777funk

I'm noticing that in my son's old Fuji Mtn Bike (that he just sold to me) that when I shift to gear 6, sometimes it only makes it to 5. If I go back and forth, it'll usually go. Is there an adjustment to firm up the rear derailleur spring?

mprince

I'd be looking at a gunked up pivot or sticking cable before a spring in the derailleur.

777funk

The cable is brand new and has slack when the thumb shift goes to top gear. I have hosed the derailleur down with oil. Seems to move freely.

However... I can push the rear derailleur over to top gear with a tiny amount of finger pressure. It just needs a small amount of help when it doesn't make it on its own. This is why I think the spring isn't up to snuff.

Troul 

is the housing new? A new cable in an old housing is like putting on the same soiled underwear after taking a shower.

KCT1986

Has the rear derailleur hanger been checked for alignment?

A few older models of Shimano RD has an adjuster, but not many have this feature. What model are you working with?

If it does have an adjuster, it's under where the cable pinch bolt is. See the white adjuster in the pic below.

Flatforkcrown

If the cable is slack then try unscrewing the H screw on the rear derailer and see if that lets it shift into the small sprocket. After that you’ll have to readjust the tension on the cable to ensure you have good indexing. If you can’t reliably shift into all the gears after that you may want to look into the hanger alignment.

777funk

Alignment... that may be part of the problem. I don't think both derailleur gears line up (as in both gears on the same plane) with the cassette's gears as they travel in and out.

oldbobcat

After verifying that the alignment is correct, try loosening the high limit screw a bit, like an eighth to a quarter turn. This will allow the chain to drop down with more gusto. It won't be enough to drop the chain past the cog, and the cable will keep the jockey pulley in proper alignment with the cog.

777funk

It seems like that quarter turn extra on the limit adjustment helps. I'll bet it is all the above (cable grime, adjustment fine tuning, wear, etc) to a certain extent. But the quarter turn extra is helping!

oldbobcat

Another way to look at it is to align the center line of of the pulleys with the outer edge of the last cog.

Andrew R Stewart 

Shimano ders went to a weaker return spring many years ago, then what they and others use and their rear shift levers became indexed (with the internal cable spool's spring) . Just like their brakes depended on a lever helping spring to fully counter cable friction their indexed STI levers have this cable "pushing" spring. . This is why twist grip shifting will see shifting into highest gear issues as the twist grip often doesn't have that cable "pushing" helper spring (compared to a STI indexed lever design with a spring loaded cable spool). Having said that we have seen many older (and generally lower cost level) Shimano rear ders with not enough spring tension to pull the cable, however clean and smooth the cable action is and whatever shifter is used. Unhook the cable and shift the der by your hand and see if there's still hesitation in the shift to high gear. If not then suspect the cable friction (however slight it might be) is too much for the spring to over come. Andy

John Valuk

I appreciate you sharing that observation. Very recently, I started seeing some problems with a mid-90s Alivio rear derailleur having trouble reaching the highest gear. I had fairly recently replaced the chain and cassette, so I was initially looking for adjustment issues. After spending a bit of time on it, it really seemed to come down to the spring not having quite enough strength, which sort of surprised me.

I swapped in a similar-vintage derailleur of the same model (in much nicer condition), and I was back in business.

tendency

Yep I've seen this (worn out derailleur springs) as the cause. Heck, I've had derailleur springs break on me and a couple 40+ year old rear derailleurs where the spring lost its 'sprang' and couldnt make or hold all the gear shifts.