fallbalance

Hey everyone - I just bought a used Kestrel 200... sweet ride, for sure... but when adjusting the rear derailleur after being shipped, I'm running into something I never have seen before.

With the b-tension screw all the maxed, I still have a slight rubbing of the guide pulley with the largest sprocket. I cannot see any way to boost the height of the derailleur any more besides replacing the b-tension screw with a slightly longer one with the same threads... I don't know if this is a good idea though, or if I should just leave my derailleur as-is.

It actually worked better when I flipped the bike back over on its wheels after working on it... the slight pull of gravity must have helped a little. As for shifting, it works beautifully - no problems other than this little caveat.

The derailleur is a Dura-Ace 7402, 7-speed.

Any thoughts?

cny-bikeman

First thing to check would be chain length. That could cause the problem you are describing.

bikinfool

Derailleur adjusting upside down just doesn't work all that well. You might be able to reverse the screw for additional length rather than hunt another down if that's the culprit. Checking chain length sounds like a good first step.

cny-bikeman

Generally one should avoid fixes like reversing the limit screw until all other causes have been checked. Dura-Ace was original equipment on that bike, so it should work. Possibly a too large cassette was substituted. Don't know what year yours is but the link I added shows a 23 tooth large rear cog. https://www0.epinions.com/bicycles_20...SCi___Dura_Ace

bikinfool

Good thought on the cassette being used!

fallbalance

Wow, this is an active forum - cool.

Well, I played around with it again this morning and.. it seems to work pretty well in the largest rear sprocket, but I have yet to test ride. It rubs the top of the teeth just slightly... maybe the tolerance with this particular setup was just designed to be *very* close??

I'm not sure of the rear cassette size - I asked the original owner if it is the original.

If it is chain length, I'm assuming a 'too short' chain would be the culprit here, right? It seems like it has pretty normal tension though - not too tight, not too loose... and well lubricated.

JiveTurkey

You can just count the number of teeth on the largest cog yourself.

There's a chance the chain is actually too long. If you're pushing the max cog capacity and chain wrap capacity of the RD leading to the bumping, it helps to have the shortest chain possible for your setup. The extra tension will pull the RD away from the cassette a little. Here's the big/big + 1" chain-sizing method to get the shortest possible chain: https://www.sheldonbrown.com/derailer-adjustment.html#chain

fallbalance

Cool - that seems most likely to me at this point. Thanks JiveTurkey.

Something threw me in that article, hopefully you guys can explain this to me...

"If the chain is too short, it will be at risk for jamming and possibly ruining the rear derailer if you accidentally shift into the large-large combination... If the chain is too long, it will hang slack in the small-small combinations. You should never use those combinations anyway, so this is not a serious problem."

Sooooo why should I never use a large/large or small/small combination? I always have when riding...

Sixty Fiver

Count the teeth on the largest rear sprocket and I bet that you have more than 23 teeth back there which would exceed the derailleur capacity and cause the issue you describe.

Using the large large and small small combinations causes cross chaining which increases wear and is inefficient and those same gearings can be found by using other chain ring and cog combinations that give you a straighter chain line which makes the gear you are using more efficient.

fallbalance

Ah yes, there are 26 teeth. What should I do? They show no wear.

cny-bikeman

If everything works and you don't mind the rubbing it is probably OK, with one exception. If you should happen to shift to the large-large combo you could cause damage either from a too short chain or the lack of derailleur capacity. That would be very expensive. You have two other options - a larger capacity derailleur compatible with your levers or a cogset with a smaller large cog.

Sixty Fiver

Like cny said, something needs to be changed if you want everything to work properly... the 7402 is a pretty little thing but there are better friction derailleurs that have increased capacity and when it comes to friction systems from this era Suntour was king.

I don't worship at the Dura Ace or Campagnolo altars when it comes to pre-indexed systems as Suntour really made the best components and made road derailleurs that have no trouble handling 26 teeth.

Thinking the 7402 would have been mated to a 7 speed and you may have a uniglide cassette there if all things are original... swapping the cassette on these is harder as they don't make uniglide cassettes anymore, and the best route is to change the hub body to an hg model.

And if you do that, I'd use a 8-10 speed hub body and upgrade the drive to at least 8 speeds as cassettes are readily available in ranges that will work with that 7402 rear d and 9 would be even better.

The hub would need to be re-spaced and the dish altered just a wee bit.

peugeophile

I'm running a DA 7402 RD on my Peugeot PKN10E with a 28T(!) large cog. The cog and pulley teeth come close, but they certainly don't touch. I'd suspect either chain length or the position of the axle in the dropout

Jon Z.

fallbalance

Hmm... well it sounds like the replacing route would be a PITA... plus I just shelled out to buy the bike, which was ridden this way for a while.

It shifts perfectly into every gear - large/large included. The rubbing is slight, but present... especially when back-pedaling. So I think I would like to tweak this current set-up to get it working better than it is.

Chain length can be remedied, but it seems to have ideal tension to me. There is no way to adjust the position of the axle in the drop-out... is there?

***edit***

I just found out that the cassette is original... so the bike was made for this derailer / cassette size combination. Thats good news, I suppose... and the cassettes show minimal wear. I also thoroughly checked the chain for wear and saw none... sooo I don't know... maybe its just designed for this really tight tolerance...?

Wanderer

IT SHOULD NOT TOUCH ! You risk serious damage if it gets hung up.........

peugeophile

"There is no way to adjust the position of the axle in the drop-out... is there?"

Sure there is: If the slot for the axle is horizontal, just move the axle full to the rear. If it's vertical, move it full to the top.

Jon Z.

"I am not a bicycle mechanic, I just pretend to be one at parties in order to pick up chicks."

DannoXYZ 

Uh, vertical dropouts should ALWAYS have the axle slid all the way to the top before tightening the QR.

fallbalance, are you getting the rubbing in big-chainring/big-cog combo? And in the small-chainring/big-cog combo? The hanger-drop distance varies from bike-to-bike and is larger on touring frames and smaller on racing bikes. I have never seen a 26t low-gear on a Kestrel 200, most of them have straight-block corn-cobs with 18t or 21t low gears.

One solution would be to get compact 34/50t crankset up front and run a 12-21t rear cassette. Would give you roughly the same overall gearing-rage as you have now.

Sixty Fiver

This works ?

fallbalance

Ya, but the cost of a good set of cassettes is a factor for me - would like to either make sure this is working or get it working properly - the previous owner said he had no problem with it, so I'm not sure at this point.

I actually cannot tell if the gears are touching... it's VERY close if not... the only way to really see would be if the chain wasn't there. It doesn't sound completely smooth though... like when I backpedal I hear some added noise.

I do have the wheel all the way up in the vertical drop-out (I quadruple checked).

DannoXYZ 

Another idea. Could be that the inner limit screw on the RD is too tight. This would prevent the pulley from being aligned directly under the largest cog. And this would cause the chain's side-plate to rub on the cog, making some noise.

Another issue could be derailleur-hanger isn't aligned in-plane with the bike's centreline.

Take a picture of the rear-wheel in the big/big gear combo and small/big as well. From the side and from behind (4 pictures total).

fallbalance

Well I took the derailer off, took the chain off, then re-attached them to make sure they were sitting correctly and that nothing had been tweaked. I've adjusted the b-tension to where it seems to work best (all the way in). I've fine-tuned my cable tension and my high/low limit screws. I checked to make sure the derailer is hanging parallel to the cassette (it is). I've taken the rear wheel off about 10 times, either to analyze something, clean the drop-outs, or make sure it's sitting properly. I think I've done everything I can do at this point.

I have positive news. I discovered that the guide pulley is, in fact, NOT rubbing on any rear cogs. It just didn't seem to back-pedal smoothly, like there was a lot of vibration... it almost seemed like the chain wasn't exactly lining up with the position of the guide pulley as it transitioned off of the cog (or visa-versa). Then I noticed that the sound that bothered me was rhythmic, following a definite pattern... and it seems to correlate with the indentation on the side of each cog (the one that I'm assuming is built in to help make shifting smoother).

Sooo, this sound is minimalized with my b-tension screwed all the way in, but still present. Everything is functionally perfect, so I'm assuming (hoping) that this noise is normal...?

If not, my best guess is that I need to adjust my chain length, because my derailer pulleys and the center of the rear cassette aren't exactly in a 90 degree line as it mentions in the Shimano installation guide. I'm not sure if this really matters much having it be slightly off though...

My only other thought would be a longer b-tension screw, but thats only if there is a problem in the first place. This seems sort of like there may be some danger in the way of damaging the derailer though... or no?

Interesting, lots of learning on my end with this one. Now I'll just have to ride it and see how it performs.

fallbalance

yeup - took it for a test ride tonight - rode perfectly... everything shifted well & seemed quiet. I may have been getting overly sensative to normal noises while working on it in a quiet shop with my ear a foot from the gears.

Anyways... I suppose I'll keep it as it is now since all seems well.

dperreno

Good to hear -- if it shifts well, that's the real test.

I just wanted to add to SixtyFiver's answer regarding cross-chaining (Big-Big/Small-Small combinations). The reason to avoid this is because the chain is designed to flex in one direction, it isn't designed to flex side-to-side. By cross-chaining, you are forcing the chain to flex sideways and that tends to increase wear mainly on the chain but also on the sprockets/chainrings.