Front Brakes Fix

Stoffer88
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Stoffer88

I have a 2020 YZ250f, I just rebuilt the master cylinder and put new pads in to try and get rid of the spongy/ nothing feeling of the front brake. After thoroughly bleeding it multiple times I still got nothing. I zip tied the lever to the bars overnight and it made a small difference, but wore off as soon as I hit it while riding. I tried using a brembo master cylinder from a KTM and still nothing. I put my yamaha master cylinder on the KTM, and it felt perfect. So what are the next steps? Is it a new brake line, or something as simple as a caliber rebuild kit? Just need some help, I'm sick of riding with barely any front brake.

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zippytech
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zippytech 7/1/2025 4:35am
7/1/2025 4:35am

It's a pretty simple system, sounds like air. 

 

Do they pump up and get hard at any point?

Stoffer88
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Stoffer88 7/1/2025 5:04am
7/1/2025 5:04am
zippytech wrote:

It's a pretty simple system, sounds like air. 

 

Do they pump up and get hard at any point?

I use a hand vacuum to bleed them, just what I have laying around. Yes they do get a little hard but only when the lever is bottomed out on the bar, even at that the brake pressure isn't great at all, I would like them to be at least a little touchy. I've tried before several times bleeding them the traditional way and I still get nothing.

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OldTech
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OldTech 7/1/2025 5:33am
7/1/2025 5:33am

I'll try to help. First use your finger over the brake line hole and see if you can bench bleed the M/C. If it doesn't feel right or you can hold the pressure with your finger, something is wrong with the M/C. Next, when bleeding make sure the M/C is the highest point, or air can get trapped in the line. Also I use a ratio rite or a jar filled with oil and run my bleeder hose off the caliper into that. With the hose submerged, just open the bleeder and pump away.

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JazzyJJ
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JazzyJJ 7/1/2025 6:47am
7/1/2025 6:47am
OldTech wrote:
I'll try to help. First use your finger over the brake line hole and see if you can bench bleed the M/C. If it doesn't feel...

I'll try to help. First use your finger over the brake line hole and see if you can bench bleed the M/C. If it doesn't feel right or you can hold the pressure with your finger, something is wrong with the M/C. Next, when bleeding make sure the M/C is the highest point, or air can get trapped in the line. Also I use a ratio rite or a jar filled with oil and run my bleeder hose off the caliper into that. With the hose submerged, just open the bleeder and pump away.

If you're bleeding via the caliper, don't you want that to be the highest spot to help the air bubbles travel up?

OldTech
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OldTech 7/1/2025 8:03am
7/1/2025 8:03am
OldTech wrote:
I'll try to help. First use your finger over the brake line hole and see if you can bench bleed the M/C. If it doesn't feel...

I'll try to help. First use your finger over the brake line hole and see if you can bench bleed the M/C. If it doesn't feel right or you can hold the pressure with your finger, something is wrong with the M/C. Next, when bleeding make sure the M/C is the highest point, or air can get trapped in the line. Also I use a ratio rite or a jar filled with oil and run my bleeder hose off the caliper into that. With the hose submerged, just open the bleeder and pump away.

JazzyJJ wrote:

If you're bleeding via the caliper, don't you want that to be the highest spot to help the air bubbles travel up?

No, the master will usually bleed itself (which is why people put a band on the lever).But you don't want to trap air in the line with a loop higher than the m/c. With the ratio rite thing on the bleeder you should see the fluid drop drastically when you release the lever 

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OldTech
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OldTech 7/1/2025 8:49am
7/1/2025 8:49am
OldTech wrote:
No, the master will usually bleed itself (which is why people put a band on the lever).But you don't want to trap air in the line...

No, the master will usually bleed itself (which is why people put a band on the lever).But you don't want to trap air in the line with a loop higher than the m/c. With the ratio rite thing on the bleeder you should see the fluid drop drastically when you release the lever 

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FredJones
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FredJones 7/1/2025 9:34am
7/1/2025 9:34am

Rebuild your caliper with oem parts.

The stock brake hose is almost 6 years old and they weren't great to begin with. 

Replace your brake hose with a new steel braided hose. 

Next, I would reverse bleed like they do on mountain bikes. (See YouTube).

After reverse bleeding I would do a  conventional  bleeding. 

If you have a good lever feel after that, get your lady's vibratory device and run it along the brake line from the caliper to the master cylinder.  Then let it sit overnight with the brake lever tied down. This will break up the remaining air and non-condensible gasses suspended in the brake fluid and let it migrate back up into the reservior.

 

williamsmotowerx 7/1/2025 9:48am
7/1/2025 9:48am

Use a massage gun to vibrate the brake line with master cylinder cap off. Watch for tiny bubbles to come up.

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Sr_Vet_Rider 7/1/2025 8:45pm
7/1/2025 8:45pm Edited Date/Time 7/1/2025 9:04pm

Lots of good advice here. Let me add the one that always fixes this issue for me in the past. 
Push the fluid from the caliper, up to the master. I gave a syringe from a feed store, used fur horses. But there is a ton of them on Amazon

Fit a piece of hose onto the syringe and fill syringe with heave fluid. You’ll need to either empty the reservoir a few times to keep from over filling it. But if you can push the fluid up, it will bring the air bubbles with it. 
 

Video -
https://youtu.be/tHiEY7sfheo?si=KaOqKWGkAJBOnlGG


lol
https://youtube.com/shorts/S6jazH4ygoU?si=O1jPuw9sZ-vQ67aG


The massage gun or vibrating device of your choice, is a relatively new method, but I haven’t tried it yet. Makes sense… 

Amazon link to syringe kit. (Reverse bleeding) -
 https://a.co/d/96dwMnl 


https://a.co/d/40iHqqs


https://a.co/d/1YxLx4K

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Ake27
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Ake27 7/1/2025 8:56pm
7/1/2025 8:56pm

Vibrator on the brake line, that’s a new one for me. If it doesn’t help maybe a little Blue Chew in the reservoir could do the trick. 

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Village Idiot
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Village Idiot 7/1/2025 9:03pm
7/1/2025 9:03pm
Ake27 wrote:
Vibrator on the brake line, that’s a new one for me. If it doesn’t help maybe a little Blue Chew in the reservoir could do the...

Vibrator on the brake line, that’s a new one for me. If it doesn’t help maybe a little Blue Chew in the reservoir could do the trick. 

It's been known to make the lever action firmer.

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FGR01
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FGR01 7/1/2025 9:11pm
7/1/2025 9:11pm
williamsmotowerx wrote:

Use a massage gun to vibrate the brake line with master cylinder cap off. Watch for tiny bubbles to come up.

Results may vary, apparently

 

Stoffer88
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Stoffer88 7/12/2025 6:05pm
7/12/2025 6:05pm

Thank you for the help, just put in a new brake line and Caliber rebuild kit and the brake feels pretty dam good now. Thanks again

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