Shifting and Derailleur Alignment Problem

[TheLastMariner]

Upon returning to my LBS yesterday to retrieve my MTB, I noticed that there was little or no clearance between the F Derailleur and the chain when the chain is shifted onto the middle chain ring (28/38/48). It's a great shop, so the mechanic put the bike back on the stand and tried to correct the problem. After many minutes of adjusting the Derailleur screws and the height of the Derailleur, the result of his efforts was that the shifting mechanism bypassed the middle ring altogether on the downshift. I could upshift to the middle ring, but the 'no clearance' problem persisted. I guess I could ride the bike and never use the middle ring. Should I simply disregard this "problem" as long as the bike rides smoothly otherwise? The entire drivetrain is new. Shimano crankset, SRAM 8-SP cassette, ZMC72S HG compatible chain, SRAM 3.0 FD, Shimano Alivio RD.

I'm wondering if I ordered the wrong F Derailleur because there are two versions of the SRAM 3.0 and one of them is restricted to 44T rings. Please share your thoughts on my situation.

 

[Retro Grouch]

It's easy to tell if your derailleur matches your big chainring. Does the curve of the arc on the outside of the cage match the arc of the chainring? If the derailleur looks kind of high with the heel of the cage almost rubbing the chainring, you've got the wrong one.

Assuming you have the right one, my advice is to start over with the installation. Check out the Park Tool website and follow their step-by-step directions. Front derailleur set ups can be touchy and every adjustment that you make can affect the subsequent adjustments. Once it's screwed up attempting a tweak here and a tweak there seldom works.

One last thing. What are you using for shifters? I've never fooled with a Sram front derailleur but, as a general rule, mixing brands of shifters and derailleurs isn't a good idea.

 

[daveornee]

Upon returning to my LBS yesterday to retrieve my MTB, I noticed that there was little or no clearance between the F Derailleur and the chain when the chain is shifted onto the middle chain ring (28/38/48). It's a great shop, so the mechanic put the bike back on the stand and tried to correct the problem. After many minutes of adjusting the Derailleur screws and the height of the Derailleur, the result of his efforts was that the shifting mechanism bypassed the middle ring altogether on the downshift. I could upshift to the middle ring, but the 'no clearance' problem persisted. I guess I could ride the bike and never use the middle ring. Should I simply disregard this "problem" as long as the bike rides smoothly otherwise? The entire drivetrain is new. Shimano crankset, SRAM 8-SP cassette, ZMC72S HG compatible chain, SRAM 3.0 FD, Shimano Alivio RD.

I'm wondering if I ordered the wrong F Derailleur because there are two versions of the SRAM 3.0 and one of them is restricted to 44T rings. Please share your thoughts on my situation.

3.0 Front Derailer from the SRAM site
Rear Compatibility 8spd / 7spd
Total Capacity 220T
Top-Middle Min. Capacity min. 10T
Top Gear Teeth 42T 48T Apparently there are two different versions, you should have the 48T one
Chainstay Angle 66 – 69°
Chain Line 47.5 – 51 mm
It sounds like you already know this, but your surmise about the wrong selection is part of the problem. If the arc isn't closely matching,,, as Retro Grouch already pointed out, you won't be able to make the proper adjustments. As Retro Grouch also pointed out, the Park Tool Repair site has details on the adjustment.... but so does the SRAM site.
Once you get the correct derailer you will need to get the height and angle dialed in.
I also wonder about the chain you are using. I am not familiar with that model number, but chain compatibility can be a potential issue.

 

[alfeng]

Upon returning to my LBS yesterday to retrieve my MTB, I noticed that there was little or no clearance between the F Derailleur and the chain when the chain is shifted onto the middle chain ring (28/38/48). It's a great shop, so the mechanic put the bike back on the stand and tried to correct the problem. After many minutes of adjusting the Derailleur screws and the height of the Derailleur, the result of his efforts was that the shifting mechanism bypassed the middle ring altogether on the downshift. I could upshift to the middle ring, but the 'no clearance' problem persisted. I guess I could ride the bike and never use the middle ring. Should I simply disregard this "problem" as long as the bike rides smoothly otherwise? The entire drivetrain is new. Shimano crankset, SRAM 8-SP cassette, ZMC72S HG compatible chain, SRAM 3.0 FD, Shimano Alivio RD.

I'm wondering if I ordered the wrong F Derailleur because there are two versions of the SRAM 3.0 and one of them is restricted to 44T rings. Please share your thoughts on my situation.

What is a ZMC72S HG compatible chain? What does that mean? Of the various Shimano chains I have (or, have used), without seeing it OR knowing all of Shimano's designations, I would take that desgination to mean that you have a 9-speed chain.

Regardless of the SHAPE of the front derailleur's cage, if the front derailleur TYPE (8-/9-speed/whatever) isn't matched to the chain, then you (i.e., your indexed shifter) will NOT be able to execute shifts properly on a triple crankset (unless you are using Campagnolo ERGO shifters on a ROAD bike).

Front derailleurs are pretty hard to trash (IMO) ... why did you change the one on your bike?

 

[TheLastMariner]

From the blueskycycling.com website:"The KMC Z72 8 Speed Chain is compatible with Shimano IG and HG systems..."

I suppose that retailer Blue Sky took that description straight from the manufacturer KMC, which is a Chinese bike parts company. Isn't HG an abbreviation for Shimano's 'Hyperglide?' Also, the derailleurs front and rear, were a definite upgrade from some low end (Shimano Tourney) components were problematic like ghost shifting and very noisy.

Thanks for all the responses. I think all that was necessary was a break-in period. Went on a 15-mile ride on Sunday and the bike performed well. The new trigger shifters and new derailleurs are o.k.