Front brake problem

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M

MEDOGROCKET

Joined
Jul 20, 2007
Messages
130
Location
PORTLAND NSW AUSTRALIA
Hi all

I have an interesting problem, over the last couple of months I have been getting air into my front brakes.
For example I ride the bike one day and a day or so later when I check the bike the front brakes are gone, I bleed them and they are fine again.
I could ride the bike several times over a period of weeks with no problems and then out of nowhere the same thing happens.
Once the system is bleed the brakes work fine with no loss of performance at all.
I thought if I had a leak or problem with seals the braking performance would fade with use
Any ideas
 
Medogrocket, I had to think about this one for a few moments, and all I can come up with is boiling brake fluid, or moisture in the brake fluid.

Can you tell us what rating brake fluid you are using?

What method are you using to bleed your brakes; vacuum bleed tool, pumping the lever etc.

Have you checked the bleed nipple on the caliper to make sure there is no dirt in there?

Have you done a fluid flush, so you have all new fluids, or is it a mixture of new and old fluids?

Inquiring minds want to know.
 
It may be air getting past the seal in the master cylinder (when the lever is released). I would put a seal kit in it just to eliminate that scenario.
 
I would be surprised if the problem was caused by boiling.
There are no signs of moisture, I have flushed the system with new fluids using different types each time to see if this would fix it.
Bleed nipple has been checked and cleaned.
Original fluid used was a Motorex product dot 4
Then I flushed and used Mobil Dot 4
Now am using Valvoline Dot 4
I normally only use the pump method using the lever but the last time it was done using a brake bleeding tool ?vacuum this was done by my brother who is a mechanic.
I have also used a syringe pumping fluid from the bleed screw to the reservoir, I will be buying a seal kit soon to see if the master cylinder is the problem.
Any advise before I do this.
 
Medog

Do you see any air come out when you bleed them?
I ask because the same sort of thing is happening to me but I can't see any visible air bubbles when I bleed them.
After I bleed they're OK but if I don't ride for a couple of weeks then they feel spongy.
Be interested if the M/C seal kit fixes it for you.

Coops
 
Before you crack the bleeder,grab the anchor with your fingers and push on the caliper with your thumbs to drive the piston in.This will push any air up in to the reservoir.Pump the lever back up and if it's good,you've got air in the system.If you want to visually confirm it,take the reservoir cap off before you push the piston back and you'll see air bubbles.Make sure your pads aren't hung on the brake pin or binding where they sit in the caliper or the slides sticking.If any of these is the case,the pads will be misaligned causing a spongy feel.Somtimes blleding when this is the case will make the brake feel better-not because of air but simply because pumping the lever repeatedly drives the pads back hard against the rotor.A warped rotor will cause a low lever because it drives the pads back in a little and therefore has to travel more distance to engage the rotor again-of course,you'd notice that while riding,not after sitting.
 
i've seen this happen also but i don't know what causes it.

a simple way to bleed the brakes....

remove caliper from the fork and push the pistons all the way in.

return the caliper to the fork

lean the bike over so the master cylinder is at its highest point.

pull the lever and let it snap back...numerous times 20 or 30
i have bled several friends ktms this way without removing the caliper. it's pretty funny. they complain of mushy brakes and i lean the bike over and snap the lever a bunch of times ...brakes fixed...and they can't get over it
 
You don't need to remove the caliper to push the piston back.Pushing on it will fully seat it.Most bikes will get some air in the M/C due to falling over,bouncing around etc.As air will rise to the top it tends to stay in the M/C area trapped around the fitting and such.It won't migrate down to the caliper.Pushing the piston back drives the fluid up and in to the M/C-along with any air trapped there.I do it to mine on a regular basis(about a 10 sec. job) and I just pump the lever until the piston is all the way out.I'm not sure what snapping it 20 times would do.
 
well i originally bled the system by tapping on the caliper and surroundings with a small hammer. i think it dislodges the air bubbles. snapping the lever seems to do the same. if you just pump the lever, you don't get any bleeding results.

if you can push the caliper pistons home without removing the caliper...all the better

like i said you can bleed the system without pushing the pistons ....just lean it over and snap the lever
 
Thanks Guy's for all the bleeding technique's but i am sure it is not a bleeding problem.

Coastie, no I do not get any visible air and just as you said once bled there fine but leave it for some time and they go spongy or as in my last case basically not there at all.
I have been told there is an interesting forum on KTM talk about this problem as I think the KTM's run the same brakes it would be interesting to have a read but I have not found the forum as yet
I'll post what I find
 
hi

i'm new to this forum ... and i experience the same front brake problems ...

my lever feels spongy ... i changed the MC and got the same problem ... i changed the brake fluid ... now i look to the caliper ...

i really don't know what to do ...

i got FTE radial caliper with FTE MC ...

thank you
 
ok medog

i suspect that you have a loose banjo bolt after a clout. i've seen it where they will let air in but no fluid out.

my second thought is that you have not ben allowing the lever all the way out. this happens when people fit bark busters. the levermust be able to open completely.

a mod on ktms is to take the banjo bolt out and drill across from the original drilling to make a cross (4 hole) drilling.

another one is that you need to squeeze the cap onto as much fluid as you dare!

suggest you also try laying the bike against a wall on it's left and then open the pads and listen for that squidgy noise as air comes back up. that is always good to do.

regards

Taffy
 

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