Dura Ace 7900 Right Hand Shifter Problem

pprendeville

Got a 2nd hand one of these with apparently low mileage. Guy seemed reasonable. Anyway, long story short, ever since I installed it about 2 months ago I've been having issues with shifting performance, mainly from smallest cog up to largest cog. Had a bit of time today to. Try and take a proper look at it.

Now I'm no expert mechanic but I've built my own bikes and been able to get shifting spot on with my old Ultegra 6700 shifters (why did I ever change). Also, before switching to the new levers the old ones were shifting perfectly so it's not the derailleur that's the problem IMO. I've been reading a few other forums about problems with 7900 shfters, specifically the right one for the rear derailleur. Have just stripped it down and lubed cables, adjusted low and high limit screws (high limit screw is slightly outboard) but no real joy.

The main problem seems to be that when its in the smallest cog and I shift back up one cog, the rear derailleur doesn't move at all. It takes 2 shifts up for it to move and then it's slightly off. Shifting from the biggest to the smallest cog all the way down is fine. Driving me mad out on the road having gears jumping or not shifting smoothly.

Brian?

Sounds like there's not enough tension on the cable to shift down. Have you tensioned the cable at the derailleur properly?

pprendeville

Ya I've tensioned it alright. Not the problem.

Brian?

pprendeville wrote: »

Ya I've tensioned it alright. Not the problem.

Ah well. Is your derailleur mounting bolt tight?

Have you tried the old shifter to confirm its a problem with the shifter?

pprendeville

The mounting bolt is rock solid. I'm half thinking of removing a link from the chain out of desperation. Should be enough clearance. Sold the old shifters unfortunately and don't have a spare one. Was messing around trying to get a look inside and it looks like there's some sort of electronics in it which is strange.

iwillhtfu

I think the known issue with DA7900 was the spring in the rear mech losing tension.

It does sound like a tension problem although if it's shifting down alright then maybe the cable is getting hung up on something somewhere along the line bends to tight.

I only installed a set of these myself recently and don't recall seeing any electronics as in your pic above

pprendeville

I changed the derailleur (also DA7900) today to an old Ultegra one and the exact same problem. I think I'll just get a new derailleur or else bring it toa bike shop.

Borderfox

They electronics are flightdeck

GTDolanator

Ive come across this in a tiagra right hand rear mech lever,changed inner and outer for new cheap stuff,bought genuine shimano still the same.It would either shift up perfectly and not shift down,or not shift up correctly and shift down bang on!!Ended up replacing it with an indentical shifter with far less use and the problem stopped.

Never found out what was wrong with it just assumed the pull ratio was off due to wear n tare

pprendeville

Borderfox wrote: »

They electronics are flightdeck

What's that mean in laymans terms?

countrykid

Two questions

Is it a 7900 rear mech?
And
Is the internal cabling in the bike heavily contorted around the BB area?

The fact that its not moving on the first shift upwards sounds like there's a slack spot in the cable and if your bike is internally cabled ( looks this way) you have no real way of telling if its tight tight...
Tension at the mech may be tight- BUT there could be a little slack at te other end if the cables not free in the frame..

clog

pprendeville wrote: »

What's that mean in laymans terms?

Its an intergrated Shimano bike computer system which they were trying to push a few years ago. They never caught on as gps systems became more popular. The electronics told the head unit what gear you were in.

pprendeville

Changed the RD cables and still no joy. It's either the derailleur or the shifter. My guess is the shifter as I've tried 3 different derailleurs today and they all have the same problem. Most annoying bike problem having gears that don't index properly.

countrykid

pprendeville wrote: »

Changed the RD cables and still no joy. It's either the derailleur or the shifter. My guess is the shifter as I've tried 3 different derailleurs today and they all have the same problem. Most annoying bike problem having gears that don't index properly.

What derailleurs did you try?

pprendeville

countrykid wrote: »

Two questions

Is it a 7900 rear mech?
And
Is the internal cabling in the bike heavily contorted around the BB area?

The fact that its not moving on the first shift upwards sounds like there's a slack spot in the cable and if your bike is internally cabled ( looks this way) you have no real way of telling if its tight tight...
Tension at the mech may be tight- BUT there could be a little slack at te other end if the cables not free in the frame..

Ya fair point but I took out both front and rear derailleur cables, reinserted them to make sure there was no crossing (internally routed) and lubed the cable housing bracket that attached right under the BB. Cables are Teflon coated but I lubed them lightly to be sure to be sure. I'm pretty sure there's no kinking or crossing as I was careful when inserting them and paid attention to this.

I cut new longer outer housing for the front (from shifter to downtube, the rear cable is long enough) and changed the exit point of the cable from the shifter. There are 2 exit points, one which has the cable at the front of the handlebars and the other routes around the back (at the riders side). It had been at the riders side so I switched it to the front but have subsequently read somewhere that Shimano recommend doing it the other way, the way I originally had it at the riders side. Anyway, both have proved to not be working.

I had a DA7900 RD on it. Has close to 8000km on it. Tried it with an Ultegra 6700 derailleur which has 4000-5000km on it and a very old Ultegra 6600 with relatively low mileage. All gave the same result.

countrykid

The 6700 and 6600 have marginally different cable pulls...so shifting would / could be off
No excuse for 7900 not being right pull wise.

Is there a small inspection plate on the side of the lever body you can remove to watch the cable tension up and rotate around the pulley as you change gear?

Would/ could tell you a lot if you can see the cable ACTUALLY move

pprendeville

countrykid wrote: »

The 6700 and 6600 have marginally different cable pulls...so shifting would / could be off
No excuse for 7900 not being right pull wise.

Is there a small inspection plate on the side of the lever body you can remove to watch the cable tension up and rotate around the pulley as you change gear?

Would/ could tell you a lot if you can see the cable ACTUALLY move

Yes, have checked this. Lifted up the hoods and the cable looks to be moving consistent distance on each shift (hazard a guess of 2-3mm max on each stroke up and down) so I'm extremely puzzled. Debated all sorts of upgrades/mix of parts today. Maybe the LBS is the best job at this stage. Just have to admit defeat.

countrykid

By the sounds if it you've been pretty thorough ...
If I was taking it to an LBS I'd be bringing it to one with a top mechanic...
Choose wisely.

pprendeville

A bit hard to make out but these show the cable to the front of the handlebars and with no excessively small radii.



Ditto on the back.

iwillhtfu

Probably of no consequence but did you put all the caps on the cable outers especially the ones at the shifter.

I'm just thinking is it maybe pulling the outer further into the shifter on the first shift therefore increasing tension and shifting on the second shift?

Sounds like an absolute pain in the hoop either way.

pprendeville

Yes, all the caps are on there. I'm going to call it a day at this stage. :mad:

iwillhtfu

Probably for the best. That's an absolute head melter.

Hopefully you've more joy with a fresh head.

Radial

May be a stupid question but are you sure your outer cables are of the correct diameter (i.e. any possibility that they are brake outers rather than gear outers). They look quite thick in your photo, but that might be down to the make of the cables.

I had a problem with rear shifting, left it into a bike mechanic who changed cables etc. and unable to cure poor shifting put the problem down to the rd hanger being too flexible (it was a Chinese frame with a light alloy hanger).

I persisted and after a lot of frustration, including changing the shifter, noticed that there was play between the outer and inner cable. went to LBS bought some gear outer cable, cut them to the same length as those already installed and that sorted the problem, perfect shifting.

Hard to believe that it might be, when changing the outer rd cables the mechanic fitted brake rather gear outers. Go figure!

easygoing39

Had this problem myself with a 6700 shifter and a 6700 rear mech.Like you it drove me mad trying to sort it. Fixed it in the end by changing the cable outer at the rear mech longer,thus giving a bigger loop.If you ever look at pictures of pro's racebikes from a few years ago (before they all went Di2) you will notice the loop of cable at the rear mech looks bigger than you'd think is needed.

iwillhtfu

[IMG][/img]

Mines similar maybe a tad bigger and no issues with shifting although they needed to be re indexed after about 500km

pprendeville

Ya, I have shifter outer cables in place, they're a smaller diameter than the brake cables. When I had the Ultegra shifters the rear cable radius was actually smaller than it is now. I made sure to make it a bit bigger. It was all fine with the Ultegra levers though. Thanks for all the advice.

Eamonnator

Probably a bit late at this stage, but have you considered a new bike?

pprendeville

Will you be quiet in case the Mrs hears you. The kitchen has been off limits today to all family members during testing of said shifter/derailleur so I don't want to upset anyone else further.

columbus_66

The 7900 rh shifter sometimes wear the teeth away on the shifting sprockets, you should be able to see it if you take the brake hood off and go through the gears. I had one that the shifting was poor on and I could see the sprockets were worn on the ratchet mechanism, Shimano replaced as it has 3 year warranty.

pprendeville

Do you have an email address for them by any chance?

columbus_66

Ususlly bring it back to where you got it from, or else the Shimano distributor in Ireland which may be JHI in Finglas, or Madison UK.

pprendeville

Finally figured out what the problem was. After stripping down the RH shifter cables again and checking to make sure they were shifting up and down evenly at each exit point on the frame (this involved keeping the cable held hand tight and visually checking at the shifter and the frame exit point the movement of the cable), starting at chainstay, then under BB and finally just hanging out of outer lever cable in free air, all in order to eliminate any possibility that the cable was getting stuck internally, it looked like it couldn't be the shifter that was the problem as it was either pulling/releasing it in incrementally equal amounts.

Had emailed the guy I bought the shifters off and he had said it could possibly be the derailleur hanger that was the problem. Luckily he's a bike mechanic. Removed the derailleur and wouldn't you know it, the hanger mounting screws were a bit loose. This must have been enough to cause the hanger to move slightly on the first up shift and this in turn had a knock on effect on that first gear change. Replaced the hanger with a new one and new screws as I didn't want to take any changes in case the old one was a little bent. Worked a charm. Shifting is back normal again. Lesson learned for the future. The new screws have some of that blue stuff on them, thread lock I believe. Must pick up a bottle of it.

iwillhtfu

Good to hear you got sorted.

Brian?

I almost had it too, when I suggested the derailleur mounting bolt.

Glad to hear it's fixed.

pprendeville

Brian? wrote: »

I almost had it too, when I suggested the derailleur mounting bolt.

Glad to hear it's fixed.

You did, why didn't you say the derailleur mounting screws while you were at it and it would saved me a lot of hassle.

wav1

pprendeville wrote: »

Finally figured out what the problem was. After stripping down the RH shifter cables again and checking to make sure they were shifting up and down evenly at each exit point on the frame (this involved keeping the cable held hand tight and visually checking at the shifter and the frame exit point the movement of the cable), starting at chainstay, then under BB and finally just hanging out of outer lever cable in free air, all in order to eliminate any possibility that the cable was getting stuck internally, it looked like it couldn't be the shifter that was the problem as it was either pulling/releasing it in incrementally equal amounts.

Had emailed the guy I bought the shifters off and he had said it could possibly be the derailleur hanger that was the problem. Luckily he's a bike mechanic. Removed the derailleur and wouldn't you know it, the hanger mounting screws were a bit loose. This must have been enough to cause the hanger to move slightly on the first up shift and this in turn had a knock on effect on that first gear change. Replaced the hanger with a new one and new screws as I didn't want to take any changes in case the old one was a little bent. Worked a charm. Shifting is back normal again. Lesson learned for the future. The new screws have some of that blue stuff on them, thread lock I believe. Must pick up a bottle of it.

Jay..s that was some saga.glad you're sorted.If you have no thread lock nail varnish works a treat.

ray o

Glad you got to the bottom of that. Painful but great experience. You'll be my first port of call if I have any problems fitting those shifters I got from you . If I ever get around to it that is. I was nearly gonna offer to sell them back to you.

pprendeville

I was fairly regretting selling them over the weekend that's for sure.