Images from here and there may be some Mountain Biking…

Replacing my Mountain Bikes Front Mech

Well now that I have managed to change a bottom bracket on my Iron Horse Azure, I found the chain catching on my front derailleur and the shifting has started to be a bit slow chaning to lower gears, sometimes I`ve had to kick the shifter, not really a good idea. Also the screw for the L-limit is seized and due to the angle to access it the head has become some what worn. So I have decided to to replace it with a new one.

After a bit of looking I found a Shimano XT 771 , (thought a nice upgrade from the current Deore jobbie) that had a top pull and now have one on order. Now just waiting for the postman to deliver it and then its out with the Zinn Bike Maintenance book again.

While waiting I also found a Grimetime article in Mountain Biking UK that described fitting a new front mech.

The tools I needed was really just

5mm Allen Key
Pliers
Philips Screwdriver

Although you would probably also need a  Chain Tool

The procedure I went through was:

1. Secured my bike to my baike stand, and removed the chain. I have an SRAM Powerlink fitted so I could just push the connectors together and the chain can be removed. So I didn`t need to use a chain tool.

2. As I wasn`t replacing my gear cables I then undid the hex bolt and released the cable. The I undid the clamp from around the frame to remove the front mech unit.

3. Clamped the new unit to the bike frame in about the same position as the old one and using the attached spacer guide made sure there was about 2mm gap between the outer mech cage and the largest chainring and retightened the bolt to set the correct height. I now retheaded the chain onto the bike.

4. Then while spinning the cranks , I pushed the mech so that the chain was on the middle chainring, to check that the mech cage was parallel with the chainrings. (if it had been wrong I would have loosened the mech from the frame and altered the position)

5. Setting the L-limit. I spun the cranks again and moved the chain to the largest sprocket on the rear cassette and allowed the chain to drop onto the smallest chainring. Now by altering the L screw I moved the mech cage so that the gap between the inner mech cage and the chain was about 1mm.

Turning the L screw anticlockwise moved the mech toward the frame, and clockwise away from the frame.

Note: Yuo should now while spinning the cranks move the mech and push the chain onto the middle chainring,  and release it so it drops back to the smallest chainring. If it is reluctant to shilft , you should turn the L-limit screww an eighth-of-a-turn clockwise and repeat the shift whilst spinning the cranks and repeat until the movement is smooth and fast. This will probably increase the 1mm gap.

If the chain is moving from the middle chainring but overshifting and dropping between the smallest chainring and the frame, the L-limit screw will need to be turn anticlockwise, an eighth at a time until fixed.

6. Setting the H-Limit. Again I spun the cranks so that the chain dropped to the smallest sprocket on the rear cassette and by moving the front mech by hand I put the chain on to the largest mech. Then whilst pushing the front mech outwards from the frame I turned the H screw so that the space between the outer mech cage and the chain was again about 2mm (should have been 1mm but I had some slippage), then utilising a third set of hands I pulled the tension tight on the cable and tighten up the securing bolt.

This gap as before is adjusted with the H-limit screw, to move the mech outwards from the frame turn the screw anticlockwise, and Clockwise towards the frame. As with the L-limit screw only move it and eighth of a turn at a time.

To test the H-limit screwspin the cranks and push the mech (or pull calble tension) and try shifting between the middle and largest chainrings. If it won`t shift up turn the H-linit screw and eighth anticlockwise and repeat until its ok. If it over shifts and the chain starts to come off, the turn the H-limit screw an eighth clockwise until its ok.

7. Now need to index the gears. Give a push on the front shifter cable to ensure the cable is tight in the mech. Spin the cranks to the middle chainring and largest sprocket on the rear, the gap between the chain and the inner mech cage should be as small as possible without touching. This I found could be adjusted using the barrel adjuster on the shifter.

Using the barrel adjuster I could move the mech outwards by turning it anticlockwise, and inwards to the frame by turning it clockwise.

Now everything seemed to be fine, so making sure the cable was tightly secured I took the bike out for a quick ride to make sure everything shifted ok.

Brillant another job done.

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