DL rear derailleur

[ssteichen]

my 15 year old Specialized Ground Control no longer shifts nice and snappy in the back. The derailleur loses uuumph pulling the chain to the 7th, 8th, and 9th gears. I've already replaced the rear cable and I always keep my cables oiled up so it's not that. I'm thinking the spring has lost tension by now. Otherwise the derailleur is in too good shape to replace . Can't I just swap out the spring? Or is there a way to remove the spring and then bend it back in order to increase the tension? Thanks for listening.

[Painkiller]

Did you replace the housing also? 15 year old oil can get gummy

[Joe_W]

I second both the housing idea and the diagnosis of the weak / worn spring. Taking apart a rear dérailleur (and reassembling) is not that easy (well, depends on type / brand, check tutorials here and on park tools homepage), lots of springs under tension etc. A new mid-range RD is not that expensive (I guess below 40 USD if you shop around and are willing to accept last year's model). Considering the time it might (will) take to source the replacement (if still available) I'd just get a new(ish) RD.

[ssteichen]

(09-01-2011, 11:13 PM)painkiller Wrote:  Did you replace the housing also? 15 year old oil can get gummy

I take my housing off and run Tri-flow through it to flush out any old lube.

[RobAR]

(09-02-2011, 08:08 PM)ssteichen Wrote:  

(09-01-2011, 11:13 PM)painkiller Wrote:  Did you replace the housing also? 15 year old oil can get gummy

I take my housing off and run Tri-flow through it to flush out any old lube.

Your housing probably has a teflon liner that is worn out?

[ssteichen]

(09-02-2011, 08:27 PM)RobAR Wrote:  

(09-02-2011, 08:08 PM)ssteichen Wrote:  

(09-01-2011, 11:13 PM)painkiller Wrote:  Did you replace the housing also? 15 year old oil can get gummy

I take my housing off and run Tri-flow through it to flush out any old lube.

Your housing probably has a teflon liner that is worn out?

After seeing how car springs flatten over time my thoughts are that the mainspring of the derailleur has flattened to the point where it can't overcome the resistance of the cable in the last 3 gears. 7,8,and 9 are the gears your derailleur has to pull to as the spring is losing tension. These are the last gears it pulls to. And these would be the first gears to go out if spring tension went down. Thanks again.

[Painkiller]

unless it is a really cheap rd i doubt it is the spring. unless by now you have jacked with it.
like a car they have cables and housing and after awhile they get old and do not function like they did when new.
I would replace my housing first. cheaper,less hassle than replacing a rd and just might take care of the problem.
All your spring does is nudge it in the right direction your shifter, chain and cogs do the rest. So unless your spring is limp and hanging loose that is probably not the problem
your welcome, again

[Joe_W]

I have experienced bad shifting due to weak springs on many bikes (ok, anecdotal evidence, but still). The spring is essential for the shifting, if it is too weak the dérailleur will be difficult (impossible) to set up correctly. New cables and housing are - of course - as important. I would guess that after 15 years the spring may be worn. The spring does not "only nudge" the RD in the right direction, it has to overcome the friction in the cable (the shifter just lets the cable slack a well defined amount), and the stiffness in the chain that has to be forced to move to a different sprocket.