Brand specific brake bleeding methods vs generic gravity bleed

My only thought on the push-pull method, which is, admittedly, backed by no specific technical knowledge to back it up, is that if there's a little nook or cranny within the caliper or lever that may trap a tiny bubble of air, it's more likely to get flushed out by applying pressure/oil flow from different directions.

ie, the fluid flows under gravity from the high point

But air wants to go the other way. Risk of air floating mid-system if you bleed top down. Makes most sense to me to push fluid up through the caliper and out through the lever, since bubbles will rise in the hoses and flow with the fluid. Tapping the caliper and hoses as you go might help but if the pistons are pushed back in there shouldn't be air traps in there anyway.

Sometimes it might work others it wouldn't.

Pushing/pulling moves a lot of fluid quickly, so air bubbles get entrapped and flushed out. letting it drip through slowly won't get them out, e.g. inside the hose and fittings.

At the lever end if the funnel is in the top of the reservoir cap, and the reservoir is empty, then it'll dribble through and out the caliper and never fill the lever/reservoir.

At the caliper end letting gravity do the job works if the bleed port is above the hose connection (and there are no high points in the caliper above that), it won't work with Bleeding edge brakes as the port is at the bottom of the brake (when located on the fork) so you can only bleed them by putting fluid in through the port.

I'm sure marshys is great for already decent systems and just as a fluid swap. Hasnt worked for me for anything else, mostly as Jameson, air can still travel up faster than the fluid comes down

IHN, maybe so. I assume the designers have thought about the filling and bleeding circuits as any dead-end is going to be hard to completely fill, regardless of the direction the fluid is flowing from.

James, that does make sense but most methods seem to prefer lever to caliper, I think to avoid any gunk being pushed back up into and messing with the reservoir seals. I don't think a bubble mid way along a hose would do anything other than stay where it was in the line of fluid, so should be released at the bleed nipple.

Out of interest, what brakes use lever down?
Shimano are caliper up
FSA are push pull (+vaccuum pull at lever)
Magura are push pull
Sram are push pull

From what I can glean on how-to videos,

Hope, they use a funnel at the lever and feed to caliper
Shimano, also use a funnel at the lever and feed to caliper
Sram, push it in from the lever end, then a bit of push pull.

Havn't considered Magura or Fsa

I watched a video on bleeding Shimano and it was by the Lost co
He never used a bleed block,gently feathered the lever to do a gravity bleed and suggested bleeding from calliper UP was forcing all the dirt and crap that’s stuck in the callipers up through the lever etc
H just did a gravity and once it was all clear no bubbles etc he nipped up the calliper
But left the lever open and put wheel in,then gently pulled lever to centre pads/pistons on to the disk
This way t topped off the lever resevoir and never left a huge air void when you were centring the callipers,Almost like a lever purge to finish
Once pads were centred he closes off lever and that’s it
He done the same formula on Sram codes

That sounds sort of right, but I always thought you shouldn't fill/bleed the system with the pads anything other than fully retracted as you are overfilling it and would then struggle to fit new pads, as you can't then push the pistons back against the full system. Doing what he does, you are filling the system with the pistons out, as though the pads is worn.

Hope are IMO best done with a conventional bleed.  Reservoir cap off, tube into jamjar on the bleed nipple spanner on bleed nipple, pull lever, open bleed nipple, close bleed nipple, release lever.  repeat till no air comes out or fresh fluid is seen.  top up reservoir every 3 pulls or so.  simple, never fails

Hope are IMO best done with a conventional bleed. Reservoir cap off, tube into jamjar on the bleed nipple spanner on bleed nipple, pull lever, open bleed nipple, close bleed nipple, release lever. repeat till no air comes out or fresh fluid is seen. top up reservoir every 3 pulls or so. simple, never fails

Unless it's on an internally routed frame or on road hydros where the high point isn't the bleep port on the reservoir or God forbid BOTH!

pushing and pulling, pressure and vacuum etc isn’t going to remove it and more then gravity is it?

Yeah, it really is. Aside from gravity pushing the fluid in the opposite direction to the way any bubbles want to go, I've certainly had bubbles that have only been dislodged by fairly sharp presses on a syringe.

If you need to replace manky fluid, best to drain it out the bottom first, but for bleeding I prefer using a syringe on the caliper and sharply pushing, then gently pulling the same (clean) fluid back and forth until all bubbles have come out the top. Then close off the lever bleed port, and gently push fluid in to fill the reservoir.

Shimano don't feed from the funnel, they collect pushed fluid from the caliper in the funnel.
Of course youtube variations exist
I can certainly see a mini bleed to clear the master cylinder of air then cracking the caliper for a gravity 'fluid change' being an option for top down maintenance.
I'm 100% sure a gravity bleed of a system that has had a replacement caliper, hose or lever that empties a decent amount of fluid is pretty much useless.

Shimano recommend caliper to lever, followed by lever down to caliper. It’s in their instructions for every brake. Also recommend minimal lever actuation during the bleed until nipple is closed, as lever actuation breaks up bigger bubbles making them difficult to flush out.

Unless it’s on an internally routed frame or on road hydros where the high point isn’t the bleep port on the reservoir or God forbid BOTH!

doesn't matter.  thats how you bleed hopes. Push fluid thru from the top using the lever.  You can have the hoses in loops and it still works

there is no bleed port on a hope reservoir

Air compressor vacuum bleeders are amazing on motorbikes and cars. Or even the old Gunson Easy Bleed that uses air pressure from a bike tyre. They suck fluid down from the master out of the calliper and IME work first time even when there are weird high points. I wish there was a push bike equivalent.

For about a couple of decades most used the open-pull-close-release. So what happened. BITD that was fine, or is someone going to suddenly suggest that it wasnt and every brake ever bled during that time and by that method werent properly done.

I think not. So many different ways now, and with them so many different problems and reports of it not being good enough. Is this just a case now of whats fashionable 😕

Magura won't work with gravity fed bleed.
In my experience you need to push from the caliper and flick the lever while moving it through 45 degrees up and down.

Well it looks like I have to eat my words about my understanding of Shimano brake bleeding as the official advice, and indeed from lots of YouTube guides, is push into the caliper and leave the funnel to collect what is pushed out. I’m pretty sure that my Google skills first showed to the contrary.

Seek and you will find, as they say.

all the dirt and crap that’s stuck in the callipers up through the lever etc

Its my experience that the crap originates in the levers tbh.

I always push it out first then gravity bleed. Because thats what m785 xt bleed instructions used to be. I guess they've changed their mind now.

The buoyancy of micro bubbles is pretty minimal if you observe them in as syringe. Throw in drag from the bubble in a narrow brake line and its easy to see the passage of fluid under gravity is the greater of the forces.

EDIT - looks like I've been wrong a long time found the bleed instructions on the shimano website. Bottom up it is.

Air compressor vacuum bleeders are amazing on motorbikes and cars. Or even the old Gunson Easy Bleed that uses air pressure from a bike tyre. They suck fluid down from the master out of the calliper and IME work first time even when there are weird high points. I wish there was a push bike equivalent.

Isn't this exactly what you're doing with a syringe threaded into the caliper and an open reservoir at the master cylinder? pull on the syringe, create vaccum, draw fluid from reservoir end?
The volume of fluid in a mtb brake is tiny so a 100ml syringe is likely enough to completely drain the system, a pumpdriven system would pull all the fluid in about half a second flat.
The issues I've had with mtb brakes almost always relate to not getting a decent seal at the reservoir end, a tiny capacity and minuscule port making it very very easy to draw in air at the same time as fluid.
Same with the hopes, you force a decent bubble from the caliper and the loss of volume draws air into the system at the top. It's fine if the brakes only had a tiny bit of air in them but anything like hose changes which introduces any significant volume and you're pulling about a pint of fluid through.

Non of the "methods" are brand specific. The basic principle is the same - you have to fill the system with fluid and get all the air out. Gravity bleeding requires being able to fill the reservoir continuously. Easy if you can fit a funnel or syringe to the master cylinder, tricky if you can't. Bottom-up bleeding with a syringe is very effective IME, but you need to inject enough to fill the caliper, then suck some out to get any air bubbles trapped in the caliper, then completely fill the system. Using both top-down and bottom-up bleeding helps clear trapped air from both ends so a combination is best if you have a troublesome brake.

The problem with bike brakes is that they're primarily designed to be light-weight so the hoses and passages in the calipers are tiny. It would be simple to make brakes that are easy to bleed, but they would be heavier and cyclists wouldn't buy them. Slightly trickier bleeding is the tradeoff for lightweight brakes.

The volume of fluid in a mtb brake is tiny so a 100ml syringe is likely enough to completely drain the system, a pumpdriven system would pull all the fluid in about half a second flat.

Absolutely. What we need is huge bucket sized master cylinders on our bikes.

Shimano instructions for caliper up followed by gravity bleed :-

https://si.shimano.com/en/dm/MADBR01/replace_genuine_mineral_oil

The buoyancy of micro bubbles is pretty minimal if you observe them in as syringe. Throw in drag from the bubble in a narrow brake line and its easy to see the passage of fluid under gravity is the greater of the forces.

Indeed. I bleed my Hopes the recommended way. You can see bubbles in the drain tube attached to the caliper when it is not fully bled. They move briskly along with the fluid when the lever is pumped, much more slowly under buoyancy when the lever is not being pumped. Add to this, brake hose has a smaller internal diameter than the tube that fits around the bleed nipple, so the difference would be even more marked. High points in the hose really isn't an issue. I guess a problem might be calipers or levers with Byzantine designs and unvented high points that can't be avoided by orienting the bike on the bike stand, but I haven't had a problem with any of my Hope brakes. Just got a bike with Shimano 4 pots on it, which clearly require a different technique as there is no reservoir lid you can remove and pour fluid into, but I will follow the recommendations for them when the time comes.

doesn’t matter. thats how you bleed hopes. Push fluid thru from the top using the lever. You can have the hoses in loops and it still works

there is no bleed port on a hope reservoir

That’s not how you bleed RX4s. You use a syringe from the calliper.

And yes, having the reservoir lower than the highest point in the system can lead to air bubbles being kept in the system. As can having the calliper not being the lowest point in the system, or even the bleed port in the calliper being lower than the highest point on the calliper.

It’s not rocket science to work this out.

apologies - I don't know road brakes.  However the basic point still stands

Just got a bike with Shimano 4 pots on it, which clearly require a different technique as there is no reservoir lid you can remove and pour fluid into, but I will follow the recommendations for them when the time comes.

Essentially the cup becomes the reservoir for the purposes of bleeding. Its relatively simple, but Shimano can also be infuriating to bleed if you're unlucky.

Shimano can also be infuriating to bleed if you’re unlucky they're Shimano brakes.

FTFY.

Seriously, I have a bunch of different Shimano brakes on various bikes. They all work fine, I'm happy with them, but they do need to be bled very carefully to get all the air out. Most important thing is to make sure that the reservoir is full and doesn't have air in it otherwise you'll get a wandering bite point if you lay the bike over.

The great luxury I have as a home mechanic is I can leave the bike dangling in the stand overnight, got some huge bubbles out the top in the morning 🙂

I've only recently learned about de-aerating DOT fluid by subjecting it to a vacuum in the syringe before using it, I don't know if it makes a difference but it feels like it should. It's going to take a while to un-learn my habit of shaking any container with fluid in it though 😮

thols2
Free Member

FTFY.

Seriously, I have a bunch of different Shimano brakes on various bikes. They all work fine, I’m happy with them, but they do need to be bled very carefully to get all the air out. Most important thing is to make sure that the reservoir is full and doesn’t have air in it otherwise you’ll get a wandering bite point if you lay the bike over.

The lad's just got a new bike, I wasn't immediately going to piss on his chips 😉

FWIW I've not got a bike with 4 pot Deores that seem as consistent as a brake should be. And another bike with a XT levers on TRP calipers that is being a complete *@~#$%^. Think that might be a leaky master cylinder though so will find out soon enough if its just normal Shimano or not

I recently did my Deore brakes. Squishy lever so I was certain air was in the system.
Did a gravity bleed. Brakes got a bit less squishy. But it wasn't until I forced the fluid from the caliper up to the lever that I got good solid brake feel again. I'd put a fair bit of liqud in the caliper before a couple of massive bubbles came out the top.

And yes, having the reservoir lower than the highest point in the system can lead to air bubbles being kept in the system. As can having the calliper not being the lowest point in the system, or even the bleed port in the calliper being lower than the highest point on the calliper.

Doing it by gravity alone won't ever purge air from the master cylinder reservoir though.

Thart's why Shimano are IME so easy to bleed. The first push up the system purges all the air out of the lever cylinder. The subsequent gravity bleed purges the high points in the caliper.

Its possible that brake bleed means many things to different people

https://bike.shimano.com/en-US/technologies/component/details/one-way-bleeding.html

doesn’t matter. thats how you bleed hopes.

It's how you did it in the 2000s .

It's considerably easier/quicker and more consistant with syringes.

FWIW, I revisited the Shimano brakes this weekend and they still felt solid and grabby after just the gravity bleed. In an abundance of caution, I did attach the cup to the reservoir and add a bit of fluid, a couple of flicks to get any air out under the cup then did the quick open/close at the caliper end with the lever pulled. No bubble "appeared" to emerge from the hose and nothing else at the reservoir end.

The brakes feel super tight now, as they did before, but hopefully I did remove any stubborn caliper bubbles.

@paton The one way bleeding name is misleading - it means that there’s only one route for fluid to flow (in either direction) around the caliper. Older calipers had areas that could be bypassed as shown in the images, which no longer feature.

It doesn’t mean that the system should only be bled from caliper to lever. The Shimano instructions I posted up there ^^^ say to bleed up, then gravity bleed. Same with all Shimano brakes.
Still tricky to get all air out quite often though.

Regardless of what the Shimano manual says, I would always do a gravity bleed first. Doesn't have to be much, but you do want to flush that dirt out of the caliper and bleed nipple first rather than push it further up into the system.

This is how the Shimano techs train their service centres to do it.

1. Gravity to flush out old fluid (don't push this back up into system again).
2. Up from caliper with brand new fluid.
3. Final gravity bleed.

Even though that's how I've been shown to do it, unless they're near brand new brakes I always do the marshy method as lubricating the pistons is the best thing you can do to help avoid wandering bite.

Going bottom to top with Shimano brakes that have been left too long between bleeds is a great way to seize the master cylinder piston.

FWIW with Shimano I get the worst of any air out of the lever, advance the pistons so I can give them a good clean / lube, push them back again, bleed down about 45 times until the fluid is finally no longer black ( 😉 ), then bleed up. Then I spend an inordinate amount of time cycling the pointless bite point adjuster in and out while flicking the lever to get more air and sludge out of the MC, angle the lever at different angles while continuing to flick the lever, set the pistons where I want them to be and finally close the system. Finally I see fluid seeping out of the MC because someone has tried to push the pistons back into the caliper when changing pads without removing the MC bleed screw and blown out the bladder, and then I process a warranty.

Then I spend an inordinate amount of time cycling the pointless bite point adjuster

Ah yes, that bite point adjuster. I’ve had 3 new XT levers delivered in the last few months. On 2 of them that ****ing screw is jammed solid

To be fair - the Shimano instructions start with telling you to drain the old oil out of the system out through the caliper first.

This is how the Shimano techs train their service centres to do it.

That’s not how Rich (one of the techs) showed me, but that could have been as it was on a relatively new set of brakes.