Stiff/seized front derailleur

I have a Shimano 600 front derailleur (tricolor kind, late 80s/early 90s) that is far too stiff. It didn't work with the STIs I put on last week - while the derailleur would move to the large chainring, it wouldn't stay there - but I put that down to dodgy shifters, as I'd been warned they didn't work that well.

I changed to DT shiters last night, and it still takes such force to change up that in order to stop the friction shifter from slipping back, I have to tighten it so much I can barely move them.

Basically, I think it's fucked. Is it repairable? Is it just something with the spring, a bit of a seize-up due to it not having been used for a while, or is it finished? I don't know my way around front mechs enough to know what to look for.

Thanks in advance

I've now taken it off and given it a clean, as I probably should have before posting this.

There was quite a lot of dirt and dried mud in the nooks and crannies, and the mechanism still sounds pretty gritty after a nice GT85 bath. How stiff is the spring in a front derailleur supposed to be? Is it supposed to glide easily or take a bit of persuading?

You should be able to move it fairly easily with your hand. A gritty sound doesn't sound right, maybe try cleaning out a bit more?
Have you checked that the spring hasn't rusted? That would stop it springing, and account for the gritty sound.

The spring looks fine, not a hint of rust. The problem seems to be with the hinge bolts that move the arm holding the cage.

Could soaking it in some degreaser, water and GT85 have any positive benefits?

I have bought a new (used) one off Hilary Stone but I'd still quite like to fix this one.

my experience is that it just takes time to work all the dirt out.

apply some gt85 or wd40 or similar, work the mechanism back and forth in your hand. Then use a cloth to get it as clean as possible and repeat. If your lucky you will gradually work out all the embedded dirt in the moving parts.

Sounds like it's just seized up a bit.
In the shop we won't bother trying to fix this because it's too much hassle, we just say buy a new mech.
Liberal application of degreaser/light oil and working it back and forward by hand then relubing with a heavier oil might eventually get it back to life if you want to save yourself the expense of a new mech.

I hate the idea of buying something new when you can work it loose with a bit of elbow grease. I've renovated loads of front mecs, some that were totally immovable when I started and ended up moving sweetly. Once you've loosened it up a bit, the easiest way to give 100s of back/forward pulls is by tugging on the cable where it runs down the down tube (use gloves or a spanner shaft to avoid cable burn).

DoctorBike