Shimano ST-R7020 105 right Shifter not engaging

[skyhigh123]

I have a Ribble Endurance SLE bought in March 2021 which has done about 500 miles. The problem is as in this post title. From time to time, the shift paddle to move to the smallest cog just stops working. The paddle moves easily, too easily , with no real resistance and no clicking or movement of the derailleur. Frequent shifting of the paddle doesn't help but after continuing to ride in an unnecessarily low gear suddenly it will begin to work again until the next time.
Anyone else had this problem or can suggest causes/solutions?

 

[wonderloaf]

Could it be a frayed cable inside the shifter? I've had similar problems on Ultegra 6800 & R8020 shifters and a frayed cable was the problem, seems to be the Achilles Heel of these shifters and quite common. I believe the 105 R7020 is of the same design so may suffer in the same way. If you pull back the hood and try operating the shifter you might be able to see if the cable is frayed.
This video might also help (although it's for 6800 shifters):

View: https://www.youtube.com/watch?v=tnXNc4dhWck

500 miles does seem a bit soon to be getting this problem though, I usually manage at least a couple of thousand mile before I have to change mine!

 

[T4tomo]

sound like you have some unwanted friction in the cable run, so either frayed at the shifter as per above, or check the inner cable is running freely through the other bits of outer cable. start with the bit near the RD, as that is most exposed to the elements.

 

[C R]

I've had something similar in my Sora RH shifter. Eventually I traced it to the way I stored my bike. Our garage is a bit tight for space, and the bike was leaning in such a way that the rear derailleur was being pushed. I assume this resulted in the cable being slack while the bike was in the garage, and somehow that affected the ratchet operation. The ratchet started operating again as soon as I had been moving for a few seconds, which I presume rattled everything into place. I am now careful to make sure that the derailleur is not touching anything when storing the bike, and the problem has disappeared.

 

[skyhigh123]

Lubrication of the shifter seems to be working. We'll see how long for.

 

[Ajax Bay]

Squirt more GT85 or similar into every orifice (of the STI). Drown it. Bike is almost new and you've scarcely ridden it. Most unlikely to be a frayed cable (in the STI) - as @wonderloaf says "a bit too soon".
Sticky pawl inside it - spray oil should unstick (as you seem to have found, so far).

 

[Chislenko]

Borrow some GT85 off Peter to spray Pawl.

 

[pawl]

Borrow some GT85 off Peter to spray Pawl.

No try W D40 I used it to remove the adhesive left on my chest after the heart rate pads had been removed
Tried everything surgical spirit didn’t work Might dissolve the shifter thoughi

 

[JhnBssll]

Also check the hood rubber isn't interfering with the mechanism underneath. If it's sitting incorrectly it can touch the shifter mechanism and prevent it from downshifting.

 

[wonderloaf]

Also check the hood rubber isn't interfering with the mechanism underneath. If it's sitting incorrectly it can touch the shifter mechanism and prevent it from downshifting.

Good shout, been there done that!

 

[JhnBssll]

Good shout, been there done that!

Me too