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-   -   Questions About Microshift Downtube Shifters on a Non-Circular DT (https://www.bikeforums.net/bicycle-mechanics/1239410-questions-about-microshift-downtube-shifters-non-circular-dt.html)

Harold74 09-23-21 04:11 PM

Questions About Microshift Downtube Shifters on a Non-Circular DT
 
I'm thinking of running downtube shifters on my 9sp Airborne Zeppelin. Some difficulties with that:

1) Reasonably priced, NOS shifters are tough to find.

2) My downtube is a stupid oval rather than a circle which messes with the boss cover. I could sand the boss cover down but I don't want to.

One option I'm considering is Microshif's DT shifters. My questions about that are:

3) Do we like 'em?

4) Am I correct in assuming that they come with a flat boss covers rather than curved ones?

5) Are they any better, geometrically, than the bar end shifters that I already have on the downtube of my bike? They kind of look like bar ends to my eye. I thought that downtubes were supposed to be longer, flare out etc...

Thank you all for any assistance.

https://cimg6.ibsrv.net/gimg/bikefor...ea754ea3c9.jpg
My bike with bar ends installed on the DT
https://cimg8.ibsrv.net/gimg/bikefor...fbd509e507.jpg
Microshift downtube shifters.
https://cimg3.ibsrv.net/gimg/bikefor...ca56cd4dad.jpg

Harold74 09-28-21 10:41 AM

A little update on my no traffic thread...

It turns out that some old Campagnolo Victory friction shifters that I had in storage will fit the oblong downtube properly. Well, fairly properly. It turns out that the right side braze on is a bit cockeyed and it tends to point the shifter on that side into the frame. Most levers won't rub on the downtube but the bar ends that I hand on originally did a bit. I imagine that a lot of the old school, non-indexed downtubeswould fit well as the Victory's do. That said, once I get it cabled, I may find that:

1) There's not enough pull for 9sp.

2) Friction shifting a 9sp is tougher than I'd bargained for. I've only every friction shifted 7 speeds in the past.

I've ordereda set of the Dia Compe Silver ratchet shifters as a backup in case the Victory's don't work. I'm not sure if even that will make 9sp friction shifting viable for me but, of the things that are available on the market, the Silvers seem to be the most promising. I believe that they are are only ratcheted on the way up, however, and just straight friction on the way down. So, on the way down, they may not be any different than the Victorys other than pull potential.

https://cimg5.ibsrv.net/gimg/bikefor...ecb08710aa.jpg
https://cimg9.ibsrv.net/gimg/bikefor...03a1310ab3.jpg

70sSanO 09-28-21 04:34 PM

Older friction shifters didn’t have a shifter boss cover. They had a stop that fit over the square boss and kept the shifter from continuing to turn after shifting to the small cog/chainring. For friction, the downtube shape has no impact.

Boss covers, as I recall, didn’t exist before Shimano’s SIS and locked the shifter internals, so to speak, in place so the lever could click into each position.

Shimano did make a flat boss that might work as it is thinner. There might be a slight gap at the radius of the downtube, but shouldn’t be any worse than using a concave cover on an oval tube.

If it were me, I’d file the concave ones to fit. They have no collectibility value to leave original.

John

Edit Added: Since you mentioned Microshift, from what I can see, they don’t use boss covers.

Harold74 09-29-21 09:21 AM

70sSanO Thank you for your comments. I may wind up filing the boss covers as you suggest but have been reluctant to do that thus far for two reasons:

1) In another of my threads, someone mentioned that the covers are notorious for breaking when filed.

2) These shifters are pricey these days. After shipping, I'm looking at $150 CAD used or $350 CAD NOS. I'm not done searching for better deals though.

Studying the parts that I have on hand in greater detail, I may have some additional options that I hadn't considered:

3) Buy flat boss covers meant for a different downtube shifter model and use them with the 9 speed downtube shifters. As far as I can tell, the boss covers on my 7 sp downtube shifters are identical to the boss covers on my 9 speed bar ends other than the radiuses.

4) Use the boss covers from my 9 speed bar ends for the 9 speed downtube shifters.

Both of these strategies hinge upon the boss covers for different speed down tubes, and for bar ends, being interchangeable. And that I'm not sure about because, frankly, I don't yet know how these kinds of shifters do their indexing.

In the small parts diagram below, would you be able to tell me where the indexing happens? As in, which part determines the number of speeds? Does it happen within part #2? Part #2 keys into part #6 but I don't think that's actually where the action is. In the parts that I have available (7sp & 9 sp), the number of depressions in those parts always numbers six rather than the number of speeds.

https://cimg2.ibsrv.net/gimg/bikefor...6a0ed373b2.png
https://cimg0.ibsrv.net/gimg/bikefor...5edb78549f.png

rccardr 09-29-21 12:44 PM

Shimano down tube and bar end indexing occurs in the indexing pod, part #2 in the diagram.
Removable indexing pods are interchangeable and will fit within Shimano 6208 and DA 7400/01/02, 7700 and 7800 (not 7850 or 7900) down tube shift levers.
Which means you can shift 6,9 or 10 speed general Shimano or 6-7-8-9-10 speed DA with one set of levers as long as you have the pods.
The indexing pod in your pic above will happily snuggle within the confines of any of the above lever sockets, with 6208 (and possibly 7400) being the least expensive.
Down side to either of thoselever sets is that you need to make sure you get ALL of the bits for the friction side-they are frequently misplaced.
Flat mounting bosses are intended to be used with oversize downtubes but as mentioned above sanding them down will yield a better fit.
Bosses do not crack when thinned unless done so to excess.

Harold74 09-29-21 04:23 PM

rccardr What wonderful information, thank you. I'd like to make a rapid purchasing decision tomorrow. To that end, what do you think of these options:

1) I buy 9 speed DA DT shifters with curved boss covers and sub in the flat boss covers from my 9 speed bar ends.

2) I buy 10 speed DA DT shifters with curved boss covers and sub in both the flat boss covers AND the shifting pods from my 9 speed bar ends. This gives me the ability to upgrade to 10 speed in the future which I've been contemplating.

3) I buy 8 speed SLR 400 DT shifters (cheap & brand new) with curved boss covers and sub in both the flat boss covers AND the shifting pods from my 9 speed bar ends.

I may ultimately grind down the curve boss covers but, for now, let's assume that's not on the table.

Lastly, do you know how the internals on a shifter pod work? Ever taken one apart? I'm quite curious to know how loosening the screw switches it over into friction mode.

rccardr 09-29-21 08:17 PM

1) This works fine, but see below.
2) This works fine as long as the 10 speed shifters are VERY early 7800 units, later 7850’s and 7900’s do not have removeable pods. Same with early 10 speed bar end shifters.
3) 400’s do not have removeable indexing pods.

However, I do have some flattiie bosses in my box here. Better than bar end bosses. Yours for the cost of postage if you PM me.

Yes, have seen indexing pod internals. Moving (not loosening) the D ring changes the orientation of an internal stepped washer.

Harold74 09-30-21 10:50 AM


Originally Posted by rccardr (Post 22250805)
However, I do have some flattiie bosses in my box here. Better than bar end bosses. Yours for the cost of postage if you PM me.

That's an incredibly generous offer rccardr. I'll save you the trip to the post office and the nuisance of international shipping however. Thanks in no small measure to your assistance, this has worked out well:

1) I just purchased a set of NOS SL-7700 shifters from a Canadian source for $120 CAD which isn't too shabby given the current market for these things.

2) I just purchased a set of 7800 flat boss covers from Modernbike.com for little more than the cost of shipping.

3) I found the compatibility chart below which confirms some of your advice.

https://cimg0.ibsrv.net/gimg/bikefor...85995b29c2.png


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