Jayrob8888

I have a 2010 Cube Attempt with a the older 10 speed 105 groupset .

I managed to break the rear mech and when in for repair I was told the new 105 rear derailleur isn’t compatible anymore as the new 105 is 11speed .

The workaround was to put a Claris r2000 on which is 8 speed . He assures me it will work perfect . I took it for a short spin and noticed it wasn’t as smooth but did seem to shift across the
10 gears ok


I’m looking for thoughts on this . Is he right or should I source an older 105 rear derailleur and insist on taking the Claris back off ?

Iride01 

If it works currently, then continue to use it till it doesn't. If you just want to spend more money, then that's on you.

Welcome to BF!


Little side details about how you ride your bike, the conditions you ride in and whether you sprint like Caleb Ewan may change my answer.

cyclezen

Cable - Not sure about any DI2...
I believe the shift ratio on Shimano DR's from 8 thru 11 are same. But that is not Pull ratio, which is dictated by the shifters. And then there's any difference in the jockey cage/pulleys width/size.
I do have a bunch of bikes using and assortment of 9 & 10 speed Shimano RDs, and all work fine.
AN 8 speed RD must accommodate an 8 speed chain width, so the jockey cage & pulley width needs to be wide enough to work... SO this may make the shift on a narrower chain a hair less precise? I don;t have 11 speed RD, so can;t measure jockey internal width (compared to 10 speed), so not sure if there is a difference, and if that difference matters...
so a long way of saying - maybe/maybe not... LOL!
When my list of 'Honey do's...' goes down, I was thinkin to get a GRX clutch RD and use it on a 10 spd road setup... The clutch RD on my Gravel Bike work great for retaining the chain in place, on some knarly, bumpy chunk sections of riding... Might go a long way to reducing any chance of front ring chain jumping off... not really a problem for me, but I love experimenting... LOL!
Ride On
Yuri

Jayrob8888

So I won’t out for a longer spin this evening and had quite a few problems. The derailer was a Not changing then jumping 2 cogs . Not coming back up on hills then jumping 2 . Constantly. Chain came off and all 😂. So I think the spacing or something if off as it’s designed for the wider 8 speed cogs ?

Iride01 

Go back to the shop that put it on. See what the mechanic says. Might just be that they didn't tighten the pinch bolt tight enough and the DR is coming out of adjustment or something else is amiss.

Since you said it was working good in the OP, I never checked the specs and such. I might do that later after I get back home. But off the bat, I'd say the mechanic is the one you need to talk to first.

Or is he not the one that put it on and adjusted it?

HTupolev

He's right. Prior to 2015, Shimano 10-speed road rear derailleurs used the same actuation as 8/9-speed (road and mountain) rear derailleurs. Since you have a pre-2015 10-speed road drivetrain, an standard Shimano 8-speed rear derailleur should be compatible.

Shimano's 11-speed road actuates differently, and new 10-speed road starting with Tiagra 4700 also use the new 11-speed road actuation.

If the shift quality has worsened since installation, and you're having issues with the chain being thrown, my first reaction would be to check that the derailleur is installed and adjusted correctly.

cyclezen

as others noted, could be any number of things.
you mentioned chain coming off - where ? - front , rear ? when ? may be separate issue
you also didn't note any detail on how you broke the RD... damaging an RD would also warrant checking the dropout hanger... It might not seem visually tweaked, but just enough to cause mis-shifting when under any load. Checking on a work stand is never the final check, shifting should be checked in an open area, riding.
2010 bike, how much usage?.
We're all making educated guesses here, which is the best you can expect.
take it back in.
Ride On
Yuri