mijome07

Suntour Arx long cage (RD-4500) thumb shifterShimano Deore XT (SL-M730) rear derailleur

Running a 1x6 (34Tx13-32T 6 speed Shimano freewheel). Got new 6 speed chain (cut to size), new cable n housing (w/ good bends) and 122.5mm BB for good chain line. I know this shifter has a hidden 7 speed but I'm running 6. With shifter set on high gear (1st mark), the chain is on the 2nd cog. When shifting to the lowest gear, the shifter passes the last 6th mark to the "hidden 7th speed". And the cable tension is tight.

I cleaned the derailleur and shifter. Both move good. Holding with my fingers and not going through pinch bolt, I can shift gears and feel the cable pulling great. But once I pull snug, bolt down cable, it becomes hard to shift to lower gears. And I'm adjusting the shifter barrel adjuster to find sweet spot.

This is all under friction mode. It does work under indexed, but not to lowest gear. So the derailleur won't shift to highest gear and it's hard to shift to lowest gear. I'll pulling the cable snug (not tight) when I tighten it.

Maybe it's something simple I'm missing. Limit screws are set correctly.

Andrew R Stewart 

SunTour friction shifting rear ders were (very likely) never even considered by ST to need an indexing compatibility, as indexing was still a few years away when the ARX was new. (I'll hedge that by saying the Positron der was an early Shimano indexed attempt that was on the market at the same time. But IIRC its cable was actually by then a solid push/pull "rod") (also ST did have their 1980 MityClick but most here won't know that).

The first thing I would look at is how far inwards the rear der must travel to get to the largest cog. As the der nears its most inward range the cable pulling geometry changes and might result in a greater force being needed (with no other problem present. The next is does the Shimano lever have enough cable pull to move the der all the way. When ST began to take over the mid bike market in the mid 1970s we found that some levers (Simplex as example) didn't wrap enough cable to allow a ST rear der to shift across 6 cogs, close but not consistently with every pairing.

Last bit I'll offer out here is that many of those "just before indexing became the way" rear ders had their guide pulley coaxial with the cage pivot. This allowed the open chain gap, between the guide pulley and the cog set's underside, to vary quite a bit as one shifted across the cog set. I have spent many hours working on ST systems that had poor shifting due to this design.

I suggest trying a Shimano der. Andy

squirtdad

only thing I can add as high/low stated to be correct, is to try to pull the cable as tight a possible (4 th hand helps) with shifter pushed hard to low (biggest cog). I recall having to do this to make a friction sunrace thumbie work 1x8 on a sram cassette

70sSanO

Why is the chain in the 2nd cog?

Also, in friction there is no hidden 7th speed.

Chain should be on the first cog when the shifter has released the maximum amount of cable (against the stop); nearly no cable tension.

John

TPL

Try removing the rear derailleur high gear limit screw entirely.... then loosen cable anchor clamp on that rear derailleur ....

After doing the above .... will the chain actually drop effortlessly onto the smallest cog ?

If NOT ....then your rear hub axle will require a driveside spacer ....a rather thin spacer, somewhere around 1/8 inch thick = 3.175 mm ( maybe less ) = if you have a few 1 mm hub axle spacers, then add them one at a time to the drive side of the rear hub axle, re-install wheel and see if the chain will drop effortlessly onto the small cog ( repeat the process until you have installed enough spacers to allow the chain to drop effortlessly onto that small cog )

Once the chain drops effortlessly onto the small cog = re-install high gear limit screw ( adjust and set it ) ....tighten cable anchor

If I had your bicycle and your wheel in front of me ....I could tell you pretty much exactly what thickness axle spacer to use

mijome07

Thanks everyone. I got a Deore XT rear derailleur to match the thumb shifter and it works now. I'll use the Suntour derailleur for another build this year