Are all braze on clamp adapters equal??

[bluebus200]

Trying to set up my new grx front mech with on my croix de fer. It’s working with a grx chainset. Front mech only came in braze on so I bought an mpart clamp adapter. Should be simple but I am finding that when the front mech is set up correctly it’s really close (nearly rubbing) the crank. This means it’s also pretty much impossible to use the 11/13 cogs without the chain rubbing the mech.

So do you think the adapter could be moving the mech too far out?

Also...I noticed there is no spacer on the bb (this is how the bike came. T’internet says there should be. 2.5mm spacer on the drive side of road bikes. So is the crank too far in board and thus too close to the mech

Confused. Com!

[Lazarus]

I think you have your own answer there
Fit a spacer move crank out 2.5mm and set it up that way.

I think I used the same part on my road bike and it worked fine

[stevenshand]

So do you think the adapter could be moving the mech too far out?

If the mech is setup correctly (correct position relative to the chainring) then it's still going to be in that same position no matter the braze-on adapter you're using no? Changing the adapter (or fitting a BB spacer) won't change the mech position relative to the crank/chain/chainring.

[Lazarus]

the BB spacer moves the crankout by whatever size it is so i whilst the mech remains unchanged the rings are further out so clearance is improved

I have assumed the mech is as far in as it goes and wont go in any further* - as i had this problem on a bike and fixed it with a BB spacer

* its either hitting itself or the bike rather than the adjustment screw

[stevenshand]

But the front mech is hitting the crank. If you move the crank out by 2.5mm, the ring also goes out and so you'd need to move the front mech by the same amount so it'll still hit the crank. I read it as an issue when on the big ring (chain rub on smallest cogs).

[Chew]

Post a few pictures up showing the issue.

It'll help with the diagnosis

[Lazarus]

@steve - yes despite even saying crank in my reply I assumed it meant rubbing the chainring and they just said crank for that
If it is as described you are 100% correct and what I suggest wont fix that at all.

As above pics needed to se whether crank or chainring

[bluebus200]

Thanks all....

Here's some pics

F413F06F-E93A-46D0-96F9-A19DBB9A63D1 by Chris Harris, on Flickr

D9BFDEF8-7025-4CFC-BA18-CA119D855AF3 by Chris Harris, on Flickr

87F7B75A-996B-440D-883A-9B20CDA84DE0 by Chris Harris, on Flickr

[Chew]

I'm assuming a GRX chainset is of the 68mm road variety so doesnt need any spacers.
I'm also assuming theres no lateral movement on the crank?

Looks like its just a case of adjusting the limit screws on the front mech?

[faustus]

I'm no front mech jedi by any means, but looks like the high limit screw needs reining in...don't think it should sit that far out once big ring is selected. It should nudge it on and settle back a touch, no? Is the mech a bit high too, can't tell from photo though...?

[bluebus200]

Yes it should be but if I adjust the mech away from the crank it then starts fouling the chain...

[bluebus200]

I'm no front mech jedi by any means, but looks like the high limit screw needs reining in...don't think it should sit that far out once big ring is selected. It should nudge it on and settle back a touch, no? Is the mech a bit high too, can't tell from photo though...?

It's 2mm from the top of the big ring... Yes you right about the top setting but it's either up against the chain or up against the crank... Weird!

[matt_brk]

I had alot of trouble setting my GRX front mech up because it's got the new style stabilising screw (that i'd not seen before).

Without setting the stabilising screw up correctly I got alot of rub as the mech flexed diagonally across the chain line. Once I correctly setup the stabilising screw, I could then get the mech to sit correctly and stopped rubbing.

Could be that without that setup correctly you're having to overcompensate with limit screws to avoid chain rub?

[fatbikephil]

Kind of looks like the mech clamp should be twisted round slightly as it looks like the cage isn't quite parallel to the chainline? Only a wee bit of rotation will help with clearance issues to the back of the crank arm. Arm to chainring clearance is fixed so spacers behind the BB won't affect anything.

[Areyoufeelingit]

I've just been fiddling with the same problem, but on a kinesis crosslight 5t. I ran into problems last weekend after fitting the GRX crank and trying to make it work with a 105 front cage - turns out that the crank is a couple of mm further out (to allow for fatter tyres). GRX front dereilleur and M Part clamp adapter arrived today.

Much more of a fiddle than any I've fitted in the past, but found these instructions. Had to go back a couple of steps (more than once) to follow the instructions to get it to sit right.
https://si.shimano.com/pdfs/dm/DM-GAFD001-00-ENG.pdf

Seems to be working smothely now - but still fiddling with the rear dereilleur.

R.

[bluebus200]

thanks all...I'll let you know how I get on..