JimQPublic

My wife's 1989 Trek 520 was built with downtube with shifters but she had the shop swap it out for bar ends when she bought it new. The shop routed the shift cables straight forward from the drops, looping back to the downtube cable guides. Housings are original; we may have replaced the cables at some point. It has the original 1989 Deore II rear derailleur with a 7 speed freewheel. Indexed shifting is pretty good although occasionally the shifter needs a little bump to trim out.

We are going to replace the cables, housings, and bar tape and I wonder if it would be safe to run the cable housing under the bar tape to near the stem? My newer (2018) 520 is routed this way.

If I use modern low-friction cables and housings (Dura Ace polymer coated), is it likely that the rear derailleur's return spring will be strong enough for clean upshifts with the friction caused by more devious cable routing?

Thanks

tyrion

Yes. I run my bar-end-shifter cables that way and it works well. With the tighter and more complex bends the cable might not last as long as with the big smoother bends, but it should last at least 2 or 3 years.

JimQPublic

I guess it doesn't hurt to try it out- if she doesn't like it we can re-do it back how it is now.

We had three bikes from around the same time frame all with the same routing for bar-ends. Somebody (shop, custom builder, I can't recall) said that the derailleur spring on a long-cage derailleur wouldn't have enough strength to fight the increased cable friction if the housings were run all the way under the handlebar tape.

Not that it matters, but I believe the derailleur is a Shimano Deore II Super Long Cage RD-MT62-SGS
I'm impressed that Shimano has data for 35 year old parts online!
https://si.shimano.com/en/pdfs/ev/RD...-MT62-0964.pdf

Andrew R Stewart 

From a bar end user from 1973- There are three common casing exit, from under the bar tape, locations along the curves of drop bars. The first and what I think the bike had is having the casing exit at the front or slightly above the front of the flat section of the bars. Second is to have the casing travel under the tape till the levers, or just below them. Three is the casing exits at the tape's upper end, near the stem.

Which is best. is somewhat opinion, bike size/fit and accessory dependent. Smaller bikes like the first or second routing to have a long open length of casing (between the tape exit and the down tube stops). Small bikes suffer from more casing stress and it's contribution to steering range limits. Accessories like handle bar bags, bottle cages or other bar mounted items can interfere with one casing route than another. And opinion/fashion within your group can be a strong motivator.

Generally, even with lined casing and redrawn cables, the larger the casing curves are and the fewer there are the less the cables will affect shifting. I will first check the accessory aspect then the amount of open casing before I decide which style I might choose. Andy

Andrew R Stewart 

Bolded- This is BS IMO. The parallelogram return spring used in the long cage versions of ders that also are offered in short cage versions are the same IME. Having pushed on, done service on and such many thousands of systems has me calling this out. It is possible that the builder meant to reference the cage pivot spring but the way this was written I doubt that.

Now, if the builder had left out the long cage der aspect I would agree that it could happen. But to any der that uses a single tension cable and return spring design. Andy

JimQPublic

I'm sure you're right. Back in the dark days before the internet I tended to believe what one or another "expert" said if I didn't have a better source. I may have also misunderstood. This was our first bar-con equipped bike but my Shimano-equipped Miyata Alumicross from the next year and our Suntour-equipped CoMotion tandem from a few years later were all set up the same way. I appreciate your comments about luggage interference- otherwise it really does come down to aesthetics and function.

Kontact 

Some Shimano derailleurs in this era have adjustable return springs. There's a flat head screw underneath with two positions.