Shimano 7800 Tech Bulletin
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Always Read the Instructions |
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When
I upgraded both our Seven
and Calfee
bicycles to Shimano 7800 Dura-Ace 10-speed, I opened up the box with the new
cassette to find an additional spacer. The directions stated to install the
spacer ring when fitting the 10-speed cassette to a 9-speed hub. Both our
training and race wheels had 9-speed hubs so I installed the spacer. However,
after much adjusting, tuning, and even fabrication, I was not able to make
the new system work to my satisfaction. I then elicited technical guidance
from the experts, for the issues seemed to be a complex interaction between
dropout spacing, hub length, inter-cog cassette spacing and derailleur
mounting. No such luck. I went through several races using only nine of the
ten gears, but the training wheel had always shifted fine. However, after a
routine cable replacement, even the training wheel mysteriously failed to
shift! I then realized that the issue had nothing to do with the frame, hubs
or the cassette but in fact was isolated to the derailleur itself! Therefore,
we encourage anyone who has trouble shifting with a Dura-Ace 7800 rear
derailleur to read further for the fix… |
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I first wrote a letter to Lennard
Zinn at VeloNews: Question
about Shimano 10-spd cassettes and 9-spd hubs Dear Lennard Zinn (L.Zinn@comcast.net), We seem to have a compatibility problem between the new
SHIMANO® Dura-Ace® 7800 cassettes and our 9-speed hubs. We have two triathlon
bikes, both with similar issues on our training and race wheels. On the training wheels, I had to remove the supplied 1.0mm
spacer ring (p/n Y-1Z8-07000) to move the cassette INBOARD and space the 7800
rear derailleur OUTBOARD in order to get the rear derailleur to shift to the
smallest 12-tooth cog. The HI limit screw is almost completely backed out.
The cassette has no play when the spacer ring is removed and the washer I
used for the derailleur is just thick enough without causing the B-tension
screw to miss the frame tab. It seems to shift fine with this setup. On the race wheels, if I make the same modifications in order
to allow the derailleur to shift, there is some play in the cassette cogs
indicating that the spacer ring is needed in order for the lock ring to
tighten down the cassette properly. However, if I add the spacer ring, the
derailleur does not shift into the smallest 11-tooth cog even with the HI
limit screw completed backed out. Further, our Calfee only exhibits the
problem with the excess play whereas our Seven exhibits both the problem with
the excess play and also does not shift. Here are the details: 1. Frames = SEVEN Axiom Ti with 41cm chainstay, CALFEE Luna Tri
with 39cm chainstay 2. Wheels = Mavic CXP 33 650C clincher rims with Dura-Ace 7700
9-spd hubs for training, Nimble Fly 650C tubular rims with Nimble HUGI hubs (www.nimble.net)
for racing 3. Components = Dura-Ace 7800 front and rear
derailleurs,7800 chain, 7800 12-23
cassette for training, 7800 11-23 cassette for racing, 7800 crankset, 7800
bottom bracket Can I get a (smaller diameter) spacer ring that fits on the
lock ring side instead of the hub side of the cassette? Is there an
adjustment to the rear derailleur I can make in addition to backing out the
HI limit screw? Thanks in advance! Sherwick Min |
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After failing to receive a reply
from Lennard, I then turned to David Nayer at Nimble
for advice. After discussing the issue with a contact at HUGI, he suggested
that I try the following: Calfee: mill off 2.0mm from outboard hub body to address ONLY
play in cogs Seven: mill off 2.5mm from outboard hub body and 0.5mm from
inboard hub body (from each of the grooves) to move cassette inboard to
address play in cogs AND shifting into smallest cog; ideally, 2.5mm from
outboard and 0.5mm from inboard would equal optimum hub length used by 7800
cassette OEM Nimble HUGI hubs length = 40.1mm inboard lip = 2.5mm Seven milled: length = 37.1mm (play
in cogs) inboard lip = 2.0mm
(won't shift into smallest cog) Calfee milled: length = 38.1mm (play
in cogs) inboard lip = OEM |
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Before (left) and after (right) modifying hubs |
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Even after all the extensive
milling, the shifting still sucked! Then a strange thing happened. After each
race, we normally swap our race wheels with our training wheels and tune the
shifting to suit. After doing this in addition to replacing the cables, my
training wheel also had troubles. Immediately, the idea arose that the wheels
may not be the problem at all! I surmised it had something to do with the
cable replacement so I removed the cable, anchor bolt and washer and… Viola!
Problem fixed! Fine-tuning revealed that the HI limit screw could now be
backed out even more. Upon closer examination, I realized that the anchor
bolt washer tab had been interfering with the travel of the rear derailleur
parallelogram, preventing it to shift into the smallest cog. |
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Arrow pointing to interference between anchor bolt
washer tab and derailleur |
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So I went about modifying the
washer tab… |
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Original washer tab |
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Modified washer tab |
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This seemed to fix the problem
(even without spacing out the rear derailleur) but I was curious why this had
not passed Shimano inspection. I went back to read the instructions in detail
and found out that the tab on the washer is NOT meant to secure the cable but
in fact is there merely to prevent the washer from turning when the anchor
bolt is tightened. If I had mounted the washer as indicated, the problem
could have been avoided in the first place! |
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Moral of the story: ALWAYS
READ THE INSTRUCTIONS! |
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Enjoy
the ride! –- Team
JaS
Special thanks to: |
