Forcing brake fluid shimano brakes

wom
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Newport Beach, CA US
1/18/2024 11:51pm

What happens if I force brakes fluid in my shimano deores like you close the top cap and force brake fluid into the bleed port then closing it while still squeezing the syringe to make the brake feel very stiff and not go down will this cause any damage to the brakes

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Kale123
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Brisbane, QLD AU
1/19/2024 1:15am

Will probably just advance your pistons onto the rotor 

HexonJuan
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1/19/2024 6:22am Edited Date/Time 1/19/2024 6:28am

Overfilling a brake is a bad idea. If/when the fluid heats up and starts expanding, it will run out of space in the reservoir. With no place to go, it starts to pump out the caliper pistons, engaging the brake making it a closed circuit. It heats up more, expands more, engages the brake more until something gives. That could be a boil over, where the fluid gasses out and all braking is lost or it could find the weakest seal and start leaking. Most folx I've heard who overfill their brake are looking for quicker engagement. If that's the case, first thing to do is make sure you have a good bleed in the first place. Once that's established, you can drop the wheel and slowly pull the lever to reset the pad gap. That is finnicky AF to do but can work. One thing with Shimano brakes I've come across is the caliper pistons not slipping through their seals enough. This is mostly due to improper assembly (which is an easy fix) but can occur over time and use as debris accumulates on the caliper, piston, and seals. That will necessitate a caliper rebuild, but here you'll have to hit the dark recesses of Amazon/Ali to find caliper rebuild kits as Shimano doesn't offer em. I've used em and they worked for me though. For background, I worked for a brake manufacturer for 9 years and have seen a few things. I'm not the usual chucklehead commenter. I'm an experienced chucklehead commenter. 

9
wom
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Newport Beach, CA US
1/19/2024 9:21am
HexonJuan wrote:
Overfilling a brake is a bad idea. If/when the fluid heats up and starts expanding, it will run out of space in the reservoir. With no...

Overfilling a brake is a bad idea. If/when the fluid heats up and starts expanding, it will run out of space in the reservoir. With no place to go, it starts to pump out the caliper pistons, engaging the brake making it a closed circuit. It heats up more, expands more, engages the brake more until something gives. That could be a boil over, where the fluid gasses out and all braking is lost or it could find the weakest seal and start leaking. Most folx I've heard who overfill their brake are looking for quicker engagement. If that's the case, first thing to do is make sure you have a good bleed in the first place. Once that's established, you can drop the wheel and slowly pull the lever to reset the pad gap. That is finnicky AF to do but can work. One thing with Shimano brakes I've come across is the caliper pistons not slipping through their seals enough. This is mostly due to improper assembly (which is an easy fix) but can occur over time and use as debris accumulates on the caliper, piston, and seals. That will necessitate a caliper rebuild, but here you'll have to hit the dark recesses of Amazon/Ali to find caliper rebuild kits as Shimano doesn't offer em. I've used em and they worked for me though. For background, I worked for a brake manufacturer for 9 years and have seen a few things. I'm not the usual chucklehead commenter. I'm an experienced chucklehead commenter. 

Damnn do you think if I let the excess out now itll be fine

1/19/2024 9:22am
HexonJuan wrote:
Overfilling a brake is a bad idea. If/when the fluid heats up and starts expanding, it will run out of space in the reservoir. With no...

Overfilling a brake is a bad idea. If/when the fluid heats up and starts expanding, it will run out of space in the reservoir. With no place to go, it starts to pump out the caliper pistons, engaging the brake making it a closed circuit. It heats up more, expands more, engages the brake more until something gives. That could be a boil over, where the fluid gasses out and all braking is lost or it could find the weakest seal and start leaking. Most folx I've heard who overfill their brake are looking for quicker engagement. If that's the case, first thing to do is make sure you have a good bleed in the first place. Once that's established, you can drop the wheel and slowly pull the lever to reset the pad gap. That is finnicky AF to do but can work. One thing with Shimano brakes I've come across is the caliper pistons not slipping through their seals enough. This is mostly due to improper assembly (which is an easy fix) but can occur over time and use as debris accumulates on the caliper, piston, and seals. That will necessitate a caliper rebuild, but here you'll have to hit the dark recesses of Amazon/Ali to find caliper rebuild kits as Shimano doesn't offer em. I've used em and they worked for me though. For background, I worked for a brake manufacturer for 9 years and have seen a few things. I'm not the usual chucklehead commenter. I'm an experienced chucklehead commenter. 

wom wrote:

Damnn do you think if I let the excess out now itll be fine

Better now than later.

1
HexonJuan
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1/19/2024 9:42am
HexonJuan wrote:
Overfilling a brake is a bad idea. If/when the fluid heats up and starts expanding, it will run out of space in the reservoir. With no...

Overfilling a brake is a bad idea. If/when the fluid heats up and starts expanding, it will run out of space in the reservoir. With no place to go, it starts to pump out the caliper pistons, engaging the brake making it a closed circuit. It heats up more, expands more, engages the brake more until something gives. That could be a boil over, where the fluid gasses out and all braking is lost or it could find the weakest seal and start leaking. Most folx I've heard who overfill their brake are looking for quicker engagement. If that's the case, first thing to do is make sure you have a good bleed in the first place. Once that's established, you can drop the wheel and slowly pull the lever to reset the pad gap. That is finnicky AF to do but can work. One thing with Shimano brakes I've come across is the caliper pistons not slipping through their seals enough. This is mostly due to improper assembly (which is an easy fix) but can occur over time and use as debris accumulates on the caliper, piston, and seals. That will necessitate a caliper rebuild, but here you'll have to hit the dark recesses of Amazon/Ali to find caliper rebuild kits as Shimano doesn't offer em. I've used em and they worked for me though. For background, I worked for a brake manufacturer for 9 years and have seen a few things. I'm not the usual chucklehead commenter. I'm an experienced chucklehead commenter. 

wom wrote:

Damnn do you think if I let the excess out now itll be fine

Likely so. Be smart in how you remove the excess. Remove the fluid from the lever end. Set the lever up like you're gonna bleed it with Shimano's bleed cup, drop the wheel out, remove the brake pads, and push the caliper pistons back into the bores. Remove the bleed cup and thread the bleed screw back in. That'll insure you have the correct amount of fluid in the system.

3
wom
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Location
Newport Beach, CA US
1/19/2024 8:46pm
HexonJuan wrote:
Overfilling a brake is a bad idea. If/when the fluid heats up and starts expanding, it will run out of space in the reservoir. With no...

Overfilling a brake is a bad idea. If/when the fluid heats up and starts expanding, it will run out of space in the reservoir. With no place to go, it starts to pump out the caliper pistons, engaging the brake making it a closed circuit. It heats up more, expands more, engages the brake more until something gives. That could be a boil over, where the fluid gasses out and all braking is lost or it could find the weakest seal and start leaking. Most folx I've heard who overfill their brake are looking for quicker engagement. If that's the case, first thing to do is make sure you have a good bleed in the first place. Once that's established, you can drop the wheel and slowly pull the lever to reset the pad gap. That is finnicky AF to do but can work. One thing with Shimano brakes I've come across is the caliper pistons not slipping through their seals enough. This is mostly due to improper assembly (which is an easy fix) but can occur over time and use as debris accumulates on the caliper, piston, and seals. That will necessitate a caliper rebuild, but here you'll have to hit the dark recesses of Amazon/Ali to find caliper rebuild kits as Shimano doesn't offer em. I've used em and they worked for me though. For background, I worked for a brake manufacturer for 9 years and have seen a few things. I'm not the usual chucklehead commenter. I'm an experienced chucklehead commenter. 

wom wrote:

Damnn do you think if I let the excess out now itll be fine

HexonJuan wrote:
Likely so. Be smart in how you remove the excess. Remove the fluid from the lever end. Set the lever up like you're gonna bleed it...

Likely so. Be smart in how you remove the excess. Remove the fluid from the lever end. Set the lever up like you're gonna bleed it with Shimano's bleed cup, drop the wheel out, remove the brake pads, and push the caliper pistons back into the bores. Remove the bleed cup and thread the bleed screw back in. That'll insure you have the correct amount of fluid in the system.

I let them out and they’re working good now also when u said if I wanted faster engagement I had to pull the lever do you mean like pushing the pistons out a bit and then bleed?

HexonJuan
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1/21/2024 12:14pm
wom wrote:

Damnn do you think if I let the excess out now itll be fine

HexonJuan wrote:
Likely so. Be smart in how you remove the excess. Remove the fluid from the lever end. Set the lever up like you're gonna bleed it...

Likely so. Be smart in how you remove the excess. Remove the fluid from the lever end. Set the lever up like you're gonna bleed it with Shimano's bleed cup, drop the wheel out, remove the brake pads, and push the caliper pistons back into the bores. Remove the bleed cup and thread the bleed screw back in. That'll insure you have the correct amount of fluid in the system.

wom wrote:
I let them out and they’re working good now also when u said if I wanted faster engagement I had to pull the lever do you...

I let them out and they’re working good now also when u said if I wanted faster engagement I had to pull the lever do you mean like pushing the pistons out a bit and then bleed?

No. With the wheel out of the drops, pull the lever once and hold. Release then put the wheel back in to check actuation. No need to bleed once a good bleed is established.All we're doing is resetting the caliper piston slip gap. Shimano have a high level of piston retraction. We're short circuiting the design memory, creating less retraction.

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Kango
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Calgary, AB CA
1/22/2024 10:12pm

But doesnt SRAM tell you to pressurize the system? 

HexonJuan
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1/23/2024 6:19am
Kango wrote:

But doesnt SRAM tell you to pressurize the system? 

They have you cycle the fluid, increasing and decreasing pressure within the brake. This contracts and dilates any air pocket in the system, making those bubbles move. Any dissolved air in the fluid gets drawn out during the pull of the plunger (when bleeding the master cylinder), resulting in 'cleaner' fluid if you will. Less air dissolved in the fluid yields a higher boiling point. They don't have you push fluid into the system and then close the bleed fitting. I haven't looked in ages, but they had a decent series of vids explaining the processes and a bit of the reasoning behind them. Def easy to get misdirected if you skip over the 'boring' parts. Folx talking doesn't seem as informative as folx working, which is how a lot of bad interpretations of the processes can be had. I'm guilty of it and I've missed key details as a result, for bike and other work/repairs. It's good to be patient and mindful watching any tech vid or reading any service instruction. A bar manager I worked under ages ago gave me the best advice for tending that also applies to damn near everything else in life but especially mechanics: You get there faster if you slow down. 

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fartsack
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咸興市 KP
1/23/2024 7:27am
Kango wrote:

But doesnt SRAM tell you to pressurize the system? 

HexonJuan wrote:
They have you cycle the fluid, increasing and decreasing pressure within the brake. This contracts and dilates any air pocket in the system, making those bubbles...

They have you cycle the fluid, increasing and decreasing pressure within the brake. This contracts and dilates any air pocket in the system, making those bubbles move. Any dissolved air in the fluid gets drawn out during the pull of the plunger (when bleeding the master cylinder), resulting in 'cleaner' fluid if you will. Less air dissolved in the fluid yields a higher boiling point. They don't have you push fluid into the system and then close the bleed fitting. I haven't looked in ages, but they had a decent series of vids explaining the processes and a bit of the reasoning behind them. Def easy to get misdirected if you skip over the 'boring' parts. Folx talking doesn't seem as informative as folx working, which is how a lot of bad interpretations of the processes can be had. I'm guilty of it and I've missed key details as a result, for bike and other work/repairs. It's good to be patient and mindful watching any tech vid or reading any service instruction. A bar manager I worked under ages ago gave me the best advice for tending that also applies to damn near everything else in life but especially mechanics: You get there faster if you slow down. 

do pressurize the dot in the syringes before you bleed your brakes. you'd be surprides how much air this will release.

2
HexonJuan
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WI US
1/24/2024 7:31am
Kango wrote:

But doesnt SRAM tell you to pressurize the system? 

HexonJuan wrote:
They have you cycle the fluid, increasing and decreasing pressure within the brake. This contracts and dilates any air pocket in the system, making those bubbles...

They have you cycle the fluid, increasing and decreasing pressure within the brake. This contracts and dilates any air pocket in the system, making those bubbles move. Any dissolved air in the fluid gets drawn out during the pull of the plunger (when bleeding the master cylinder), resulting in 'cleaner' fluid if you will. Less air dissolved in the fluid yields a higher boiling point. They don't have you push fluid into the system and then close the bleed fitting. I haven't looked in ages, but they had a decent series of vids explaining the processes and a bit of the reasoning behind them. Def easy to get misdirected if you skip over the 'boring' parts. Folx talking doesn't seem as informative as folx working, which is how a lot of bad interpretations of the processes can be had. I'm guilty of it and I've missed key details as a result, for bike and other work/repairs. It's good to be patient and mindful watching any tech vid or reading any service instruction. A bar manager I worked under ages ago gave me the best advice for tending that also applies to damn near everything else in life but especially mechanics: You get there faster if you slow down. 

fartsack wrote:

do pressurize the dot in the syringes before you bleed your brakes. you'd be surprides how much air this will release.

Depressurizing the fluid is the correct term, but yes, it really draws a lot of dissolved air from the fluid. But that's done prior to hooking up the brake (generally at least). 

Digit Bikes
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Irvine, CA US
2/9/2024 10:58pm
wom wrote:
What happens if I force brakes fluid in my shimano deores like you close the top cap and force brake fluid into the bleed port then...

What happens if I force brakes fluid in my shimano deores like you close the top cap and force brake fluid into the bleed port then closing it while still squeezing the syringe to make the brake feel very stiff and not go down will this cause any damage to the brakes

If you force it enough you can burst the diaphragm in the master cylinder. 

3
smelly
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Colorado Springs, CO US
2/10/2024 3:23pm

Another way to yield quicker engagement is use thicken rotors. Shimano come with 1.8mm rotors, so use 2.0 or larger rotors for quicker engagement without futzing with pad position.

I’ve found Shimano brakes work much better with frequent lever bleeds. 

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HexonJuan
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WI US
2/11/2024 1:32pm
smelly wrote:
Another way to yield quicker engagement is use thicken rotors. Shimano come with 1.8mm rotors, so use 2.0 or larger rotors for quicker engagement without futzing...

Another way to yield quicker engagement is use thicken rotors. Shimano come with 1.8mm rotors, so use 2.0 or larger rotors for quicker engagement without futzing with pad position.

I’ve found Shimano brakes work much better with frequent lever bleeds. 

That's pretty smart right there. Shimano's design had me wondering if the system has air in it from assembly. Every stock Shimano brake I've worked on has had an air pocket in the MC. Decided to check out the internal structure and ports (had a dead SLX MC and a bandsaw) and was surprised to see they don't have a compensator port, that hole that sits right behind the primary cup seal on every other brake. Guess is that bit of air between the primary and secondary seals remains after factory bleed, but gets slowly released into the reservoir. Their system is designed well enough that the air stays in the reservoir unless the bike gets flipped upside down, which allows the air to migrate into the MC bore. That may explain why they seem to need more love initially then other systems. When I worked at a shop, I'd always do a quick lever bleed when assembling a new bike. Extra work but not terribly time consuming and def worth the peace of mind that the owner wouldn't regret new bike day.

1
WMullins
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Blind Bay, BC CA
2/19/2024 11:43am

I haven't ridden Shimano in a few years due to hating the wandering bite point but I have been lightly pressuring my code R/RSC's for a few seasons now with no adverse side effects to the bladder/performance. That being said, it is a very light amount of pressure, I only weigh 160 with gear, and I don't ride a ton of park laps. I would suggest the aforementioned method of advancing pads and regular lever bleeds, or better yet, follow my lead for this season and grab some TRP'sSmile

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