... am I doing wrong? HELP ME TUNE THIS STUPID MUSCLE BIKE

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I noticed the shift cable. I would route it along the frame, keeping it as short as possible so there's as little flex when you shift. But I would first get a derailleur that matches the original. Then come back here to show it off or get more advice as how to get it shifting perfectly.
 
I noticed the shift cable. I would route it along the frame
That could be a contributing factor, especially is the housing is limiting the movement of the derailleur.

Another factor is the shifter itself. What you have isn't stock. Is that a Suntour? Is it a click shift? If so, then you've got to get precise, especially with the old shifters. Hopefully it's friction. Regardless, let's move on with the adjustment advice.

We'll assume the housing is allowing full movement, the dropouts are straight, and the derailleur is straight.

Your first adjustment needs to be the cable. Assume the tension is wrong. Break it loose at the derailleur and turn the adjustment stops all the way in at the derailleur and if there is one up by the shifter, up there too. Those are used for fine tuning your cable tension, since that is what is used to actually move the derailleur. Remember what I said about precise? These are what gets those there. So, once you've released it, and turned in the stops, pull it though again hand tight, then tighten down the cable.

The next adjustment is the high gear stop. That's the smallest cog. There is a screw on the derailleur, and I believe it's the one inserted into the face, that stops the cage's movement before it pulls the chain farther than the highest (smallest) cog. Turn that until the chain is running straight on the cog, and there is no pulling (no clicking sound) from the derailleur. Now, shift down to 3rd gear, then back up to 5th. The chain should fall from 4th down to 5th, then go no farther. If it struggles to fall into 5th, then loosen that screw a little while you're pedaling until it falls and is quiet.

Next is the low gear (largest cog) stop. Do the same thing as above, except with the other screw. This one is important because it has to be loose enough to allow it to get into 1st gear, but tight enough to prevent the chain from falling behind the freewheel, or before the derailleur rubs the spoke protector. (This is where checking for verticalness and twisting will pay off.)

After that, you need to fool with the cable tension. Tight enough to allow smooth, quick drops into low gear, but loose enough to allow smooth quick moves into higher gears. This is just an art, and you have to play with it. If it's friction it will be a lot more forgiving because you'll have to find the spot where the bike is quiet while you're riding. If it's a click shift you have to find the balance in the tension to find the sweet spot. The problem is: In this old 60's technology, there may not be a quiet sweet spot. Or it may be very difficult to find.

Tips: Lube the chain, lube the derailleur, lube the freewheel. I use chain oil for the chain, and silicon spray for the freewheel and derailleur. (Spray the actual mechanical guts of the freewheel. The chain will take care of the cogs.

Hope this helps.
 
I've had a chance to cool off for awhile. My anger was because I got this in August 2014. I got around to fixing it up around Feb 2015. I had difficulty with it when I got it done later that year.

I had to track down a replacement brass fitting for that deraileur because the old one was broken and no modern replacement would fit. I found a broken donor at Indy this past Feb. Everytime I look forward to popping wheelies on this, something goes wrong and I end up losing my precious time with it. This bike was to be ridden to a local parade yesterday morning and when the deraileur crapped out again, I blew a fuse.

The kicker is...everyone who saw me buy this at MLC and saw me hunting deraileur parts has told me that the Huret Alvit was "rare", "great quality", and that "Schwinn used them". Boulder dash!

So yeah, two years off and on tinkering with this and I can't ride more than two miles!!!

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To CRASH...you sir have been a BIG help and very informative! Thank you EVERYONE!

The deraileur I have in the shed is a very nice Shimano RD-Z501 from an old 10-speed. Will that work?

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You'd have to figure chain capacity and match it to derailler cage length: (largest cog teeth - smallest cog teeth) + (largest chainring teeth - smallest chainring teeth).
 
You'd have to figure chain capacity and match it to derailler cage length: (largest cog teeth - smallest cog teeth) + (largest chainring teeth - smallest chainring teeth).
Since the teeth are small, would I need a set of calipers for that?

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Every time I work on a bike it's all new to me. No two of my bunch are the same. When I can't figure it out there is always this forum. BUT, it amazes me that often the answers can be found on a youtube or Google search...

Carl.

sent from a crowded phonebooth...
 
Give crash a minute to unload the next volume and episode of everything you wanted to know about a derailer an then some :)
Sweet!

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The deraileur I have in the shed is a very nice Shimano RD-Z501 from an old 10-speed. Will that work?

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The RD-Z501 might work....you may need to make a change or two...

Duchess mentioned chainwrap capacity and how to figure out how much capacity your set-up requires. No, you won't need calipers for that. You just need to count the teeth on your front sprocket(s) and your largest and smallest rear sprockets. You subtract the smaller from the largest front, and then subtract the smallest from the largest rear. Take those numbers, add'm up, and that's how much chainwrap you're working with. In the case of your purple musclebike, you only have a single front sprocket, so that counts as zero. Now, Crash said your stock rear cluster might be a 14-34, or it might be a 14-28. If that's the case, your chainwrap is either 20 or 14. Either way, you're covered b/c the RD-Z501 is good for a chainwrap capacity of 30t....

The situation that might cause you some trouble is, the rd-Z501 takes a max cog of 28t. IF your freewheel is a 14-28, then you're good to go. On the other hand, if it's a 14-34, your RD won't be able to shift into the largest rear sprocket. (If it were me, i'd just swap in a 14-28 freewheel and run the RD-Z501 from there. Freewheels are cheap/plentiful/often free...and the original one is likely worn by now regardless.)

The other potential issue s with the shifter. If that shifter is friction only, meaning it doesn't index, then you'll be fine. If it's indexed but it's not Shimano, then you won't index properly. If it's Shimano but it's Positron, then it won't work either. If you can tell us what brand/model the shifter is, and/or show us a good picture of it, we can advise you from there. However, i suspect it's friction and it will work fine with the RD-Z501 derailer.

Also, as other folks mentioned, try to get that rear derailer cable under control. Get some zip ties or cable guides and try to strap it to the frame a bit. Less slop that way....

For reference:
http://velobase.com/ViewComponent.aspx?ID=124bf03e-f75c-4abd-9231-4cfb663742e7&Enum=108

HTH
Rob
 
Thank you all so far for the help! This is also useful info for my next rat build, which will have a custom drivetrain.

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THe advice you've gotten so far is very good. Yes that Shimano set up should work as described. I'll just add that I've worked past the prescribed chain wrap before without problem with older systems, which are forgiving, but less precise. If you're friction, you should be fine.
 
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