my 750. It took for fricken EVER to get any pedal at all on the rear. I was starting from bone-dry - filled it up, and pumped / drained at the nipple for over an hour. I even put some fluid in via the nipple opening with a small tube, on the upstroke of the pedal so it would suck it in, just to get some down in the caliper quicker.

It took a long, long time to get any pedal at all, longer than I thought it would, and then it finally came together, and they are pretty stiff now.

Hope that helps.

Hello, My rear brakes leaked dry awhile back and just want to share what I did,it might help. I replaced the piston cup in the rear master,and I always fill the master cylinder while sliding-in the pistons, It's a bit messy but it insures that there is already some fluid inside to assist flowing the fluid coming from the reservoir. Then I bleed it by filling the reservoir (make sure it doesn't go empty while bleeding),opening the bleed screws, pumping the lever,till I see a steady stream of fluid coming out,Close the bleed screw, pump the lever 5-6 times then keeping it depress while opening the bleed screw, closing it immediately when brake lever hits bottom,I do this a couple of times,tighten the bleed screw and your done . Had no problem since the fix.

Post edited by: jeffreygp, at: 2007/03/13 14:16

How many miles on the chassis? Has the fluid ever been changed / flushed?

28K -- the fluid has not been changed to my knowledge... I just picked this one up in January.

How much fluid was in the resevoir when you added fluid to the resevoir. What color was it?

Almost no fluid left... amber in color slightly darker than the new fluid.

Could you see any moisture or dirt buildup anywhere on the exterior of the brake parts?

There was some dirt, grease, and other misc. black crap on the hoses / calipers

I would think that its the master cly, look inside of the dust boot see if its full of crap, if so that is where the problem starts.
I would rebuild both the master and the caliper, install new pads, also go with dot 5 fluid, it dosent eat paint has a higher boiling point, just better all around

shaftie1100 wrote:

I went to take out my kz yesterday, and when I depress the rear brake pedal I encounter no resistance (and no stopping power!)

Was the rear brake working before?

Hey guys,

I went home last night and basically worked the entire system over with a series of solvents and degreasers to clear all of the old crap out. It took over 2 hours of soaking and blowing out the lines with an air compressor to get all of the crud out.

Then I refilled the reservoir with new dot 5 brake fluid, and began the long and arduous process of bleeding my old crummy brakes. I must have pumped that damn brake lever by hand for 30 minutes before I got all of the air out!

Well, now I have a rear brake again, though I don't have nearly as much stopping power as I'd like... Is this caused by a bad master cylinder? I have a single disk rear on this 1100 LTD, by last bike (750 ltd shaft) had a rear drum.

How do I get more stopping power?

#1. What were you using for solvent? Brake seals (and even brake line) are usually NOT solvent-proof. You might have put yourself in line for a complete rebuild, needing new master and brake cylinder insides, and a new hose.
#2. I use a cheap vacuum bleeder I picked up at Advance Auto and a hand vscuum pump. Especially on a system loke a bike rear brake, where there is very little "downhill", it can be slow doing a traditional bleed.

Yeah,

I'm an engineer in a specialized machine shop... I used a solvent called C-22. It is the only solvent that will remove oil, grease and tar from petroleum based products without decomposing them.

I think that the hoses are all toast anyway... Does anyone make a drop-in stainless set?

Still, how do I get MORE braking power??? I'm considering modifying the entire system... I want to use the rear master cylinder from a ZX11, and slot the rotor on our mill at work. Any other ideas?

Somehow flying along at 100+ with 105hp motor strapped between my legs just doesn't seem right if I can't get some more stopping power!!!

be carefull over doing the back brakes,the front brakes are what do the majority of work slowing you down