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so i am trying to find out the differences between top swing vs. bottom swing front deraleurs. i have a hardrock pro and i want to know if they are inter changeable.
 

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Old man on a bike
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Good ol' Sheldon Brown's explanation:

Most front derailers use a parallelogram which is fixed (attached to the derailer body) at the top, with the moveable cage attached to the bottom link of the parallelogram. Many of the newer Shimano units are built "upside down": the bottom of the parallelogram is fixed in place and the cage attaches to the top link.

A peculiarity of Top-Swing ® derailers is that the limit stop adjustment screws are reversed, so that the outer screw limits inward travel, and vice versa.

Top-Swing ® derailers clamp on to the seat tube lower down than bottom-swing units. (Some don't even attach to the seat tube, but are held on by the bottom bracket mounting ring.) Some frames made for use with top-swing derailers will not permit the installation of conventional bottom-swing derailers, because there's a bottle braze on in the way. Some suspension frames also require a top-swing front derailer for clearance reasons.

Top-Swing ® or bottom-swing derailers can be (and are) made in either top-pull or bottom-pull versions. (This has to do with the direction from which the cable approaches.)
 

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wfredlund said:
i want to know if they are inter changeable.
Generally, no.

Top swing derailleurs came about to address the confined space requirements of full suspension bikes, where there was no room on the frame for a high clamp. Some full suspension frames use a bottom swing, but have no room to fit a top swing.

Hardtails, which traditionally use bottom swing designs, can sometimes use top swing, but often have a deformed seat tube where it approaches the bottom bracket, preventing the low clamp of a top swing mech from clamping properly.

Of course there are tons of exceptions, but my general advice is to use a bottom swing (high clamp) whenever you can. Compare the two styles side by side and you'll immediately notice the beefier, simpler construction of the bottom swing compared to the excess pivots and reliance on stamped metal of the top swing.
 

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the top-clamp/bottom-swing type will NOT work with a hardrock unless the bottle mounts are removed. i did this to my hardrock, sanding the bottle mounts will not affect the structural integrity of the frame, after all, they are for bottles...

i am now running a SRAM X-gen front derailleur thats bottom-swing, with no problems other than the small modification you have to perform to the frame.
 

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If I have my druthers based on the frame, I use a top swing. It may be my imagination but for some reason they seam to shift alot smooother.
 
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