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Old 08-05-08, 10:36 AM   #1
cooker
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Advice on DYI rear gearing replacement and friction shifters

(thread title should say "DIY")

Hi all, hoping for some advice on maintaining the “retro” aspect of my bike.

As detailed elsewhere, I commute on a 1984 Trek 520 with downtube friction shifters. Earlier this year, when the obsolete helicomatic rear hub couldn’t be maintained any longer, I got a 27’ wheel from another older bike. However that one had worn-out cogs, on a uniglide hub, and I managed to salvage that by installing five cogs from a new 7 speed cluster (I filed off the wide tab) and for the 6th cog, I flipped the original locking cog around so the “good” side of the teeth would mesh with the chain.

Unfortunately along the way I broke the original Suntour Mark II rear derailleur, and I couldn’t find a similar one on eBay, so I bought a new mid-length Sora rear derailleur. So I have a working 6 speed rear cluster, but spaced like a 7 speed and in fact a slightly better lowest gear than I had before (28 vs 26 teeth).

Things sort of work, but I still have a problem with the chain skipping. I think it is because the derailleur doesn’t work well with the cassette or maybe with the friction shifter. If I am in my highest or lowest one or two gears I have no problem, but if the chain is in the middle of the cassette and I decide to sprint, I sometimes feel it jump – I think it is going sideways, not forward. In other words I think I am getting unwanted shifting under load. However, I’m not sure: I can’t reproduce the problem on my "workstand" (hitch-mounted car rack), because I can’t apply the same torque.

The guiding wheels of the derailleur seem extremely close to the cassette cogs, and also the friction shifting is very tricky…hard to get it precisely where you want it. Also I may have left the chain a bit long to accommodate the larger 28 tooth cog – there’s a bit of slack in the lower run.

Getting to the point:
So what do people think the solution is? Is the Sora derailleur not intended to work with friction shifters? Is it possibly mounted wrong? I’m not sure why there’s so little clearance where it feeds the chain onto the cogs. (I can post pictures later if necessary). Would an extra washer between the derailleur and the hanger fix that? It's mounted on a built in hanger with no "claw" part, so maybe it's too close to the wheel?
I'd rather not switch to indexed shifting unless I have to. Would removing a chain link help? Do I need to tear apart the cassette and get slightly wider spacers so the cogs are spaced more like an original 6 speed and not like a 7 speed? Should I post in C&V? Any and all comments welcome

Thanks all.

Last edited by cooker; 08-05-08 at 10:59 AM.
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Old 08-05-08, 11:44 AM   #2
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For me, the subject line is accurate.

Do Yourself In = Do It Yourself

Though it is still fun.

You might want to ask someone to ride with you to determine exactly what's happening as you feel the jump.
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Old 08-05-08, 03:15 PM   #3
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Your new rd has a "b" screw which can be used to position the jockey pulley closer to or further from the cogs. Try tightening it a bit to get more clearance. Also, if your chain is longer than needed to safely shift into big-big, shortening it should improve the situation too.

One other thought, what width chain are you using? If it's the old "wide" chain from the 6-speed freewheel, it will interfer with a 7-speed spaced freewheel or cassette. You need a 7/8-speed chain.
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Old 08-05-08, 04:35 PM   #4
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Originally Posted by HillRider View Post
Your new rd has a "b" screw which can be used to position the jockey pulley closer to or further from the cogs. Try tightening it a bit to get more clearance. Also, if your chain is longer than needed to safely shift into big-big, shortening it should improve the situation too.

One other thought, what width chain are you using? If it's the old "wide" chain from the 6-speed freewheel, it will interfer with a 7-speed spaced freewheel or cassette. You need a 7/8-speed chain.
Thanks. I'll have to figure out which is the "B" screw, and I think I will remove a chain link.

I'm not sure there is a different chain for 7/8 speed clusters. I thought that only applied when you got up to 9 or 10 speeds.
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Old 08-05-08, 05:23 PM   #5
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I'm not sure there is a different chain for 7/8 speed clusters. I thought that only applied when you got up to 9 or 10 speeds.
7 and 8-speed cassettes use the same chain, commonly known as 8-speed chain these days. 9-speed chain is narrower and 10-speed is narrower yet.
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Old 08-05-08, 07:35 PM   #6
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Hi...

YOU CAN USE ANY TYPE OR RD WITH FRICTION!!!!! no matter what brand or type of RD u want to use, with friction will work fine because u are the one who is doing the shifting... i'm pretty sure u got the idea.

Regarding the chain? the regular 8 speed one should work fine if you cant find one for 6 speeds that is a little bit wider. But probably even a 9 speed chain will work fine. The nice about using a narrow chain is that the bike will get a little bit more silent (here is where u have to ask why???).

Somebody said something about the B screw? the B screw is a screw that basically push the RD backwards (or inwards) with the RD hanger, in the rd hanger u have the hole and a little thing under it, like a lip, the rd has a screw that touch that lip, once it touchs it, the rd spring starts working (im sure u'll find it). Basically what hillrider says is that u have to move the RD backwards using that B screw, in that way the Jockey Wheels will get a lit bit far from the frame or as u said, from where the chain feeds the cassette cogs. Probably that will fix your problem.

http://www.sheldonbrown.com/deakins/lowgears.html

there you have a few pictures of a b screw and what is it for.

Did you check if the RD hanger is straight vertically? That will make the RD to work in a bad position and would make your gears to skip.

The next option should be that the cassette is pretty worn out. A new cassette might help you. U said something about putting a cog backwards? Usually cassette cogs have only one position because the teeths have only one way to work, usually the back face is flat and the front face is pretty polished and contourned. For example if you put the 16T cog backwards for sure the chain will start skipping and doing weird stuff.

Thanks
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Old 08-05-08, 08:22 PM   #7
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Originally Posted by ultraman6970 View Post
Regarding the chain? the regular 8 speed one should work fine if you cant find one for 6 speeds that is a little bit wider.
The OP needs a 7/8-speed chain. He replaced the original 6-speed freewheel or cassette (I'm not certain which) with 5 cogs from a 7-speed cluster and held it all together with a thread on top cog. So, for 5 of the 6 cogs he has 7-speed spacing.
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Old 08-05-08, 08:43 PM   #8
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The OP needs a 7/8-speed chain <-- i said "the regular 8 speed one should work fine"

Where is the problem then?
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Old 08-05-08, 09:26 PM   #9
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Thanks everyone.

I'm pretty sure the new chain I have is a 7/8 compatible. i may still have the box in the garage. Probably LBSs don't sell a 6 speed-only chain unless you specially request it.

Another idea I got from Sheldon's site is to check for autoshifting due to cable friction under the bottom bracket so I will lube that area in the am.

The derailleur hanger appears straight.

Ah, so the B screw the one that butts onto a jutting out ledge on the bottom of the hanger and rotates the derailleur body forward or back. I did screw it quite far in when I mounted the derailleur in the hopes of solving the gap problem. Maybe I need to go still farther.

EDIT" Ultraman, thanks for the Sheldon link - I hadn't found that page. I have a feeling I will need to get a longer 4 mm B bolt and/or put it in backwards as shown, since I recall now that I already screwed the B screw (I didn't know its name then), far enough that I thought it might go off the ledge due to the changing angle of contact.
Attached Images
File Type: jpg b screw.JPG (5.2 KB, 4 views)

Last edited by cooker; 08-06-08 at 05:50 AM.
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Old 08-06-08, 07:12 AM   #10
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Originally Posted by ultraman6970 View Post
The OP needs a 7/8-speed chain <-- i said "the regular 8 speed one should work fine"

Where is the problem then?
Not a problem but here is what you wrote above; "......the regular 8 speed one should work fine if you cant find one for 6 speeds that is a little bit wider." (my emphasis)

I took that to mean that a 6-speed chain was more desirable but a 8-speed would do if the OP couldn't find a 6-speed one. My point was that the OP NEEDS a 7/8-speed chain.
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Old 08-08-08, 09:38 AM   #11
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Hi, everybody and thanks again. I think with your help I have corrected the problem. When I first installed the derailleur, I screwed the B blot (I didn't know it's name then) most of the way in as shown in post 9, but that apparently wasn't enough.

On Wednesday I took the derailleur off and tried to reverse the bolt as suggested on Sheldon's page, but it interfered with remounting the derailleur, so I put it back the orginal way and simply screwed it in all the way (a tiny bit farther than before, and it still made adequate contact with the derailleur hanger's nub). I also lubed the shifter and the cable guides, since there may have been a bit of grittiness that interfered with precise shifting.

For whatever reason, it seems to be better now, and I am gradually increasing how much torque I am willing to apply - so far no skipping/autoshifting.

So hopefully the problem is solved. Thanks.

Robert
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