Bicycle Mechanics - 6 spd cassette problems

I have been working on an older Mangusta 1000 road bike. Since I re-ran the chain and reset the rear der, i have not been able to get the der to shift to the lowest gear. I have the der set the lowest I can, but it won't even skip over to the gear. It is an older Suntour der. The other problem is I don't know if this was an existing condition before I worked on the bike. The bike was in disrepair when I started on it. Any Help would be appreciated on getting this working.

If you have the limit stops set correctly --so the jockey wheels are aligned with the smallest and largest gear-- then the problem is probably the cable binding somewhere. Could be rust in the housing or a kink.

I don't understand how that could be possible, as I just replaced the cable on the rear der all of a week ago

Another thought: Since the der won't allow the chain on the last cog, could it be possible to tighten down the cones on the axle, to bring the whole assembly closer together, allowing the der to line up with the last cog?

Never tighten the cones unless there is side ways play in the wheel. And then only enough to take out the play. If you tighten them too much the wheel won't spin.

Did you lubricate the cable before assembling it Did you cut it to the proper length? Most new cables and housings are too long. Did you lubricate ALL the pivot points on the derailleur? Are you sure the limit stop is set correctly?

Check the Barnet manual here in the mechanic section for more complete details.

Sounds like the angle of the derailleur may be off. Crank that little screw in to bring the jockey wheel away from the cog. If its that old the wear could be excessive and it'll never work right.

I don't understand how that could be possible, as I just replaced the cable on the rear der all of a week ago

Did you use a cable cutter? Are you sure you didn't kink the housing? Any flash on the end of the housing? Has the cable stretched? I'm betting that your repair wasn't completely correct.