In this article I’m going to provide you with a few pointers on how to adjust Shimano thumb shifters. This proces should work on any thumb shifter, not only old ones, but this article specifically addresses Shimano thumb shifters.
In a previous article I installed these 1987 6-speed Deore XT thumb shifters for my Koga Miyata Adventure. After the initial setup I always take the bike for an actual spin to see if both shifters work accordingly and finetune the adjustment if need be.
Finetuning shifters with the barrel adjuster
Shifting under load (with you riding the bike) behaves differently from shifting on a stand or by pulling the rear wheel from the ground and giving the crank a push.
That’s the reason why, after an initial setup, I actually ride the bike and use the barrel adjuster to further finetune shifting mishaps.
The barrel adjuster sits between the cable housing and the shifter itself. It’s a ratcheting device around a hollow bolt that can either extend or decrease the length of the cable housing. By doing so you either slacken or tighten the shifter. cable.
- turning the barrel adjuster clockwise shortens the cable housing, releases tension, moves the front derailleur towards smallest chainring and the rear derailleur towards the smallest sprocket
- turning the barrel adjuster counter-clockwise lengthens the cable housing, increases tension, moves the front derailleur towards biggest chainring and the rear derailleur towards the biggest sprocket
Step 1. Adding more wiggle room to the barrel adjuster
My rear derailleur was set up too tight. However, I didn’t have any wiggle room left at the barrel adjuster. It was already turned all the way into the shifter.
When this happens I add 2mm. of slack to the cable. I achieve this by releasing the bolt that tightens the cable at the derailleur, while holding the cable with a pair of pliers 2mm away from the bolt.
If the cable loosens the pliers will edge against the bolt and prevent the cable from moving any further.
Step 2. Adjust Shimano thumb shifters with the barrel adjuster
Re-tighten the bolt and you’ve got enough slack to play around with the barrel adjuster. In my case the slack proved to be too much, 2mm. usually is.
But putting more tension on the cable is done by rotating counter-clockwise, and I had more than enough room for that in the barrel adjuster. A couple of trial-and-error laps later and I had the adjustment I was looking for.
And that’s how you adjust Shimano thumb shifters! If you like this article give it a thumbs up. If you have any questions or suggestions for new articles, let me know in the comments below. Cheers.