xenologer

Have a used bike with Shimano RX100 downtube shifters.
haven't had prior experience with dt shifters.

Was examining them closely, and don't see an obvious tension adjustment for them.
The mounting bolt just tightens down onto a fixed central sleeve independant of the lever's moving parts.
They work fine, but in the future if they do loosen up, is there a tension adjustment?
How about with more modern ones?

Thanks

Sorry, don't have a photo of them.

HillRider

The tension on the front (friction) shifter is adjustable by tightening the center mounting screw. The rear (indexing) shifter just fastens in place with the center bolt and there is a collar around it with a D-ring that has SIS (indexing) and Frict. (friction settings. You turn it to select which mode you want.

xenologer

That was my inital assumption as well, as suntour dt shifters, as well as many barend shifters I have seen work as you describe.
However it does not seem to be the case for the rx100s that I have on hand.

For left side (front shifter) the mounting bolt clamps down onto a central hollow post that protrudes through the lever, making no contact with the lever itself or any keyed washers to affect tension; in fact there appears to be no keyed washer at all (as common on other designs) simply a locknut at the top holding the levers internals together and hidden away. Tension is unnafected by the bolt torque, in fact it remains constant even with the bolt removed and the lever dismounted from the bike.
Could this paticuar model simply be of an unusal older design that is not meant to be adjustable?

HillRider

Hmmm, I was reporting from my memory of downtube shifters from Sun Tour, Campy and Suguino but your posting made me go look at the one bike I have using Shimano downtube shifters (mounted on Kelly Take-Offs BTW). The front lever is a part of a Shimano 7-speed 105 set (SL-1051) and the tension is indeed indepenent of the fastening bolt torque. I loosened the bolt until it nearly fell out and tightened it hard and neither way made any difference to the effort needed to shift with it.

So, as you noted, they are not adjustable. However it should make you feel better to know this particular shifter has been in service for many years on my rain/beater bike so it gets a lot of abuse and has never loosened up or developed any play.

FastJake

Unfortunately those shifters don't have adjustable cable tension. Maybe you could add a barrel adjuster somewhere? That would probably be really tacky though. It's tricky to get the cable tension correct because you have to tighten the pinch bolt on the FD just right. But once you set it you don't have to worry about it going out of adjustment because it's only a friction shifter. As long as the cable doesn't go slack and start bouncing around on the downtube I wouldn't worry about it.

ThermionicScott 

The RX100s on my bike don't seem to behave any differently when I loosen the mounting bolt. On the plus side, I rarely hear of these things wearing out.

xenologer

-FastJake
perhaps tension is not the clearest term, maybe 'resistance' is a better description
not concerned about the cable adjustment, rather the holding ability of the lever / force needed to move it.

probably not much to be done, seems the ones I have lack adjustability; I am a little curious though if a modern shimano dt shifter is any different