Continuing on now with our tune up, we will be looking at our front derailluer, if you have one! Front derailluers may seem a little tricky at first, but they are similar to rear derailuers and actually, are easier to adjust many times. Lets take a look……..
Note the limit screws, their identification, and the alignment of the cage with the chain rings.
The front derailluers travel inboard and outboard of the crankset is determined by these little screws. They are (unsurprisingly) called “limit screws”. Genrally, they should not have to be tweaked, but checking their settings is always a wise thing to do. Shift your front derailluer into the smallest front ring. Then, we will manually actuate the derailluer to find if the limits are set correctly. (Your first clue that something is amiss already would be if your chain drops on the bottom bracket shell, or won’t shift on to the smallest ring. Just manually place it on the smallest ring for now.)
By rotating the crank by hand and pulling on the derailluer cable, you can check the limits of the front derailluer.
By pulling the cable that operates the derailluer by hand while rotating the crank with your other hand, you can find out if your limit screws are set correctly. Pedal at a moderate pace and pull gently on the cable downwards. (See photo above) As the derailluer reaches its limit of outward travel it should pull the chain up on to your largest ring on your crank set. If the chain starts to come over the chainring to the outside, simply lessen the tension on the cable with your hand to keep it from falling off. If this happens, the limit screw is going to need adjustment. (Hold that thought for a moment) Before we get to that though, you need to release the cable gently to allow the chain to be pushed back down on to the innermost chainring on the crankset. (Keep pedalling with that other hand!)
Okay, your chain should be on the smallest ring on the crankset again after you release the cable completely. Check with the shifters now. Is it working properly? If it isn’t, here are the adjustments and things to check on:
#1- Chain fell off to the inside of the crankset. Adjust the low limit screw, (Either having an “L”, or “Low”, marked next to it, or use the inner most screw on most mountain bikes), by turning it clockwise, limiting the travel of the cage to the inside. Small adjustments! Maybe a 16th to an eighth of a turn on that screw. Re-check.
The cable adjuster is normally found where the cable exits the shifter body, as on this Shimano shifter.
Down tube mounted cable adjusters.
#2- Chain won’t go into the smallest ring on the crank. Check the shifter. Did you have it shifted all the way into the lowest setting? If so, check the cable tension. It should have some tension, but not be real tight. If it feels pretty tight, loosen the adjuster at the shifter, (Or down tube boss if a road bike is being tuned. See images above) and recheck. If that doesn’t do it to your satisfaction, you can adjust the low limit screw, (Again, marked with either an “L”, “Low”, or usually the inmost screw on older mtbs) by turning it counter clockwise. Again, small adjustments! Re-check to see if it works.
#3- If your chain went over the top of the outermost chain ring, then adjust the high limit screw, marked “H”, “High”, or the outer most screw on most older mountain bikes. Turn the screw clockwise a little and recheck. Make small adjustments until a satisfactory result is reached.
#4- If you shift into the big ring, (outer most ring) up front and your highest gear in the back, (smallest cog), see if the chain rubs the cage of the front derailluer. If it does, you may need to increase the cable tension by turning the cable adjuster counte clockwise at the shifter or downtube. Small adjustments make big changes. If this doesn’t work, the limit screw may be needing to be turned counter clockwise just a hair. Make sure to use the “H”, “High”, or outer most screw!
#5: I’ve tried everything so far. It still doesn’t work!- Try looking at the cage of the derailluer from above. See if the cage plates are parallel to the chain rings. (See picture #1) If the derailluer looks askew in relation to the chain rings, you will need to adjust this by using the deralluer’s mounting bracket. Make sure you are shifted into the smallest chainring up front to relieve the cable tension. Loosen the clamp,(See photo below), or fixing bolt if it is a braze on deralluer, and align the cage to be parallel to the chain rings. Tighten the clamp or fixing bolt, recheck the cable tension and adjust if necessary, then re-check the shifting.
The up and down position and the alignment with the chain rings for the front derailluer can be adjusted by loosening that bolt on the band clamp for this front derailluer.
#6- Sometimes a clamp was loose and the derailluer creeps down the seat tube. The cage may scrape the chain rings while shifting to larger rings. Or the cage may be too high above the chainrings to shift effectively. In either case, loosen the clamp bolt or fixing bolt, align properly, retighten the fasteners, and re-check the shifting. You will most likely need to adjust the cable tension, and I’d recommend doing that at the anchor bolt. loosen it slightly, just enough to pull the slack out of the cable, or allow some cable to pass through, depending on the adjustment. Re-tighten the anchor and check the shifting.
A trick that helps down tube routed cables is to lube the nylon plate the cables drag across when you shift. Try it!