YA Brifter Conversion Thread
 

I'm pondering going to the darkside with my old steel bike. This seems like a growing trend with the vintage group here, so I figure this would be a good place to ask a question or two about the process.

My 1988(ish) Nishiki has its original SunTour alpha-3000 hardware on it with downtube shifters, and while the shifting is smooth enough after a tune-up, it seems to drift pretty quickly. After reading up it appears to have been SunTour's first stab at indexing and that they had issues. I'm also not overly happy with the brakes; I'm having trouble finding pads that fit to replace my worn pads. The calipers themselves have very low clearance and I recently had to return the koolstops I got because the post of the pad was too long and was hitting the quick-release lever on the calipers. Any pads I go with look like they'll have to be on the very small side.

I like the bike, but I think with an upgraded drivetrain it could be a ton of fun. I measured my rear fork and I get 130mm worth of width, which looks to be correct for doing this sort of thing. I'm pondering grabbing a Shimano Sora groupset after reading a few of the other brifter conversion threads, and I have a couple of questions.

1) The wheels I have are newer, and I believe that the hubs were replaced at the same time. Can I keep the wheel hubs or will I have an issue moving from the old SunTour freewheel to the newer Shimano?

2) Is the Sora a good groupset to go with, given that I'm trying to keep this build on a budget? A quick look turned up a few 8sp groupsets for a reasonable price on fleabay.

Main considerations with the build are to have a good bike to fit my commute (~6.5 with a large hill that accounts for 1/3 of the mileage), not to go crazy with the budget, and to keep enough respect for ye olde steel that nobody from the forums hunts me down. :) I'm new to wrenching on bikes, but I'm mechanically savvy and have enjoyed learning as I go.

Bike in question, after a wash, lube, new tires/tubes, and some fresh handlebar tape:
http://bikeforums.net/attachment.php...hmentid=481643

So many ways to go with this, but one thing needing clarification is the rear hub - what is it exactly? Even if it is newer, you're still running 6 speed with the a-3000, correct? If it is a freewheel, you don't want to go bigger than 7 speed. Even if it is a cassette, it probably won't go past 7 speed.

If you really love the steel bike, you could find some mid-90's aluminum bike (who likes aluminum anyway?) with functioning STI parts, strip it and transfer it all over. $250-ish dollars later and you could have a new drive train including wheels. Sell the frame for $50 and call it a day.

If the wheels you have are newer, and in fact 130mm OLD, I'd just step up and find an older 9speed shimano setup. I converted my old Lemans RS to 2x9 Sora, and had a grand total of $130 in upgrade parts, including the wheels. Possible if you bargain shop.

Questions before answers.

How did you measure the rear dropout width? You should have measured from the inside of one dropout to the inside of the other with the wheel removed. There is little chance that a 1988 steel bike would have come from the factory with 130mm rear dropout width. I could believe 126, if the bike came with a 6-speed freewheel.

You wrote that the wheels are newer. Is the rear wheel made for a freewheel or a cassette? What is the width of the wheel from the outside of the locknut to the outside of the locknut on the other side?

About the only thing that Sora has going for it is that it's newer than the original 8-speed groups (Ultegra 6400, 105, RX100, and RSX. The original 7-8 speed STI design is both robust and rebuildable with replacement parts available. The newer 8-speed and higher groups are not rebuildable and parts availability is very poor.

There are people on eBay who can rebuild/refresh/restore 8 and 8 speed Ultegra, 105, RX100, and RSX Brifters with metal bodies. Brifters with plastic bodies (like Sora) are not rebuildable.

If you want to go to 8-speeds, first make sure that your rear dropouts are at least 126 (you can squeeze 130mm wide 8,9,10 speed wheels into the frame without permanant modification. Then look for a pair of metal 8-speed brifters that you can send in for service (if they are not working when you get them. Expect to pay about $33 for one or $60 to repair two.

You can use any Shimano 7,8,9 (or 10) speed derailleurs, but 8 speed derailleurs are usually less expensive. Older generations of double pivot brake calipers will accept wider tires and fenders much easier/better than newer generations which are too narrow for wide/comfortable tires, and the installation of fenders. My personal favorites are RX100s, because I like the tough, durable, silver polished finish. Ultegra 600s are almost the same (with a single part being painted dark gray).

I actually like Ultegra crankrings (five arched supports) the best, and my favorite crankset would be Ultegra 6400 (again with silver polished finish) and square taper mounting. Although the RX100 crankset with Ultegra rings would be a very close 2nd.

You have plenty of good reasons to upgrade the drivetrain. A3000 wasn't Suntour's first stab at indexing, but it was the lowest-end group, and never worked well. Your bike is likely an '86, Nishiki gave up on low-end Suntour after that. My co-workers at Suntour and I visited Nishiki warehouses around the country to retrofit those bikes with new freewheels and chains, to improve the shifting. Even with the updated components, shifting performance was substandard. Nishiki wouldn't let us send replacement parts to their dealers, they insisted we swap out the parts ourselves, and it was pretty much a nightmare. I did a couple of hundred bikes myself over a week, had back problems for years afterwards. No one in the 21st century should have to suffer with A3000.

Your smoothest transition to reliable indexing is to make sure shifter, rder and cassette match, by brand. Forget the Suntour freewheel/wheel, get a rear wheel with a Shimano freehub and cassette. SRAM cassettes are usually interchangeable with Shimano, that's the only stable substitution. So Shimano brifter, Shimano rder, Shimano/SRAM cassette. Match the brifter/cassette speeds (ie, don't try to shift an 8spd cassette w/9spd brifter). Then bob's yer uncle.

Doesn't mean you can't get mix-and-match to work, but lots of times you won't, and why cause yourself pain? As has already been helpfully mentioned, your easiest, and maybe cheapest, path may be buying a donor bike with the parts you need.

What they said, and nice rims. Welcome to the forum.

-Beware bike shop naysayers on the upgrade.
-Best to have a donor bike and swap the drivetrain.
-Best to go with rear hub that holds Shimano/SRAM 8/9/10.
-7sp RSX, you only have to swap freewheels and get a new chain, solid metal shifters.
-8sp RSX, 105, RX100, 600/Ultegra are the best bet, will require different rear wheel. (8sp DA only if you also get the RD)
-Sora is OK for a budget upgrade, and will shift fine, but you're already swapping wheels, so you are better off with a donor or used group.

-Cheapest upgrade:
--swap 6sp freewheel for 7sp. $15 new.
--pick up new or used 7-sp STI shifters, $80-$100
--pick up new chain, $15 new.
--used calipers with more clearance for commuter tires, $25
You'll be on the same bike, running 7 speeds, modern shifting, minimal fuss/expense.

Remember, you'll need STI housing, new shifter cables. And work on things to say when passing other cyclists.

http://www.bikeforums.net/attachment...3&d=1444359204

Nice looking Nishiki! If you're looking for a cheaper solution, I'd actually suggest trying out a higher-end vintage friction system rather than going with brifters. Nothing against them other than they're ugly. I think Suntour Cyclone would look great on your bike, and if you set it up with a narrow 8 speed chain I think you'll find it is incredibly smooth shifting. I won't say "perfect", but I could. You could keep your wheels and crankset and just swap out the shifters and derailleurs.

I believe that matching-parts Alpha-3000 six-speed setup will work well with the substitution of any Shimano 9s chain.
The index shifter should be oiled internally and the cable housing loop should be clean modern housing with appropriate ferrules!
The cable indexing adjustment should be done first, followed by the low-limit screw, which should not intrude on the indexed low gear position!

Any 9s chain will work very well on a 6s Suntour freewheel, and the Shimano 9s chain has the narrowest pin width and widest sideplate reach of any 9s chain, which will really improve shifting performance, especially in terms of the service interval.

As for STI, I believe that any Sora shifters below the 9s 3500 vintage will discourage a rider from discovering the merits of a road bike's performance potential, due to not being able to safely shift to a higher gear from the drops. What total garbage (this rider's opinion).

I myself might add inexpensive Microshift 7s STI-style levers together with a Shimano or Microshift rear derailer, Sunrace 7s freewheel and narrower chain. The rest of the gruppo should be fine, and the brake pad posts can be cut down as needed.

Long-reach brakes may offer no improvement in terms of tire clearance unless some lengthening of the fork leg length exploits their added reach! I would not count on any newer caliper to improve tire clearance at all, though certain ones very well might (a little research is warranted imo).

The Nishiki is quite worthy of a modest upgrade budget imo, since your gas-pipe frame most likely has the best geometry for all around riding. Do make sure the headset turns most freely.

Cool insight, thanks for the info. Most everything I've read about the a-3000 has been less than complimentary.

You're right, I measured from the outside. Inside measurement is 126mm.

The hubs are newer; Quando brand. I could not find a serial or part number. Not sure how to measure the hub axle width, since both hubs have a quick-release on one side. Measure from the base of the quick-release to the end of the post? Rear hub has a 6sp freewheel attached to it. I believe the freewheel is the original SunTour.

Based on all of that, it sounds like a 7sp freewheel/cassette might be the best idea? Is the threading on these generic hubs pretty universal, or will I need to replace the hubs to fit a shimano freewheel? If the treads are the same a move to a rx100 with a shimano hyperglide 7sp freewheel might be the best course of action, as I could keep my current hubs.

But then I'm pretty new at this stuff.

RX100 seems to turn up as 8-speed, not 7-speed. These early STI levers are rather heavy btw.

There was a 7-speed RSX gruppo back in those days around 1996.
Again, the old shifters are weighty parts, and somewhat prized for upgrading old freewheel bikes.

Freewheel threadings are all the same as far as your setup and any newer freewheels are concerned. All English threading.

You measure the "axle width" at the points where the axle locknut's grip surfaces contact the frame, should be the same as the inside measure of the frame of course.

Quando hubs have decent bearings in them I've found.

What is this "post width" you mention?

I meant axle width. I'm a scotch or two in. :). I'll edit my post.

Shimano makes a 7sp 11-28 freewheel that it looks like I could use in lieu of buying a new hub to take a cassette. It's pretty cheap, too ($15), and seems to be well accepted. I'd imagine it'd be fine for my non-race style riding (I just do this for fun and for commuting).

Have you ever ridden a bike with downtube shifters? I can assure you that shifting while in the drops is no big deal. It's loads easier than riding "no hands". In fact it's easy to shift with downtube shifters while in the drops, on the hoods, or on the flats, and many people find that's it's no problem to shift downtube shifters while standing and cranking/sprinting.

Why would you suggest using a narrow chain on freewheels and cranks with wide, uneven spacing between cogs? The narrower the chain, the worse the problem with wide spacing and narrow chain dropping or jamming between the cogs or chainrings. And the worse the problem caused by the uneven spacing between the high and low cogs on a Suntour spaced indexed freewheel will be.

There is nothing wrong with Ultegra 600, 105, RX100, and RSX 7 and 8 speed brifters that are in good condition. While older, they are made of better stuff than the plastic that Sora brifters are made of, and they are rebuildable, whereas Soras are not. 7 and 8 speed drivetrains have the same spacing as 6-speed systems and are more reliable, an less sensitive to adjustments than 9, 10, and 11 speed systems.

First generation dual pivot brakes (7 and 8 speed) are reliable, functional, accept wider wheels and tires than newer generations of dual pivot brakes, and are less expensive than the latest versions.

An 11T top gear is a pretty stiff row, unless your big chainring is a 50T. When I was riding a lot, I seldom pushed the 12T top cog on on 7-speed cassettes. A 14T was more to my liking with a 52Tor 53T. I took the 12-28 cassettes off my bikes and usually sported 14-28, although I'm running 13-28 on a lot of my 8-speed bikes now.

A 7 speed Shimano freewheel should go right on your existing rear wheel. Then all you need to get is 7-9 speed Shimano rear derailleur, and a set of 7-speed brifters, or some indexed downtube 7-speed shifters.

Careful there. 7s spacing is close to 8s, but 6s is much wider and won't play nicely with either of the other two. If you are talking hub OLD spacing, then 8s is 4mm wider than 6s/7s.

You're going to spend close to $90 for a set of working RSX brifters, more for the 8s varieties mentioned. Does anybody know if the geometry of SunTour a-3000 will work with Shimano SIS/STI? I'd think you'd need a complementary RD too. If so, you're about halfway into a donor bike with only two parts...

A few points about your comments above:

Suntour Accushift systems were designed for relatively primitive chains, and as such the shifters are designed so as to "over-shift" when moving to a larger cog. This actually became quite problematic when the 7s versions arrived, and many dealers never ordered another Suntour-equipped bike ever again.

Suntour freewheels, whether used for index or friction shifting, work better when paired with modern, 8s or 9s chain than they ever did back in the day.
The cog spacing on 6s Suntour Accushift freewheels is "standard", same as Shimano 6s. The spacings are uniform, no "uneven spacing". I have used many Accu-6 freewheels together with 9s chain, and shifting always improved, regardless of the shifter used.

I see very few people rebuilding their STI shifters or having them rebuilt. Usually some sort of soak-job is as far as anyone wants to go because Shimano does not supply any small parts for them.
I recommended the Microshift levers because they are new, fairly light, and cheap. I just bought another pair myself.

The 9s chain, especially, will widen the range of rear cogs usable without having to "trim" the front derailer position, so much so that I typically use the entire cog stack together with the big ring over an entire ride.
The newer chains are also far more tolerant of cross-chaining, and tolerant of sparse lubrication, yet can last many thousands of miles.

9s chain sometimes does not play nice with older chainring spacing, but usually it works perfectly under all conditions, even on 40-year-old Schwinns and Peugeots. Certain cranks like older Stronglight and SR Apex have particular problems with even 8s chain though, but this is easily corrected with minor modification to the small chainring, something I have been doing from time to time for over 20 years since it is always worth the effort to be able to use narrower, better modern chain.
Often an 8s chain would be a better choice on an old Accu-6 drivetrain, but note that with Accu-7 the 9s chain improves rear shifting quite dramatically, and Shimano's 9s chains have an edge above all other brands in terms of their ability to grab teeth.

I don't know why your post started with teaching me the merits of using downtube shifters. I do almost all of my riding using downtube friction shifters myself, so am also well-versed in riding with, and fine-tuning these old drivetrains, using modern chain exclusively.

The Sora shifters are a disaster imo, since they require the rider to swing their hand around the shifter in order to reach the mouse-ear lever while riding at high speed. This is many times more dangerous than dropping one's hand down from the drop bar to execute a DT lever shift, since one's hand will tend to bang against and snag the STI lever during that swing-around move, as one is riding over possibly rough ground at the highest speeds (right when you would want to shift to a taller gear). A downtube-lever shift is a comparative non-event! Let me say that for spirited riding at a bike's highest speeds, the Sora levers are dangerous imo, as I have seen riders swerving quite sharply while trying to execute a shift to a taller gear from the drops. It is made only worse when one considers the often-twitchy behavior of so many bikes that have been adjusted to fit the newer, less-fit rider, so I tend to use the mere sight of Sora levers as a warning to stay well clear of the bike/rider I might be passing.

So I will recommend keeping the DT shifters firstly, if the OP isn't set on using integrated shift/brake levers!

It's a fact that the cog spacing between cogs 1,2,3 and 5,6,7 is different on Suntour freewheels. It's documented, and it's visible if you look. Maybe the narrower 9-speed chains help improve shifting on Suntour index systems because they help overcome the difference in cog spacing? But what about the problem with the narrower chain jamming between chain rings because the chain is narrower than the space between the rings?
Maybe I misunderstood the meaning of your post. Seems to me like you made it sound like the only shifters that are worth using are 9 or 10 speed brifters? You didn't explain that what you didn't like was the thumb shifter button on the side of the least expensive shifters. I got the impression that you didn't feel downtube shifter were worth considering for a road bike.

Early metal brifters are repairable. There are posters on this site who have DIY explaining how to service them, AND you can get 7-8 speed metal brifters serviced by multiple individuals on eBay for about $35 each or $60 a pair There are also limited new parts available on eBay, but I think the least expensive way to get replacement parts is to buy donor brifters on eBay. The cost of new hoods for the 7-8 speed metal brifters is around $55 a pair, and you could get a pair of used brifters for as little as $15. In contrast to no parts availability offered for plastic brifters or 9 speed and higher brifters from Shimano, and NO ONE offering repair services for the 9 speed and higher or plastic body brifters.

Yes, the early brifters are heavy, and a new set while rare is still expensive. I still remember when the Ultegra STIs were first introduced and they sold for $500-$600 a pair, which is more than a complete, nice, new (aluminum or steel), road bike with a good tube set and downtube shifters sold for out the door.

I have a set of plastic Sora 8-speed brifters salvaged off a Felt F90 that cracked it's frame. This is the first set of plastic brifters I've had. Very little wear on them, and they appear to be working fine. I have not formed an opinion about the thumb button yet, other than seeing that it seems to work fine.

You seem to have a hangup about re-positioning/moving your hands. I don't see having to move to the hoods to shift as a big problem, any more than it is to move your hands off the handlebars to reach downtube shifters, although the hoods are the position that I am least likely to be in (I ride on the flats and the drops mostly, with little time spent on the hoods). Riding on the hoods is a habit developed by people who are used to using brifters, and not downtube shifters or stem mounted shifters (which I have no problem with either).

People adapt to the shifters they have. Just because a bike has Sora or other brifters with thumb shifters does not make the rider incompetent. What about the Campag STIs with thumb shifters? They have a considerable investment in their rides, enough so that you should consider them to be serious riders, yet you dismiss them because the bikes they are riding have thumb shifters?

So it sounds like you are recommending plastic (for lighter weight) brifters without thumb buttons. Is that the point you are trying to make?

The OP has a bike that is spaced 126mm at the rear drops. Are there any plastic brifters without thumb buttons for 7-speeds?

I would go with friction barcons, 7 speed freewheel or cassette, and a 110 BCD crank with 48/34 chain wheels. Then watch for a 90's 7 sp brifter bike on CL.

Sora is a perfectly fine group to use for such a conversion.
Posters calling it junk and low end are either snobs or out of touch with the quality. Sora 9speed shots just as well as Tiagra 10speed.

If you are wanting another option, consider Microshift. On Amazon, there are a few different groups to consider.
Pretty sure 9speed brifters plus front and rear derailleurs are something like $100. Some Tektro bike calipers would be $50-60.
Add a new cassette for $25 and some new cables for $20
This all assumes you can put the correct cassette on your wheel.

"...It's a fact that the cog spacing between cogs 1,2,3 and 5,6,7 is different on Suntour freewheels. It's documented, and it's visible if you look...."

My reply:
The OP's bike has a 6-speed Accushift freewheel. All cog spacings on this freewheel are identical.
A nine-speed chain handles all of the various spacings that any 6 or 7-speed Suntour freewheel might have.
The nine speed chain offers dramatic improvement on the Accu-7 and Ultra-6 freewheels.


"Maybe I misunderstood the meaning of your post. Seems to me like you made it sound like the only shifters that are worth using are 9 or 10 speed brifters? You didn't explain that what you didn't like was the thumb shifter button on the side of the least expensive shifters. I got the impression that you didn't feel downtube shifter were worth considering for a road bike..."

My reply:
I recommended the 7s brifters only because they are compatible with a 7s freewheel hub, and are new, inexpensive and have levers accessible from the drops.


"You seem to have a hangup about re-positioning/moving your hands. I don't see having to move to the hoods to shift as a big problem, any more than it is to move your hands off the handlebars to reach downtube shifters, although the hoods are the position that I am least likely to be in (I ride on the flats and the drops mostly, with little time spent on the hoods). Riding on the hoods is a habit developed by people who are used to using brifters, and not downtube shifters or stem mounted shifters (which I have no problem with either)..."

My reply:
I advised that the sora lever format is dangerous for fast riding, where the rider needs to be able to shift in both directions, from the drops.
I have used and watched others experience too much bike swerve when moving their hand up, around and over these levers for each shift at high speed.
No such problem with downtube shifters that I have witnessed or experienced myself, since there is relatively little upsetting movement being applied to the handlebar.


"People adapt to the shifters they have. Just because a bike has Sora or other brifters with thumb shifters does not make the rider incompetent. What about the Campag STIs with thumb shifters? They have a considerable investment in their rides, enough so that you should consider them to be serious riders, yet you dismiss them because the bikes they are riding have thumb shifters?..."

My reply:
I didn't say the riders were incompetent, but that I have learned to be wary of riders on our brisk rides who are still using these awkward beginner levers.
The Campagnolo Ergo levers are completely different from any or the pre-3500 model Sora levers. Campag Ergolevers are shifted in both directions from the hoods or drops, since the lever positioning is designed to allow this. Sora levers deliberately discourage a rider from shifting to a bigger gear once they move their hands to the drops, which serves only as a governor on the rider's speed. These are targeted at beginning riders who will have to upgrade their bikes before they can fully and safely enjoy their improving skills and confidence within a brisk peloton of riders!


"So it sounds like you are recommending plastic (for lighter weight) brifters without thumb buttons. Is that the point you are trying to make?..."

My reply:

Any of the integrated shifters having both levers accessible from the hoods and the drops should be fine. I don't really expect any of them to rebound from crashes though some are surely more durable than others.


"The OP has a bike that is spaced 126mm at the rear drops. Are there any plastic brifters without thumb buttons for 7-speeds?..."

My reply:
The Microshift integrated levers are available in 7-speed versions for about $60 a pair. Plastic main body, both levers are positioned behind the main brake lever which is ONLY a brake lever. These levers are made by Sunrace BTW, though also have also been sold under Nashbar, FSA, Sturmey-Archer, Forte, Sunrace and other brandings. I have little experience using them, just a few miles. The main lever is alloy.
Here is Amazon's photo of the levers which they list for $65:


http://ecx.images-amazon.com/images/...dL._SX522_.jpg

Again though, I firstly recommend the OP get the DT shifters working at their best using modern chain, which could cost just $20 or so.

I'm not too keen on the downtube shifting; I think my upgrade will include brifters, should I be able to find a pair at a reasonable price.



Thanks for the info on the 11t vs 14t. I've got a 14t used with a Sugino 42/52 crankset now, and with my ride having many slightly downhill segments (lots of up/down on my commute ride), I find myself spinning out on those segments. I figure an 11t might help in those sections.


Since the threads are pretty standard, I think my plan of action will be to keep my existing rims/hubs, pick up a 7sp shimano freewheel and pick up a Shimano rx100 rder, fder, crankset (rebuild my current bracket) and pick up new brakes, as the springs on mine are pretty shot.


Looking around, the local craigslist is pretty sparse on donor bikes (with the exception of beat up mountain bikes), but ebay prospects don't look bad.


Hopefully I'm not doing anything too wrong with this approach?

The problem with buying a bike on eBay is the cost of the shipping. Unless of course you come across a bike that is local, you go can go pick up.

I found the 2004 Felt F90 that I parted out on Craigslist. For some reason many Felt Sellers/Owners seem to think that their used bikes are worth more than they sold for new. Recently, I spotted a Felt F90 on eBay that the Seller was selling in a package with some clothes, a helmet, and a u-lock. His opening price was $900, and the bike cost $600-$679 when it was new back in 2005-2006. The bike I bought had a cracked frame (at the headset) so it was done. I offered the Seller $80 up front (his ad was make offer), and he accept it without hesitation. I barely found $80 worth of parts in it (to my thinking), when I broke it down. I mean I got a pair of Alexrims AT450s that were worth $110 when new, a set of Sora 8-speed brifters (in great shape), a Claris FD (in good condition but low product level), a Tiagara 9-speed RD (in great shape, looks like the 105 RDs that I use), seatpost, threadless handlebar stem, handlebars, a set of low grade OEM Tekro Interupter Levers, and a FSA crankset with nice generic sealed cartridge bottom bracket. Not a screaming deal, but an okay deal, based on the parts I can reuse.

This is the kind of deal you should look for. A broken frame holding a collection of parts that you can use. There are lots of bikes for sale to choose from here in SoCal, but not many screaming or even okay deals to be had. You need to be patient if you're looking for a deal on a donor bike, and be ready to walk away if the deal is not going to yield the parts that you are looking for.

Front derailleurs on the 7 systems are friction, and since the spacing is the same, you don't have to replace the front derailleur until you are ready to (use existing FD with brifters or downtube shifters). I picked up an eBay deal with RX100 mini-group consisting of: FD, RD, and dual pivot brake calipers a couple of weeks ago from an eBay Seller for about $23 shipped. The calipers need cleaning/polishing, and there is a plastic trim piece missing from the cable adjusters, but they should clean up fine. The derailleurs look fine. I'm planning on putting these parts on the 1994 Trek 1400 that I'm restoring (originally came with RX100). The Felt wheels and threadless handlebars stem, Felt handlebars, and Sora shifters are going on this bike. The Felt F90 came with Tekro dual pivot brake calipers, but I prefer the RX100 brake calipers, and am going to sell the Tekros (or keeping them as spares).

Just a couple points about one of your points...

When you say that Accushift was designed for primitive chains and so had to overshift on the downshift, you are essentially correct. But the reason for the overshift approach wasn't so much because of the chain, it was because Shimano's tight patents prevented Suntour from copying Shimano's superior hyperglide cog tooth profile and centeron self-centering upper/guide derailleur pulley. Shimano's successful indexing relies on the cog teeth aggressively grabbing the chain on the downshift, with the centeron pulley automatically centering itself to maintain tooth/chain alignment and keep the drivetrain quiet. Suntour had to rush indexing into production and were unable to find analogs to Shimano's cog tooth/pulley without infringing on Shimano's patents. The overshifting on the downshifts was the only way they could make it work.

The click in Shimano's lever just had to get the chain close enough to the cog centerline for the twist-teeth to grab the chain, while Suntour had to bully the chain onto the flat teeth by overshifting and praying the teeth, with enough grinding, would pickup the chain. Accushift upshifts rely on precisely dumping the chain onto the cog, praying the cog centerline will be centered well enough to accept the dumped chain. Consequently, Accushift was very intolerant of off-spec components and frame dimensions, and setup/adjustment was finicky even when everything was dead-nuts on-spec. SIS was much more forgiving, was always easier to setup, and seldom needed adjustment.

Another complication was Suntour claiming that rear derailleur shifting geometry was consistent across the entire product line, requiring only one indexing disc/pattern for Std-6 and only one for Ultra-7. This was not true, there were at least 3, maybe 4 different geometries, which should have required dedicated indexing discs. Consequently, some lever/rder combinations were more marginal than others.

One upshot of all this is that though a modern chain may improve Accushift performance, Accushift's problems are much deeper than just the chain. Flat teeth combined with an overly-long rear dropout "drop" dimension (axle-center to rder pivot-center), crappy cable/casing and poorly-matched lever/rder can still potentially cause problems. I'm not at all discounting your own extensive experience working on this stuff, I'm just cautious from having spent many, many hours manning the Suntour dealer line, trying to help righteously-pixxed dealers, at a time when we had hundreds of thousands of under-performing drivetrains in the market. The first wave of 6spd drivetrains were horrific enough for any sane dealer to never order another Suntour-equipped bike, and that's pretty much what happened.

But if I can ever drum up enough enthusiasm to install an indexed Suntour drivetrain on one of my bikes, though I'm not sure that day will ever come, I will certainly try using a modern chain.

Good points pcb, especially wrt those pesky patents.

So here I am thinking how clever I was, getting Suntour indexing systems, Command shifters et al to work properly, and all I was really doing was violating a bunch of patents by using Shimano's and other's cabling and chain, and in one case by making Suntour's B-pivot spring fully active (actually balanced in use with the cage pivot spring), which likely would have been another patent violation.

I remember that it wasn't until the 2000's that SRAM's chains began to have outward-bulging sideplates that finally updated their 8 and 9s chains. This was to finally move toward catching up with the chain that changed the world, Shimano's first bushingless chain, the (~1986) "UG Narrow" model which begat the dimensionally-identical (1989) "HG" chain. But these Shimano chains were still too wide for optimum shifting on Suntour's Accu-7 freewheels and cassettes, so in those (early 90's) days I preferred slightly-narrower chains, like the "old-but-refreshed" Sachs Delta(?) chain, to best help deal with the overshift issue.

But it is true with a lot of old drivetrains, that having these modern chains and cabling at our disposal, one can enjoy friction shifting or Accu-shifting that truly is better than it ever was back in the day, giving some old gruppos and friction shifters relevance they might otherwise not enjoy today.

Just swapped an SRAM 850 onto my GPX and definite improvement resulted. Ramped cogs would ice it.

Now remember what pcb just said about Shimano's twist teeth "grabbing" the chain, and imagine how that will work with Accu-7's generous overshift freeplay. Likely there would be some momentary overshifting to the next-larger cog than you are wanting to shift to.

I assume that your GPX gruppo is 7-speed, so if you can get a Hyperglide cassette spaced to Suntour dimensions (I can supply the needed cog spacer dimensions), then a narrower-yet chain (something I wished I could buy back in 1992) will be the ticket to moderate the effects of the generous overshift, the aggressive cogs, and the narrowed spacing between Suntour's larger three 7s cogs.