I have a 2011 Tarmac SL3 pro with the red group, I replaced the stock cassette with a SRAM red 11-23 cassette. I have roughly 1000 miles on the bike. On Sunday I rode a century and about halfway through I noticed that I could not shift to my lowest gear on the rear. This happens in either of my front chain rings. When I push the lever it will make the shift, but when I release pressure it returns to the next higher gear.

After the ride I put the bike on the stand and played with the low limit screw on the derailleur but there was no change. It seems that the problem has to be in the shifter. It is not holding that gear position. Has anyone here experienced anything like this?

Barrel adjuster - not limit screw.

IMO, most likely a cable tension issue. You can check by pulling on the cable with your hand @ the downtube and see that it will shift into the lowest gear. You probably do not want to mess around with the LL screw next time because that could lead to bigger problems.

You can either fine tune by using the barrel adjuster or to get it 100% right...

- Manually shift to the highest gear (small cog) in the rear and small ring in front.
- Untension the cable
- Turn the barrel adjuster all the way in (clockwise) and then unscrew a quarter turn to half a turn (1-2 clicks).
- Retention cable, then fine tune tension by turning the barrel adjuster counter clockwise until desired shifting is met.

Also, your LBS should be able to service the cable issue for free since the bike is new if you are not familiar with adjusting the cable tension yourself. Usually, cables stretch within the first 500 miles or so, leading to the issue you are experiencing.

A $5 tip or 2 slices a pizza and I'm sure your mechanic will be glad to show you what he is doing when adjusting the cable tension if you do not know already.

Sorry - i should have mentioned everything I did. Years ago I was a bike mechanic so I know the basics. I did play with cable tension and that is not the issue. If I am in my second from lowest gear and I push on the dérailleur, it will move to the next gear and as long as I hold it it will stay there. If I do the same with the shifter it will stay in the gear until I release pressure on the shifter. The next stop is the LBS, but I would like to know if anyone has seen this issue with red.

Does the derailuer sit on the smallest cog when you have the shifter set to the smallest cog and give the shift cable slack?

Not here, I have close to 10,000 mi on mine, I've never even had to even tighten the cable on the RD in that time, but it sounds like something that SRAM's two-shifting-directions using one single-direction-lever design might be susceptible to over time with wear. Not at 1000 mi.

They're a great company. Take your bike to the shop, show them the problem. The shop may have to take the shifter off and send it to SRAM to inspect and repair or replace, but maybe the shop can get a replacement shifter shipped to them while you continue to ride i, then call you, and you can schedule a quick while-U-wait change, and not miss a ride, and then SRAM can examine the broken unit after the change-out. That would be best for your interest.

If the shop is SRAM-authorized to disassemble and replace a defective internal part on site under warranty, that should work too.

Unless evidence is found of abuse, you should get a new shifter or internal part replaced at no cost to you.

Did you install it yourself? You can install the cable through the rear derailleur wrong and have this happen (I learned this first hand). Look closely at the tech sheet and your routing.

Thanks - I will bring it by the LBS tomorrow.

I think it is right (I unboxed it, but one of the LBS guys routed the cables) - and it did work properly for the first 900+ miles, but I will take a look tonight.

The shifting was fine for 900 mi. You changed cogs, didn't have to touch the cable. The new cog could be the problem, e.g. some misalignment.

Put on the old cog, and see if it works. If so, the problem is in the new cog. That's always a good trouble-shooting lesson: reverse what you did, if possible, e.g. as in an elective part switch, and see what happens.

If the old cog now doesn't work, I would suspect your problem is a chipped-off or mal-forged/cast shortish tooth on the cable-spool mechanism in the shifter. Or else the spool-bearing may out of alignment, so the ratchet and spool teeth can't catch each other solidly.

I will put the old one on to check - but I replaced it at about 100 miles, so i doubt that is the issue.

Sure sounds a lot like cable stretch to me

Yea, SRAM Red comes with built-in HTFU.....Buy campy if you wanna be a pansy



lol

But OP said he did adjustments on the cable. I assumed he knew how to do this. If somebody hadn't done this, yes, cable tightening can be the issue. That or the stop screw.

BTW, I was having trouble on a bike after ca. 300 mi, I thought it was a cable/stop issue. It was a crap-design crank. I'm not that strong, but the crank loosened (and did it again afterLBS repair), and I had spindle free-play. I never saw that before, but you learn somethin new the longer you ride. I may demand a new crank. I can reset it, it's been the LBS doing it once and me twice in maybe 600 mi, but I shouldn't have to do this. It's an FSA crank.

Could be cable tension.

Are you missing/adding a spacer to the cassette? Can you shift past the largest cog (into the wheel) in the rear?

No spacers on Sram Red cassette's.

Start at the beginning its simple.
#1 Shift lever all the way down to the smallest cog
#2 remove cable clamp (turn in all barrel adjusters)
#3 Double check lever make sure its to the last gear selection
#4 remove chain if you can (if not it's ok but better to see)
#5 Looking from the rear set jockey wheel with limit screw so it lines up with the smallest cog.
#6 Push rear derailleur with thumb all the way to the largest cog and set its limit screw so it lines up with it.
#7 Check B screw if the clearance is not correct from jockey wheel and largest cog.
#8 Pull cable with fingers and tighten clamp on rear derailleur
#9 Using barrel adjuster remove any slack
#10 Shift up one gear if chain doesn't move to next cog turn barrel adjuster while spinning crank till it goes up one cog.
#11 Shift up one more it will shift to next cog.
#12 It's just a matter of fine tuning by shifting thru the gears and slight adjustment of barrel adjuster till it shifts well at this point all movement will be very small.
NOTE: If you do this and shifting does not work correctly you have other issues, bent hanger could be one, cable guide under BB is cracked or split some place or defective lever.