Lost brake pressure in the rear!!

[yogurtpooh]

I hadn't ridden my bike in six days.
It started up fine. The first day back I rode around for about 90 minutes in 85 degree temp. and I lost brake pressure in my foot completely.
I pulled over and waited like 5 minutes and I got pressure back, but the pedal feels mushy and not as affective. A few hours later, the brake feels fine again.

I just replaced my caliber because something similar to this happened when I first bought the bike. Should I replace the brake lines? The brake is like at 17,000 miles or a little bit more now.

This hasn't happened since the first time.
Could it be because I was riding the brakes a bit?
I have a tendency to do that because my last bike had drum rear brakes.

Thanks.

[csmith12]

Originally Posted by yogurtpooh

Could it be because I was riding the brakes a bit?
I have a tendency to do that because my last bike had drum rear brakes.

Thanks.

Yea, classic signs over overheating and your actions support that. You might hear all kinds of stuff about overheated brakes, but honestly... I have found most of them to be unfounded.

Now the caliper seals melting... that is one you might want to look closer into. If this is a habit that you have, you might also want to look into the type of brake fluid you use and select one with a higher temp rating. Organic pads are also gunna be more prone to doing this.

Bottom line... ya need to stop riding the brakes.

[Ghostt]

Sounds like you favor the rear brake too much, compared to the front?

If this is the case, you need to adjust your braking habits, and style, for your personal safety.

One must remember that the front brake is the primary stopping force, especially in a panic stop it's almost 100%.

Here is my write-up on the braking system, including diagnostic, repairs, recommendations etc.... Hope it helps.

For those of you whom are scratching their heads, here you go,*


Front Caliper Service (also rear as well)

Many folks have posted here with a Varity of front brake problems.*

*Many of which are attributable to the lack of proper maintenance.

*Here’s how you can always have a brake like when your bike was new.

A short list of the problems and the causes.

Soft lever or lever goes to the bar.

The usual cause is the pistons are pushed too far back into the caliper by a flexing a warped, coned, disc.*

*Using up too much piston travel before the disc is pinched.

Juddering in sync with wheel rotation.

The disc is worn, and its thickness varies. *This causes the caliper to “sink” into the thin part and when the thick part comes around, it gets wedged into a smaller space causing a tightening of the brake. Then the tight spot passes through and it like the brake is released. Then repeat, repeat.

Cupped, coned, or warped disc.

Unfortunately this is a common problem with EX’s the cause is the disc is stretched in the center due to being rigidly bolted to the wheel. *The huge force of braking is transmitted to the wheel through the webbed center of the disc which gets stretched and becomes larger than the space it occupies in the center of the disc. This causes the center to push to the side trying to find room for itself.*

*Resulting is a cone shaped disc.

Soft lever 2

The caliper has pistons only on one side, so as the pads wear the caliper must shift sideways apply even pressure on both sides of the disc.*

*To allow this the caliper floats on two pins. *If these pins get dry (no grease) dirty or bent. The caliper won’t center itself and bends the disc to wherever it is.

*This take up lever travel and when released pushes the pistons further back than necessary.

**If not fixed will eventually destroy the disc (warp it).


Ok how to prevent all of the above.

When new pad time comes around, resist the temptation to just pop in new one and go.

*Every time you must do these things.

Remove caliper disassemble and clean it.

Clean and re grease the sliding pins.

Polish the caliper pistons to remove dirt. If you just push the pistons back into the caliper leaks will result. Or binding.

Tools required:*
12 mm socket
8mm open end wrench
3” or bigger C clamp
a supply of new bake fluid.*
wire brush and or steel wool.

Remove the caliper from the fork leg but leave the brake line on.

Remove the old pads and the mounting frame (the sliding pins)

Remove the cover from the Master Cylinder on the Handel bar.

Attach the C clamp to one of the pistons but don’t squeeze it. *Pump the lever on the bar slowly to push out the other piston almost all the way. *Put the C clamp on that piston and push out the other one.

Remove both pistons by hand.

Remove all the rubber part from the caliper, the seals are in the grooves in the caliper and dull pointed thingy will get them out easy.

Disconnect the caliper from the brake line.

Soak all the rubber parts in new clean brake fluid * ONLY!!!!! * Rub them with you fingers till as clean as new.

The caliper can be cleaned with a wire brush or even a Moto tool for the internal grooves, NOW’s the time to paint it if you wish.

Polish the pistons till they are smooth and shinny. They are chrome plated. If any of the plating is chipped or damaged below the dust cap groove. *Replace it.

The master cylinder is the subject of another write up and we’ll assume it in good working order here.

If you suspect your disc is bad, your bets bet is to replace it with an after market one fro EBC or Galpher.

*Don’t remove the disc unless you intend to replace it. *It will assume a new shape if it is * stressed and will not be flat again. You can try to check its condition by placing a straight edge across the face of the pad swept area looking for any distortion.

Re assembly

Take the nice clean rubber seals and install them into the caliper then the Dust covers.
Wet all the rubber with new clean brake fluid and partially fill the caliper with new fluid.

Push the pistons though the dust seals and into the caliper body until the dust covers snap into the grooves.

Fill the MC with new fluid and pump the lever while holding the Line above the MC till clean fluid flows.

Connect the line to the caliper while holding it above the MC.

Pump the lever with the bleeder valve open till fluid flow from the bleeder.

**Hold the caliper so that the bleeder is the highest point.

Close the bleeder and pump more fluid into the caliper but don’t push the pistons all the way out.

Then squeeze the pistons all the way back in and install the new pads.

Re grease the slider pins and assemble the dust seals and re mount the caliper on the forks but leave the bolts loose.

Now clamp the caliper to the disc with the brake lever.

Look at the space between the fork lugs and the caliper, clamp and release a few times as you tighten the bolts by hand. It one lug touches much before the other the odds are you mounting bracket is bent. You can straighten it.*

*After you get it the best you can. Some shim washers made from alum can stock can be fitted to the loose side.*

** *What we are doing here is trying to minimize the bedd in time and gets the best pad life.


Ok with everything tight you should be through, Notice we don’t need to bleed the brakes, but if you screwed up in any of the above steps, you might do that here.

Be careful to Bedd in the new pads gently.

**Too much pressure too soon will burn the pad material as only a small area will be gripping at first. You also won’t have full braking power till the pads are fully familiar with the disc

[yogurtpooh]

so my symptoms seem normal? The fact that it goes back to normal after the brakes don't over heat means that I'm riding it? Could it be any other problems? It seems like one moment the pedal worked fine, then another moment later it sank all the way down.

Do all rear brakes have that problem if you use them too much?

would replacing the brake lines with steel brake lines help? I already have a galfer set here, but I haven't replaced them yet because someone mentioned that they would provide too much stopping power.

yes, i really need to readjust how I brake, but I live in Vietnam and most of the time I cruise like 30 to 40 miles at best, so I get lazy and use the rear brakes.

[csmith12]

Originally Posted by yogurtpooh

so my symptoms seem normal? The fact that it goes back to normal after the brakes don't over heat means that I'm riding it? Could it be any other problems? It seems like one moment the pedal worked fine, then another moment later it sank all the way down.

Do all rear brakes have that problem if you use them too much?

would replacing the brake lines with steel brake lines help? I already have a galfer set here, but I haven't replaced them yet because someone mentioned that they would provide too much stopping power.

yes, i really need to readjust how I brake, but I live in Vietnam and most of the time I cruise like 30 to 40 miles at best, so I get lazy and use the rear brakes.

Normal yea.... Letting them cool to within operating temperature allows them to work properly again.

Do all brakes have this problem? Yep, they sure do and yea... even cars and trucks. Ask a race car driver at Talladega (they glow red) or an over the road trucker with 7 miles of downhill in front of them if brake temp is important with 60,000lbs in tow (ask yourself why they engine brake).

Would replacing with a steel line help? Nope, in fact... it just might make the problem worse by allowing you (the rider) to transfer more brake pressure with less effort.

Do steel lines create too much braking power? Not at all, the braking force that is applied is 100% in the riders control. For better.... for worse.

[crazymadbastard]

I would rebuild or replace that rear master cylinder. At very least remove boot and inspect, do a full brake fluid flush and bleed .

[alex.s]

old brake fluid saps up water which overheats and boils much much quicker than the oil itself. its also spongey when its not boiling.

[Motofool]

Brake fluid surrounded by high air humidity goes bad really quickly, especially if the seal of the master cylinder leaks humid air in.

Dragging the brake generates enough heat to form compressible bubbles of steam where only non-compressible liquid should be.
Those bubbles keep putting more pressure than the one your foot applies on the pads, which generates more heat to create more internal steam.

The mass of brake fluid is so small that a stop of a few minutes cools all steam down, which condenses and becomes water mixed with the brake fluid again: no internal steam or air = firm feeling.

Don't change the lines, but check that air seal in the master cylinder's reservoir, replace your fluid frequently (around six months) and un-learn dragging the brakes.

[yogurtpooh]

thank you guys for the response.

The caliper is brand new. My old one failed, I still used the old brake lines though. It worked fine until yesterday.

if it cools down and works again perfectly, then it's safe to say that it was me dragging on the brakes and nothing wrong with the bike?

[yogurtpooh]

thank you guys for the response.

The caliper is brand new. My old one failed, I still used the old brake lines though. It worked fine until yesterday.

if it cools down and works again perfectly, then it's safe to say that it was me dragging on the brakes and nothing wrong with the bike?

why is the rear more likely to lose pressure than the front?
Would riding the front brakes cause it to completely lose pressure too?
I feel like when I am riding a long time, my front brakes will go in more and require me to pull in deeply slightly. but after it cools down, the lever pressure is hard again. but remember, i brake more than I throttle because of the traffic in Vietnam.

[csmith12]

Originally Posted by yogurtpooh

thank you guys for the response.

The caliper is brand new. My old one failed, I still used the old brake lines though. It worked fine until yesterday.

if it cools down and works again perfectly, then it's safe to say that it was me dragging on the brakes and nothing wrong with the bike?

why is the rear more likely to lose pressure than the front?
Would riding the front brakes cause it to completely lose pressure too?
I feel like when I am riding a long time, my front brakes will go in more and require me to pull in deeply slightly. but after it cools down, the lever pressure is hard again. but remember, i brake more than I throttle because of the traffic in Vietnam.

Yea, it's a pretty safe to assume you draggin' on the brakes is "helping" a subtle problem along. Don't take chances with your brakes. Since you're losing a lot of pressure, it also safe to assume your fluid is contaminated (water/air). Start with a fluid change to remove any possible contaminants and good bleeding to ensure all air is purged, then give it a test. You don't really need any fancy tools, I use a mt. dew bottle and a rubber hose (gas line). lol

Getting any brake setup (fluid and/or hard bits) too hot will lead to a loss of braking effectiveness, it don't matter if it's front or back. The rear is more prone to temp issues due to the smaller size of the rotor and it getting less airflow due its location. The front is less prone to temp issues due to it's larger size, getting more airflow and better temperature dissipation ability in relation to it's size.

Thing is, many riders feel their brakes are pretty firm and good until they feel someone's that is near "perfect".

[Ghostt]

Originally Posted by yogurtpooh

thank you guys for the response.

The caliper is brand new. My old one failed, I still used the old brake lines though. It worked fine until yesterday.

if it cools down and works again perfectly, then it's safe to say that it was me dragging on the brakes and nothing wrong with the bike?

why is the rear more likely to lose pressure than the front?
Would riding the front brakes cause it to completely lose pressure too?
I feel like when I am riding a long time, my front brakes will go in more and require me to pull in deeply slightly. but after it cools down, the lever pressure is hard again. but remember, i brake more than I throttle because of the traffic in Vietnam.

Okay first, when you say new, you mean brand new out of a Kawasaki OEM box? Or new/used?

Did you flush and fill the entire rear brake system with brand new sealed DOT brake fluid? If so what kind, and type DOT#?


I've never had any brake lose pressure not without a leak somewhere, in one case it was a very very old brake hose, it was swelling when I applied the brake, but I knew it was bad, just from looking at it, dry rotted.

I've had fade, and glazed some in my days.

Why are you even riding any brake in the first place? Have you attend an MSF course???

Did you read my caliper service write up? What is the condition of the rotor? Did you check it per the guide I provided?

Condition of the pads, used? contaminated? Brand? Type? Etc......

Have you done any physical diagnostics??????? RDI????????