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Where is the "B" Tension Screw on My Rear Derailleur? SunTour Experts HELP!

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Where is the "B" Tension Screw on My Rear Derailleur? SunTour Experts HELP!

Old 06-04-14, 01:23 AM
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Where is the "B" Tension Screw on My Rear Derailleur? SunTour Experts HELP!

I am posting this on this forum because it is a vintage derailleur and I'm certain someone can help me. I have a SunTour XCD 6000 rear derailleur on my bike. See velobase: VeloBase.com - Component: SunTour XCD 6000 Rear Derailleur

When in small chainring and largest cog, the guide pulley is too close to the teeth on the largest cog. Normally I would adjust the "B" tension screw, which normally sticks out the back and when turned clockwise pushes against the derailleur hanger "stop". My derailleur doesn't have this, but has other markings & things I don't understand.

On the back of the derailleur it has the "H" & "L" screws, a barrel adjuster, and just above the barrel adjuster the letters "A" & "B", but no additional screws for these letters "A" & "B". Where the "B" tension screw normally resides there is a cutout piece of black plastic which is screwed in from the side (the screw head is toward the center of the bike). I removed that little "L" shaped wedge of plastic and didn't see anything obvious that I could do to change the situation. I screwed that little piece back in. Here are some close photos. I don't have a graphic program to draw arrows on the photos. Hope you can see what I'm referring to. Otherwise indexing works great, just need a little more space between guide pulley and largest cog teeth.

Thanks.
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Old 06-04-14, 04:52 AM
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It doesn't have one.
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Old 06-04-14, 05:05 AM
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Originally Posted by miamijim View Post
It doesn't have one.
+1... I use a zip tie to hold my XCM back enough to clear the large cog

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Old 06-04-14, 08:19 AM
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@miamijim - thanks for the reply. What is the purpose of that black plastic cutout piece screwed in from the side in place of where B screw would be? I think that's what confused me. I presumed that was some sort of newfangled Accushift way to adjust the body angle.
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Old 06-04-14, 08:35 AM
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Originally Posted by Velocivixen View Post
@miamijim - thanks for the reply. What is the purpose of that black plastic cutout piece screwed in from the side in place of where B screw would be? I think that's what confused me. I presumed that was some sort of newfangled Accushift way to adjust the body angle.
The purpose of the plastic piece is to fix the angle in a fixed position, there's no adjusting it.

What gear ratio's are you running? What's the angle look like when your in small/small?
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Old 06-04-14, 08:51 AM
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That's surprising that it doesn't have a B screw. I would have thought that the purpose of that RD and the level at which it was at would kind of require that unit to have the capabilities for larger cogs.

Can you put a shim in where the B screw would be?
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Old 06-04-14, 08:55 AM
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@miamijim- it's rear cluster is 13-30 Suntour Alpha, and smallest chainring front is 28. I'm fairly certain it's all original. Here are some photos. Sorry for the cluttered background.
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Old 06-04-14, 09:15 AM
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I had this same problem on my Trek 400 when I tried to get a 30 or 32 tooth cog to work with a Superbe Pro RD. I REALLY wanted it to work. Ended up going to XC Pro and XC Comp.

Viva Accushift!
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Old 06-04-14, 09:37 AM
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Thanks everyone. I NEVER ride in this combo anyway, but I thought I'd lost my mind. Was in the garage until MIDNIGHT trying to figure it all out. I did other things too. Need brake pads and a little more tweaking and should be good to go. At least I got Accushift to index. Even took apart the rear shifter, cleaned, reassembled. First time didn't work, then re-assembled and works like a charm. Let's just say that it helps to have the right tool for "C" clamp install/removal!
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Old 06-04-14, 10:26 AM
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Originally Posted by Velocivixen View Post
At least I got Accushift to index.
Viva Accushift!
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Old 06-04-14, 10:39 AM
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Can I see a full side pic of the gear system in small/small?
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Old 06-04-14, 10:58 AM
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@miamijim - I'll be home shortly and I'll get that to you. Had to remove a link because in the small-small combo the guide pulley & tension pulley were rubbing each other vigorously! I use couple methods for chain length. Chain is long enough to safely do large-large (I never do this), and short enough so that in small-small the chain doesn't droop and pulley teeth don't rub each other.

I'll get that photo up within an hour. Thanks for your help.
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Old 06-04-14, 11:58 AM
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Shorten the chain? I wonder how that would fly when you're on the big chainring? Obviously, on a vintage triple, you're never really meant to run large/large or small/small combo, though on my modern MTB, both seem to work fine.
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Old 06-04-14, 12:28 PM
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@miamijim - ok here it is:



I think I may have something else wrong that may or may not be contributing to this. I didn't notice it at first because my indexing works great. I think my derailleur hanger (frame type) is bent. I notice the derailleur "arms" between the guide & tension pulleys are angled in. Chain is in middle chainring and center cog in this photo (sorry I don't know why this photo uploaded side ways):

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Old 06-04-14, 01:03 PM
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Vv, that looks more like the RD's cage is bent, a typical sign that the RD has had an unexpected near-life-ending event. FWIW, bending a cage is a lot easier than bending the DO on the frame. If you mount another RD (you don't have to bother with the chain or cable, just pull them aside) does it look crooked too? If not, then it isn't the hanger.

However unless something else is bent or broken I don't see how that should affect the effective chain length.
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Old 06-04-14, 04:22 PM
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@jimmuller - thanks for the info. I don't know how to bend a derailleur cage. Is the cage the parallelogram part or the part that hangs down from the guide pulley to the tension pulley? Well anyway I have an appt. tomorrow at the LBS to have them check and straighten if necessary. I'll keep you posted. I was hoping miamijim would chime in and give his idea.

Thanks.
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Old 06-04-14, 05:21 PM
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Originally Posted by Velocivixen View Post
short enough so that in small-small the chain doesn't droop and pulley teeth don't rub each other.
That's my primary way of sizing a chain...make it as long as possible but so it doesn't sag or drag on the pulley's.

Looking at your pictures there's not much you can do, the systems at the limitation of what the derailleur can handle. And as jimmuller mentioned the derailleur body/cage is bent but not the frame. That's wont change anything and if you want just grab hold of the derailleur and bend it back.

The one thing you can try is sizing the chain in the big/big...make the chain as short as possible as it will pull the upper pulley away from the cog. As you know, if the chain is too short you wont be able to shift into the big/big but who rides big/big anyways.
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Old 06-04-14, 07:33 PM
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Originally Posted by miamijim View Post
... if you want just grab hold of the derailleur and bend it back.

The one thing you can try is sizing the chain in the big/big...make the chain as short as possible as it will pull the upper pulley away from the cog. As you know, if the chain is too short you wont be able to shift into the big/big but who rides big/big anyways.
miamijim's reply is about what I would have said. The cage is the set of plates which hold the pulleys, not the parallelogram itself (though that would have been a good guess). They are usually not so strong. A stiff sideways pull or accident or other unnatural event can bend them. The two plates are clamped together by the pulley bolts, but only the inner plate is anchored by the cage pivot. Since that's where any resisting force will act, the usual bending mode is for the inner plate to bend near the pivot mount. The end result is that the pivot axis is no longer perpendicular to the plates. You can sometimes just bend everything back enough to make it functional again. If you can't, well nothing is lost in trying.

I would quibble with mj's comment about not riding big-big. No one does it on purpose but it is real easy to shift the rear to one more lower gear, having forgotten that you are already on the next-the-last big gear and still on the big ring. I've done it quite a few times, and been grateful that I kept the chain long enough to accommodate it.
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Old 06-04-14, 08:54 PM
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Shortening the chain worked for me when I was trying to get my Superbe Pro to climb onto a 28 t cog.
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Old 06-04-14, 10:06 PM
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OK, I'll check out the chain situation again. My BIG question is this: Since I can index shift just fine do I have to do anything for the hanger (if it's bent) or to the derailleur cage (if it's bent)? This is a different question than my original "B" tension screw question. The derailleur indexes pretty darned good. I'm afraid of having the cage toward the spokes when I'm in a bigger cog and don't want a crash due to this.

So....what would you do? Also I might sell the bike. Just bought it and it's not really "calling" to me. I think I just wanted a project.
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Old 06-04-14, 11:50 PM
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@Velocivixen
The rear derailleur B tension is only adjustable by two settings with that little black plastic bit for this series of Suntour derailleaurs.
When you take off the screw that's hold it in, flipping it and re-inserting gives you either less or more load on the spring.
One end lays flush, while other end project out further, like if you screwed in the B-screw.

Hope that makes sense.

I wouldn't bend the cage....correct thing is to check the dropout alignment, with an alignment tool. Any good bike shop will have the tool and it's a 10 minute job to check and bend it straight. If the dropout is true, and RD cage is still misaligned, then the RD is whacked.
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Old 06-05-14, 12:05 AM
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@WNG - knew that plastic piece screwed on had meaning. It wouldn't just be there with no function - that doesn't make sense. I took it all the way off & looked at it and screwed I to, noting that it sort of looked like a puzzle piece that could maybe go in two similar ways. I will fiddle with it tomorrow and maybe also shorten the chain by 1 link. I could get away with that but not more.

I have an appt. Tomorrow to drop off the bike at my LBS for some hanger alignment if needed.
As an aside I'm finding I'm not too attached to the bike. The stem makes it too long. I have other handlebars that I could use & stems to make it better, but not sure I want to go through the whole procedure. And the wheels aren't true. I sort of know how to do basic lateral trueing, so I could give it a go.

Thanks to everyone who has encouraged me. I appreciate your generosity.
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Old 06-05-14, 04:00 PM
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UPDATE: For anyone following this thread. Took bike to LBS and they said that the derailleur hanger was "significantly" bent. It's fixed now.
I turned that tiny piece of plastic the other way and moved the derailleur angle back a tiny bit.

Now I have to learn to true the wheels and maybe it will be fun to ride. :0
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Old 07-11-20, 10:37 AM
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ah, the value of old threads

I recently snagged an Offroad (brand) mtn. bike with suntour accushift XCD 6000.
Everything seems original and complete.
With a little tuning it shifts smoothly through all the gears...except in the next-to-largest rear cog
the top edge of the derailler cage rubs on the largest cog. I, too, was looking for a B screw, but only found that
mystery plastic piece. I'm about to flip it around, 'cause I was going crazy trying to solve the rub.
Thanks guys.
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Old 07-11-20, 06:32 PM
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One thing about these index-era Suntour derailers with a "tension spring" in their mounting bolt pivot:

The spring only serves to pull the derailer back while the wheel is removed, helping to facilitate an easy wheel-change and keeping the chain taut and orderly.

When the wheel is installed, the sprung pivot returns to it's forward-stop position, so does not float like a Shimano derailer between the two sprung pivots.

I have surmised that this might have had to do with a Shimano Patent, although Campagnolo would initially adopt what looked more like Shimano's sprung pivot on their earliest Ergo-era rear derailers circa ~1991.
What I did in those days (since I often ran Command shifters with a Superbe Pro RD having a "stopped" rear derailer with a tensioning spring), was to re-drill the anchor holes in the derailer spring area so as to adjust the spring tensions independently, even though there were no adjusters to begin with. I ended up getting it to work like a Shimano derailer and figured that the high-end Suntour derailers used on team bikes probably got the same sort of tweaks so as not be be potentially constrained by any patents at the highest levels of racing. Of course by then there suddenly were declining numbers of riders or teams using Suntour equipment.

I'm noticing that the OP's bike has what looks like an Accu-7 freewheel, which will index best using Shimano 9s chain. The shifting in front will also likely improve substantially using the modern chain.
For this bike, I would start by experimenting with chain tension changes at the rear axle in conjunction with changes in chain length. Once the best chain tension arrangement is found, I would then switch to modern 9s chain, expecting the new chain to be a bit shorter by the amount of wear on the old chain.
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