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Hi, I have rebuilt a 1990 kdx E2, I have fitted a kx125 2000 USD front end on it.

I bought a new brake hose but cannot bleed the air out of it. Despite my best efforts the lever is spongy and will pull to within and inch of the bars. I have posted on here and following advice I have tried

Standard Bleeding

Gravity bleeding

Reverse bleeding with a syringe

Pulling fluid through at the caliper end using a syringe

Bleeding using pressure (via a modified cap) from the master cylinder down.

I have rebuilt the master cylinder and done all of the above, again with no luck. The front end I used from the kx was complete and before stripping the brake was razor sharp so I did not have much faith the master cylinder rebuild would work but I could not think of anything else to do!

The bike has not been used since the rebuild as I cannot get the front brake strong enough to pass the braking efficiency test we have in the uk. It is a lovely bike and I have put soo much into it.

Now spring is here I decided to have another go, I tried again today but no joy I don't know what else to try. I really don't want to have to sell because I cannot sort the front brake but I want to ride this year!!

If anyone can help I would really appreciate it.

I have pushed the pistons back into their bores and they moved ok, bled again and still no joy - the pistons did move out so that's something I guess


Help!!!

I use something similar to this, never had a problem,

hi, thanks for responding, it is the only thing I have not tried.

I could not see the difference between this and the syringe pulling it through, or for that matter a pressure feed through from the master cylinder (approx 15 psi).

I guess I might have to try one, they are £50 in the UK, might just have to do it if there is nothing else to try.

all the best

It sounds as if the M/C is not working properly IMO. How was the condition of it (bore) when you rebuilt it? Have you tried a different one? I would try finding one that matches the KX front end.

Hi,

this is the original master cylinder that came with the KX front end. The only thing I changed was the front brake line, I needed a new one not to foul the front light to make it road legal.

The m/c worked fine on the original KX set up - I got the entire front end, so checked it before I fitted it to the KDX. The only new bit was the brake line - it must be air in the line but how to get it out is beyond me!

You can always bleed the system while it is off the bike. Pull the caliper, put something between the pads to not let them push out to far, and raise it above the M/C and try bleeding it. Air is lighter than the fluid so this way you are pushing the air upwards and out and letting gravity help you. You can also tap/shake various parts where you think air might be trapped to help move it along. It is the only other way I can think of to bleed the system since you have tried all the other methods. I know it may sound crazy but it was a trick I picked up from an old rider back when I was a kid and it has worked for me before on a problem system.

+1
it took me forever to get mine to work properly, I'd bleed for a while, tap, bleed more, get po'ed then walk away. do it again a few hours/days later and it finally worked after using 2 bottles of fluid.
patience is your friend at this point,

With a mity vac it takes about 5 minutes and you are done

I always remove the bleed screw and wrap the threads with teflon tape since the vac will pull air right through the threads


Have you tried the KDX m/c ?

Another thing to try is to zip tie the brake lever as tight as you can to the bars overnight. I tried it on mine and it made the brakes a lot firmer. Almost too much for the way I like them.

Hi Guys,

thanks for the suggestions very much appreciated. I am feeling slightly more philosophical this morning and will have another go.

I tried placing the caliper higher than the m/c last time without success, was hanging there for a few weeks as I recall as I got so di*ked off with it. However, I have not tried the tapping approach so I am thinking of using a mityvac (need to get one), on the suspended caliper whilst tapping it. If that does not work I will give up!

I have taped the threads to stop air ingress and I have tried the KDX m/c, I was not impressed with that when I bought the bike to rebuild but it was much better than I have managed to achieve with the KX m/c. I did swap it out but achieved much the same level of squishyness!!

All the best and thanks for the suggestions!

Hey UK....I'm right there with you. Can't get mine to firm up either. I've tried everything but the mityvac. I hope it works for you. Looking forward to an update...

Hi,

I was beginning to think it was only me who could not sort it!

I will be purchasing a mityvac or sealey vacuum pump this weekend and will let you know how I get on. To be honest I am not confident!

all the best

gertie6car wrote:Hi, I have rebuilt a 1990 kdx E2, I have fitted a kx125 2000 USD front end on it.

I bought a new brake hose but cannot bleed the air out of it. Despite my best efforts the lever is spongy and will pull to within and inch of the bars. I have posted on here and following advice I have tried

!

Perhaps you are expecting too much out of this brake and it is operating properly?

I can pull mine to within a 1/2" to the grip

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If I pull hard on mine it will go to the bars, But the front tire will lock up far before that.

Mine looks about like Wibs, maybe a bit less squishy. It will lock up on dirt with two fingers at low speeds.
For the OP, all kinds of little things can add up on a new installation like you've got. I'd get it as firm as you can and ride it a bit to set the pads in and get the hardware settled down.

Bleeding brake! still not sorted! have used a vacuum set up and still kin useless!! help!

I feel your pain. On my sons KX, I must have squeezed the lever over 500 times, easily. I did eventually get it though.

Just out of curiosity, have you tried going back to the factory brake line?

I agree with Mr. Wibbens, use the mighty vac. It's worth every penny. I once spent four days trying to bleed my front brakes and it still felt like crap. I bought the Mighty Vac and had my brake dialed in five minutes.

scheckaet wrote:+1
it took me forever to get mine to work properly, I'd bleed for a while, tap, bleed more, get po'ed then walk away. do it again a few hours/days later and it finally worked after using 2 bottles of fluid.
patience is your friend at this point,

+1