View Single Post
Old 12-24-13, 10:36 PM
Andrew R Stewart 
Senior Member
Andrew R Stewart's Avatar
Join Date: Feb 2012
Location: Rochester, NY
Posts: 11,867

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1825 Post(s)
Liked 78 Times in 60 Posts
There is no linkage between what the limit screws do. One only can effect the outer travel as the other can only change the inner movement. Yes, the cable tension is important. And the front sprockets are usually called chain rings.

So lets get down to basic set up. The first thing i do with Ft ders is to not use the shift lever to move the der during initial set up. I do this by pulling on the cable part way along the down tube. why? Because this separates the "raw' adjustment of the ft der from the lever's built in cable moving function. Set the ft der at the right height off the large ring when the cage is moved so it's outer plate is even with the large ring. The outer cage plate's lower edge is usually about 2-3mm's above the large ring's teeth. Then rotate the der/cage on the frame so it's about parallel to the rings. This is one of the set up aspects that often needs trial and error to get the best position. But this fine tuning starts after the initial set up. Attach the cable to the anchor bolt on the right side of the bolt (The failure to do this correctly will cause all kings of rubbing issues). Then shift into the large cog (easy gear) in back and place the chain on the inner ring. Turn the inner limit screw so the inside or the inner cage plate JUST clears the chain. Shift into the smallest rear cog (high gear) and "shift" (and by this I mean pedal and pull the ft cable by hand to move the ft der outward) onto the large ring. Turn the outer limit screw so the inside of the outer cage plate JUST clears the chain.

Now begins the fine tuning. I still will do the der moving and fine tuning by pulling the bare cable, the coordination with the shift lever waits for now. Shift the rear back into the large cog. Try shifting (pedaling of course) the ft up and down onto and off the middle and small rings. Note how easy the up shift is and how quick the drop down to the small ring is. Shimano ft shifting with STI levers is so abrupt that to prevent overshifting down (and dropping the chain onto the BB shell) you might have to limit the der's inner travel so much that the chain has a slight rub when on both inner cogs (large rear and small ft). Next move to the rear small cog and shift from the ft middle to large and back (yes this means that you'll be holding the cable enough to not shift onto the small ft). What i watch for is how the chain rides up on the large ring's teeth before settling down into them. When i look down from above (my head will often touch the seat) I can see the chain's flexing and side to side movement during the up shift. You want to have a complete up shift with out dropping off to the outside. (Again with STI you sometimes have to accept a BCH of rub when in highest gear to prevent overshift and chain drop). This is the step where ft cage rotation is most sensitive. If you try to slightly change the cage rotation (and parallelness to the rings) then you have to back to the adjustments of the small ring before you can go back to the adjustments of the large ring travel.

You can see how there can be a lot of back and forth between cage rotation and inner/outer limits. Of course with experience this process goes quickly and without it can be frustrating. Especially if you forget to reestablish the inward movement before continuing the outer movement adjustments. Once you think both "ends" of the ft shifting are equally good then move the chain to a Central rear cog and repeat the ft shifting, but now across all three rings.

In an ideal world you won't shift onto the granny ring unless you are already half way up the rear cogs and likewise won't shift onto the large ring unless you're off the easy rear cogs. But the middle ring should hopefully be able to be used with all the rear cogs.

After all this trial shifting by using the cable only and the fine tuning to get the best shifting performance across the ranges now it's time to get the shift lever in play. To use the shift lever before this point often only confuses and hides issues with the basic der set up and fine tunings. Go back to the start with the rear large cog and small ft ring. Reattach the cable (note proper manor) and while tightening the anchor bolt pull the cable tight (of course the lever should be in it's lowest position). Now shift the lever to the middle position while pedaling and release. The chain should climb up onto the middle ring. If your lever has a middle position trim feature the der will likely have a touch of inner cage plate rub. Trimming the lever BUT still maintaining the middle shift position should eliminate all (or the vast majority) of the rub. Many riders don't understand the trim function or can feel it. THIS IS IMPORTANT TO LEARN HOW TO DO. If there is a lot of chain rub after trimming the lever then the cable needs to be slightly looser. If no rub then tighten the cable till is almost does rub. This tension adjustment can be done with a casing barrel adjuster or with the cable anchor bolt. But keep in mind that allowing the cage to move inward now will also keep the cage from moving outward for the large ring's shift. So next shift the chain into the smallest rear cog and try lever shifting the ft onto the large ring. If the cable is tight enough then the shift will go well and little/no rub will be present. Again there might be a trim feature for the large ring so DO UNDERSTAND TRIM.

If you were able to shift the ft der with only pulling the cable well then you should be able to fine tune the cable tension so that with the lever controlling the der movements the same good shifting can be had. Trying the ft shifting with the chain in the small, middle and large rear cogs again before deciding that you've gotten things ASAP.

All of this presumes that all the components are compatible and of the same brand. Wait, did i say the same brand (like crankset or chain)? Yes I did. Any deviation from the system that Shimano intended can cause a drop off of performance/increased rubbing/slower shifting. The off brands of parts will always claim otherwise, that they design to Shimano's spec. But Shimano will never agree to that.

As i said before there is a lot of back and forth then re base lining before going back to where you had to try something different. As the system wears in cable tension needs to be kept on top of. When tapered square cranks are retorqued on the BB spindle the limits and cable tension needs rechecking. If you shift under power (JAM SHIFTING) and don't know how to soft pedal during shifting that all these adjustments will not matter too much. Andy.
Andrew R Stewart is offline