difficult RD downshift
 

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Is the Suntour BL RD a reversed derailleur in that the low gear is the default setting?

The reason I ask is that normally the RD is at the high gear or small sprocket and you pull it up to the low gear or large sprocket. I run Suntour barends on several bikes (but with Shimano, Sachs-Huret, and Campagnolo RDs) and they work great.

Did you set the RD at the smallest sprocket and the shifter in the furthest down position, and then pull all the extra slack out of the cable and retighten the pinch nut?

Screw the adjuster barrel out until it starts to pull the derailleur.

Try pulling the cable with a 4th hand tool when installing.

Reversing the position of the cable through the pinch bolt may help (or hurt).

That's all I got.

Those were my favorite price to point RD of the period for racing.

"If I loosen the bar-end pivot bolts any more, the bar-ends will not hold the RD."

is this the problem? is it a barcon friction problem? one where it will downshift through all the gears but won't stay in place? and if you tighten it enough to stay in place then it's not easy to downshift?

have you overhauled the barcons?

have you tried another barcon? like the other one in its place?

let's try to narrow the issue.

there's a reason these were so popular. they usually work great and are basicslly bombproof.

with all that said, i never install them on my builds. i prefer dt shifters for their simple and sleek utility, and i can easily sell suntour barcons on craigs for $35 regardless of the month.

i always get all the slack completely out of the cable by tightening the rd's high limit screw several turns before tightening the anchor bolt, then i loosen the limit screw back to its specific mark and recheck. it's trial and error, but it works for me.

I think you are saying that, when the chain is in the smallest cog, to shift to a larger cog you have to apply more force than you'd like to the bar end lever.

I would leave the bar end lever in the position for the smallest cog (shift lever pointing toward the ground), and try shifting by using your fingers to pull the cable away from the downtube. See if the derailleur and cables work okay, without the shifter being involved. The RD should start moving and the chain derailing, as soon as you start pulling the cable, if not then adjust out any slack using the barrel adjuster, limit screw, and if necessary the cable clamp bolt. Also check that the RD cage is vertical (viewed from the rear), the pulleys don't have too much side to side play, and that the upper pulley is not too far below the cogs.

Then shift to the largest cog, by pulling the cable with your fingers, then stop turning the pedals. The cable will now be slack. Push and pull the cable to make sure it slides freely in the housing and ferrules. Also move the bar end shifter through its range to see if there is anything binding up.

Then remove the rear wheel and, while pushing the RD inward with your fingers and letting go, see how much you have to tighten the bar end shifter to hold the RD in position against the RD's spring. You might use a drop of blue loctite if you're worried about the screw coming loose on the road.

Assuming all of that is working normally, then I'd say the force required for the shift "is what it is". I can't think of anything else, anyway.

yeah, that definitely shouldn't happen. you should be able to hold the loose, uninstalled shifter in your hand and move the lever back and forth. it should "click" in one direction and move silently (and more firmly) in the other. the 'bolts' should tighten the body to the shifter, making it more firm to shift/move. if it does all this, it should also do this when installed if the cable and housing are properly in place.

also check this shifter against the other to understand which is working properly and why.

let us know tomorrow.

If you're using unlined cable housing, as with the "Bell"-branded kits sold at WalMart, perhaps there is your problem.

The effects of friction on the inaccuracy of shifting transmission between shifter and derailer are literally multiplied by the length of both cable and housing, so un-lined housings will have the greatest detriment to the quality of bar-end style shifting.

Further, if the housings are routed to follow the tight bends in the handlebar, the problem is made much worse.

This assumes that the shift lever is ratcheting properly and so not producing friction force in the "downshift" direction (to larger cogs).

BTW, the industry typically refers to "downshifting' as shifting to a smaller cog or chainring, quite the opposite of the motorized transport world.

Suntour derailers are not noted for having excess return-spring force, and these bar-end shifters should impose no friction force at all on the "downshift" motion, so it pretty much leaves the cables as suspect #1 .

Do check the cable routing for any sort of kink or snag, with front derailer cable, or with housing/ferrule seatings or steps/edges in the bottom bracket cable guiding.
Note that a stainless steel cable guide, as used on certain Treks, can cause huge friction against stainless cable wire, a really short-sided decision on Trek's part!
I've managed to crimp a length of heavy-walled poly tubing into the cable-retaining tabs of those particular guides, since grease alone wasn't helping.

"BTW, the industry typically refers to "downshifting' as shifting to a smaller cog or chainring..."

really??

that's seriously confusing. i've always thought of downshifting like the op defines it -- shifts to either cog or ring to allow lower, smaller gears for climbing. conversely, upshifts allow higher, bigger gears for descending.

All good advice. However, bar end shifters will always require significantly higher shifter force due the extra length of housing required and the shorter levers. Run as short a housing as possible and always used lined compressionless housing (i.e housing for indexed derailleurs). Make sure the ends of the housings and ferrule holes are burr free, A small burr can cause a lot of extra cable friction.

^ glad you narrowed down the problem. good luck.

I'll bet that $4 of modern lined/compressionless shifter cable housing, a couple ferrules, and carefully squaring off the housing cuts with a file will make a difference.

I have that same derailleur on my 1971 Raleigh Super Course. I think part of the problem is that the return spring is very strong, requiring a lot of force. I have the same problem you do. I'm using thumb shifters, and I have to call them palm shifters. My wife, with her less hand strength, would not be able to shift it at all.

I hope that solves the problem for you, but I am using that housing on one of my Barcon bikes, and there is no frictional issue.

I have ridden Suntour Barcon bikes that were all original, and while the shifting action was rubbery between the lever and the derailer, it didn't seem all that hard.

The OP mentioned using the stock, unlined, stainless steel housings. The original cables were of the compound-wound type, with a great number of strands, and were not stainless steel.
Likely the OP is using modern, stainless wires in the stainless un-lined housings, which would be inherently sticky, as stainless-on-stainless tends to microscopically cold-weld, even in the presence of lubricant.
Modern Shimano zinc-plated cables are widely available for just a couple of bucks (I've bought them online for .99 on occasion), and would be entirely compatible with the unlined housings, for those who prefer to retain the original look.
I actually have a 1975 Raleigh Pro that the previous owner fitted with these stainless housings, as brake(!) cable housings (using plastic sleeves to give the toptube clamps some grip), and it actually works fine in hard use using plated inner wires.

https://c1.staticflickr.com/3/2095/1...42de3317_o.jpg

good tip and spring action is often adjustable, at least a little bit.

Ah ah! Any way to modify the spring?

Really, guys, we need desmodromic shifting.

Thank you for the vocabulary word! And yes. And this is what ratcheted shifters attempted to do, n'est-ce pas?

So, you want to go back to 1st generation Positron, with no derailleur springs and a dual cable system? ;)

Maybe an improved version . . . Suppose two shift cables are run through a single housing (maybe two liners, maybe one large diameter liner). The cabling then need not be any more complex than it is today.

Wouldn't that triple or quadruple friction? The in cable and the out cable would rub against each other as they passed each other.

most rear derailleurs have multiple positions for the end if the pulley spring for fine adjustment.

campy nr only has two positions. suntour should have at least that many.

I think the OP is wanting to relax the force of the return (cable tension) spring, not the cage (chain tension) spring.

As for running two cables in one housing, I've thought about this in the past, seems like even with a single liner, and with the cable tensions not fighting any sort of return spring, perhaps the friction of the two cables would be negligible.

It sounds like the OP's particular model of Suntour derailer has a stiffer return spring than some of the better ones. A V-series derailer seems to have a gentle return spring, while Suntour's derailers made from steel become hi-effort as the largest cog is approached, much as with a Campagnolo Gran Turismo derailer. It might be that this is because the older and lower end derailers have designs that harken back to the five-speed era, or that less effort went into designing the springing for a smooth, linear return force. The coil count and other factors affect how the spring force will manifest at the shift lever.
I am recalling now that my Motiv Defiant road bike from 1988 or so, with friction levers (this was a Costco bike, LOL), requires a hard push to get up to the largest cog, this with a Suntour steel derailer and six-speed freewheel.

https://c2.staticflickr.com/4/3853/1...09119a5c_c.jpg

"I think the OP is wanting to relax the force of the return (cable tension) spring, not the cage (chain tension) spring."

oh, right. gotcha.