OLD KTM BRAKES: MR.-KNOW-IT-ALL

To the honorable and all-knowing Mr. Know-It-All,
I am the proud owner of a 2003 KTM 525EXC. It has been very reliable over the last 17 years and has been through thick and thin with me.

One thing that has never worked as well as I wish is the front brake. It has always been mushy and spongy, and I finally decided to do something about it. I made an appointment at the dealer to have the front brake properly bled and inspected. The result was them saying the front-brake components were worn out, and that they all needed to be replaced. They were not interested in getting the repair kits for the master cylinder or the caliper to rebuild them. I thanked them for looking at my bike and bleeding the front brake to check for proper operation.

I ordered the repair kits online and attempted to rebuild the front caliper and master cylinder myself. I did everything exactly according to the instructions and watched several videos regarding the procedure. Once I had the system all back together, I went to refill the system with brake fluid and bleed it. I gravity-fed the system at first, and then used a vacuum-pump device to suck out the air in order to get it working.

I don’t know what went wrong or why I can’t get the brakes to work. I took my bike back to the dealer and asked them to try to bleed the brakes and get it working. They agreed to look at it, but couldn’t get it to work this time, either.

At this point, I am willing to buy a new caliper, master cylinder and hose to get the front brake working so I don’t lose an entire season of riding. Unfortunately, the complete units do not seem to be available from KTM or from anyone I can find on the internet.

I refuse to believe that something cannot be done to resolve this situation in an acceptable manner. I refuse to believe that I must retire an otherwise perfectly good motorcycle that still has many rides left in it.

Surely you must know the solution to this problem. You must know of some company, somewhere, that will rebuild my components or sell me new ones. Is it possible to retrofit Japanese brake components to my bike? At this point, I am willing to try almost anything.

As it sits right now, my bike is unrideable and worthless. I need to get it running so I can sell it and get a down payment for something new, or at least have something to ride right now.

I humbly beseech you to look into my request and hopefully provide me with an answer.
Ed Jenssen
Via [email protected]

 

I turned to Jeff Slavens, a KTM aficionado for his sage on this query.

Hello Ed, your issue is twofold. The front brake was less than stellar when new, because it was never bled correctly. I had an ’03 300EXC with the same issue, and it took more than one attempt to get it on point.

My bleeding method: I’ve never had success with vacuum bleeders and prefer pushing fluid from the caliper up to the master cylinder. I use a large syringe with a hose connected to it and the bleed nipple. Be sure to zip-tie the hose to the nipple or it will come off and spray fluid everywhere. Make sure there is no air in the syringe or the hose when you connect it. The last step is to get the micro-bubbles out of the system. Let the bike sit overnight so the micro-bubbles bunch up and create larger air bubbles that you can bleed. You can use the syringe for this, but I often remove the master cylinder cap and move the bars back and forth to tilt the master cylinder while flicking, not squeezing, the lever. You should see small bubbles come out. In the center of the master cylinder is a white plastic ring with a small hole in the center. That is where the bubbles will exit. 

The current issue with your brake system is that the bore in the master cylinder is worn. It is no longer true (round), and the rebuild kit won’t seal. Master cylinders are nothing more than a high-pressure hydraulic pump, and your pump is worn out.

To get back on the trail now, purchase a master cylinder and brake line for a 2020 500EXC-F. Your caliper is probably okay. The components are currently available from KTM.

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