Bicycle Mechanics - Have some chain jumping on the rear 6sp freewheel, can you help

first off the set up is...

C-record cranks with 52 / 39t rings newish rings.
zeus 6 speed freewheel 13 / 18t was new old stock
SRAM chain brand new
C-record 1st gen front and rear derailleurs
C-record friction shifting levers.


Ok my problem is the rear part of the drive train only will run in the 15t cog with out skipping, essentially in every other gear the chain will jump strait up and back down on the same cog over and over.

coincidently this is the cog in the strait chain line position, it works on both the large and smaller chain ring. and skipping on all other cogs happen on both chainrings as well.

i will add that while on the stand it shifts flawlessly but under load it skips.

chain tension is set to what I think is good, while chain is on the largest front ring and the largest rear cog I can pinch and turn the chain overlapping about one or so links..

and lastly I do realize there is a sweet spot in friction shifting, but it only seems to exsist on the one cog at the moment, I spent the day ridding up and down the street trying to figure if it was just that I haven't been hitting the right spot, but it doesn't seem to be the case.

any help would be fantastic, it is driving me mad... built up a sweet ride with gears and seems I am destine to be a single speed rider for life.

cheers

Are you shift levers tightened enough? On the first road bike I ever had, I couldn't figure out what the heck was going on, because as I tried to shift to the bigger cogs, it wouldn't go. Turns out a little tightening of the shift levers was all it took. This is all I can think from what you're describing.

yep, they are really cranked down...

Except for the one cog that works ok, I was thinking of a worn chain. Measure 12 inches of the chain pins for excess wear.
Sheldon Brown's worn chain page (http://www.sheldonbrown.com/chains.html)

edit-- I see your chain is new. Nevermind.

I had this happen to me as well, I replaced the freewheel, and the problem was gone.

I have the same issue with every new chain. After 100 or so miles it gets better, just use gear combinations that don't skip!

How wide is the chain? It's not one of them new-fangled 9 or 10spd ones is it?

My bad is the new chain the same as the old one? My LBM went to a narrower chain for me this year that skipped in every other gear on my freewheel. After going back to a 7 speed chain things got better.

I have the same issue with every new chain. After 100 or so miles it gets better, just use gear combinations that don't skip!

If this happens, it implies that your cassette needs replacing. I had this happen in my most used gears when I left it too long before replacing a chain. What is happening is that after 100 miles your new chain has worn to fit your cassette.

First, chain "tension" and length, derailleurs and shift levers have nothing to do with the problem. Your problem is very unusual in that typically with a new chain there will be one or two cogs that will skip and the rest are OK, not the reverse. The only scenario that makes sense to me is that the cog was actually not new but rather used and cleaned up and soemone installed a new 15th cog.

. The only scenario that makes sense to me is that the cog was actually not new but rather used and cleaned up and soemone installed a new 15th cog.

Or the chain is too narrow to properly seat on the cogs.

First, chain "tension" and length, derailleurs and shift levers have nothing to do with the problem. Your problem is very unusual in that typically with a new chain there will be one or two cogs that will skip and the rest are OK, not the reverse. The only scenario that makes sense to me is that the cog was actually not new but rather used and cleaned up and soemone installed a new 15th cog.


I thought the same thing or that someone just rode in the 15 the whole time.

I thought the same thing or that someone just rode in the 15 the whole time.

I meant to say cassette was mostly new but assembled with used cog. If someone rode in 15 all the time and if it is true that the chain is new then the 15 would be the cog that would skip.

the chain is too narrow or your chain isn't tensioned enough. shift to the smallest front and rear and see if it sags.

ok, thank everyone...

I did have a more narrow campy chain on previously, but changed it out to the SRAM due to it being so narrow it got stuck between the two front rings... so that was solved, but the skipping still persisted.

the cogs were looking pretty new when I first mounted it,

Now about the chain tension... when the chain is on the 13t cog and the 39t ring it does have a little bit of slack (by the touch it feels a bit loose)... but if I get them on the 18t and 52t the rear derailleur is nearly straight, straight being where the chain is on a straight line through the jocky wheels in appose to "s" curving through. So I was afraid if I shortened it any further it might distress the rear mech?

would a pic of each position help?

ok, thank everyone...

I did have a more narrow campy chain on previously, but changed it out to the SRAM due to it being so narrow it got stuck between the two front rings... so that was solved, but the skipping still persisted.

the cogs were looking pretty new when I first mounted it,

Now about the chain tension... when the chain is on the 13t cog and the 39t ring it does have a little bit of slack (by the touch it feels a bit loose)... but if I get them on the 18t and 52t the rear derailleur is nearly straight, straight being where the chain is on a straight line through the jocky wheels in appose to "s" curving through. So I was afraid if I shortened it any further it might distress the rear mech?

would a pic of each position help?

Again, chain "tension" (actually length) has nothing to do with your problem. The skipping happens only under load, in which case the only tension involved is the chainwheel pulling on the cog via the chain. You could eliminate the rear derailleur entirely for any one gear, cut down the chain and you would have the same problem.

I don't wish to pull rank, but those who say it's chain tension or other theories probably don't have over 20 years experience as a mechanic.

Check your frame. To me, this sounds like ghost shifting from frame flex, which usually only shows itself under hard uphill efforts. A crack in your frame could cause this at slow around-the block speeds. Just a guess, but worth checking out!

Also could a bent axle or loose hub cause this too? Just trying to think of things that would cause the freewheel to rotate all wobbly.

Tight link in chain? backpedal and watch for link that doesn't straighten, grab and flex side to side to loosen.

Sorry, should have mentioned earlier - to determine for sure, just put on ANY other freewheel. If the cogs mesh OK then the 15th cog must be the problem. No, it's not frame flex or a tight link, otherwise it would not be limited to only one cog.

I would try a different brand chain. Back in the day Regina chains would only work on Regina freewheels. Using a Regina chain on any other brand freewheel would exhibit the problem you have. Guess I'm showing my age, huh?

Sorry, should have mentioned earlier - to determine for sure, just put on ANY other freewheel. If the cogs mesh OK then the 15th cog must be the problem. No, it's not frame flex or a tight link, otherwise it would not be limited to only one cog.

You need to read closer "the drive train only will run in the 15t cog with out skipping", now since the rest of us clearly know nothing any better ideas?

Sorry, should have mentioned earlier - to determine for sure, just put on ANY other freewheel. If the cogs mesh OK then the 15th cog must be the problem. No, it's not frame flex or a tight link, otherwise it would not be limited to only one cog.


You need to read closer "the drive train only will run in the 15t cog with out skipping", now since the rest of us clearly know nothing any better ideas?


Stated wrong but still the correct troubleshooting step. Should have read "If the cogs mesh on a different freewheel then the freewheel is the problem." I never said others know nothing but I have not seen a logical explanation of how the other supposed causes could cause the specific symptoms of skipping under pressure in all cogs except one. The OP needs to switch out the freewheel, otherwise everyone keeps on guessing.

Lube or replace the cable housing, especially the one before the RD.

well replaced the zeus with a campy ergal I got for cheap, seems to have done the trick.

but the chain still seems a bit slack on the small cog and ring... how tight can I make the chain?

I will ride around a bit more but hopefully that is it..

well replaced the zeus with a campy ergal I got for cheap, seems to have done the trick.

but the chain still seems a bit slack on the small cog and ring... how tight can I make the chain?

I will ride around a bit more but hopefully that is it..

As suspected the problem was the rear set of cogs. As far as the chain goes, put on the large frt-large rear combo, should have approx 1 full link (inner/outer) of slack.