masi61

Just curious if anyone knows if the holes for the “B” pivot spring can be adjusted for crisper upward spring of the upper pulley to help the RD to more tightly wrap chain on a triple chainring bike while in the small chainring in front. I am running a road triple with a 9 speed “racing” 12-23 cassette. I had an upper “B” pivot bolt that had gotten almost seized up so I worked on it and it now pivots easily. Problem now is that when in the 30 tooth front chainring and climbing, the chain is wanting to come off the cassette cogs when under torque.

I have checked into a lot of different contributing factors and I am still a bit baffled. I’m thinking I might be able to wind the B spring a bit tighter by using a different hole in the end plate but I don’t know which is which so this may be a bit of trial and error. I plan to back out the B screw some more to help the upper puller come up tighter for more chain engagement.

The other thing I plan to check is cassette cog wear using a Rohloff HG cog wear tool.

Thanks in advance for any comments folks might want to add about this….

rydabent

The "B" screw is NOT and chain tension adjustment.

masi61

I’m not referring to the B screw. I’m taking about the rear derailleur spring tension itself. On my RD-6500 GS I believe there is a least one other hole for the tip of the B spring to go into which could change how much force that B pivot exerts to keep the upper pulley as tight against the cassette cog as possible. Like I said, I rebuilt the upper B pivot recently when it had gotten seized and I freed it up well but there may be a few more tiny adjustments I can carry out that will optimize the chain tracking. I know something is still off because I’m still having some dicey moments when standing to climb getting some chain disengagement (mild crunching).

Andrew R Stewart 

What rear cogs are you using when in the granny ring? How old/miles is the cog set? Don't exclude the ring teeth wear too, we see what at first glance seems to be rear cog/chain skip that turns out to be the chain "slipping/skipping" on a chain ring due to those worn teeth.

Here in the rust belt we see a fair number of older Shimano equipped bikes that see either year round use or live outside with frozen B pivots. Most every time a break down, cleaning and lubing are enough to restore the pivot's correct action. I don't recall seeing optional spring tang holes in either the pivot bolts or der knuckles, could you be referring to the cage pivot (the "P" pivot that few talk about)? On some older ders the cage pivot did have optional spring tang positions (as example the SunTour V series had a P pivot bolt with 6 slots on its head for that spring tang to fit into). I haven't needed to service cage pivots anyway near as often so can't recall if the more current ders from Shimano have this option.

I think most who study this stuff will say that the B screw is meant to adjust the open chain gap, between the cog underside and the guide pulley. The larger this gap (or the more links that span the gap) the slower the chain's engaging the adjacent cog will be. The closer/smaller this gap is the quicker the shifting usually is. Using the B screw to adjust the chain wrap around the cogs is fine as long as the guide pulley never contacts the cog's undersides. How long the chain is, in how much rotation the cage needs to take up slack, is another factor in how much wrap around the cogs there is.

I highly recommend The Dancing Chain (Frank Berto) as a text on der design and how all this stuff interrelates. Andy

Atlas Shrugged

As per usual you get responses not related to your question, which was easily understood. Rather people pick holes in the phrasing and play silly bugger.

Yes, there is an option to increase spring tension on the cage by using the second attachment point. I would assume the additional point was placed there to compensate for spring wear or in situations such as yours.

70sSanO

In defense of others who have responded, B pivot and P pivot are 2 completely different assemblies of a RD overhaul.

Since the OP already did an overhaul of the B pivot assembly, it is pretty safe to assume that he already knows the answer as far as the spring holes. Of course if people didn't connect the two threads there would be no way to know. I only figured it out because I remembered a recent thread on cleaning out the B pivot and it happened to be the OP's thread. There are a Youtube video where it shows how to add an additional hole, though that is not the question at hand.

John

Bill Kapaun

Check the chain & cog wear first.

masi61

Thanks Andrew R Stewart , 70sSanO , Atlas Shrugged 7 rydabent -

My upper pivot seems to have acceptable spring action right now so I won’t take apart the B pivot again, not yet.

Turns out I was able to loosen the “B’” adjustment screw and able to see the upper pulley move in closer to the cassette cogs. I loosed the screw too much to where the upper pulley was making contact with the smaller cogs. I tightened the B screw again just enough that it pulled the upper pulley away from these small cogs and allowing better chain engagement from what I see. I did some test laps around my neighborhood with a few light pressure standing drills and it seems as if the shifting is drama free. I’ll be departing on my bike club ride and plan to ride about 45 miles tonight. I will report back later tonight on how it goes.

Next frustrating mechanic job: sorting my Shimano Flight Deck bike computer! I keep wishing that the classic & vintage Shimano mechanics out there would publish a thread or a guide to troubleshooting the Flight Deck system for road bikes.

Andrew R Stewart 

What you. masi61, did is basic der set up stuff. Glad it seemed to help.

I can't help much with the Flight Deck's calibrating or the various versions/fit options but some of us can help with some of the mechanical aspects. I suspect there are old threads here (and likely in other forums) concerning Flight Deck stuff. Perhaps you are motivated enough to spend the time to search and compile them and post the links or produce a FAQ or problem chart. It seems that no others have, so far. Andy (who thought the idea of the FD was pretty cool but was bothered by the requirement on running Shimano shifters)