Bicycle Mechanics - bottom-pull FD on a top-pull frame? how?
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05-30-09, 10:17 AM
I was transferring components from a full-sus. mtb onto a new frame. it has a sram bottom-pull FD, and the new frame doesn't have routing under the BB, only a top-pull stop on the seat tube. is there anyway to make this FD work with this frame? am i missing something? do they make some kind of pulley to adapt it? suggestions appreciated, as are specific part number from qbp, hawley, or bti
You can buy a cheapo plastic under BB router. From the factory they are screwed or riveted on. But since the tension of the cable(s) tends to keep in place you could just put a dab of silicon glue (or somesuch) under it to keep in place.
You would still need a cable stop for it on the downtube. They do sell clip and bolt-on ones.
05-30-09, 10:29 AM
My early '90's Trek MTB came with a bottom pull fd and routed the cable along the top tube and down the seat tube.
To make it work they added a anchor bolt just above the bottom bracket at the back of the seat tube to attach the inner cable end. Then, the fd (a Deore LX) had it's anchor bolt replaced by an adapter that accepted the end of the cable housing from above. So, front shifting is accomplished by the housing being pushed down on top of the fd's arm. It's easy to see but tough to explain.
05-30-09, 11:08 AM
Many cyclocross bikes route the front derailleur cable along the top tube and still use a "bottom pull" derailleur. There are pulleys that mount below the derailleur to make this possible. They even make clamp on type for bikes that originally weren't designed for that routing.
Like this one: http://cyclocrossworld.stores.yahoo.net/clwipu34news.html
05-30-09, 04:36 PM
I have this situation on my current Schwinn hybrid. I made my own direction change pulley out of a 3- speed aluminum guide pulley and a handmade frame clamp. Allows you to operate a bottom pull front derailler on a frame designed for top pull deraillers.
The pics aren't the greatest quality but do show you what I did:
05-30-09, 04:49 PM
It might be cheaper (and easier) just to install a new FD. I've had good luck with the X Gens (which can handle either top or bottom pull, and come with shims for all 3 standard seat tube sizes). It's hard to beat $9 + shipping: http://shop.vendio.com/benscycle/item/921220753/index.html
05-30-09, 07:20 PM
Are you sure that particular FD isn't dual pull to begin with? Some FDs can do bottom OR top pull without any sort of adapter. The one on my 7.3fx is like this, a top swing dual pull.
Do a Google search on the model FD and see what pops up...
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