Dura Ace 7800 Triple - Gears not fully working

Mrdeece

Hi All

I going mad trying to get my the gears to work smoothly on the rear. I have a full Dura Ace triple 7800 setup. The issue i have is I cannot seem to get the gears to work smoothly on the rear cassette. I get problems of basically bad changing but it seems strange as I can either get smooth gear changes on the smallest 4 gears or smooth gear changing on the largest 3 but not both. The issue i get is either when i change up the chain does not move to the next highest sprocket or if I change down it may not change down and I have to do one more click and it will jump down two sprockets. I have tried the following:

1. A new chain
2. A new Casette
3. New Gear cables.
4. Adjusting the B screw on the rear cassette
5. Adjusting the limit screws on the rear mech
6. Adjusting the cable tension on the rear mech
7. Pulling the inner gear cable to check for free movement


The bike is a Scott addict and I have done about 3000 miles so far with no accidents.

I am thinking it could it be the rear mech or the STI which may be faulty? I cannot seem to think what it could be and it is driving me mad

desweller

Try fitting a longer outer housing loop to the rear derailleur. It's quite easy to cut too small a length, which increases friction as the radius is too small.

It's unlikely to be a faulty shifter or derailleur unless they've taken an impact at some point.

Wooliferkins

It's a race frame, triples rarely run nicely as the shorter wheel base than an audax/leisure bike doesn't lend itself to a triple. The exaggerated deflection of the chain usually confines you to the outer sprockets on the big ring middle on the middle etc. When you get to the edges of these envelopes slick shifting exeunt stage right. We spent hours trying to get my colleagues Principia to work with a triple it was never good never mind perfect. He is heartily happy with his SRAM Apex compact which gets his larger body up all the same hills the triple did but changes slickly.

desweller

I never had any trouble with the triple on my compact-framed BeOne. Certainly not as far as the back block was concerned.

Mrdeece

Des - When I replaced the gear cables i did not cut the rear outer at all and it does not have any agressive bends in it.

Wooliferkins - I know what you are saying as triples are never as good as doubles. My old winter bike now turbo bike has an 8 speed double 39/53 has the best change ever. I do however have another 10 speed triple bike which is also short wheel based and this changes OK.

The gearing on the Scott has never been perfect and I assumed it was because it was a Ten speed triple however after converting another bike from 9 speed trple to 10 speed triple I am wondering if it could be a defective Rear mech or STI.

It is funny but i do not have an issue with the very largest or smalles gears e.g The 25 to 23 is ok and the 12 to 13 is ok. Main issue is with the middle gears I can get some of them working fine and then find others do not work fine. I know it is not a bent sprocket as I have several 10 speed cassettes I can try.

desweller

I don't understand. How did you fit the new outer if you did not cut it?

Dales1

Des - my DA cables came with a short piece of pre-cut outer housing, especially for the rear loop.

Dales.

desweller

In that case I would definitely consider that it might be too short. How can the supplier possibly know what the relative positions of the mech barrel adjuster and the frame stop are?

Just try it, that's all I'm saying ;-).

Mrdeece

I will take a look. The Park Big Blue book has a diagram showing the Rear Mech and the right cable length.

As Dales1 states the DA cables come pre cut 2 x 600 mm and one short piece not sure of length.

Dales1

My DA outer cables were 2 x 600mm plus 1 x 320mm (as it says on the box!).

Dales

desweller

Hm, 320mm should be plenty. Is the mech hanger straight?

Mrdeece

Rascal - The mech hanger is straight.

I had a very good look today. Took the rear mech off inspected all parts and re fitted. Lubed the Gear cables with Very Expensive Shimano SP41 Grease. I also decided to remove all the Finish Line wax lubricant off the chain (In case it was sticking) and replace with normal Finsih Line chain Oil. I also adjusted the B screw as it was almost fully screwed in.

Gears are working fine now, fingers crossed. I think it could have been the B screw and also Wax lubricant sticking. Still sorted out now and ready for a good long ride test tomorrow.