I have a 1992 Trek 950 Single Track frame that needs a front derailleur, and I have not been able to find one that fits this particular frame. It's a top-pull unit for a 31.8 mm seat tube. That part is pretty straightforward, but the cable attachment has me flummoxed. On this frame the cable housing goes all the way from the top tube to the derailleur. In the Trek catalog they specify the Deore LX M561, but all the ones I've seen on Ebay appear to be the type where a bare cable attaches to the derailleur. I don't know if the FD I need is some special sub-variant or what. This BS where they change their gear every year makes me hate Shimano, Would anybody know the actual derailleur this bike used, or have any other suggestions? I could put a clamp-on cable stop on the seat tube, but would prefer to find the correct FD.

I wouldn't blame Shimano for this problem, it was probably made by Shimano in that configuration at Trek's request!

I don't think that yours is really a top-pull derailer, rather it is a modified bottom-pull derailer I think(?). Depends on whether the moving arm is getting pulled up by the cable or pushed down by the housing stop.

I've seen and may have the cable stop that attaches to the moving arm that gets pushed/pulled downward to effect an up-shift. It's a tiny chromed barrel with a protruding threaded stud iir.

I think that the inner wire on your bike gets anchored to the seat tube, then with the housing "stopped" by the fitting on the moving arm of the derailer(?).

You're right, there are rather few bikes (or derailers) to be found with this setup and I suspect it lasted but one or two years as a Trek-only thing.
I believe that I've seen the studded cable stop sold separately for the purpose of converting a normal bottom-pull derailer for use on these particular Treks. Again, I may have one (and one can also be fabricated without too much effort).

On a 95 Singletrack 930, the front derailleur was Shimano STX FD-MC32. This was 31.8 clamp on with Top Pull, but no housing stop.
You could use a clamp on housing stop with one of those.

I've done a few old Treks with that style of cable routing, I wish I took good pics at the time. If I recall there is a special clamp on the derailleur that is actually a full housing cable stop, and there should be a bolt (looks like a rack or bottle cage bolt) at the bottom of the seat tube, near the bottom bracket. You run the cable housing to the derailleur, and then clamp the cable to the bolt farther down the seat tube. It was tricky to get right, I think it was a workaround until purpose-built top-pull derailluers became more readily available. Some other bikes had a pulley down at the bottom and no cable housing stop on the derailleur to solve the same problem (I think)/

dddd, I believe you are right about the modified bottom-pull FD. I checked the frame and yes, there is a small cable anchor bolt that screws into a fitting brazed on the back side of the BB.
So, this set-up was made to use a bottom-pull derailleur, but with the cable coming in from the top tube. The housing connects directly to the FD arm, then the bare cable continues down to the BB where it is anchored. The FD arm would be pulled downward by the cable, and move back up via its spring.
Possible solutions (I think):
1) Find a bottom-pull FD which has a cable stop that accommodates the cable housing. Anybody have a lead on one of these?
2) Use a standard top-pull FD, along with a cable stop clamped onto the seat tube.

The required cable stop on the derailleur itself is a bolt on item. It has a little plate that secured it under the existing cable clamp, and a swiveling housing stop.

Some of those Trek frames have the cable anchor on the bottom of the BB, some are more obviously on the back of the BB shell where you can see it.

https://www.ebay.com/itm/28476907449...gAAOSwN~diWke4

If you want the spec top pull Deore, there's one for auction. But you knew this already.

https://www.ebay.com/itm/164136586891

At the time some bikes came with top pull cable routing and bottom pull FD, they used a pulley at the back of the BB/ST to reverse the cable pull (newer bike in the pic, same arrangement).

Fr. Derailleur Housing Stop Prob. - Old Trek 950

​​​​​​Weird Front Mech - Help!