XT V brake levers (M739) - adjustment questions

[petitpal]

Was busy stripping and rebuilding my M739 XT V brake levers prior to fitting last night and noticed that above the cam (on the lever) there's a bit of black plastic with a tiny screw holding it in place that. It looks like this is used to limit the movement of the cam in it's slidy channel and I'm just wondering what that's actually for. This is the first set of XT V brake levers I've owned - used to ride with Avid SLD 2.0s (or something like that). Is the cam movement limiter thingy just a hark back to the days when V's were still new technology and allowed the levers to be used with cantis?

Can't actually test the effect yet as still trying to sort out a stem, cables, brake shoes, crown race collars, etc, etc

See what retrobike has reduced me to? Spending my Sunday nights with a toothbrush, a tin of GT85, a set of allen keys and a V brake lever!

 

[drystonepaul]

The M739 V brake lever originally came with two of those plastic bits in each lever to limit the movement of the servo wave roller cam thing.

Basically the more bits you remove the greater the braking power at the end of the lever stroke. This only works if you set the brakes up so you bite point is at least a third of the way through the lever travel.

The idea is that the first part of the lever stroke pulls alot of cable with a low leverage force, and then as the roller cam mechanism comes into effect there is less cable pull but more leverage and more power as the brake pads hit the rim.

There was a warning on them too stating that by removing both of the plastic bits then you'd get huge amounts of power which in the hands of an inexperienced rider could cause instant death and the extinction of a rare butterfly or something. (I paraphrase of course).

In practice I've always run my M739's without the plastic bits since 1997. I'm still alive and they give a very powerful if slightly mushy feel at the brake lever.

As far as I know there have been no extinctions as a direct result of this.

 

[petitpal]

Quality reply, thank you. So - out of interest - roughly how far away from the rims do you run your brake blocks then (assuming new shoes)? I always used to set my Onza HOs up with minimal clearance from the rim but from the sound of it this would give problems with Vs.

Also, what shoes do you use? Straight XT ones or something koolstop-ey?

Thanks
Paul.

 

[FluffyChicken]

They work as mentioned above and that warning and usage is still the same in the current M770 XT lineup.

Set everythign up as normal, then use the barrel to adjust the distance and get the point of contact setup for you. It's when it hits the rim that that extra force pulls the roller thing inwards. There is no specific point (unlike the servowave before hand under SLR Plus of M900 and XT/DX a bit later fame where it follows a route iirc, but that's for traditional super low profile canti's, e.g. M900/M737 cantis and not 'V')


Onza HO's are canti, if so then if you used the M900 era servo-wave with them you'd get a better setup and not need them so close. It's a best of both world approach, I beleive DiaComp PC-something or others are similar.

Grab the M770 manual from shimano website and have a read for how they are setup.

 

[dyna-ti]

Quality reply, thank you. So - out of interest - roughly how far away from the rims do you run your brake blocks then (assuming new shoes)? I always used to set my Onza HOs up with minimal clearance from the rim but from the sound of it this would give problems with Vs.

Also, what shoes do you use? Straight XT ones or something koolstop-ey?

Thanks
Paul.

Sometimes you just have to go on faith

 

[petitpal]

Grab the M770 manual from shimano website and have a read for how they are setup.

Solid advice, thanks. I didn't even think of that - presumably because everything has changed so much in the past 'x' years and modern kit is sooooo much better :roll: )

Sometimes you just have to go on faith

Last time I did that it ended up in a tree

 

[DegsUk]

Great posts Ive just cleaned my levers and they have no adjustment bits , but can they be still bought ?