Brake pressure question

[pagheca]

Me again,

There’s also one thing I can’t figure out: every time I take the wheels off, the brake system loses pressure. What’s weird is that after a few squeezes of the lever, pressure comes back and the brakes feel normal again. Since it’s a closed hydraulic system (and there’s no visible reservoir like in a car), I don’t get how that’s possible. Any ideas?

Cheers

 

[Pyr0]

sounds like your brakes may need bleeding

 

[VWsurfbum]

Sounds like not enough fluid in the brakes.
Shimano by any chance?

 

[pagheca]

thanks for the quick answers, guys.

Yes, maybe there is air, but why the system works after a few squeeze of the levers if there is air inside?

And yes, they are Shimano.

 

[VWsurfbum]

thanks for the quick answers, guys.

Yes, maybe there is air, but why the system works after a few squeeze of the levers if there is air inside?

And yes, they are Shimano.

If there's not enough fluid, it will create a vacuum behind the cylinders and draw them back.

 

[Bear-uk]

As above. A lever bleed should sort it

 

[pagheca]

I spoke with customer support, and they told me that the brake issue is normal. It can happen when the bike is laid on its side (as I did to transport it in the car) with the wheels removed, and then returned to a vertical position.

They weren’t able to provide a detailed technical explanation, but I suspect it might be due to air bubbles moving around and then back up into the small reservoir located above the brake lever.

Does that sound reasonable to you?

 

[VWsurfbum]

Kind of what we're describing. so you can either live with it or do a quick lever bleed/fill.

 

[pagheca]

I think I will do the bleed soon, thanks. Is it something feasible at home? Does it requires specialized tools?

I am quite good at mechanical works but no experience on this.

 

[VWsurfbum]

dead easy, but to make it easier, either get the bleed "bucket" or a set of syringes. Epic bleed solutions do some good kits and fluid.

 

[MeatBike]

You could try a "ghetto bleed" first.

Zip tie the levers to the bars as tight as you can and leave them over night.

 

[RustyIron]

I think I will do the bleed soon, thanks. Is it something feasible at home? Does it requires specialized tools?

I am quite good at mechanical works but no experience on this.

Bleeding brakes is just a common part of owning a bike. Even when your brakes are running fine, you should bleed them periodically anyway to keep the system free of contaminants. Since you're already competent with other mechanical contraptions, you'll get this figured out. It might take a couple times before you're a pro, but anything that requires skill is like that.

 

[ncs]

no visible reservoir like in a car

Hi, reservoir is small in levers, when you upside-down bike it can take air that in normal position is on top of lever.....so not worry about it. If it work like you describe - I think bleed not need.
When it stop braking - check pads - bleed system.

 

[Ndanger]

Me again,

There’s also one thing I can’t figure out: every time I take the wheels off, the brake system loses pressure. What’s weird is that after a few squeezes of the lever, pressure comes back and the brakes feel normal again. Since it’s a closed hydraulic system (and there’s no visible reservoir like in a car), I don’t get how that’s possible. Any ideas?

Cheers

Most likely, when you remove the wheel/rotor the process slightly moves the caliper pistons away from the rotor. When you reinstall the wheel, the first movement of the brake level is moving the pistons back to the original position of the pistons/pads. It may feel like a loss of pressure.

 

[Ndanger]

Also best practice is to not turn the bike upside down when removing the wheels, I understand that it can introduce air into the brake system at the master cylinder. I ignore the caution and never had a problem

 

[irie]

When you remove wheels always put pad spacers in the calipers. Just saying.

 

[Stihldog]

When you remove wheels always put pad spacers in the calipers. Just saying.

This^^^.

Magura brakes need constant bleeding. Shimano brakes not so much. A lever bleed doesn’t require much; 2.5mm Allen key (or torx), small bleed funnel and a bit of mineral oil. Once ready for a lever bleed, pump the brake lever and watch for bubbles to rise in the funnel. When the bubbles stop …you’re done.

Remove the funnel, replace the bleed screw, test the lever action. Takes about 4:52 seconds for each side …unless you’re really good at it.

 

[pagheca]

You are totally right @irie!

Actually this was suggested to me long ago by my ebike's seller. I just forgot the spacer at home the other day. It is also risky because if you must repair your tyre you risk not to be able to insert the wheel anymore in the brake pad if you don't have the tools with you.

 

[VWsurfbum]

Magura brakes need constant bleeding. Shimano brakes not so much.

Don't agree with that. I don't get any issues with mine on any bike. Bleed once or twice a year, depending on use.

 

[Stihldog]

Don't agree with that. I don't get any issues with mine on any bike. Bleed once or twice a year, depending on use.

I can’t explain it.
Every 1-2 months I must do a lever bleed. But I love the feel and action. I’ll put up with some more maintenance and regular servicing. However the MT8’s on my Fuel EXE don’t need as much attention.

I gladly traded my Shimano brake system’s for some MT7’s. The guy hated the MT7’s…I didn’t. I’ve had some bad Ju-Ju with the Shimano brake systems.

Half the bikes in my little circle have MT7’s. Most of us need a regular lever bleed.

 

[Downhillr]

Me again,

There’s also one thing I can’t figure out: every time I take the wheels off, the brake system loses pressure. What’s weird is that after a few squeezes of the lever, pressure comes back and the brakes feel normal again. Since it’s a closed hydraulic system (and there’s no visible reservoir like in a car), I don’t get how that’s possible. Any ideas?

Cheers

Pistons may not be fully retracted and system needs to be re-bled.

 

[Jay🍺dur]

I store my bike vertically, hanging on the front tire on a wall. Never a problem with brakes.
I flipped my bike upside downrecently and remove the rear wheel to clean the sprockets and chain.
I’m sure this got air in the system, but it didn’t show up until a couple weeks later. I don’t know why. One day I started a ride and the brakes went to nothing. I could pump up a little at first, but it quickly went to nothing.
In the process of bleeding the brakes at the rear, the first pull of the syringe was a huge amount of air. I was shocked. The fluid was a dirty, dark gray as well. I’m told that is due to overheating or oxygenation. I’m going with oxygenation.
The bike is two years old.
It’s been working great so far after five or six rides.
Hope that helps. Good luck.

 

[CaptChip]

Me again,

There’s also one thing I can’t figure out: every time I take the wheels off, the brake system loses pressure. What’s weird is that after a few squeezes of the lever, pressure comes back and the brakes feel normal again. Since it’s a closed hydraulic system (and there’s no visible reservoir like in a car), I don’t get how that’s possible. Any ideas?

Cheers

Bleed the brakes, air will get in there a tiny bit at a time.