Bicycle Front Derailleur Adjustment

Joined
Aug 30, 2004
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CA
Have a 2004 Specialized HardRock Sport Mountain Bike with a Shimano Acera Front Derailleur. I have a *slight* chain rattle during hard pedaling while operating on 3/7 and 3/8. I still don't understand what the H/L screws mean...I tried turning them, but I didn't see any movement of the derailleur...perhaps I'm not looking hard enough? TIA.
 
Joined
Jun 20, 2006
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210
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SoCal
The H/L screws are high/low limit for derailleur cage travel, which is basically how far in/out it moves. Here is a link on the excellent Sheldon Brown website that should answer all your questions much better than I.
 
Joined
Jun 11, 2002
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3,346
Location
Clarksville, Tennessee
quote:
Originally posted by Steve S: also the angle of the chain may be too much in those gears.
Depending on what type of sprockets, and how wide they are apart you might not "be able" to run those gears no matter how much adjusting. Just becuase you have a 27 speed bike doesn't mean you can use all 27 of the gears. The chain alignment just won't allow they "effecient" use of the gear range. Yes you can get into the mentioned gears, but you will have rubbing/rattling. It might be okay for a few strokes of the pedals or for a short time (like an intecipation of upshifting) not not just riding around with the rubbing going on. Typically you never want to use the extre 2 gears in the back depending on which front ring your running. For instance you don't want to be in the "big" ring on the front and run the "easy" 2 gears in the back, same goes for the smallest chainring in the front you don't want to use the "hardest" 2 gears in the back. With the center ring (if you have a 3 ring front) you can take that down to only the biggest and littlest gears in the back. You should be albe to run all the rest. Now that I throughly confused you, maybe someone else can explain it better. PS I ride with this guy and his gears are rubbing the entire time and he has a $2000 trek, I wish he would either figure out how to adjust or which gears he can run, It's very annoying on a 3 hour bike ride.
 
Joined
Nov 6, 2002
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Saskatchewan
By 3-7 or 3-8, I assume you mean the highest two gears? Those shouldn't rub. Either the high limit screw needs to be backed off a little to allow more upward movement of the derailleur or the cable needs to be tightened.
 
Joined
Feb 27, 2006
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Columbia, SC
Just my .02 but here goes: The H:L limit screws do two things. The L limit makes sure the chain doesn't fall to the inside of the bottom bracket when shifting to the "small" ring. The H limit stops the chain from going off the other side. You can only adjust the L for effect when you are in the "small" ring. When you loosen the screw, you should see the derailleur move. Same thing applies for the H screw. You have to be in the "big" ring. One of the easier ways to get things semi right is to adjust the barrel's a little bit to give you some playing room. When you get the H:L screws set, you can fine tune with the barrel adjusters. If you have finite patience, I would not recommend adjusting derailleurs as it can be very tedious and frustruating. If you have OCD or are anal (like me), you will drive yourself nuts tryingto get it perfect. And as the general rule, and as was said, you should avoid small/small and large/large combos as much as possible.
 
Joined
Sep 16, 2003
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Austin, TX MSA
this is why I run friction shifting on my front derailleur. all I have to do to trim it is to move the lever a little bit.
 
Joined
Mar 6, 2004
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Location
Calif.
It takes a little while to adjust them but not too difficult. Since it rattles on 3 (highest gear), set the shifter to 3 and adjust from there. You can see the derailer move but not a whole lot, enough to get rid of the chain rubbing. I typically leave the front at number 2. Re tightening the cable is a tedious job but patience is all you need.
 
Joined
Dec 12, 2006
Messages
2,507
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NY, NY
There should be a small adjustment knob on your shifter housing where the cable goes in. Just make a small adjustment in or out so the derailleur has a little more room for the chain. I did this on my wife's bike. She'll ride along with the same noise, it drives me nuts. She doesn't notice it at all. I watched what gears she rides in most and adjusted the cable to work best there.
 
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