Originally Posted by
SDHawk
Thanks for the detailed info! I took off the cover. It's not full\y exposed, but I can see 1 long-ish pawl (see pic). It engages the spool fine with no load, but was slipping under tension. I'll try the things you and others suggested and cross my fingers.
I only see the 1 pawl... do you think there's a second one?
Had a similar issue with the same shifter (ST-M739) and upon inspection found that there was a 'chip' in the pawl. See the attached. (Sorry for the less than perfect pic, this is the only one that I seem to have saved.
The way that this pawl works is that it engages the gear and
pushes the ratchet to shift to a lower sprocket. On my shifter, because of the 'chip', the 'push' of the thumb shift lever has to be upwards during the rotation for the pawl to engage the ratchet.
Try inspecting the pawl more closely to check if there is any damage. You should be able to rotate the pawl away from the ratchet to get a better view.
Let us know what you find.