84 ST500 rear derailleur - what model works well

[Steven Chain]

I'm getting my 1984 ST500 into riding condition. The original rear derailleur never worked well and died when it argued with the spokes and lost. The dealer replaced it with a Suntour XC which worked better but is not a good match. Does anyone have experience with a rear derailleur that works well on an ST500? Also, has anyone converted an ST500 to indexed shifting?

 

[black lightning 1987]

I would have guessed that the XC would work pretty well for friction shifting. Do you still have the 6 speed 13-30 New Winner freewheel? I'm not sure if that was standard width or Ultra (narrow) but guessing it was standard. Pretty sure for indexing you could use any long cage SunTour Accushift derailleur (such as XCD 6000 or XCE 4050) with Cyclone down tube shifters. SunTour also made 6 speed Accushift bar end shifters, but you will likely have to pay more for them than downtube shifters. I have built my '85 ST500 with 7 speed indexed SunTour, using an XC Pro derailleur, GPX shifters, and SL cassette hub. Pics below. This could also be done with a SunTour freewheel. I have lots of SunTour stuff on the shelf and can test run a couple of setups if needed.

Another option would be to convert to a 7 speed Shimano setup. Pretty sure your frame has 126 mm rear spacing, which should allow for a swap to a 7 speed freewheel with no modifications. Hard to find any ratios other than 14-28 or 14-34, but those two are easy to find new. Use most any long cage Shimano 7/8/9 speed era derailleur and 7 speed DT, bar end, or STI shifters. You will need a MTB derailleur if you want the 34 cog. I have gone the 7 speed Shimano route with my '85 ST400. Pretty sure I have a 14-28 freewheel, XT derailleur, and SL-BS50 bar end shifters.

 

[Steven Chain]

Thanks! It's always nice to get more help than you expected. I would like to convert it to index shifting. Especially since I can keep the freewheel which is a Winner 13-30. I measured the frame and it is 126 mm spacing.
I did some quick looking and found both the Suntour derailleurs you mentioned. The difference in price is negligible so which would you suggest? Also, they are often offered as sets with the front derailleur. It makes sense to do both. Should I anticipate any problems there. If testing some setups is not too much trouble I would greatly appreciate it. I would like to get this right the first time.
Finally, I'm pretty sure that the derailleur hanger is bent. I put a straight edge on it at these is a very small, less than a mm, gap that shows it is bent inward. No matter how I adjust the current derailleur the chain won't go onto the smallest wheel. I've read and watched YouTube videos and heard the opinions on bending an aluminum hanger and the one that makes the most sense is, "what do you have to loose?" Any thoughts?

 

[black lightning 1987]

Best to have the hanger checked with an alignment gauge, like the Park. It shouldn't be a problem to tweak the hanger slightly. Your high limit screw is probably preventing the derailleur from reaching the small cog. Turning it out should allow it to move farther. You may also have to adjust the cable attachment.

https://www.ebay.com/itm/Park-Tool-...h=item3d7c753656:g:oLkAAOSwpYxcDW51:rk:8:pf:0

The XCD is one step above the 4050 in the line, but functionally they should be the same. I'm sure I have an XCD and the Cyclone shifters here, and will set them up on a frame and check function. I probably don't have the exact freewheel you have but should have something close. Front derailleur change is up to you. If your front shifting is good now, there's no reason to change unless you just want one that matches the rear. All the shifters I mentioned except STI have friction front shifting, so will generally work with any front derailleur.

 

[black lightning 1987]

I tried the XCD/Cyclone setup a bit last night. I did find a 6 speed freewheel with a 30 cog, but it's an Ultra and has a big jump from the 22 tooth 5th cog to the 30. It didn't shift very well onto the 30 and oddly had trouble shifting to one of the smaller cogs as well. It actually worked better with a modern Shimano that is wider spaced. There are still things I can try, including GPX shifters and a different chain.

I'm going to need to know exactly what your freewheel is. The New Winner could be either regular or Ultra spaced. Read the section on freewheel bodies here:

https://sheldonbrown.com/suntour-freewheel.html

Have a close look at your freewheel and you should be able to tell if it's regular or Ultra spaced.

 

[Steven Chain]

So the simplest way seems to be to measure the distance between gears with calipers and I consistently got results around 5.5 mm. However, the outer body extends past the cover plate by slightly less than 2 mm. But the gears spacing is always abut 5.5 mm. So I don't think this is an Ultra. Also, there is no mention of Ultra in the Cannondale literature for 1984.

As for the bent hanger I live in a tourist town in a very popular mountain biking area. So I figured the local bike sales and rental shop probably had experience with bent hangers. It is now fixed and the derailleur works much better.

 

[black lightning 1987]

Sounds like it's not an Ultra, but it's hard to get a good measurement of either spacers or cogs on a freewheel that's built up.

Do you still want to pursue an indexed setup?

 

[Steven Chain]

I've been read up on index shifting and did not realized the changes in all that is related - chains, gear spacing, gear shape and so on. I also realized that the large gear on my chain ring is bent. This bike and I were once in a serious wreck (I woke up in the emergency room) so I need to stop and do a complete exam on this bike before proceeding. No mechanic ever told me the frame was bent but I think it is time to check out everything before proceeding. Right now suggestions on what and how to do that would be useful. I'll keep you posted.
Thanks for you help.

 

[black lightning 1987]

Chain ring can probably be straightened with a big adjustable wrench.

What was the nature of the accident? There should be some evidence of any contact hard enough to bend the frame. Exception might be front impact, which could bend the frame and/or fork without scarring up the paint.

 

[Steven Chain]

The nature of the accident is based on evidence as I have never remembered any of it. I was riding alone coming down out of the mountains (west of Denver) on a low traffic road. Someone passing by found me on the road and called an ambulance.I woke up in the hospital, likely an hour or so later. I remember a doctor introducing himself as a neurosurgeon and telling me if my brain started to swell they would have to take me to surgery and open up my skull. Now I don't ride out of the driveway without a helmet.

The front wheel of the bike was badly mangled with not one straight spoke. I don't remember what the bike shop did as far as assessing damage. So yes, it must have been hitting something with the front of the bike. In any case I saw a YouTube video on how to build a gauge and check to see if a frame is straight and will do that in the next couple days. I'll post results here. I will also see how badly the chain ring is bent. It has just enough wobble to be noisy unless the front derailleur is positioned exactly.