Front brake degraded

My sons 05 300 exc front brake has become very squishy at the lever. I bleed it with a vacuum pump but it didn't get any better. It will still top you, but the lever pulls back to the bars. What's the most likely cause a line, master cylinder, or caliper, and what's the best way to go about diagnosing?

Get a large syringe and a piece of tubing and "push" fluid from the caliper to the res.. Often, When the vacuum method won't work, the back bleed method will.

It's possible for air to be pulled past the threads of the bleeder nipple, so I always like to wrap them with teflon tape to eliminate that possibility.

So you don't think it's possible there's anything wrong with the system?

Its possible you may need to rebuild the MC but I would try the reverse bleeding first. Its the only way to bleed the brakes on these bikes IMO. Be patient, it can take some time to get all of the air out.

Get a front brake master cylinder from a CR. Its the best and cheepest cure, will always have stronger brakes than the stock Brembo!!

Get a large syringe and a piece of tubing and "push" fluid from the caliper to the res.. Often, When the vacuum method won't work, the back bleed method will.

It's possible for air to be pulled past the threads of the bleeder nipple, so I always like to wrap them with teflon tape to eliminate that possibility.

do this exactly like he says ... Open the bottom bleeder nipple and start pumping till you see fluid coming out the top . Close off the nut WHILE YOU ARE STILL PUMPING brake fluid up and it's dripping out the master cylinder. If this doesn't work , try it again . If still no luck, you may have to rebuild something.

Before you do any bleeding you must push the pucks all the way back into the caliper. This gets out any trapped air inside the caliper. I do this every time I wash my bikes.

You have to bleed the banjo bolt at the master as well as the caliper. Sometimes air can be trapped in it as well. I have a vacuum bleeder and I have tried every kind of bleeding method. Nothing works as well as the old method of pump, hold and crack the bleeder method. It just takes time, a clear plastic hose with a catch bottle and two people to do it. There is no short cut method that works as well.

My front brakes work so well that I have seen several of my friends go over the bars when I let them ride one of my bikes. All it takes is fresh fluid, metallic brake pads, proper bleeding and a good cleaning of the rotor and brake pads.

P.S. It helps if the lever is adjusted all the way out from the bar.

 Funny thing is, how did the air get in there in the first place? I hadn't worked on the bike, one day while riding he pointed it out.

 

I'll give reverse bleeding a try, nothing lost.

 

Where's a good place to get a MC rebuild kit? Before this incident the brakes worked great!

 Funny thing is, how did the air get in there in the first place? I hadn't worked on the bike, one day while riding he pointed it out.

 

I'll give reverse bleeding a try, nothing lost.

 

Where's a good place to get a MC rebuild kit? Before this incident the brakes worked great!

Bent rotor will cause this.

Get a front brake master cylinder from a CR. Its the best and cheepest cure, will always have stronger brakes than the stock Brembo!!

 

THE ONLY CURE!!!

Bent rotor will cause this.

Definitely another thing to check! If the rotor is bent it will push the piston up in to the caliper. So when you pull the lever the is much more distance for the pads to move to come in contact with the rotor while giving a really soft feel at the lever. Did the bike take a spill around the same time this started?

Guys, a bent rotor will cause brake judder. Nothing to do with the brake going soft.

 

The KTM front brakes are notorious in gathering air, reverse bleed, brake kits etc all last for a week and then you get the same soft spongy brake. I have done every thing and the only cure is a Nissin grom a Honda CR.

Here's a little trick that often works.  Wrap a bungee cord around the lever, pulling it tight against the handlebar.  Let it sit overnight.  If there's air in the system, this will compress it and it can migrate up the line.  Then it goes out into the reservoir when you release the lever.

 

I also like the tip about pushing the pucks back into the caliper to release trapped air that someone else mentioned.

 

BTW, a buddy of mine has a 2013 350XCF and I was helping him load it on the trailer the other day.  Grabbed the front brake, and nothing.  We bled it and now it's OK.  No idea how it sucked air in the line since it was just sitting in the garage between rides.

A quick fix for a spongy front brake (from the bike just sitting) is to kneel down next to the front rotor and press your knee against the caliper (a rag in between makes it more comfortable). If your caliper sliding pins are greased and clean you should be able to hold each side of the front wheel with each hand and press hard against the caliper with your knee until the pistons retract most if not all of the way (may need to remove master cylinder cap). Now pump the lever until the pistons are contacting the pads and the lever feels firm(ish) again. Repeat the process 10 times or so and your brake should be feeling much better. Try to keep the brake hose below the height of the master cylinder while doing this (one less high spot for air to collect). If it's no better you likely have bigger issues such as a leaking seal or loads of air in the line.

 

I've had my front brake lever go from mushy back near the bars to rock solid out where it should be just from following the above sequence 15 times or so (KTM Brembo).

 

Worth a shot and you can do it on the side of the trail without any mess.

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