Hello,

A year ago I started bicycle commuting on an old DiamondBack mnt bike that my friend had rotting in his garage.

When I realized I liked the whole thing, I got a road bike with drops.

Now my friend is trying to start riding, so I've loaned him the DB.

For reasons I can't tell, I've never been able to get it to shift into all three chainrings, and since it was supposed to be a 21 speed, the 14 speeds which are available are more limited (or at least off balance) in range than, say, the 14 speeds on my 7x2 road bike. (this is despite more than a few nights with screwdrivers and playing with the derailer, moving it around, and doing all I could think of)

Well, my friends a clyde, and he realized that the seat kinda sucked too.

And the seatpost is some ghetto fabulous wallmart-special-style that is permanently attached to the seat and allows the seat to rotate on a vertical axis with no means of stopping it I can find.

Further this is an aluminum bike that rides like the bad type of aluminum bike, but still weighs more than 5 lbs more than either of my steelies (I'm sure the 26x1.5" tires/wheels have alot to do with that.)

So, I could get a brooks,
and a seatpost
and take it into the LBS and blow $30+ to get the gears working

and then I'd have an old mountainbike that may shift properly, has a good saddle, and still weights a ton, has mediocre brakes etc.

But I really can't bring myself to throw away a bicycle that still, for all it's flaws DOES operate, and doesn't have any defects that would make it "unsafe" per-sei.

I'm not sure what to do.

-- James

sounds like work you could do yourself if you're even halfway handy. The front derailleur problem might be as simple as a limit screw turned too far in, for instance by somebody who thought granny gears were sissy and locked out the small chainring. If that's the case (or the reverse, for the big ring), it's a 10-second fix with a screwdriver. You could pull and lube the shifter cables for free, or replace them for a few dollars ($5 to $8, I imagine). I can't figure out what you're saying about the seat post, but my guess is that there's some way to adjust/secure it that you're just missing. If not, a new seatpost can be as cheap as $10 or so on sale. Brakes will improve dramatically with aftermarket pads, but that's $15 you might not want to spend. Cleaning the pads and rims and lubing the cables so they work smoothly might help a lot. Sand the pads lightly to remove the glaze if necessary.
You don't mention what model DB it is, and that would help with the decision. Some of the low-end ones (I think Sorrento may have been one; can't remember) were pretty basic. But with a couple of hours work and not much money, you could have a bike that runs fine, won't let you down and that nobody wants to steal. That's not a bad thing.

offer to sell it to your friend for peanuts and let him fix it up

begin saving for another bike

I spent a solid 4 hours screwing with limit screws, adjusting the placement of the derailer on the seattube, making sure it was aligned with the chainrings, and lubing and cleaning everythign in case there was dirt restricting it's range of adjustment. No love so far.

The seat and seatpost could be an easy fix.

Did you unclamp the cable AT the FDER and start from scratch?
https://sheldonbrown.com/derailer-adjustment.html

Has the FDER been changed at some time?
Was the bike originally a double? (I had an old DB FleetStreak that was)
What model is it?