The components are:

Dia-Compe ENE road friction shifters mounted on thumbies
7-speed cassette, 14-26, 1-7, respectively (six hyperglide cogs secured with a threaded uniglide cog)
Deore XT RD

The shifters are assembled correctly, thanks to a diagram posted in my previous thread about my initial shifting problems (thank you!). The shifter bolts are tight, but not overly tight. Cables, housings, cassette, shifters, and chain are about six months old. I ride the bike almost everyday for shopping and slow commuting.

I can shift from 1 to 6 smoothly, but I often tend to slightly over-shift to have the chain drop down on the target cog, and then I trim a bit if needed. This is not a big deal.

The problem is the shift to 7: the inner limit screw stops the RD perfectly, but when I release the shift lever the chain always drops down to 6. From what I know, this should not happen, provided everything is in good mechanical order. Of course, if I loosen the limit screw to allow for an over-shift at 7 the chain will go into the spokes.

Anybody know whether the need to slightly over-shift is common with this ENE rear shifter? Is it possible that I have a faulty shifter?

As always, any input is greatly appreciated.

Doesn't sound like you're doing anything wrong. Since they're friction shifters, everything can be adjusted on a gradient and I'd say tweaking it until it's just right is likely the solution. I would suggest messing with the limit screw a bit more; obviously not to make it over-shift, but just a bit farther than directly under the largest cog.

If you say that the shifter bolts are on tight enough, then the shifter cannot be at fault if it isn't slipping. It could be the rear derailleur.

IIKC the Dc shifters are the modern version of SunTour barcons. As such there is a float to the lever as it sits on the ratcheting core. So when pulled to the limit of cable travel (note i didn't say der travel limit) the lever will settle back to the last ratchet position. this could be essentially no movement back or it could be almost all the lever movement between two adjacent ratchets. Try to adjust cable tension so the lever has no resettling movement and engages the last ratchet as the der also hits it's limit.

If I'm wrong I'm sure others will say so. Andy.

Hmm, so there's a ratcheting system in an ENE friction shifter? How's it still "friction" then?

Also, the OP says they're mounted as thumb shifters, presumably using down tube shifters on adapters whereas the design for Barcons is bar end. Would that make a difference?

vstkrc, that's a pretty fine adjustment, but I'll give it a try. And yes, they are downtube shifters mounted on my handlebars with adapters, commonly referred to a thumbies.

Andy, I was going to mention cable tension in my post, but a few searches beforehand told me that cable tension is not a factor in friction shifting. Could this be wrong? The FD shifter has a very faint ratcheting sound and it clicks at certain positions. I can't detect any ratcheting in the RD shifter.

Again. I'm not hands on familiar with the DC shifters. Only Interweb smart But i used the first gen and second indexed gen Sun Tour bar cons for 20+ years so am REAL comfy with the ratcheted feature.

The center of the lever has a pure friction design with metal and plastic "plates" on either side of the outer housing. Tightening down on the through bolt will compress these plates and trap the housing in place with varying amounts of friction. With a traditional and friction only lever this outer housing is the "insides" of the lever. But with the ST design the lever fits over the outer housing. the housing has on it's OD many tiny teeth that are angled in one rotational direction. The lever has a leaf spring that acts as the ratchet pawl as it rides up and over or engages the teeth. hence the small "clicks" when the lever is rotated in one direction and no clicks rotating in the other direction. Now when a cable is installed in the lever and hooked up to a der with a spring the lever will pull the der and have the der's spring to tug back. The ratchet slips over the teeth as the lever is pulled against the der's spring (for the rear this is usually shifting into an easier gear), Only the very slight friction in the lever ratchet pawl and cable casing is felt, besides the der spring's force. Then as the lever is let go the ratchet pawl (and lever) rotates a small amount that it takes for the pawl to engage the closest tooth. This then holds the lever in place by the friction "plates" inside the housing. When the lever is pushed (as to shift into harder gears) the effort of overcoming the friction inside the housing is off set (to a degree) by the der's spring.

So in an ideal world of lever, cable run, der spring match up the feel at the lever to move it in either direction is nearly the same.

Shimano had a similar design goal with their early bar end lever (and some stem and DT levers) that used a spring in the housing to counter act against the der's spring force. But this design didn't survive the market place to any where near the same amount of preference as the ST ratchet friction design did. There are some who say the Shimano is superior but I don't agree.

Additionally to show the ST's better design and performance (as is my opinion) just look to the tandem world and which bar end lever they choose to use as a drum brake lever. Andy.