# Gt100 Adjustment



## drglinski (Aug 4, 2016)

Does anyone have an adjustment/operations diagram for the GT100 rear derailleur used on the Collegiate?  I'm trying to troubleshoot mine.

Thanks


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## drglinski (Aug 7, 2016)

drglinski said:


> Does anyone have an adjustment/operations diagram for the GT100 rear derailleur used on the Collegiate?  I'm trying to troubleshoot mine.
> 
> Thanks



Looking for any help I can get on one of these.  It's on my Father in Laws bike and I'd like to figure out how to get it working better so he can have his bike back.  I get how a derailleur works; adjustment screws, chain length, etc, but this one is stumping me.


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## Metacortex (Aug 7, 2016)

The biggest problem with these is that the main hanger pivot spring is prone to breakage or disengagement from the hanger, which dramatically hurts shifting performance. Also note that when the spring is engaged it has two settings, 5 or 10-speed. For best performance I recommend the spring always be set to the 10-speed (stiffer) setting even when being used on a 5-speed bike.


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## drglinski (Aug 8, 2016)

So does the spring (that needs to be set in the 10 speed hole) need to hold the arm up towards the wheel stay, or away from?  The issue I'm running into is the whole idler wheel assembly is too high when I'm trying to shift into the larger gears and it catches and hits (on the larger cogs).


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## Metacortex (Aug 8, 2016)

With the derailleur removed from the bike the hanger pivot spring should forcibly drive the hanger towards the cable adjuster, as seen in the following pic:






When mounted on the bike this spring tension drives the body of the derailleur down and rearward (away from the chainstay), thus providing more distance between the upper (jockey) pulley and the freewheel. When this spring is broken or disengaged the body of the derailleur flops forward, allowing the pulley to hit the larger freewheel sprockets.

 Note in the above pic that there are two holes surrounding the main bolt attaching the hanger to the derailleur, one marked "5" and the other marked "10", and that the end of the spring can be seen in the "5" speed hole. With the spring set in the "10" speed hole the tension is even greater, further insuring that the jockey pulley will be pushed down and back to clear the largest freewheel sprocket.

With the derailleur removed if the hanger can flop back and forth then the hanger pivot spring is broken or disengaged. Quote a few of the GT-100s I've seen have this problem. If the spring is simply disengaged then I merely re-engage it (in the 10-speed hole). On one I had where the hooked spring tip was broken off, I was able to simply bend the end of the spring 90 degrees to form a hooked end to engage the hole in the hanger. This had the side effect of slightly increasing the overall tension as well.


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## drglinski (Aug 8, 2016)

Ok thanks...there must be something wrong with the spring inside the one I'm working on.  I know it's installed in the 5 speed hole but the spring is noticeably driving the derailleur in the opposite direction of what you described.


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## drglinski (Aug 9, 2016)

I put the spring in the 10 speed hole and it works much better now.   Thanks very much for the assistance.  I was at my wits end with this thing and now I can feel confident giving it back to my f-in law.


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## Metacortex (Aug 9, 2016)

Thanks for letting me know the outcome, glad it worked out!


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## Metacortex (Aug 21, 2016)

Recently found this GT-100 bulletin from July '71 showing how to change the main pivot tension from 5 (weaker) to 10 (stronger) speed mode so I thought I would add it here for reference:


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