RubeRad

Here's what I do once in a while for my Shimano hydraulics:


I don't have a Shimano bleed kit, and I don't plan to get one because this works good enough.

So when a bike is upside-down for a while, and you right-side it and want to ride, the brake levers need a lot of pumping until they work. Does that mean there's more air up at the lever, or down at the caliper (which used to be 'up' when the bike was upside down)?

Would a burp or 'lever bleed' be more quick/effective if you upside down the bike for a few hours first?

travbikeman

That tells me your brakes need fluid to be added, yes and burped to get the air out.

Putting the bike upside down for few hours won't resolve the issue. It needs more mineral oil.

Also, you don't really need a full bleed kit. An $8 funnel and mineral oil would suffice.

https://www.amazon.com/RSN-Sports-St...s%2C122&sr=8-3

RubeRad

I have the funnel and the oil, I have done the burp many times before, I'm not asking whether having the bike upside down would solve the problem, obviously it would just make the problem worse. I'm asking whether forcing the levers to be full-spongy would facilitate the burping, move the air up into the levers where it will burp out better?

travbikeman

Ah! OK and thanks for clarifying.....

Will wait for someone else to chime in on that. Not sure if that would help.

RubeRad

I'm thinking since air bubbles rise (?) having the bike upside down might concentrate them at the caliper. Although after the bike's been upside down, you experience the sponginess at the lever, but maybe that's just because that's the only point of contact with the hand.

Crankycrank

Try this. With the bike right-side-up, squeeze the levers and use a strap to hold them all the way on. Leave the straps on for 12+ hours and tap the lines at least a couple times during this time to jar any stuck air bubbles loose. When releasing the straps let the levers snap back as opposed to releasing them back slowly. This can remove small amounts of air and as mentioned you may need to check your fluid level first. If it doesn't remove all the air after 2 tries you may have to bleed the brakes.

RubeRad

Interesting, so the idea is that would save time vs standing there flicking the levers until the bubbles stop?

Would you do this with the upper bleed port open/funnel attached to allow mineral oil to flow in/bubbles bubble out?

Even the normal burp/lever-bleed instructions, they mention 'flick' the brakes, rather than just squeeze and release. Is there something about the flicking that dislodges air bubbles? Does it like send a little shockwave through the hydraulic system?

Greg R

Good thread as I'm new to bike hydraulics. The Trek gravel bike I got 3 years ago has Shimano hydraulic disc. It spent about a year in vertical storage with the front wheel up. I took it out last fall and the rear (right) brake lever just bottomed out. No sign of leakage and perfect function before storage. The LBS said to just pump the lever until it got firm and I should be OK. It worked as they said but I'm wondering if it's low on fluid. What is the correct fluid for Shimano disc? Thanks.

RubeRad

Shimano takes Shimano brand mineral oil (which is nicely non-toxic compared to some other brands require highly corrosive DOT fluids).

I think there is at least one other company that makes a compatible mineral oil for shimano brakes (Finish Line?), and believe it or not, some crazy cheapskate once started a BF thread about using regular J&J Baby Oil !!

I'm not surprised an upside down (or front-side-up?) bike would need the levers pumped quite a bit and then work apparently ok. Happens to me all the time (like the bike might be upside down while I deal with a flat or a tire change)

Here's the True Story that led to me starting this thread. I got a new crank on my MTB. In order to make that happen, the bike was horizontal in the back of the car for overnight, my wife took it to the shop, who knows if they had it upside down for some reason (doubt it), it was horizontal again to get home, and then it stood (upright) in the garage for two weeks before I got a chance to ride it.

That ride was yesterday morning. I took my time airing up the tires since it had been so long, rode a few donuts in the culdesac spinning the new crank and shifting through the gears, making sure that was all ok.

Then I headed down the hill to the main road.

At which point I discovered both my brake levers were 100% ineffective.

I had enough experience to start pumping like mad, and had a few seconds to decide to bail out, put my feet down, try to turn into the side wall, but fortunatley the brakes started coming back, and I was able to control my speed enough to make the right turn into the bike lane. And it was 7am on a Sunday morning, not a car in sight.

But I thought, hmm, maybe it's time to burp those brakes.

Greg R

Good to know about Shimano oil. I totally get the correct fluid; as a pastime I work with older or vintage automotive/truck and brakes, plus English Girling once in a blue moon on older American clutch systems. Great video presentation, now I have heads up what to look for.. Thanks!!

RubeRad

This video is also good. More aimed at newbs, so it's longer, but it also has a 'one minute' version at the end.

cxwrench

I tend to agree w/ this. I'll stand the bike up on the rear wheel, bounce it on the tire and pump the lever. This will generally cause the lever to go soft if there is air in the system. It's nearly always confirmed by removing the bleed screw and not seeing any fluid. The reservoir should be FULL.

RubeRad

Question: I was riding with a friend yesterday, and he was complaining of his brake levers traveling too far. I told him he should burp them. They are hydraulics that take mineral oil, but they are Tektro, not Shimano. Will the same funnel screw into the fluid port, and is all bicycle-hydraulic-brake-mineral-oil equivalent? Or does he need to get Tektro-specific supplies?

travbikeman

My TRP's use the same funnel as my Shimano's. My prior Tektro's (think they were 275's?) also used the same funnel. BUT, a prior Tektro I had, believe they were Aurigo's required a different connection and just a hose needed, not funnel.

travbikeman

OK, I just double checked and was wrong, the Shimano funnel does not fit the Tektro's. It does TRP's, You will need the connector here:

https://www.amazon.com/TEKTRO-Basic-...00771823&psc=1

Sorry about that, I must of confused it with our Shimano 200 brakes.

Darth Lefty 

It seems like you are fussing. The calipers feed bubbles to the hose. The master cylinder ports and reservoir do all the burping required when you pump the lever, that’s how they work, that’s what they’re for. Unless they are overdue for an oil change, or you are installing or removing them, or they are actually leaking, why would you open them?

RubeRad

Are you saying one of those little pieces would screw into the fluid port and allow the funnel to screw in? I don't want to buy a whole bleed kit (my friend probably wouldn't either). If it's not generally true that Shimano fluid&funnel would work with Tektro hydraulic brakes, I'll just recommend he take it to a shop.

travbikeman

No, the funnel does not screw into the pieces I had shown on the prior link. It's a separate kit....only $15 though.

But like Darth Lefty stated above, it's possible your friend just needs to pump the brakes a few times to get the fluid moving?

Iride01 

Seems like the first thing that should be checked when the levers travel too far is the rotor thickness and the pad thickness. If they are beyond their limits then the pistons might be pushed out to far and simply leak fluid which will bring in air.

I haven't had to bleed my 2 year old hydraulic brakes. I can tell that I'm getting more travel in the levers. But not spongy levers.

RubeRad

Yes, I did advise him the first thing to try is to spend a minute or two frantically working the lever while the bike is upright. I think he had just had the bike sideways in the car to get to the trailhead to meet us, and that might have contributed

Darth Lefty 

That shouldn't be. That's not how they work.

People have been complaining that Shimano brakes from the top half of the MTB lineup, M9000 and it children, have a "wandering bite point" pump up problem. Variously blamed on air in the caliper, dirty pistons, Servo-Wave, machining after anodizing, oil viscosity, and witches who live in the woods. The only common thread is that they say a lever bleed doesn't fix it. Which is a shame because everyone seemed to love Shimano brakes before that, and avoiding them screws up the whole i-spec system

RubeRad

Hmm, I hadn't heard of that 'wandering bite point' problem. I came to Shimano hydraulic brand loyalty after struggling with the 'turkey gobble' on some avid brakes.

Iride01 

Well how do they work.

While I know some earlier hydraulic brakes for bikes had reservoirs as do automobile brake systems, I was imagining the current Shimano brake systems as being a closed system with no reservoir and simply fluid in the lines, brake cylinder and their master cylinder in the levers.

So with no reservoir and no vent, when the levers are released the master cylinder should pull the brake pistons back to their original position. Unlike most automobile brakes that I've worked on that simply relax pressure on the pistons and they only move back an very tiny amount from the rotor.


Regardless, if my brakes are giving me troubles, I'd check the pads and rotors to make certain they are in spec first. Bleeding isn't a normal thing for brakes unless maintenance has been performed on them that allows air to get into the system.

I'll suppose that someone doing a lot of off road biking getting sand, dirt and other crap up on the rotors will eventually cause the seals in the piston to fail or score the cylinder so it will leak.

All the bleeding in the world isn't going to solve the problem then, they'll just continue to get air in them until the seals are fixed or the brake cylinder replaced...... IMO.

Darth Lefty 

https://cdn.sram.com/sites/default/f...s_overview.pdf

They still have reservoirs. That's the lump on top of the master cylinder. There's usually a bladder or something to keep air from mixing in the reservoir. Sometimes that's really obvious, like on all the SRAM levers. Sometimes it's hidden or clever. The new Shimano ones have kind of a balloon coming in from the outer end cap, but it seems like they don't encourage service of it and I can't find any photos. Not sure what my Tektros have. They're cheap. They might be open bath.

The timing ports in the master cylinder equalize the front side of the piston with the reservoir at top out.

The caliper pistons slide hardly at all in the seals, only a tiny bit at a time in response to pad wear. The seals have a square cross section and sit in a rectangular trapezoidal cross section gland, so the piston and caliper remain in static friction with the seals and the seals twist when the pistons squeeze and come back to the resting shape when pressure is released, pulling the cylinders back in. The amount of twist in the seals is what sets the bite point, the distance from the pad to the rotor. There's only ever enough extra oil coming in to fill the volume behind them so there's not really anything sucking them further back than that when the lever returns.

At rest, at top out, there is zero pressure. The master piston is equalized with its reservoir and the seals are not twisted and the pads are pulled back their set amount.

As the pads wear more fluid can come down from the master reservoir to fill the volume created when the pistons do slide in. That's really why there's a reservoir. So that bite point distance should remain pretty constant.

This is all done with a real minimum of parts, especially on the caliper end. It's really clever. Arguably simpler than cable rim brakes, especially considering the easy adjustment and minimal maintenance.

RubeRad

Really? that's interesting. Do you know of a video that gives a visualization of this?