As avid mountain bikers, we all can understand the frustration of encountering shifting issues. If you're experiencing shifting problems with your new SRAM Transmission mountain bike drivetrain, fear not! In this comprehensive guide, we'll delve into common troubleshooting techniques and uncommon techniques to help you diagnose and resolve issues, ensuring seamless shifting on every ride.

Issues with shifting can be disappointing. The new and pricey Transmission drivetrain is supposed to shift incredibly well even under load. Thankfully the shifting performance is incredible once Transmission is working, but depending on the specific issue being faced it can be a headache to get the drivetrain shifting correctly.

The forum posts discussing these issues are listed below and all relevant information is listed in one place in this article.
MTBR: Got Sram Transmission? Got problems? Post here.
Reddit Reddit: SRAM Transmission Micro Adjust
VITAL MTB: Sram Transmission issues
Pink Bike: SRAM transmission micro adjust issue

This is a long post and here are the various things we will cover that lead to bad shifting performance and a noisy SRAM Transmission drivetrain:

1. Not following setup instructions precisely

2. Entering incorrect information into the SRAM AXS app when getting setup instructions

3. Improper pairing of AXS components

4. Incorrect chain length

5. Powerlink is not shut completely

6. Using the wrong setup key position

7. Incorrect installation of the bushing frame insert

8. Improperly torqued components

9. Using the wrong setup cog

10. Slack in the chain after setup

11. Misalignment of the knurled ring mark with the mark on the full mount of the derailleur

12. Failing to use micro adjustment for alignment

13. Testing the drivetrain in the bike stand only instead of testing under load

14. Firmware issues

15. Wearing in the components to reduce noise

16. Missing spacers or bushings

17. Bad manufacturing tolerances in the bike hub, driver, end-caps, cassette, or derailleur

18. Bad manufacturing tolerances in the UDH compatible frame

Following set up instructions carefully and precisely

Make sure that you have read the reference materials and watched the SRAM installation videos. It seems like many issues are resolved by slowing down and carefully following the setup instructions. The Transmission set up is unique compared to other drivetrains on the market.
Installation manual: https://www.sram.com/globalassets/document-hierarchy/user-manuals/sram-mtb/drivetrain/eagle-transmission-user-manual-english.pdf
Installation video: https://www.youtube.com/watch?v=bknKhIvDJks

SRAM AXS App

Using the SRAM AXS app is critical for setup. This app is used to find the right setup settings, but it is also important for firmware updates which need to be paid attention to in a software driven drivetrain. Not having the most up-to-date firmware can cause issues with shifting which will be covered later. Also, failing to use the correct setup instructions can cause shifting issues.

If you have more than one AXS component you need to pair all of your AXS components together before using the app. These instructions vary by number of AXS components and videos can be found on the SRAM website here. If you have a Reverb AXS dropper post and/or a Flight Attendant system the pairing instructions will be different from the Transmission manual. Once AXS components are paired with each other, open the app, add your bike if you’ve not already, and add your AXS components. After the components are added go to “System Guides and Resources” in the app.

Chain Length

Go to the “Chain Length & Setup Key Guide” and enter in your bikes details. Be careful to enter in the correct model, frame size, geometry, and front chainring size. If your bike is not listed be careful to enter the correct chainstay length and other information. During this process you may need to remove links from your chain or close the Powerlink. It is best to use high quality tools that won’t damage you components and become a source of more headaches. Here are links to the Park Tool Chain Tool CT-3.3 and the Park Tool Master Link Pliers MLP-1.2. Chain length can vary by frame size, chainring size, geometry, etc. These instructions begin on page 20 of the Transmission manual and are pictured below.

Make sure the chain links are being counted correctly which can be done with the chain on the bike if needed by starting at the Powerlink. Also make sure that the Powerlink is closed completely. If it is not closed completely you will hear skipping every time the Powerlink hits teeth in the drivetrain. If the chain is not the correct length you will not have the correct b-stop distance between the guide pulley in the derailleur and the cogs of the cassette and will have poor shifting performance.

Setup Kay

Interestingly enough, many users have found that the setup instructions for their bike versus the setup instructions for their chainstay length can be slightly different. It can be helpful to try both sets of instructions. This was the case for the YT Capra 29er in XXL which suggests a setup key of B with no sag for the bike model/size/geometry and a setup key of A with 20% sag for the bikes chainstay length (443mm). The final settings used on this bike were the instructions for the bike make/model rather than those used for the bike’s chainstay length, but some users have reported getting better results with their bikes chainstay length. Using the wrong setup key will lead to bad shifting performance.

The bushing frame insert

The bushing frame insert protects the frame and provides an additional 1.5mm of spacing. Installing it incorrectly or failing to install it can lead to poor shifting performance and damage to your frame. Proper installation is described in the SRAM Transmission manual and pictured below.

Torque Specs

Having the correct torque specs is critical to ensuring you drivetrain works without issues. Before going through the remainder of the setup instructions in the SRAM Transmission Manual it is worth checking the torque on the cassette to ensure that it is at 40Nm. Properly removing the cassette, reattaching it, and/or checking the torque requires some additional tools which are listed here: Park Tool SR-12.2 Sprocket Remover (with chain whip), Park Tool FR-5.2GT Cassette Locking Tool with Pin 12mm, Park Tool TW-6.2 Racheting Torque Wrench 10-60Nm Drive Tool 3/8-Inch, and Park Tool SBS-1.2 Socket And Bit Set.

During installation make sure you are using the correct setup cog. Using the incorrect setup cog will lead to bad shifting performance.

After the installation it is important that the thru axel (specs for torque can be found on the thru axel and are usually between 12Nm and 18Nm) and the Transmission mount bolt (35Nm) are at their correct torques. Incorrect torque can lead to bad shifting performance and it is fairly common for bike factories and shops to forget to tighten components.

Final Setup Instructions

With all of the torque specifications checked you check that all of the slack is removed from the chain and the knurled ring mark is aligned with the mark on the full mount of the derailleur. Slack in the chain or a misaligned derailleur can lead to bad shifting performance.

The next step is to micro adjust to try and perfect alignment of the derailleur with the cassette. The instructions from the SRAM Transmission Manual are pictured below. Not optimizing the alignment using MicroAdjust will lead to poor shifting performance. It is also important to test shifting performance in a bike stand as well as under load. The Transmission drivetrains are designed to shift under load and if there is not enough power transfer providing tension throughout the system you can see poor shifting performance. Once you believe you’ve found the best MicroAdjust position in the stand get on the bike and ride it before making additional adjustments.

Unfortunately, the new Transmission drivetrains only come with 14 stops of micro adjustment. This means that the derailleur can only be moved 1.7mm inboard or outboard relative to the cassette from the position it mounts at naturally. If you’ve followed the manual and videos, read the instructions above, and consulted a professional bike mechanic, but are still unable to get good shifting performance there are additional advanced steps for troubleshooting. Using the same YT Capra mentioned above, after all of these steps shifting performance was best in the MicroAdjust position 1/14, but was still performing poorly under load. Videos of the shifting performance at 7/14 and 1/14 can be found below.

Factory reset all AXS components and install the latest firmware

There are a myriad of user reported issues that have ended up being the result of firmware issues. To delete the current firmware, reset to factory setting, and solve these issues do the following on each component in the AXS system:

1. Hold down the the AXS button

2. Remove the battery while continuing to hold down the AXS button

3. Wait 3 seconds while continuing to hold down the AXS button

4. Reinstall the battery while continuing to hold down the AXS button

5. Release the AXS button

6. Confirm the indicator light in blinking yellow

7. Use the AXS app to install the latest firmware

8. Repeat this for every AXS component

9. Pair all AXS components

10. Redo the Transmission setup from the beginning

You may also consider contacting SRAM directly using their ticketing system to discuss alignment issues if you feel like you are close to being completely aligned. SRAM seems to be aware of these issues and they were able to push a beta firmware to me that is supposed to move the derailleur inboard an additional 0.6mm. (Update: This functionality is now part of the generally available firmware and you no longer need to request the beta from SRAM) This firmware beta did not work for me, but it is worth a try. Believe it or not, firmware issues can lead to bad shifting performance.

If the issues you are having are minor it might be worth riding the bike for a few hours. Personally, I felt like the Transmission drivetrain was still noisy in the 1/14 setting although it was shifting ok after reinstalling all firmware. After riding for a few hours and cleaning the drivetrain the noise decreased noticeably. Presumably the components just needed to wear in a little.

Manufacturing tolerances

The Hub Assembly

There are a large number of components that need to be within tight tolerances for everything to line up with less than 1.7mm in offset. The end-caps, the hub, the driver, the cassette, and the derailleur can all be sources of issues. Step one is to make sure that the distance between the smallest cog on the cassette and the end of the end-cap is exactly 3.4mm. SRAM has also mentioned to several users that the distance from the little shelf of the freehub body to the end of the end-cap should be 44.1mm +/- 0.3mm. If the distance between the smallest cog on the cassette and the end of the end-cap is not 3.4mm you likely have a manufacturing tolerance issue with the driver, end-cap, or cassette. A measurement other than 3.4mm could also mean that you have the wrong end-cap or that a part in the hub assembly is missing or damaged. An image of the correct spacing is below.

If this spacing is incorrect the next step is contacting the manufacturer of your hub assembly or having the bike shop where you purchased your bike reach out to them. Take photos and measurements of every component in the hub assembly. Find an exploded view or engineering drawing of all of the parts in the hub assembly online or by contacting the manufacturer. Make sure that all of the parts, spacers, and bushings that are down in the assembly are there. While removing parts to measure them this is also a good opportunity to check to make sure that any threading in the hub assembly is not stripped or cross-threaded and that it is assembled correctly.

The inspiration for this article was a YT Capra Uncaged 12 with wheels from Crankbrothers. Below you can find some of the measurements taken that were shared with the manufacturer as well as the exploded view of their hub assembly that was used to rule out the hub assembly as the source of shifting issues. In this case a missing free hub spacer or hub seal could lead to alignment issues. Installing the end caps for the steel hub when using an alloy hub or vice versa is also a potential issue.

The DERAILLEUR and cassette

At this point, if the source of the poor shifting performance and alignment issues is still unknown it is time to try a new transmission derailleur and cassette. The manufacturer of you bike or the bike shop you purchased your bike at should be able to either send you warranty replacements or, if they are a local bike shop, try other Transmission components they have at the shop.

The Frame

As a last resort you may consider replacing the frame or the rear triangle. SRAM has standards for frame manufacturing for UDH that they share with manufacturers. The engineering drawings that appear to be relevant for Transmission are show below and linked here.

If you've meticulously followed these steps and troubleshooting tips and your SRAM Transmission drivetrain still exhibits shifting problems, it might be time to seek professional help. A qualified bike mechanic can diagnose complex issues, perform more advanced adjustments, and ensure your drivetrain is functioning optimally. If you are a professional it might be time to seek out a second opinion.

This drivetrain is amazing once set up and well worth the extra effort if you are one of the few people having issues.