Shimano bleed

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flag Will022505
Posted: Jan 9, 2021 at 23:02 Quote
Have a set of M9120 4-pot XTR brakes. after about a week the front brake master cylinder broke and was replaced under warranty since then, I've noticed that the front lever has way less throw than the rest before grabbing. I've noticed that this doesn't occur on many other shimano's I've ridden, is this just down to the bleed? Any techniques to help equal out the throw? Thanks guys!
flag Reaperactual
Posted: Jan 10, 2021 at 0:26 Quote
One possibility could just be down to a different freestroke adjust setting on the new lever?

You can try to rotate the freestroke adjust screw anti clockwise, the lever will start to move (away from the bars) then reset lever back into it's original resting point using reach adjust knob which will bring bite point towards the bars.

Another possibility is a bleed after the lever was replaced without a bleed block which would have put more fluid into the sytem (overfilled) and bought the pads a bit closer to the rotor?

For this you can unmount caliper and remove pads then open the lever bleed port screw. Wrap a rag around the lever or screw a bleed funnel on to catch any excess fluid while pushing the pistons fully back into their bores. Fit a bleed block then top up fluid, replace lever bleed screw and refit everything as normal.
flag vercorin1
Posted: Jan 10, 2021 at 1:50 Quote
Yep all that is right. If you did not replace the lever and master cylinder then all sorts of things could have been done or not done by the tech that did it. But also note that XT and xtr are notorious for relatively random bite points. I have had a lot of shimano hydraulic brakes and in comparison with hope and sram, they are good in many ways, but the random bite point problem is a known one, and something that other brakes are not so prone to. Personally it doesn’t bother me, I just get used to it. The self bleed design when the bike has been turned upside down, laid down or transported is a good one, but seems to be the main reason for the wandering bite point.
flag Reaperactual
Posted: Jan 10, 2021 at 2:17 Quote
Ditto on my rear SLX. Tried (nearly) everything, given up. Not wandering more two distinct bite points, normal then less lever travel 'ramp up' after a few pulls. Living with it too. Rolleyes Hopfully an easy fix for the OP and not the wandering issue.
flag Lando406
O+
Posted: Jan 10, 2021 at 7:55 Quote
Shimano’s wandering bite point led me to Hope brakes. Never looked back. Lots of people want to buy Shimanos, so I was able to sell them while they were still on my bike.
flag Danzzz88
Posted: Jan 10, 2021 at 8:27 Quote
I had m9120 brakes previously now running m9120 levers and Magura calipers. I had no wondering bite point with either setup, prior to those I had Hope V4's and found they are considerably less powerful. I think a lot of this is setup and bleed, you should spend a lot of time bleeding properly, say 30mins per end, tapping the lever and caliper occasionally and sucking and pumping the fluid back and forth whilst watching for air bubbles to escape. I know even when I was bleeding my Hopes you can be there for 10mins bleeding then suddenly you tap the caliper and a large air bubble will appear. But as for wandering bite point never had that, did have it with a really old generation of Shimano XT's back before they change to the new cylindrical style master cylinder. As for the front brake engaging sooner, that is almost always the case with any brakes due to the shorter hose length to the front compared to the rear so there is less 'flex' in the overall system. Bleed it again and play around with the freestroke adjust, make sure the caliper is centred properly over the rotor and use bleed blocks.
flag m1dg3t
Posted: Jan 10, 2021 at 17:27 Quote
Danzzz88 wrote:
I had m9120 brakes previously now running m9120 levers and Magura calipers. I had no wondering bite point with either setup, prior to those I had Hope V4's and found they are considerably less powerful. I think a lot of this is setup and bleed, you should spend a lot of time bleeding properly, say 30mins per end, tapping the lever and caliper occasionally and sucking and pumping the fluid back and forth whilst watching for air bubbles to escape. I know even when I was bleeding my Hopes you can be there for 10mins bleeding then suddenly you tap the caliper and a large air bubble will appear. But as for wandering bite point never had that, did have it with a really old generation of Shimano XT's back before they change to the new cylindrical style master cylinder. As for the front brake engaging sooner, that is almost always the case with any brakes due to the shorter hose length to the front compared to the rear so there is less 'flex' in the overall system. Bleed it again and play around with the freestroke adjust, make sure the caliper is centred properly over the rotor and use bleed blocks.

Why the hell would you draw contaminated fluid out and then force it back in? That has to be the stupidest thing I heard today. Syringe on the caliper with fresh fluid, funnel with some fluid on the master. Push fluid through using the syringe while manipulating the lever and tapping the master.
flag Danzzz88
Posted: Jan 10, 2021 at 18:14 Quote
Obviously I mean after flushing the dirty shit out or in the case of buying new brakes it's irrelevant. I like to think common sense applies and that if someone is capable of bleeding brakes they have at least enough intelligence to know they need to flush the shit out first. Once shit is flushed out, proceed to bleed in both directions if that makes it clearer.
flag jase111171
Posted: Jan 10, 2021 at 21:50 Quote
Only gravity bleed Shimano brakes.NEVER use a syringe.Watch how the Syndicate pit team do it.Perfect bleed first time every time.
https://m.youtube.com/watch?v=piWBVDh1pTE
flag vercorin1
Posted: Jan 11, 2021 at 0:07 Quote
Obviously the key difference between Hope-SRAM and Shimano is the use of DOT in Hope and SRAM and mineral oil in Shimano, DOT absorbs water from the air, mineral oil does not. So after a while you have to do a full bleed to get contaminants out. Other sources of contamination are there in the mineral system - mainly any products of minor seal breakdown and fine participle of dust entering past the caliper seals. But to maintain hydraulic action DOT needs replacing more frequently than mineral. It doesn’t matter whether you bleed from the back up or top down - the system doesn’t know this - all it ‘knows’ is whether it has air in it. Where the air IS matters - if at the top you can tap it out of the hoses with the top up cup in place, watch for bubbles (always more than you think) and make sure the master is full. Worst place and most irritating is in the caliper, behind the pistons. Both top down and bottom up bleeding can still leave some lurking there. I lean the bike to get that lump of air out into a syringe and then bleed upwards and/or downwards to get the air out of the lines. Always end up with rock solid brakes and don’t use excessive oil/DOT.
flag Reaperactual
Posted: Jan 11, 2021 at 0:08 Quote
jase111171 wrote:
Only gravity bleed Shimano brakes.NEVER use a syringe.Watch how the Syndicate pit team do it.Perfect bleed first time every time.
https://m.youtube.com/watch?v=piWBVDh1pTE

Just another method of a fluid flush, nowt special, just messy and because a race team are doing it that way don't make it the only way it should be done.

My little bleed nipple cap has never come off and got dirt in it, if it did that dirt would end up in the funnel along with the rest of the old fluid. 2 cents
flag jase111171
Posted: Jan 11, 2021 at 9:16 Quote
Reaperactual wrote:
jase111171 wrote:
Only gravity bleed Shimano brakes.NEVER use a syringe.Watch how the Syndicate pit team do it.Perfect bleed first time every time.
https://m.youtube.com/watch?v=piWBVDh1pTE

Just another method of a fluid flush, nowt special, just messy and because a race team are doing it that way don't make it the only way it should be done.

My little bleed nipple cap has never come off and got dirt in it, if it did that dirt would end up in the funnel along with the rest of the old fluid. 2 cents
yes it is,but after trying that method,I'd never use the syringe method again.its so much easier and the bleed is far better.It is a little messy,but nothing is extreme.This method is easier for a novice aswell.
flag Danzzz88
Posted: Jan 11, 2021 at 9:34 Quote
I bleed my Shiguras in both directions and they work perfectly, no bite point issues or trapped air...in fact I never had any problem with the bleed on any brakes I've owned to the extent I can run them for a couple of years only needing to change pads. I think people need to spend more time bleeding their brakes to ensure all cavitated air is out, which is part of the reason to bleed in both directions to not only fill the system with fluid but to create a vacuum and suck through any cavitated air...once it appears in the syringe tilt the syringe up and let it rise to the top behind the fluid in the syringe then proceed to push the fluid back through back and forth many times. Like I say I never had problems doing it tbis way and can't see any logical reason why it would cause a problem unless you had fauty seals somewhere in the system drawing air in under suction, in which case it's not the bleed method that is the issue but faulty seals / brakes.
flag Reaperactual
Posted: Jan 11, 2021 at 10:50 Quote
jase111171 wrote:
Reaperactual wrote:
jase111171 wrote:
Only gravity bleed Shimano brakes.NEVER use a syringe.Watch how the Syndicate pit team do it.Perfect bleed first time every time.
https://m.youtube.com/watch?v=piWBVDh1pTE

Just another method of a fluid flush, nowt special, just messy and because a race team are doing it that way don't make it the only way it should be done.

My little bleed nipple cap has never come off and got dirt in it, if it did that dirt would end up in the funnel along with the rest of the old fluid. 2 cents
yes it is,but after trying that method,I'd never use the syringe method again.its so much easier and the bleed is far better.It is a little messy,but nothing is extreme.This method is easier for a novice aswell.

I'm not dissing this method at all and will likely try it seeing as I've tried every method in the book to ensure a good bleed.

At this stage 2 years on I still don't know how to stop wandering bite point but I can safely say it has nothing to do with a bleeding issue, in my case at least.
flag vercorin1
Posted: Jan 11, 2021 at 12:15 Quote
Having had many many sets of Shimano, and still running them on many many bikes, and knowing inside out how to rebuild and bleed brakes, I concur with the Reaper. They wander. The reviews say they wander. And they do. It's fine. You get used to it. But they do.
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