CityParkCruiser

Hey all,

I've got a set of Dura Ace downtube shifters, 7400 flavor. It's on a bike that has a regular HG/Shimano freewheel that I've set up with an 8 speed freewheel. Friction mode let it get the range in the stand, but it didn't love holding the gear on some of the steep hills around town, and I'd really prefer SIS. I was reading somewhere that I can change out the indexing ring and use the 7400 shifters as 8 speed SIS? Does anyone know the shimano part number and is it available? Can I just buy a ring and pop it in to have 8 speed SIS on my 7400 shifters? Is the ring universal so if I got some other 8 speed downtube shifters, I could disassemble them and use that ring?

I'm otherwise totally OK with them, and would prefer downtube shifters to SIS levers.

I suppose if anyone has a decent set of Dura Ace 8 speed downtube shifters, I'd be interested, too, but can't seem to find any that are affordable.

smd4

What do you mean, "affordable?" Several on eBay right now for less than $100.

dddd

Indexing DT levers too often are sold in a worn-out state, such that the big-cog position does not go far enough inward.
This is due to shifters having been used for a long time with the lo-limit screw set ever-so-slightly too tight, such that frame flex acting cyclicly on the cable wears out the indexing detent for low gear.

Take note of the wording on the item's condition description, to be sure that the item can be quickly tested and still returned if the lo-gear detent turns out to be worn.

As for the existing friction-mode failing to hold low gear position, try loosening the lo-limit screw!

With integrated levers (Shimano, SRAM, some newer Campagnolo) having "ratcheting" internals, over-tension from frame flex and from merely shifting into low gear very often leads to the premature failure of the cable at one end or the other, due to the cable experiencing over-tension from an over-tight lo-limit screw.
The other symptom of an over-tight lo-limit screw would be that the cable adustment seems to lose tension prematurely.

One common cause of the above maladies is a rider or shop making a small adustment to the cable's tension, for a different wheelset, without re-visiting the lo-limit screw adustment.
But it is all too common for owners/mechanics to routinely over-tighten the lo-limit (or FD high limit) screw "to be on the safe side" of a chain jumping free of the front or rear sprockets. There are consequences though to either extreme of adustment.

smd4

Well, I don't know the answer about whether the shifter internals can be changed out to 8 spd, as the OP asked. If not, I would look for a set of new levers. At that point, yes--they may not be "affordable." But this hobby isn't cheap, especially at the Dura Ace end of the spectrum.

madpogue 

But the spacing is different, meaning the throw of each click stop is different, right? Isn't that what requires a different indexing ring?

dddd

In the context of using a different indexing ring, that's only a Campy thing afaik.
Guts can be swapped, but those seem to only come from other levers these days.
I don't know that Shimano really even stocks the vintage small parts any more, they used to have a huge catalog of such, 20-something years ago.

7 and 8s Shimano shifters and clusters have subtly-different (3.1 vs. 3.0mm) spacing, and with one more-thicker (3.3mm) spacer between the 2nd and 3rd-smallest cogs on any Shimano 7s freewheel or cassette.

A phantom click at the end of the lever's travel will typically not produce the same clicking sound as the other clicks since it's not a true detent (certain thumb shifters excepted).

rccardr 

The entire indexing pod needs to be swapped out to change the number of SIS gears being shifted. 6,7,8,9 and 10 speed pods are all interchangeable, although the 9 and 10 speed ones will not work well with 740X RD’s.
Loose Screws had a number of 8 speed indexing pods a while back, check with them. Every once in a while a right side shifter will pop up on eBay.
Be patient, 7402 stuff is getting harder to fiind and is very popular.
As a side note, I’ve never come across a right side 7402 shifter that didn’t work properly even if it appeared trashed.

JohnDThompson 

The indexing mechanism is part #3 in the diagram. The part is interchangeable between Dura-Ace, 600, and 105 SIS downtube shift levers.

madpogue 

^^^^ And is it safe to say that part #3 can be swapped with everything inboard of it (including the lever) held safely in place, thus avoiding the actual assembly becoming as exploded as the diagram?

3alarmer

.
..unless you are fixated on the shifters needing to say "Dura Ace" on them somewhere, just buy these.

Shimano SL-R400 DownTube Shifters Braze-on

They work well, and I've used them on a few projects. They've been bargain priced for use in 8 speed Shimano setups for years now.

Edit: There was some incompatibility on pull ratios, between the early Dura Ace indexed stuff, and the rest of the Shimano indexing stuff. You needed to use the Dura Ace shifters with the similarly marked rear derailleur. So I'm not 100% for sure these will work with your rear derailleur (without some creative cable routing.) Probably better to forget I mentioned it. Maybe someone else will chime in about why these won't work for you.

smd4

I am…love Dura Ace.

rccardr 

Yes