getting the most out of (new xt) m775 disc brakes

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getting the most out of (new xt) m775 disc brakes

33 posts & 16 voices | Started 1 year ago by tom84 | Latest reply from U31

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tom84 - Member

Hello Forumites,

I have never been perfectly happy with these and it is driving me a bit spare.

I have recently upgraded to organic pads at the front which i hope will help, and i am yet to install goodridge hoses, so that is all to look forward to.

But they should be at least 'good' without these thing right?

The main area of consternation is the bleed though. I am meticulous, always start again if i worry that i still have bubbles, and use propriety fluid and proper tools, but i still can't get it to a satisfactory point. I can't even tell what that point is/should be, maybe my bleeds are perfect and i am just too heavy or something?

Neither are the shop bleeds i have had done been satisfactory really, i am going to another shop today to get their opinion. i might sit and watch them do it to check i am doing it all right.

I can say that the rotors (180mm back and front) are not contaminated and the seals are fine. they are very new.

Can anyone help? Magura?

Many thanks.

Posted 1 year ago #
Gnnr - Member

Hi Tom, what do you think is wrong with them?
It might help you get a better answer.

Posted 1 year ago #
bigyinn - Member

Im guessing you feel they lack power or are spongy?
Not an issue if they're all setup correctly.
When you bleed them is it from lever to caliper or vice versa? Bleeding from Caliper to lever is often quite effective at shifting stubborn bubbles. Another thing i discovered is to gently pump the pistons out and gently push them back in, but have the lever reservoir cover off, seems to shift stubborn clingons at the lever hose union. I managed to shift a few more bubbles by doing this and has finally seen off the pumping up that i used to get.

Posted 1 year ago #
belgianbob - Member

*Having just received brand new M775s, I'll watch this thread with interest*

Posted 1 year ago #
tom84 - Member

yeah spongy not that nice solid feeling, i'm nearly there on the back one, i definitely think that it is bubbles.

thanks for this bigyin. i do bleed from caliper to lever and have experimented with a kind of to and fro, lever to syringe and back again attack to come at it from both ends.

Posted 1 year ago #
mtbfix - Member

Try using an elastic band or toe strap to pull the levers in to the bar and leave it, sat upright on the floor, overnight. This will open the curcuit up and lets air into the reservoir. This did the trick in sorting out my hatchet job hose shortening.

Posted 1 year ago #
bigyinn - Member

After quite a while of playing about mine are ridiculously firm and the lever moves perhaps an inch, i'd like a little more lever travel but nice and solid.
Its the pushing piston in with reservoir cover that seemed to sort it for me.

Posted 1 year ago #
tom84 - Member

I went to have a go at a re-bleed and try the piston thing. When i did there seemed to be a unending amount of little bubbles coming out the left side of the inside of the resevoir on the r-hand lever. I was concerned about this so swapped it with a spare xt caliper and re-bled. I did this and the little bubbles did appear again but stopped. Feeling quite smug i tried the lever but it was still squidgy. i then started to bleed the other way (top down). Huge massive bubbles came into tube at the bottom, i couldn't believe it, i was so gentle and deliberate when bleeding the first time. After a while these bubbles settled down, but still the lever was squidgy.

My opinion is that I am not being thorough and patient enough. I convinced myself the air had gone on first evidence each time, so it is my fault. But at the same time, i am a person of average intelligence (when it comes to these things) and average patience, and the care that is required to get this right seems excessive. I gave up in the end.

Other things that are on my mind is the 'free stroke' screw was turned all the way in when i did the bleeding, and possibly air is coming in through somewhere else....?

grrr!

Posted 1 year ago #
Northwind - Member

Mine have always been really easy to bleed, then again, I'm used to motorbike brakes and that's basically what they are, simple open top brakes. But I did have a caliper seize up, so replaced it with a £20 XTR one that came with £10 worth of pads. Otherwise very pleased with them, they don't quite have the power of my Oros but then the Oros don't quite have the subtlety.

Oh, and the free stroke screw as far as I can tell does nothing.

Posted 1 year ago #
johni - Member

Try MTBFIX's suggestion. It has worked for me too. I've never really had trouble with bleeding Shimano brakes though.

Posted 1 year ago #
bigyinn - Member

XTs can take quite a few go's to get them just so. Keep at it and it'll come good.

Posted 1 year ago #
tom84 - Member

i almost sold them today but have been watching the shimano youtube video, hilarious voiceover, and have made a slight improvement, still a long way from solid, levers bite, then go a good 2cm further when pulled. both are now tied up with the caps off over night. i guess no matter how hard you try, it won't happen until you get it right.

thanks for above help and support, i was very exasperated, almost -dare i admit it?- upset at one point.

Posted 1 year ago #
bigyinn - Member

Keep at it and they'll come good.
I've also been known to take the caliper off the frame and let it hang vertically down from the lever to help the little bubbles make their way to the lever. A little tapping to help them on their way wont hurt either.

Posted 1 year ago #
cynic-al - Member

Ooops mis-post.

Posted 1 year ago #
hora - Member

Jesus I think I'll keep the SLX's (different bleed circuit) order going then- I was thinking of swapping them for the XT's

Posted 1 year ago #
scruff - Member

AHH, the free stroke does affect bleeding. I took mine to a shop as I couldnt get them working, mechanic (the one at Glyncorrwwiggg) told me the screw was all the way in or out (I cant remember which) and they wont bleed properly like that. So, put it halfway.

Posted 1 year ago #
mieszko - Member

My mate had a go at bleeding mine. His SLX feel very good and solid, but my XT's were soft and spongy. They felt worse than my old LX. Took the brakes to The Bike Chain, they did a great job and now I'm pretty impressed with how the brakes perform. Most powerful and best control of all the disc brakes I owned before.

It seems You need to keep bleeding them until they work as they should. Also I started using organic pads and they do feel much better than standard pads I had.

Posted 1 year ago #
Grimy - Member

Oh, and the free stroke screw as far as I can tell does nothing.

Turning the freestroke ajuster screw anticlockwise allows the cam roller attached to the end of the master cylinder to travel further into the wave slot machined into the lever. This ensures more fluid is displaced per degree of lever travel until the cam moves back across the wave slot to the power side, effectivly increasing leverage once the pads are in contact. It absolutly does work and has a marked effect thats like night and day. Trouble is, the instructions are flakey, the grafix can be percived to be backwards, and not everybody understands how to adjust them correctly. Take a couple of minutes to look at the cam mechanism and how the screw limits the cam travel, and youll soon realise whats going on, and that the reach adjuster may also need tweaking to make the most of it. If you still cant percive a stark differance, then perhaps something else is wrong, air perhaps?

On a side note, you should have the freestroke adjuster screw turned quite a way anti-clockwise when bleading the brakes, as this will push the most amount of fluid per pump, helping to flush that air out.

Posted 1 year ago #
hora - Member

Grimy for £26 difference would you get the XT's over the SLX?

Posted 1 year ago #
Grimy - Member

Hora - Come and have a go of mine and make your own conclusions. Personally, for £26, hell yea. (I'm in all day today)

Posted 1 year ago #
hora - Member

I've got a better idea. I just buy the XT's and I pop them round you show me how to turn the bite-adjustors as I cant get my head round on your description above. (unless I can figure it out in person)

I've also got alot of time for mieszko

Posted 1 year ago #
Grimy - Member

no worries

Posted 1 year ago #
hora - Member

Thanks grimy - sent you an email as well previously hope the other half is ok now

Posted 1 year ago #
bigyinn - Member

Grimy, you sure about the freestroke screw? Just to be clear its the silver screw in the black part on the top of the lever at the end of the reservoir.
If you look at it, it pushes onto the end of the master cyclinder and not the cam. Looks like it expands or reduces the chamber size.
Sure you're not getting confused with the cams on the old servowave v brake levers?

Posted 1 year ago #
SpokesCycles - Member

Hmmm. I bled mine 2 days ago (I'd smashed the reservoir cap so loads of air was in there).

Are you closing the bleed nipple and pumping the lever every 15ml or so of fluid (you'll need the bleed block in obviously)? And have you completely flushed the fluid through so it's only new fluid appearing? I've filled mine with Total mineral oil which is BRIGHT green so very obvious when new fluid is appearing.

Without actually seeing what you're doing it's hard to say as it could be you or you could have a duff set that to be honest just need sending back. Get your bike shop to speak to Madison, I'm sure they'd be helpful. We've had similar problems with sets of Giant's MPH brake and they just send out new sets when there's a situation like this.

Posted 1 year ago #
Grimy - Member

Bigyinn, Your absolutly right The freestroke screw actually pushes on the end on the master cylinder, limiting its return travel when you let go of the brake. If screwed all the way in, the piston cant travel far enough out to allow the cam to move right across the wave slot. Although the screw dosent act directly on the cam, that is indeed what is being adjusted. Changing the chamber size of the master cylinder has no direct affect on the brake operation, its just a means to an end.

Posted 1 year ago #
Oscillate Wildly - Member

my rear xt brake has never felt solid like the front one, its always felt spongy, and the front brake feels amazing and solid, but its felt like this from day one from a trained mechanic who did them should i go and get it bled again to make it solid? i assumed it was just normal to be honest without thinking to much of it....then when it gets wet its almost touching the bars, whilst the front one stays firm with a real great feel....owned 6 months and never touched, other than cleaned etc, but the spongy feel has felt like that from day one any ideas?

Posted 1 year ago #
bigyinn - Member

Read the thread from the beginning and follow the suggestions on it.
Try strapping the lever to the bars for a couple of days, help the bubble migrate back to the master cylinder. Give a tap every now and then to help shift the bubble, but deffo go for a re-bleed first.

Theres some gems in there....

Posted 1 year ago #
hora - Member

I used to do this periodically on my Saints. Worked wonders.

Posted 1 year ago #
bigyinn - Member

Thought your saints were crap these days Hora?

Posted 1 year ago #
13thfloormonk - Member

Not having used these brakes I can only be of so much help, but:

My old XTs always feel rubbish after a bleed. A couple of days riding seems to see them right, and they remain good for a long time after. Perhaps next time you bleed you should give them two or three good rides before deciding?

Also, I thought a consequence of the servo wave system was a spongy lever?

Certainly on my old V-brake levers, you could set them up with loads of modulation, at the expense of lever firmness. My XT hydraulics are wound in very close to the bars which gives a similar feel, and also have slightly spongy levers.

Posted 1 year ago #
hora - Member

I used to do this
bigyinn- I started to realise when I borrowed someones disc-braked Shimano-basic hybrid-disc bike from work. His brakes were AMAZING compared - sharp, immediate and powerful whereas mine felt like they were covered in engine oil.

The last straw was this weekend when I had 4 fingers gripping in the rear with nothing happening!

Posted 1 year ago #
U31 - Member

Ellaccy band and burping work wonders.
Pads out/ pistons in while bleeding from calliper to lever, then top cap on while still injecting.. then as you nip up the bleed nipple a gentle push on the lever to send a little fluid out

Posted 1 year ago #

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