Most of the content on this site is aimed at Di2 beginners and people wanting to build a Di2 bike from scratch.. but what if you don't actually want to build a bike? What if you're buying one second hand? What do you look for when inspecting a second hand bike? What should you look out for?
I'll list the things that are important to me when buying Di2 components. However, this list is by no means complete. Definitely get in touch or leave a comment at the bottom of this page if you feel something is missing.
While I tend to do all maintenance and bike building myself, I'm hardly the authority on buying second-hand bikes. I'd rather point you in the right direction of some other great sources than try to hash out a half-baked version of my own. I will just focus on the Di2 related aspects of buying a used bike.
Older Di2 series
One of the reasons for buying a second hand Di2 bike could be their price. Buying a used bike is a lot cheaper than buying it brand new, but there are some things to keep in mind when buying a bike with older Di2 parts.
Stay away from 7970 series Di2
While there is technically nothing wrong with the DURA-ACE 7970 series Di2 on its own, there is one very good reason to stay away from this series.
It uses a different connector / plug from all the other series and is not compatible with any of them.
This means that if any of your 7970 components break, you will have to replace that component with a 7970 component. Considering that the 7970 series was released twelve years ago (2009), chances are that something is going to break at some point.
Shimano don't make these parts anymore and bike shops are unlikely to have any of these just lying around, so you would have to turn to ebay or facebook marketplace to get your replacement parts. They are hard to get and relatively expensive.
I therefore recommend you do not buy a 7970 Di2 bike, no matter how cheap it is.
Be aware of 10 speed Di2 risks (6770)
The next groupset on the list that's worth mentioning on its own is the Ultegra 6770 10 speed Di2 series. Released only two years after the 7970 series, the 10 speed 6770 uses the E-Tube wiring just like all other Di2 series since. All components are connected using the EW-SD50 Electric Wire and the system is compatible with all newer shift levers, junctions and batteries (except the SM-EW67 junction).
However.. 10 speed derailleurs will only work with 10 speed derailleurs. Both derailleurs in a Di2 system must be either 10 speed or both 11 speed. If your front derailleur or rear derailleur break you would have to find a 6770-series derailleur to replace it, or buy two new derailleurs and upgrade the bike to 11-speed.
I'm not saying you should stay away from Ultegra 6770 like I did with DURA-ACE 7970, but it's definitely something to be aware of.
Note: it is actually possible to mix 10-speed and 11-speed derailleurs on the same bike, but it involves downgrading firmware by renaming files and using older E-Tube versions.. and not ever updating any of the firmware. It is for very motivated users only and not for the faint of heart. Read more on Carlton Bale's Di2 site.
Hydraulic disc brake bike? Check the levers
More and more bikes are equiped with Hydraulic Disc Brakes (HDB). There are two things worth knowing here, but let's start with the most important one: check the levers.
You'll want to make sure there is no brake fluid leaking from the levers. Pull back the lever hoods and double check there are no traces of brake fluid behind them. If there are, this could by caused by either a sloppy installation of the brake hose, or worse - a hairline fracture in the lever itself.
If you do find something is off then just ask the owner about it. It is not possible to repair a leaky lever or brake fluid reservoir and Di2 shifters are an expensive item to replace.
Also, the Di2 Hydraulic Disc levers do not have the dedicated sprint shifter port. This means you cannot use the SW-R610 Sprint Shifter. The alternative is the SW-R9150, but these are a lot more bulky than the older sprint shifters.
Ask about the battery
The battery that is installed on the bike matters. If you want to use Synchronized Shifting you need the BT-DN110 internal battery or the BM-DN100 External Battery Mount. Synchronized Shift will not work without them. The same applies to the D-fly /wireless module. It will not work without a current generation battery.
Besides features, also ask the seller about their charging habits. How often do they charge their bike? Personally I tend to charge mine every 3000-4000km, or every 3-6 months. Charging the bike every week is really not necessary and may be indicative of a battery drain issue or a battery that is no longer holding charge.
Di2 battery lifetime
Shimano state the battery should last about 300 full charge cycles. This means that if you were to charge the bike every month it should last 25 years. You probably shouldn't worry about the battery's age, unless - as I've written above - the owner is charging their battery way too often.
And yes, some batteries fail way before the reach the 300 charge cycles... that's electronics. Most of them really do outlive the bicycle itself though.
What junction is installed?
This junction is meant to be used with external batteries only. It does not have a charge port, so using it with an internal battery would be cumbersome. Also, the Shimano Compatibility charts state it simply wouldn't work.
This means updating your bike's firmware or changing settings will not be possible.
Of course you could buy the SM-PCE02 diagnostics tool and use that to connect your bike to a PC, but it's relatively expensive.
Other questions you should ask
Other questions that are worth asking are, in no particular order:
Who built the bike?
Has the bike been built and maintained by the owner, or by a bike shop? Do you trust the owner to have done it right? Do they have any tips?
Has the shifting ever stopped working?
Have there ever been any problems with the Di2 system? If there were, how were they resolved?
Does it have a Wireless Module installed?
The Di2 D-Fly or Wireless Module is an addon for road / gravel bikes that enables BluetoothLE / ANT communications. Without this module you will not be able to use the E-Tube Mobile App to update firmware or change settings. You also will not be able to see Di2 information on your bike computer or head unit.
Your bike will work perfectly fine without the Wireless Module though. it is a nice-to-have and in no way required - you can change settings and update the bike using a Windows PC for example.
If it does have a Wireless Module or display installed, ask the owner for the PassKey, or ask them to reset it for you. You can also do this yourself, but you'll need a Windows computer.
Have I missed anything in this list? Do you have any suggestions? Please leave them in the comments below or send me a message.