Ktm front brake spongy after crash, Help!

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9/26/2020 4:20 AM

So I crashed hard last weekend, got up and my front brake was locked. Upon inspection I found the dust cover was wrapped up in the lever causing the lock up. After that though on the way back to the truck it would work at full power if you pumped it a few times.
Got home and figured it had air in the line. Bleed it and bleed it and never got anything but half power at best. I put new copper washers on, replaced the master cylinder plunger and seals with an old set I had. Still half power. I took apart the caliper and checked everything. Still half power.
When I pull the lever all the way into the grip the brake works. The wheel is locked but no way is the system working correctly. I am at a loss. I order new seals, and a new line thinking there might be an issue there? I would love to hear some input and your thoughts. Thank you......


9/26/2020 4:39 AM

Bent rotor?

Paw Paw


9/26/2020 6:41 AM

I would put in a new plunger, the. leave master cylinder cap loose and pull lever towards the grip and zip tie it in the pulled in position ,, let sit overnight to get all air out of system


9/26/2020 8:11 AM

I bent one of the pins that the caliper slides side to side on and had the same issue. I have seen this twice. Once on a friends yz250 and once on my cr250.


9/26/2020 1:45 PM

I tried the master cylinder trick last night. The brake held pressure but still no power. The bent pins make sense. I will check those. The front end was all twisted up and the pistons may of took a hit. The wheel is hanging up right now which leads me to believe the pins might be bent and not allowing the caliper to return properly.


9/26/2020 2:07 PM

In addition to the sliding pins being bent, the caliper bracket itself might be bent and I have also seen the mounting lugs on the fork get bent and be a really nuisance to troubleshoot.


Powerband in every gear !

9/26/2020 7:02 PM

I pulled everything apart again. The pins seem to check out ok. All the seals seem to be in good order. The plunger looks ok also. I cleaned everything and now just waiting for parts to show up. I am going to replace everything including the line. For some reason I have a suspicion it's the line. I think the crash and excess pressure on the lever after the crash did something to the line. Bummer is I have wait until Tues for the parts to show up.


9/30/2020 8:44 PM

So I replaced everything and still only half power. I noticed the caliper was grabbing the disc at an angle. I pulled the caliper off and pulled the lever and got full power. It appears that the upper slider arm seems to pointed slightly upward.
My buddy brought his KTM over and we started swapping parts. First the slider pin. Same result. I replaced the caliper mount arm and same result. Swapped the whole system from his to mine and everything worked perfect. So that means the fork bracket isn't bent.
After all said and done it appears the caliper mount for the brake pin is bent outward. How in the heck can this happen? No marks of damage or stress. I can't see this bending without breaking but it's the only thing it can be.... Any thoughts?


9/30/2020 9:56 PM

Yep.. weird stuff happens. Must have whacked it just right. Seems you've narrowed it down pretty well through process of elimination.


Powerband in every gear !

10/1/2020 12:27 PM

It is air. It get stuck right after the number plate ends (top) and all the way to the bolt into the canister. And it also gets stuck inside the brake fluid reservoir.

Losen the banjo bolt at the canister and rotate the brake line down so you have a falling line. Also turn the brake reservoir slightly upwards. Turn the handlebars to the left and flip with the brake lever for a minute or so while knocking gently at the brake line around fork protector height. Then turn bars the other direction and it should come some air out that gets stuck passed the bleed holes in reservoir.

I have had major issues with ktm mushy front brakes. Filling them backwards with a big syringe did not help and neither did putting complete caliper in brake fluid.

The above works every time I do it.


10/7/2020 6:58 AM

So here's the verdict. The cerakoted caliper is the old one. The silver one is a new one. If you look closely you can see the brake slide pin is pointed upwards on the old one. It turns out it's 3 mm taller at the end. I've changed the slide pins and it's still 3 mm taller. Somehow that caliper got bent. For the life of me I have no clue how this could possibly happen without damaging other things along the way. What a frustrating journey. But I got it all figured out. I ended up finding a new caliper on eBay with the pads which are brand new shipped to my door for $100.
I appreciate everybody's input on this and hopefully it never happens to you guys.