RD-RX805 / RD-RX815 / RD-RX817 Di2 Rear Derailleur installation guide

The Ultegra RD-RX805 and GRX RD-RX815 / RD-RX817 rear derailleurs are direct mount derailleurs that also feature a clutch mechanism (chain tensioner). Installing them is relatively easy, you mount it to the frame, disable the clutch, set the limit screws and do micro-adjustment if necessary.

Disable the derailleur’s chain tensioner before you do anything – this will make mounting the chain and setting the limit screws easier. To do this just flip the switch.

Clutch switch lever

Mount the derailleur to the frame

While these derailleurs are all direct mount ready, you can use them with a standard mount frame no problem. The first step is to identify the rear derailleur mount on your frame. Generally, direct mounts are in line with the seat stay, while a standard mount will make a sharper bend down. The image below should help you identify the mount on your frame

direct mount vs standard mount

Standard mount

On a standard mount frame you install the derailleur with the B2-link plate attached. It should come this way out of the box. If the B2-link plate is not installed, do so now – it is colored green in the image above.

Apply a small amount of grease to the mounting bolt and secure the rear derailleur to the frame. Before tightening it fully, make sure the stopper plate touches the B-tension stop, with no gap between them.

You will need a 5 mm hex wrench to do this and the recommended torque is 8 – 10 Nm.

attach standard RD to frame

Direct mount

Is your frame equipped with a direct rear derailleur mount? Then remove the B2-link from the rear derailleur so that you can mount it directly onto the frame. You do this by removing the bracket axle using a size 5 hex wrench. Remove the link and attach the derailleur to the frame using the bracket axle.

attach direct mount RD to frame

Connect the electric wire

If you haven’t run the EW-SD50 electric wire to the rear derailleur yet, do so now. Now use the Di2 plug tool to push the electric wire into the connector. Push firmly until you feel (and possibly hear) it click into the socket.

RD insert e-tube wire

Set the end adjustment screw

In order to finalize the derailleur setup make sure the rest of the system is installed and make sure you can shift both derailleurs. We will now set the end adjustment screw (or b-screw). This will set the angle of the rear derailleur and change the distance between the guide pulley and chain on the cassette.

Shift the front derailleur to the smallest chainring and the rear derailleur to the largest sprocket. Use a size 2 hex wrench to turn the adjustment screw and move the guide pulley as close to the sprocket as possible but not so close that the chain gets jammed.

RD set the b-screw

Now shift to the smallest sprocket and make sure the chain does not get jammed. If there is any slack in the chain in this gear use the adjustment bolt to eliminate this slack.

Micro-adjust the rear derailleur

Before setting the high/low limit screws you will have to micro-adjust or index the rear derailleur. Note that this is different from how you would set up mechanical rear derailleur – there you would set the limit screws first and then do indexing.

RD adjustment 5th sprocket

  • Shift the front derailleur to the small chainring.
  • Shift the rear derailleur to the fifth sprocket.
  • Press and hold the button on your junction box until the red LED illuminates, indicating you’re in adjustment mode.

You can now adjust the position of the rear derailleur using the shift buttons:

RD adjustment switch X

  • Press the [X] button while also turning the crank to move the guide pulley towards the 4th sprocket.
  • Keep doing this until the chain makes contact with the 4th gear and a subtle noise is heard.
  • Note that while you are in adjustment mode the guide pulley will overrun slightly and then move back a bit. When checking the position of the guide pulley and gear, make sure the derailleur has come to a stop.

RD Adjustment Y switch

Now press the [Y] switch five times in order to move the guide pulley five steps back towards the smallest sprockets. The rear derailleur should be indexed now. This will be the starting point for all future adjustments.

To leave adjustment mode just press and hold the button on the junction box until the LED turns off and you will leave adjustment mode.

Use both the front and rear derailleur to shift through all the gears, making sure no chain rub occurs in any of them. If it does, go back to adjustment mode to tweak the rear derailleur indexing.

Set the low/high stopper bolts

Adjusting the low/high stopper bolts is a relatively easy affair. Let’s first set the low stopper bolt.

  • Shift the rear derailleur to the largest sprocket.
  • Now use a size 2 hex wrench to tighten the low side stopper bolt until it just touches the low side stopper. This is the bolt with an L next to it.

Now we’ll set the high or top side stopper bolt.

  • Shift the rear derailleur to the smallest sprocket.
  • Tighten the top stopper bolt with a size 2 hex wrench until it just touches the top-side stopper. This is the bolt with an H next to it.
  • Turn the top-side stopper bolt counterclockwise one turn to loosen it and allow for the rear derailleur to overshift.

RD stopper bolt

You should take care not to overtighten the stopper bolts. According to Shimano, one of the following could happen:

  • Gears do not shift to the smallest sprocket or largest sprocket. Even if the gears are shifted, the gear may shift back by 1 gear after approximately 5 seconds.
  • Chain noise does not stop.
  • The battery level drops quickly because extra load is being placed on the motor.
  • The motor may be damaged due to overload (irreparable).