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Old 09-02-07, 06:08 PM   #1
sykerocker 
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Questions on Shimano 100GS

A couple of days ago, my wife dropped by the local transfer station (aka, county dump) and comes home with a GT Passage (21 speed hybrid/city bike) complete and seemingly in good condition despite the usual rust on the fasteners, etc. It's condition was proven to me by my promptly pumping up the tyres and taking it for a mile ride. This is the first bike that I've ever gotten from the dump in (almost) ridable condition.

It's obviously their low line (although it came from a local bike shop) model as evidenced by no quick release on the rear axle and Shimano 100GS components throughout. I've never messed with this line, and they're obviously cheap although they seem to do their jobs nicely. Now, I've yet to start tearing into the bike, and it's going to get a complete work over before it replaces my Raleigh Sports at work as the lunchtime errand runner. I've got a couple of questions in the meantime:

1. The shifters are sticky. The rear one works half the time, always works on going down the cluster, hangs up half the time when I try to get the derailleur to climb the freewheel. Obviously it needs cleaned out. Anyone have any favorite method, chemicals, etc. on doing so?

2. The front shifter climbs the freewheel perfectly. Going down, it immediately snaps from third to first on one push of the button. Am I correct in assuming we're talking cleaning, or was this a cheap and dirty deliberate design on the part of Shimano?

Otherwise, this looks like one of the easiest jobs I've had in ages. Wire brush the rust off the fasteners, disassemble, grease, polish, reassemble. I'm amazed how nice the frame paint is.

Thanks for the assistance.
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Old 09-02-07, 06:51 PM   #2
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Shimano 100GS group (xx-M100) was made 1991-2. I know of no on-line docs for the group.

1) Wash out/soak the shifter with something like WD-40 until it works, then spray in a light lube if you have one. Exact procedures vary.

2) It's probably a matter of adjustment of the FD, but giving the left shifter the same treatment couldn't hurt.

Also check that the cables are smooth in the housings.
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Old 09-02-07, 07:01 PM   #3
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Shimano 100GS group (xx-M100) was made 1991-2. I know of no on-line docs for the group.

1) Wash out/soak the shifter with something like WD-40 until it works, then spray in a light lube if you have one. Exact procedures vary.

2) It's probably a matter of adjustment of the FD, but giving the left shifter the same treatment couldn't hurt.

Also check that the cables are smooth in the housings.
Thanks. I had a feeling that WD-40 was going to be in there somewhere. My two favorite tools on cleaning up a junkyard bike: WD-40 and compressed air.

I also had a funny feeling that this 100GS line was not exactly one of Shimano's majors when I did a search on eBay and came up with NOTHING . By the way, thanks, you've also dated the bike for me. I was wondering what era they would have combined 100GS with BioPace chainwheels (which I thought had disappeared in the late 80's).
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Old 09-02-07, 07:37 PM   #4
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Biopace is alive and well! Check eBay. If the rings are in good shape you might consider selling them.

Looks like 100GS was a low-end mountain group. No reason to keep it intact if something needs replacing.

Be aware that WD-40 is a lousy lubricant. It's main asset is that it drys, then mostly goes away.
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Old 09-02-07, 10:00 PM   #5
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"2. The front shifter climbs the freewheel perfectly. Going down, it immediately snaps from third to first on one push of the button."

I had an Altus front shifter that wouldn't "catch" the middle when going up or down. WD-40 did the trick!
After a couple "flush cycles", when SLOWLY easing the shifter down from BIG, I could start getting it to catch the MIDDLE. Progress was pretty quick from that point, with another flush.

Edit-
This link helps identify the era of some components.
http://www.fa-technik.adfc.de/Herste...o/Gruppen.html
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Old 05-07-12, 01:42 PM   #6
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"2. The front shifter climbs the freewheel perfectly. Going down, it immediately snaps from third to first on one push of the button."
I happened upon this old thread and thought I'd add to it.

I just got a Trek 800 with Shimano 100GS shifters and the front one was doing the same thing. Yes flushing with WD40 will almsot certainly do the trick, but I prefer to take the cover off. It makes it easier to clean.

Below is the shifter with the cover removed (one phillips screw holds the cover in place)



The arrows point to the cam which is the culprit. As the factory grease thickens with age, it dampenss the cam's movement, causing it not to "catch". I find it easiest to use a solvent such as brake-kleen, and physically move the cam up and down many times to get the old grease out. Then I re-lube with WD40.

You can tell at once, with the shifter in your hand that it is working properly before re-installing. I have yet to see a shifter that has failed due to mechanical flaw or wear. They all just seem to become gummed up in the old grease.

Hope this helps!

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Old 05-08-12, 07:40 AM   #7
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That right there, as simple as you'll ever see it, is what goes wrong with STI most of the time.
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Old 01-12-13, 02:07 PM   #8
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I just stumbled into this forum today looking for help with a similar bike. My 91 era GT Passage's rear derailler fell off. I am looking for a replacement or the proper nut to re attach. Any thoughts? THX in advance
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Old 01-12-13, 02:12 PM   #9
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I just stumbled into this forum today looking for help with a similar bike. My 91 era GT Passage's rear derailler fell off. I am looking for a replacement or the proper nut to re attach. Any thoughts? THX in advance
A picture would help - there are a number of potential failure points, but it's not common for a rear derailleur to simply fall off.
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Old 01-12-13, 09:22 PM   #10
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Yeah, I have never seen an entire derailleur 'fall off.' I would like to see a picture too.
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Old 01-13-13, 10:44 AM   #11
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Originally Posted by scoostraw View Post
...The arrows point to the cam which is the culprit. As the factory grease thickens with age, it dampenss the cam's movement, causing it not to "catch"....
It's a pawl, not a cam.
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Old 01-14-13, 11:30 AM   #12
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It's a pawl, not a cam.
You're correct. It is called a pawl, not a cam. My error.
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