PhoenixBiker 

I've been building up an old Trek 520 touring frame into a gravel grinder, and I think I've reached my level of incompetence.

The bike is 95 percent built. Today I hooked up the shifters (Ultegra 8-speed barcons, double or triple) and tried to adjust the shifting. I got the front derailleur working just fine, which wasn't terribly surprising since it's friction-shifted. The problems came when I tried to adjust the rear derailleur. Getting the limit screws set was no problem, but getting the gears to index correctly proved impossible -- at least for me, with my limited experience in bike mechanics. I could get the mechanism to shift through all eight gears, but sometimes it would shift two gears at once, usually toward the small end of the cluster. When I got that corrected, it wouldn't shift into the smallest cog.

I fiddled with the barrel adjuster at the derailleur, the barrel adjuster at the downtube cable stop, and with the cable tension at the pinch bolt. Nothing seemed to work. It seems like I've watched every rear-derailleur trouble shooting video on YouTube, but so far nothing I've seen (and tried) has worked.

Edit: The shifters are 20 years old, but had less than 1,500 miles on them when I retired the 520. The cables, housings and downtube cable stops are brand-new.

Does anyone have any idea what might be going on? I'd really like to figure this out without dragging the bike into the local bike shop. I'm trying to learn how to do this stuff, and I'll never learn if I have to turn the bike over to someone else when the going gets a little tough. Thanks in advance for any wisdom you might be able to impart.

Crossthreaded88

I've had the same problem many times and I'm sorry to say it was a different culprit each time. Get the obvious stuff out of the way right away. What kind of derailleur are you using and is it Shimano compatible? Is it a derailleur that can accommodate an 8 speed? An old 520 was only a 7 speed, no it couldn't be that easy right? Found out the hard way myself long ago that Sram and Shimano are not compatible but now Sram does make Shimano compatible shifters so go figure. A bent or loose derailleur hanger can do what you describe or a derailleur that has been bent, bumped or dirty. The latest one to come across the stand was a worn cable and housing. Gear housing, at least good cable housing, has a Teflon liner that is constantly abraded by the shift cable which acts like a fine file gnawing thru liner little by little until it starts to hang up. This is the hardest one to spot as from the outside all looks good. Maybe one of these is your problem but don't give up cuz you never know exactly what it is. Like being told by the owner " It's a new chain" only to find out that it was new just not the right size. You learn from working on other peoples bikes to question everything and not to take anybody's word for anything.

frogman

I also have a Trek 520. I converted it to index shifting with Campy brifters. I had similar problems when I was getting mine set up.
Everything was compatible, cassette, derailleurs, etc but I was having erratic shifting also. What I finally discovered was that I had a bent rear derailleur hanger. It wasn't bent that much but when I straightened it out then it shifted fine. It would be a good starting point to check your rear derailleur hanger, as I found out they don't have to be out very much to screw up the shifting.
Bob

PhoenixBiker 

Thanks for the input, Bob. I'm almost dead sure I'm working with compatible components. The cassette (Shimano 11-34) is the same one that came on the bike. So are the Deore XT rear derailleur and the Shimano 105 front derailleur, and the Ultegra 8-speed barcons. The only thing that has changed is the crankset; I ditched the original Shimano 52-42-30 in favor of a Shimano Deore LX 48-36-26. The chain is new.

dsbrantjr

Fiddling doesn't work so well. As suggested you need to make certain that your deralleur hanger is straight. Then try this systematic approach, starting at the beginning and not skipping any steps; https://www.parktool.com/blog/repair...eur-adjustment Make gradual adjustments so that you don't overshoot the sweet spot; 1/8 turn or less is a good increment.

frogman

Let us know how it goes. As he said, make gradual adjustments, around 1/8 turn. For example, when you are in the smallest cog in the rear and it jumps two cogs, give it a little finesse and just tweak the tension adjuster (about 1/8 turn at a time) its easy to go right by the sweet spot and become frustrated, Ask me how I know this

Bob

andrewclaus

I just had one this week, had me going a while. The culprit was an inline adjuster that had been threaded all the way out and introduced just enough slop. I always start by turning all adjusters all the way in and resetting the cable in the derailleur pinch bolt, but I missed that one, very close to the bar tape.

As others propose, check the hanger. If the bike was inactive for a while, or got moved in a car, it could easily have gotten bent.

Troul 

Make sure the rear der is healthy. By healthy; check that it pivots as it should without any hang-ups, the function of its holding position is within acceptable tolerances, & that you have good lubrication applied where it is needed.

Colnago Mixte

Pull on some of the exposed cable, and make sure it's moving the RD back and forth without obstruction or hesitation. Especially watch as you release the tension, make sure the RD returns back fully to where it was. If it doesn't, your shift cable in hanging up somewhere, could be any one of a dozen places.

One place I always check is underneath the bottom bracket where the cable guides thread through. Sometimes grit or something sticky gets under there.

PhoenixBiker 

Thanks, folks. It will be a couple of days before I can get back to the project, and I'll try to take a more measured and systematic approach when I do. I'll let you know when your advice works. Thanks again!

cny-bikeman

The number one cause of problems shifting to smaller cogs is cable/housing friction, as only spring tension is performing the shift. Everyone seems to be mentioning hanger alignment these days, even when it's an unlikely candidate.

rosefarts

There are two possibilities.

First, a bent hanger. It's a steel bike and fixable. It's worth getting it checked.

The second is too much friction. It's usually the loop to the rear derailleur. They come from the factory too short. The shop puts a new one in, also too short, etc. Its an exposed place that is easy to tweak. It is vulnerable.

If you don't have a slick cable, start with that. Replace the rear loop with one a tad longer. Use cable cutters, not side cutters to cut the cable. Use a thumbtack to widen out the plastic liner after the cut. Make sure the housing ends are on well. Before you install, run the cable through. If you feel resistance, it's wrong. Look for drag.

You can easily shorten cable on a install. You can't make it longer.

Other than aesthetics, I greatly prefer the simplicity of cabling a bike that the rear cable runs along the top tube. The rear loop on my Voodoo is nearly straight. Awesome for shifting.

Retro Grouch 

This. ^^^^

Make sure everything is in the default mode: hanger in alignment, 8-speed shifters (count the number of stops), 8-speed cassette.

practical

Are the chain and cassette new or used? If used, could the chain be stretched? Could some of the middle gears of the cassette be worn?

cny-bikeman

There's really little reason for wear to cause the symptoms being described. Certainly the OP needs to eliminate friction as the cause before proceeding to other possibilities.

PhoenixBiker 

I finally have the shifting problems solved. After two more hours' worth of attempts to puzzle through it, I took the bike to a friend who has been professional wrench for more than 40 years. He showed me how to sort things out properly.

Now all I have to do is install a new set of V-brakes. After that's done and the bars are wrapped, I'll be good to go. Thanks everyone, for your advice. Much obliged!

cny-bikeman

After several of us went to the effort of helping you It would be helpful to know in return how he managed to "sort things out properly".

PhoenixBiker 

I'm sorry. That was a horribly poor choice of words. I honestly meant no offense, although I now can see how those words could offend. What I should have said was that I wasn't able effectively use the advice you offered. I tried, many times, to use the systematic approach so many of you recommended, but I just couldn't make it work. Once I could see the process demonstrated with my own eyes, and then to duplicate what I'd been shown, the light finally came on.

Again, my apologies for my unfortunate choice of words.

cny-bikeman

I don't see that you said anything rude at all. Just curious what your friend determined was the problem and how he solved it. I'm sorry I was not more clear.

PhoenixBiker 

Actually what he did was to detach the shifter cable and swung the derailleur cage by hand to its inward and outward limits to rough-set the high and low limit screws. Once he had the rough settings, he reattached the cable and, with the chain on the big ring and the smallest cog, fine-tuned the high-limit setting. With that done, he shifted up to mid-cassette to set the indexing using the barrel adjuster. Once he had the indexing sorted out pretty well, he shifted to the the largest cog and fine-tuned the low limit screw. He then fine-tuned the indexing with the cable-stop barrel adjuster. The part I'd been missing was detaching the cable before attempting to rough-set the high-low limit screws. Yeah, I know. Duh!

Troul 

it reads to me that you had insufficient cable tension. Once it was detached & the der was aligned to the gear position then the cable reattached, it enabled for the appropriate tension to be set during reattaching of the cable; enabling shift setting to be trimmed in.