Technical issue - Shimano 10 speed - Trek Madone

[Hellchops]

Hi guys

I have an interesting problem that I'm unable to solve :roll:

Bike: Trek Madone 5.9 (2005)
5700 105 10 speed STIs
6600 Ultegra rear mech, short cage
105 10s 5700 cassette
SRAM PC1050
Rear wheel: DT Swiss R1850

Problem: Shifting is slow from 8th to 9th AND 9th to 10th (1 being low, 10 being high).

This is what I've tried in order to remedy it:
New inner and outer cable
Checked hanger (it's straight)
New 105 chain
New 105 cassette
New 105 5700 rear mech
and a few combinations of the above...

Freehub body is fine, and there's no play on the hub axle.

The problem is the same! When pedaling the bike in the stand and manually pushing the mech to the lowest gear and releasing it changes gears as fast as expected across the range. So the mech is fine. Also, from 1st to 8th gear there are no issues. The lever indexes perfectly both in the work stand and on the road. The only problem is shifting from 8th to 9th and 9th to 10th, under load (reasonable load) on the road.

Front chainset is a non-series 10speed CD Shimano FC-H600.

Anybody have an idea of what can cause this, and how to fix it? I have tried everything that I can think of :facepalm:

 

[monty dog]

Are the spacers in the cassette correct? If the cassette is made up on sub-clusters on a carrier i.e. if 8/9/10 are mounted on a single carrier, then that would be where I'd start i.e if the spacer between 7 and 8 is the incorrect size, which would throw all three out.

 

[JamesM]

Is it not simply because you are shifting under load? In the smaller sprockets the chain tension is higher and there are less teeth engaged meaning the pressure/friction between the chain and the teeth is higher so it will be more difficult to drag the chain up and off those teeth. And because you are shifting into smaller sprockets you are relasing cable and the shift is performed by the spring in the mech, so because of the high chain tesnion the mech may not move all the way across immediately. When shifting the other way you are pulling cable in so if the shifter indexes the mech has to have moved the correct amount (cable strentch aside), plus the cassette has thingies to pickup the chain when shifting that way too.

 

[Hellchops]

@monty dog - yes, I have checked that on the old and new cassette.

@James - I've considered that it may just be a combination of the things you've explained. It's not on my own bike, but the owner is convinced it was not like this before...

Thanks for the replies.

 

[mattr]

Are all the cable guides clear? e.g. No paint blobs touching the cable, or squeezed/dented guides.
Are the ends of the cable outers clean and square e.g. Not crushed by using cheap or blunt cutters. (Whipping through them with a Dremel works wonders)
Did you do *all* the outer, including from the shifter to the first stop? (I've seen some who claim that they replaced the outer without removing/replacing the bar tape!)
Is the final loop big enough?
Did you use new, clean ferrules?
Is the shifter sticky at all? (Blast of oil works wonders)
Is it internally rooted at all? (BIG blast of oil works well!)
How is the B-tension screw set? And what size cassette is it?

You get problems at that end of the block (12/13/14/15 sprocket) due to the rear mech spring being at the low force end of its action, so it's quite often cable drag or sticky shifters. Further up the block you tend not to notice as the spring is applying more load to the cable. It's unlikely to be a mech issue (as you changed it) so my money is on the cable or shifter.