deacon mark

I am a competent mechanic and wheel builder but at a loss on this. My Habby (exposed cables) has Shimano 6800 groupset with 26,000 miles on them since 2017. Generally they have worked perfect never missing a shift. Today I had a flat and got that fixed. Then I notice my rear shifting went bad. It would not upshift of downshift unless I hit it numerous times. I got home and went through everything. Normally it is a binding issue. I put on housing and new cables on the shifter. Still does this no help at all.

I checked at the shifter and if I put the cable in and hold tension against it with my hand it clicks 10 times up and back. Does not seem to drag or be binding but those last two high gears seem like not much cable is being pulled. I am not sure if the ratio changes as you move up. It could be the rear derailleur but it seems like it moves free and generally rear derailleurs are pretty stout and work. I know it seems to be a tension and binding problem but I wonder if anyone else has had this issue. About 1 week ago it was doing the same thing and I came home clean up things and re-tensioned the cable and it work prefect for till today.. During that time since I have road about 350 miles. I have been riding about 800-1000 miles a month. I did ride 2 days with some rain which I normally do not but I have tried new housing cable.

Could the shifter be bad? Anything else to check. I appreciate and help because I am mechanic and if I cannot get it then it is not like I can go too many places?

Crankycrank

I would first try flushing and lubing your brake/shifter mechanism. 26k miles is a pretty long run without having re-lubed at some point. You can just spray some WD-40 or other solvent such as Kerosene or Odorless Mineral Spirits and run the shifter through the gears a few times. It may take a few days for the solvent to fully dissolve the factory grease so just ride it a few times to see if it improves. If it does just blow out the solvent with compressed air or spend some time wiping off as much of the shifter as you can. Add some light lube afterwards. Something similar to Tri-Flow works and is easy to clean out when more lube is needed at some point. Also make sure to wipe any WD-40 off the brake hoods as it tends to soften the rubber if left on for too long. Let us know if this works or not.

deacon mark

Now I am wondering if it is not rear derailleur itself. I have the cable threaded through but it seems like something may have broken off inside the hole as it exist toward the clamp bolt. The hole it is now big and putting on the barrel adjuster with the spring and ferrule, the shimano has a small plastic end piece that fits to keep the cable away from the metal side of the derailleur as it exist. The plastic part has nothing to sit on is is just a large hole. A longer threaded barrel adjuster will go all the way through and start coming out from the side facing the clamp bolt. There is no place that the plastic guide will set into.

SoSmellyAir

Assuming that the flat was on the rear wheel, Occam's razor dictates removing and reinstalling that wheel to see if the shifting issues improve.

deacon mark

What an idiot I am. So today I worked with the rear derailleur. I did notice a piece leading out the back of where the rear barrel adjuster screws in was on the floor. A small round metal washer/type fitting that sets into the hole so the plastic end cap can fit down without coming out. I push it back in and used the plastic end cap and shifting improve but still off. Well I took the bike off the hook I had hung the front wheel on and place the bike in the stand right side up. Then all of a sudden the rear derailleur seem to drop down into place like it has been catching on something in the mechanism.

Bingo the bike started shifting perfect really. Small adjustments after this and now it basically shifts like it did before. I guess then I installed the wheel after tire change the rear derailleur must have got push up just enough to not allow full movement. What baffles me is when in all the shifting and cabling I did yesterday it did to once drop into place. I moved it around did all sorts of things and today.......Clunk.