Shimano Dura-Ace 7800 Shifter Trim Question

[jberenyi]

Can't remember but does this front derailleur have a middle trim going down from the large chainring? My friend's bike which I am trying to fix up goes down all way to the small ring and I've tried working with it but that's the best I can get out of it. If the down trim should be there, any idea the cause of not working?

[dave thompson]

Originally Posted by jberenyi

Can't remember but does this front derailleur have a middle trim going down from the large chainring? My friend's bike which I am trying to fix up goes down all way to the small ring and I've tried working with it but that's the best I can get out of it. If the down trim should be there, any idea the cause of not working?

It does so you can trim the der when it’s on the big ring and you’re going to bigger rear dogs.

If it shifts to the small ring with one click of the shifter it sounds like there’s too much cable tension.

[regularguy412]

Originally Posted by dave thompson

It does so you can trim the der when it’s on the big ring and you’re going to bigger rear dogs.

If it shifts to the small ring with one click of the shifter it sounds like there’s too much cable tension.

^^This

But it could also just be worn out, after all these years.

Mike in AR

[jberenyi]

Originally Posted by regularguy412

^^This

But it could also just be worn out, after all these years.

Mike in AR

I hope shifter is not worn out. I told my friend to buy this bike . I'll clean things up, lube cable and play with the tension more.

[Dead Man]

Do a wd40 soak and see if that brings back the trimmer click. Even if the shifter is worn out, which is unlikely, you ought to be able to replace it for $50 or less .. so NBD.

But give this one a chance - those things pretty much never wore out. But they did/do/will kinda gum up and act like they're broken when they ain't.

[oldpotatoe]

Originally Posted by dave thompson

It does so you can trim the der when it’s on the big ring and you’re going to bigger rear dogs.

If it shifts to the small ring with one click of the shifter it sounds like there’s too much cable tension.

Agree or the upper limit screw is too tight, need to back it out a wee bit.

[dddd]

Doing a "WD40 soak" means different things to different people, is not warranted at this point and often leads to recurring problems and/or a worst-case episode of slimy lubricant film under the hoods, i.e. hoods never the same.

Start by adjusting the cable a few clicks looser, per dave thompson's advice, as this is (very) most likely to solve the problem.
And be sure to follow up with setting the Hi-limit screw so that it is backed out about a quarter-turn from the top-gear lever position AFTER all cable adjustment is completed.

Only those symptoms that suddenly appear with the onset of cold weather, and after diagnosing proper cable tension, are indications of a shifter needing a flush or re-lubrication. When the levers still works well when actuated very slowly for instance, flooding the shifter mechanism with a non-thickening lubricating oil from an aerosol can usually restores years of proper lever function, but one must position the bike or handlebar to a 30-degree downhill attitude to avoid lubricant immediately flowing between the hood and lever body, which is not a simple problem to remedy. I first place a pan or bucket under the lever before flooding the shifter innards, as much liquid will issue forth.
A suitable lubricant will be mostly oil, not solvent, and will remain in a penetrating state without thickening (as can TriFlow) before the pawl pivots are fully saturated with oil, which often takes considerable time. I use this:




Levers that are in a fully non-working state from many years of garage storage, no matter how slowly that the levers are moved, usually are best flooded first with Finish Line Citrus Degreaser, which is an aggressive petroleum-based aerosol product. This is then followed up immediately with a second flush using the Lubricating Oil, once the lever pawls are all free and responsive to rapid lever movements.

Possibly the OP's lever problem is gumming, and not a cable tension issue, though much less likely than a simple over-tight cable. The most common problem with damaged "worn-out" levers seems to be when an already-lubricated lever allows the big lever to follow the motion of the small lever, locking up the mechanism's movement. That is a failure of the anti-carryover latch tip at the inside pivot of the small lever, and is irreparable without disassembly and using a donor lever to source a newer small lever.
And again, if the hi-limit screw is perhaps interfering with the (lever and cable)'s full travel, the trim position may appear to be the hi position, leaving "no one home" when the hi-trim position is called for, as the derailer falls fully to the small-ring position.