Dura Ace 7800 rear derailleur no longer swinging back
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Dura Ace 7800 rear derailleur no longer swinging back
I have a ~16 year old Shimano Dura Ace 7800 rear derailleur on one of my bikes that seems to be reluctant to fully spring back to its rear-most position when in the larger cogs. At first I thought I could fix this by adjusting the B Screw, but that appears to already be screwed all the way in.
When I backpedal in either of the 2 or 3 largest cogs, the upper jockey wheel is pressing the chain against those cogs, causing some grinding noise. If I manually pull the derailleur backwards while doing so, the noise stops.
So it basically seems like the upper-knuckle spring isn't doing its job. Does this seem like an accurate diagnosis, and (more importantly) is that a user-replaceable part? Thanks.
When I backpedal in either of the 2 or 3 largest cogs, the upper jockey wheel is pressing the chain against those cogs, causing some grinding noise. If I manually pull the derailleur backwards while doing so, the noise stops.
So it basically seems like the upper-knuckle spring isn't doing its job. Does this seem like an accurate diagnosis, and (more importantly) is that a user-replaceable part? Thanks.
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Shimano rear ders are well known for their B knuckle pivots becoming tight. Typically from grit/grime and/or corrosion. This is one bushing/bearing that nearly no one thinks to maintain (until...) Andy
I should have not hit the send too soon- The pivot bolt (that also threads into the hanger) has a squared off "E" clip that keeps all contained. Slide off this clip with a small slotted screwdriver end and watch out as the spring shows you it's really fine. Clean all, I'll use either steel wool or really fine sand paper to remove any corrosion/discoloring. Reassemble with thick grease on all surfaces. I find using a 5mm "L" hex wrench in the bench vise to steady the der and pivot bolt. Rotating the pivot backing plate (with the B screw) so it's tab fits over the knuckle's knob while the spring fights you is rewarding when you finally get it. I have been told that there's vids of this on line somewhere.
I should have not hit the send too soon- The pivot bolt (that also threads into the hanger) has a squared off "E" clip that keeps all contained. Slide off this clip with a small slotted screwdriver end and watch out as the spring shows you it's really fine. Clean all, I'll use either steel wool or really fine sand paper to remove any corrosion/discoloring. Reassemble with thick grease on all surfaces. I find using a 5mm "L" hex wrench in the bench vise to steady the der and pivot bolt. Rotating the pivot backing plate (with the B screw) so it's tab fits over the knuckle's knob while the spring fights you is rewarding when you finally get it. I have been told that there's vids of this on line somewhere.
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Last edited by Andrew R Stewart; 02-17-21 at 09:36 PM.