lostforawhile

I just got the replacement crank derailer for my 72 super sport, it's a genuine Schwinn approved old part, the only difference I see is the new one has stop screws built in, from studying the operation it appears one is the stop for low gear and one is the stop for high gear, these just give you positive stops instead of the old move the lever until it stops clicking? if I'm wrong please correct me, I assume just shift the bike into both ranges and adjust the screws until they just touch>?

Andrew R Stewart 

Pretty much all front der. since forever have had some provision to limit the cage's travel. Sometimes it's not a limit screw per say. So i suspect your old der. had travel limit designs. But to answer your question- yes. The limit screws are turned to the point where the cage can travel through the range needed to shift the chain from the small to the large rings, without falling off. The cage should be roughly parallel the the rings' plane and sit about 2-4mm above the large ring.

Some of the schwinn ders. were Huret made and assembled with nuts and bolts. These can come loose and be lost. Or the pivots can bind up if the hardware is too tight. Andy.

dsbrantjr

The various adjustments of the front derailleur interact and need to be performed in a logical sequence since each adjustment depends upon the ones before it being made correctly. Follow this procedure from beginning to end without skipping any steps and you should be in good shape: https://www.parktool.com/blog/repair-...ur-adjustments

lostforawhile

this one would be Huret, actually both appear to be, I will locktite everything when I put it back together

lostforawhile

is the cage supposed to be parallel to the rings? it turned out the new one I got was for a different size frame tube and wont fit. my original one was there, the mechanical part is still ok, but the derailer cage had broken off at the weld, i swapped this cage onto the original mechanism, but the rail is at an angle to the rings, this cage has wear marks that match this same angle worn into it, is it supposed to sit like this? without the cable attached it shifted into the lower gear and the chain isn't hitting, i discovered the original cable was too frayed to install it back,so I'm going to steal some cable off of a junk mountain bike I have. If the cage is supposed to sit parallel, I can machine a spacer if I have to to move it outward, if i tilt the cage parallel the chain rubs

dsbrantjr

"is it supposed to sit like this?"
A few clear, well focused photos might help us help you.

Andrew R Stewart 

Front shifting adjustments are more involved then rear. That's why i say things like "roughly parallel" instead of "must be". the mechanic must use their experience and some trial and error to figure out the best set up. In general one starts with a base line (as I mentioned) and looks at the chain movement then makes small changes and looks again. Some times these changes include a little bit of bending to the cage's tips to both push the chain as well as catch it as it shifts. For some one who has not worked with a lot of arrangements this fine tuning can be frustrating. Andy.

lostforawhile

I would have taken some pictures, but my camera lens went out and my phone was hit my lightning, so that's not possible right now, the derailer must sit at an angle because if it sat parallel it would hit the pedal crank, the existing wear marks on the cage also match the chain when it sits at an angle, I'm a pretty good fabricator and mechanic, but I usually work on cars, but I don't get frustrated with mechanical things, it's just a matter of figuring it out

onespeedbiker

Actually your post makes some sense. The OEM Schwinn Approved derailleur you have is probably the old push rod Huret Alvit. These derailleurs can be adjusted for high and low stops, however it is different from your newer version derailleur, probably a GT290 with the H/L screws on top (the GT290 was a re-branded Huret Challenger with a solid cage) . To adjust the Alvit, there is spring held screw sticking up from the top, this is you low stop. To adjust the high stop, on you loosen the nut that is holding the rod (which is attached to the cage) in place. This allows you to move the cage forward or back for the high adjustment.

#1 if the new to you derailleur has a clamp that is too large there are shims available that would allow you to use the clamp as well as the cage. OTOH, I'm still not clear why you can't install the front derailleur so the cage is parallel to the chainrings (that would be the outside wall of the cage, not the inside). Your crankset should have a built in chain guard for that year, so how the derailleur could get past the guard is unclear to me.

lostforawhile

I'll try and get some pictures, whoever worked on this bike before had no idea what he was doing, he was riding it for a short period of time with a bearing missing in the headset if that tells you anything, I have all the missing parts coming, but it's going to take some work to make this right again. I used to work on these when I was younger, but it's probably been two decades since I last owned one, so I cant remember everything. If anyone has one of these bikes and had a good picture of the proper derailer and chain guard that would be a huge help

lostforawhile

the new derailer isn't too big,it's too small, both derailers look identical except for the two top mounted adjustment screws on the new one, and it's diameter for a smaller post