dbruening80

Bike: Mid to early 90's Univega Via Carisma Hybrid
BioPace Cranks
Shimano Exage 300 FD
Shimano STI trigger shifters, 7 speed (assuming original equipment)

I picked this bike up as a project, I needed a bike to tool around on and this fit the bill. When I bought it, both shifters were gummed up pretty bad, I cleaned and lubed them and I am assuming they are working.

Here is my issue, I set up the front dérailleur limit screws using the park tool website instructions. The dérailleur height is set correctly, cage is parallel to the chain. Small to middle ring shift is fine, middle to big ring shift required increased wire tension to complete the shift. However, when I shift down from the big ring to the middle ring the chain rubs on the inside dérailleur plate. The park tool website says to decrease wire tension to eliminate the rub, but when I decrease the wire tension to eliminate the rub, I can no longer make the shift up to the big ring. The chain does not run in the middle ring when shifting up from the small ring.

Any help would be appreciated.

JOHNinIL

Sounds like FD is not freely moving when shifting down. Try downshifting as you described from outer to middle, can you then push by hand the FD further? Try lubing the shifter cable and pivot points on FD so it's smooth.

dbruening80

I cannot push it further. The cables are brand new and the derailleur was cleaned and lubed before being re-installed. wondering if I might have a chain line issue?

dsbrantjr

Make sure that when you set up the low limit screw that you do not leave more that a small amount of clearance between the cage and the chain. If you leave too much you are likely to run out of cable pull at the high side.

I am also confused by the statements "Small to middle ring shift is fine" and "The chain does not run in the middle ring when shifting up from the small ring." These seem contradictory to me.

cny-bikeman

I believe the OP means that it does not shift from the small to the middle ring well either when tension is decreased.

To the OP - The chain line is the same whether you are shifting to the middle chainring from the small or the large, so that can't be the issue. The derailleur should be in exactly the same position for a given lever position, so you have to use some thought to see what the problem is. When you shift outward your pressure on the lever pulls on the cable, moving the derailleur. When shifting inward the lever releases a set amount of cable, and the derailleur spring then must pull the cable through the housing so that the derailleur can move far enough to reach the next chainring. If the derailleur is not moving in to the same position that it was in when shifting out then there must be a source of friction that is keeping it from moving freely. That is by far the most likely cause of your problem (the other being a very odd lever problem). The fact that the cables are brand new does not mean that there is not a kink in cable or housing, a poorly finished housing end or something similar causing friction. I advocate a light oil (NOT grease) on the portion of cable that is inside the housing, even with lined housing. I would except only die cut stainless cables. The only other possibility is that the derailleur is very gummed up or dirty.

dbruening80

Thanks all, I will double check the cables and their routing when I get home and report back

Kotts

Here's a theory, based on a mistake I made seting up my wife's bike. If the high limit screw is in too far, you will have to increase the chain tension in order to force the shift to the big ring. That increased chain tension will put the whole thing out of whack, by moving the derailleur towards the big ring in the middle and "granny" positions.

With the chain on the middle ring, reduce the cable tension and back off the high limit screw by 1/2 turn. Shift to the big ring, and increase the tension until it just shifts up, then until it just stops rubbing the outside of the cage. Work your way back and forth through the gears, but, if my theory is right, you should now be good to go.

digger531

Compresionless cable housing?

cny-bikeman

Any diagnosis/solution needs to account for the fact that the middle derailleur position is further out when shifting from the large chainwheel. A poor inner limit screw adjustment does not fit that criteria.

dbruening80

So as it turns out it was a shifter issue. I would shift from the small chain ring to the middle chain ring with the shifter, then shift from the middle to the large chain ring by pulling on the shift wire. I let go of the wire and dérailleur downshifted to the middle ring perfectly, so I figured it had to be the front cable loop (which was set up/housing ends finished correctly) or the shifter itself. I also noticed I was not getting a lot of "clicks" enabling trimming for the front dérailleur. I went ahead and flooded the shifter with some lube and all is well.

Kotts

High limit is the outer limit screw, which could account for exactly what you describe. I'm just glad he got his problem solved.

cny-bikeman

Incorrect - the high limit screw has absolutely no effect on position of the derailleur on the middle chainring when shifting in either direction, and it's the middle that was the problem. I'm glad he solved the problem also, and would point out that the cause was one that I pointed out as a possibility - friction or obstruction. It is relatively rare for the lever to be a problem but it does occur. I could have noted the solution of rinsing/lubing the levers but it's best to address and eliminate the most likely causes first.

billnuke1 

You did the right thing when you isolated the problem by taking the shifter out of the equation! I work on a lot of older, neglected bikes and almost always clean and lube the chain, shifters, cables and derailleurs first. Then I just yank the cables and release them to highlight any problems. Process of elimination!