SRAM eTap Front Derailleur Adjustment

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goldmine848
Posts: 45
Joined: Thu Aug 12, 2010 3:01 pm

by goldmine848

I was watching a SRAM-produced video on setting up eTap. In the section on adjusting the front derailleur it says that adjusting the high limit screw while the derailleur is in the inboard position can permanently damage the derailleur. This seems odd to me since in that position the screw would be pushing against air. Can someone enlighten me on this?

by Weenie


Bliquid
Posts: 16
Joined: Wed Aug 23, 2017 9:50 pm

by Bliquid

Might be completely off but I wonder if it's because of what might happen when the derailleur then moves out rather than it being to do with the actual adjustment of the HL screw whilst inbound.

Depending on geometry and chainset there can be very little clearance between the derailleur and the DS crank arm (had this challenge both on my Canyon Ultimate and my SS Evo).

Basically, if you fiddle with the outer limit screw whilst its inbound and then shift into the big ring and turn the cranks you could knock the derailleur (LL screw) with the crank arm if it's incorrectly adjusted.

TobinHatesYou
Posts: 1372
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

You could probably damage the servo with the high limit screw preventing the cage from moving outward.

Also yes, clearance between the FD housing and the inside of the crankarm is pretty tight with some cranks and braze-on mount positions.

morganb
Posts: 539
Joined: Wed Mar 15, 2017 5:30 pm

by morganb

I have to run the tail of the derailleur more inboard than ideal to not hit the crank arm on my S3. 3D+ cranks.

TobinHatesYou
Posts: 1372
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

morganb wrote:I have to run the tail of the derailleur more inboard than ideal to not hit the crank arm on my S3. 3D+ cranks.


Yep. But it goes beyond the wide end of the yaw cage. If you back out the limit screws enough, the screws themselves can scrape against some cranks.

goldmine848
Posts: 45
Joined: Thu Aug 12, 2010 3:01 pm

by goldmine848

Thanks for the tips. I have been having some trouble dialing in the high limit. Have very occasional chain drops, maybe once every 100 shifts. Not sure why that would be.

TobinHatesYou
Posts: 1372
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Outboard chain drops can be the result of many things. I set my high limit very close...the cage is <1mm away from the chain in 50x11. If it's still dropping, yor derailleur may need to be rotated, lowered or possibly even raised slightly. The last adjustment seems counterintuitive, but it makes shifting overall slightly lazier with less of a chance to overshift.

As someone pointed out earlier, the correct angle for the derailleur cage almost puts it in contact with the crankarm as it passes the tail end.

If you are running compact gearing up front, you might need an angled shim. I'd say 90% of the time the shim makes shifting worse, so only try as a last resort.
Last edited by TobinHatesYou on Wed Sep 06, 2017 1:21 am, edited 1 time in total.

goldmine848
Posts: 45
Joined: Thu Aug 12, 2010 3:01 pm

by goldmine848

That's interesting. I think that the angle is correct since the marks on the derailleur line up with the top of the large chainring. But it does not look to me like the crank is in danger of hitting the trailing edge of the derailleur. I already have it a bit higher than the specified 1-2 mm, primarily because the top of the chain was scraping against the tab that is attached to the front edge of the outside of the cage.

I am running a 52/36 if that matters. Would you recommend changing the angle to put the trailing edge closer to the crankarm, moving it higher or just trying to get the high limit dialed in better.

by Weenie


commendatore
Posts: 181
Joined: Mon Dec 30, 2013 1:51 am

by commendatore

morganb wrote:I have to run the tail of the derailleur more inboard than ideal to not hit the crank arm on my S3. 3D+ cranks.


Same on my R3. Something went out of adjustment a few weeks back and they started to touch, rose home in the little ring.

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