How do I adjust free stroke on XT M775 brake levers ?

BG2000

My question is as per subject...

Just to clarify, the M775 levers are the Dual Control version. I want to adjust the 'bite point' and not the lever reach.

I currently only need to make the tiniest squeeze on the front brake lever to activate the brake (I'm talking millimeters). I don't want it to be this 'tight' and would like a little more 'give' if you know what I mean. Also, you need some movement in the lever to get past the 'diagonal' section of the 'Servo Wave Mechanism'. The stroke is so short at present that it only gets half through the initial part of the servo.

I've gone through Shimano's Tech Docs, and they only show how to adjust the lever reach: http://techdocs.shimano.com/media/techd ... 688493.pdf

I've noticed a red anodised adjuster ring surrounding the lever's hydraulic push rod where enters the lever body. I've tried turning this in each direction, but it makes no difference. And I'm wary of adjusting this part as it doesn't appear to be documented anywhere, and I don't actually know what it is !

flowpro

Don't know if the XT775 are the same as the XTR975 but if they are then it sounds like they are over bled. Lose a little fluid and they will easy up.

It's a bit of a black art you will only need to lose the smallest amount of fluid.

Best bet is to lose the fluid from the caliper end rather than the res as you might lose to much and have to completly re-bled.

If you need help let me know as it's a really easy job but there is a method to follow.

nicklouse

see the red small to large "swooch" above the adjuster screw?

The Northern Monkey

ahhh.... the little screw that maks no difference whatso ever

Northwind

Yup, mine do nothing as far as I can tell.

nicklouse

well i think we have a set at the shop so i will have a play later.

Dirtydog11

I think its one of the reasons the XT brakes dropped points in the recent brake test.
Its strange Shimano don't provide any details on how to adjust it. It appears to be some sort of stop/limit screw for the master cylinder.

I've not tried adjusting mine but will follow this thread to see how things develop.

jairaj

+1 for the "they don't do much."

nicklouse

right they do do quite a bit.

but they do not really do what you would expect.

oh and i dont like the way they work.

will write it up and post again in a bit.

The Northern Monkey

I'd be interested to know what they do do

I had them on the saints too, but again didn't notice any difference

nicklouse

right these are arse over tit.


first have the screw fully in. and pull the lever a few times. if you have a spare body get them to do this while you have a look at the pads and how much (or not) they are moving. then have a good feel of the lever and if you can watch the pads.

Ok you know what is happening now..


now to the screw.

if you unscrew the cross head screw you will see the lever move away from the bars !!!!!!!

err i thought that the adjuster on the lever was for reach....

Ok pull the lever a few times. so how does it feel now? the same or different? how far is the lever pulling more or less. where is the "stop" point?

now have a look at what the pads are doing. the other body should be back from the fridge with a cold one by now.

Oh i would say unscrew the screw by quite a lot (8mm) or you may not notice anything

what seems to be happening with the screw is that it is increasing the throw of the lever action so that the brake is started to be applied earlier in the stroke and further away from the bars. BUT the stop point stays the same.

so for a longer throw and a closer stop point you would have to move the reach in and the free stroke screw out.

but is is a bit more complex than that is that we seem to remember something that Mr Shimano Nordic said about a two stage braking system... where the first part of the stroke is a low pressure movement and the second stage is the power stage and this screw seems to play with the balance point. not convinced.

anyway Ben could you play with your screws and see what you think.

Dirtydog11

Nick,

I've been messing around with mine and I think it relates to where in the stroke the power comes in.

I think these brakes are designed to give a non linear power delivery. The power automatically ramps up for the same given lever pressure depending on its position, its an adaptation of Servo Wave.

If you look under the lever body you can see an L shaped groove which looks like it actuates the cam mechanism. As the lever passes the right angle of the L shaped groove the cam is activated and power is increased, by unscrewing the stroke adjust screw the lever remains 'off cam' for longer.

I've not had a chance to ride it to see if I can feel any difference in the way the power is delivered but it doesn't appear to make any difference to pad/rotor clearance or the amount of lever throw. It would also explain why, on the face of it, they don't appear to do much.

BG2000

Hi guys,

Thanks for the replies - but you're all talking about the wrong levers - it's Dual Control M775 I've got:



I think flowpro's suggestion that they're 'over-bled' sounds feasible - so I'll give this a go.

But if anyone else has experience of these levers, please let me know about the free stroke adjustment.

nicklouse

opps. yes there is no adjustment on them

me and my BL-775 and ST-775

before a re-bleed just try pushing the pistons home and resetting them again by pulling the levers a few times.

BG2000

Thanks Nick,

That's a shame about adjustment. CRC clearly states: " Adjustable free stroke enables you to fine tune the amount of lever pull before pad and rotor engagement". I'll ask them for their comment.

I think Shimano just call both levers 'M775' which is effectively the caliper code. Mine are certainly the rarer of the two. Everyone stares at them wondering what the hell they are, even in bike shops !

I'll try giving the pistons a shove backwards. I'll need to remove my reservoir cap first as it's rammed full of fluid with no air gap, which may explain why the pistons are sitting in their current position.

It probably doesn't help that the Shimano yellow plastic piston spacer I use when bleeding isn't as thick as a pair of new pads plus rotor.

At least having too much fluid is better than having air in the line. I think my brake bleeding technique is too efficient, which is good of course.

nicklouse

and my and my typos....

just corrected it 775 is the version the BL and the ST designate the use,

BL Brake Lever and ST errr no idea but like the road lever/brakes as STI i guess similar.


yes it does sound like too much fluid from what you say about the spacer.

BG2000

nicklouse wrote:

.


yes it does sound like too much fluid from what you say about the spacer.

Yeah, the problem is when you use the spacer to bleed before fitting new pads. If the spacer was the same thickness as new pads + rotor + 1mm then it would set the pistons in just the right place. Odd one that...though with Shimano there's usually a good reason...

BG2000

Just to throw a spanner in the works, took the following photo of my lever at the weekend:



So back to my original question, how does this free stroke adjustment work, which bit am I supposed to move and is it documented anywhere ?

The Northern Monkey

nicklouse wrote:

*snip*

anyway Ben could you play with your screws and see what you think.

sorry nick I missed this.... I shall have a play tomorrow after work, i need an excuse to get out

nicklouse

BG2000
I would say just the same as i have explained above.

BG2000

Is it possible I'm the only BikeRadar member with these levers ? I do have a taste for odd bike parts !

I didn't notice any change when I turned the red dial. But I'm hesitant to undo something I shouldn't. I'm going to try contacting Shimano again.

Dirtydog11

BG2000 wrote:

Is it possible I'm the only BikeRadar member with these levers ? I do have a taste for odd bike parts !

I didn't notice any change when I turned the red dial. But I'm hesitant to undo something I shouldn't. I'm going to try contacting Shimano again.

I've given my take as to what I think they do, I suspect yours will be the same only the adjusters are in a different place.

If you hear from Shimano I'd be interested to know what they say. Its strange, there's very little info on the subject and nothing on the Shimano site as to how/what the adjustment achieves.

knightrider3000

The tighter u screw in (clockwise), the lesser the distance between pads and rotors.
In other words, with just a bit of a squeeze of the lever, pads will grip the rotors and braking is done.
Correct me if im wrong. This is what a SHIMANO Certified mechanic told me

BG2000

Thanks for the reply.

Well, if I ever meet anyone from Shimano, I'll ask them to demonstrate that to me, as it's near impossible to turn the dial. You need finger nails of steel - and there's certainly no tool that would fit inside. If I was desperate, then a screwdriver and hammer would probably move it. But I don't like tinkering without official manufacturers instructions - makes me think the whole thing was an afterthought. It's most unlike the Japanese though, especially considering the near perfection of all other XT/XTR bits...

supersonic

I dodn't think an open system could be adjusted that way.

I think Nick has it right - the adjuster alters the mechanical leverage to the master piston.