Rear Brake Not Effective

[ruffrider]

Hi,

Just pulled my lads '04 125 out of winter mothballs, ready for some summer riding

Found that the rear brake wasn't working and reservoir empty.

So we added fuid to reservoir and bled it, many times to ensure no air, using syringe on rear calliper.

There's no leaks that we can see and we've run quite a bit of fluid up the system to clear out any air

Now the rear brake sort of work, but has a lot of travel on the lever and doesn't give such a strong braking effect

There's a small amound of visible movement on the pads, as you'd expect, although they don't appear to move for the first 50% of pedal movement.

Any suggestions what we do next to get the full braking effect?

Not sure if the symptoms point to bleeding or adjustment ?

Not sure what else we can do to bleed the system.

Not sure how we take some the the free movement out of the lever.

We'd be grateful of any suggestions.

[neo]

Hi RuffRider,

I'd still suspect a slow leak if I where you.....probably the caliper.

But check out this GasGas video it might help.

Also before doing this remove the pads and clean the caliper pistons and seals up with something that wont eat up the seals (soap and water or Lanilin spray and an old toothbrush). Then push the pistons flat into the cliper. And wedge something big and tough (block of wood) in there to keep the pistons held right back while you work.

Keep the caliper held as high above the master cylinder as possible.

Let us know how you get on.

Best of balance.

Neo

Edited April 10, 2009 by Neo

[copemech]

As a quick ck, pull the pedal and loosten the master cyl enough to remove the outer boot and inspect for fluid and dirt entry. If there is evidence of fluid and dirt entry, the seals are gone on the MC.

As a sidenote, I pack this area with silecon grease to prevent corrosion, dirt and water entry, seems to work.

I will also add here that my bronze bearing on the pedal has held up well over time and the pedal is still tight with good feel, as compared to those little rollers that go to crap in no time. I may need to get more of these if others want to try them, or enough demand.

I peddle(pun) these here, only upon an experimental and non-profit basis!

[ruffrider]

Neo/Copemech,

Thanks for the replies.

I stripped the thing right down today (bit sad I had to remove swing arm to get master cylinder off).

There doesn't appear to be any leaks anywhere (nothing to speak of anyway).

The calliper pistons were tight and moving too free so I worked on them a tad. Given I could move them by hand I think they were then free enough.

Rebuilt but the're still not enough 'power' to brake the rear wheel properly, no matter how hard I pump the pedal.

It's fully bled but I can press the pedal right to the limit and there's only mild resistance to stop the rear wheel, again with no evidence of leaking.

So it does appear the master cylinder is unhealthy, so I guess I'm in the market for a new one.

Thanks again for your guidance :-)

[copemech]

So where did the fluid go then?

If you remove the muffler you can manipulate the master cyl enough to crack the banjo bolt and get air out.

[neo]

Not quite what you suspect but might help with the process of eliminiation...CLICK

Also, I'm sure you can get MC kits....just be sure that the cylinder inside MC is spotless.

Best of balance.

Neo

Edited April 12, 2009 by Neo

[ruffrider]

Thanks again guys, I appreciate your help. I'm in new territory here and learning.

No idea where all the fluid went, unless it slowly seeped out over the winter (but from where!!!??). Would have expected to see fresh leakage when I topped it up.

With what I've learnt so far I have to suspect MC is just not building up enough pressure.

I'll be stripping it all down and building it up on bench ... should be interesting .. and make it easier to ensure ALL air it out ... before testing again.

Then, I'll fit an MC kit and probably calliper kit too.

Any tips on fitting these kits before I start (probably next weekend)?

[copemech]

Primary tips!!!!!

Cleaner the better! Get a can of brake cleaner that dries quickly with air!

Clean smooth bores with no corrosion.

Use the brake fluid as an assembly lube, lightly, to assure no dry internal workings that could damage new seals. DOT 4 fluid!

[ruffrider]

Hi Guys,

Well, I stripped the rear brake system all right down.

The master cylinder appeared to be working just fine with good solid pressure so I left it alone.

The calliper wasn't quite so good so I fitted a new kit.

Brake seems to work better but only about 80% of the stopping force I expected. My 97 Techno needs about half an inch of movement on the brake pedal to lock up the back wheel.

Watching closely, the pads extend when the pedal is pressed right down but retract when it's released. There is definitely no air in the system.

So, I'm thinking, and please tell me if I'm wrong, that the rear line needs priming.

I think if I attach a tube and 'header' tank to the calliper bleed valve, press the pedal so the pads extend, open valve and release the pedal. Fluid should be drawn in rather than pads retracting.

Does this make sence and sound like a workable solution.

As I said before I'm in new territory here so any guidance you can offer would be hugely appreciated.

[copemech]

If the pedal is still soft, there must be air somewhere. I would prepare a syringe with hose, bleed the air and attach to the bleedre nipple purging all air before opening the nipple, then crack the line at the top of MC and push fluid backwards through the line to remove any air, then cap it, close the bleeder and see if it firms up.

M2C