diff --git a/draftlogs/7684_change.md b/draftlogs/7684_change.md
new file mode 100644
index 00000000000..93797426c49
--- /dev/null
+++ b/draftlogs/7684_change.md
@@ -0,0 +1 @@
+ - Set default layout.axis.tickmode to 'sync' when axis is overlaying [[#7684](https://github.com/plotly/plotly.js/pull/7684)]
\ No newline at end of file
diff --git a/src/plots/cartesian/dragbox.js b/src/plots/cartesian/dragbox.js
index 0aa0caceee2..e66ec74628d 100644
--- a/src/plots/cartesian/dragbox.js
+++ b/src/plots/cartesian/dragbox.js
@@ -732,7 +732,10 @@ function makeDragBox(gd, plotinfo, x, y, w, h, ns, ew) {
             for(i = 0; i < axList.length; i++) {
                 var axListI = axList[i];
                 var axListIType = axListI[axisType];
-                if(!axListI.fixedrange && axListIType.tickmode === 'sync') activeAxIds.push(axListIType._id);
+                var axId = axListIType._id;
+                if(!axListI.fixedrange && axListIType.tickmode === 'sync' && !activeAxIds.includes(axId)) {
+                    activeAxIds.push(axId);
+                }
             }
         }
 
diff --git a/src/plots/cartesian/layout_attributes.js b/src/plots/cartesian/layout_attributes.js
index d1ce0158ace..d7c207fd21f 100644
--- a/src/plots/cartesian/layout_attributes.js
+++ b/src/plots/cartesian/layout_attributes.js
@@ -35,7 +35,8 @@ var tickmode = extendFlat({}, minorTickmode, {
     description: [
         minorTickmode.description,
         'If *sync*, the number of ticks will sync with the overlayed axis',
-        'set by `overlaying` property.'
+        'set by `overlaying` property. When no other tick info is provided,',
+        'overlaying (non-categorical) axes default to *sync*, while other axes default to *auto*.',
     ].join(' ')
 });
 
diff --git a/src/plots/cartesian/tick_value_defaults.js b/src/plots/cartesian/tick_value_defaults.js
index 68b9207ee62..faa2d36f03b 100644
--- a/src/plots/cartesian/tick_value_defaults.js
+++ b/src/plots/cartesian/tick_value_defaults.js
@@ -5,8 +5,7 @@ var isArrayOrTypedArray = require('../../lib').isArrayOrTypedArray;
 var isTypedArraySpec = require('../../lib/array').isTypedArraySpec;
 var decodeTypedArraySpec = require('../../lib/array').decodeTypedArraySpec;
 
-module.exports = function handleTickValueDefaults(containerIn, containerOut, coerce, axType, opts) {
-    if(!opts) opts = {};
+module.exports = function handleTickValueDefaults(containerIn, containerOut, coerce, axType, opts = {}) {
     var isMinor = opts.isMinor;
     var cIn = isMinor ? containerIn.minor || {} : containerIn;
     var cOut = isMinor ? containerOut.minor : containerOut;
@@ -14,35 +13,40 @@ module.exports = function handleTickValueDefaults(containerIn, containerOut, coe
 
     function readInput(attr) {
         var v = cIn[attr];
-        if(isTypedArraySpec(v)) v = decodeTypedArraySpec(v);
+        if (isTypedArraySpec(v)) v = decodeTypedArraySpec(v);
 
-        return (
-            v !== undefined
-        ) ? v : (cOut._template || {})[attr];
+        return v !== undefined ? v : (cOut._template || {})[attr];
     }
 
     var _tick0 = readInput('tick0');
     var _dtick = readInput('dtick');
     var _tickvals = readInput('tickvals');
+    var _overlaying = readInput('overlaying');
+    var _categorical = axType === 'category' || axType === 'multicategory';
 
-    var tickmodeDefault = isArrayOrTypedArray(_tickvals) ? 'array' :
-        _dtick ? 'linear' :
-        'auto';
+    var tickmodeDefault;
+    if (isArrayOrTypedArray(_tickvals)) {
+        tickmodeDefault = 'array';
+    } else if (_dtick) {
+        tickmodeDefault = 'linear';
+    } else if (_overlaying && !_categorical) {
+        tickmodeDefault = 'sync';
+    } else {
+        tickmodeDefault = 'auto';
+    }
     var tickmode = coerce(prefix + 'tickmode', tickmodeDefault);
 
-    if(tickmode === 'auto' || tickmode === 'sync') {
+    if (tickmode === 'auto' || tickmode === 'sync') {
         coerce(prefix + 'nticks');
-    } else if(tickmode === 'linear') {
+    } else if (tickmode === 'linear') {
         // dtick is usually a positive number, but there are some
         // special strings available for log or date axes
         // tick0 also has special logic
-        var dtick = cOut.dtick = cleanTicks.dtick(
-            _dtick, axType);
-        cOut.tick0 = cleanTicks.tick0(
-            _tick0, axType, containerOut.calendar, dtick);
-    } else if(axType !== 'multicategory') {
+        var dtick = (cOut.dtick = cleanTicks.dtick(_dtick, axType));
+        cOut.tick0 = cleanTicks.tick0(_tick0, axType, containerOut.calendar, dtick);
+    } else if (axType !== 'multicategory') {
         var tickvals = coerce(prefix + 'tickvals');
-        if(tickvals === undefined) cOut.tickmode = 'auto';
-        else if(!isMinor) coerce('ticktext');
+        if (tickvals === undefined) cOut.tickmode = 'auto';
+        else if (!isMinor) coerce('ticktext');
     }
 };
diff --git a/test/image/baselines/20.png b/test/image/baselines/20.png
index 230a6baf8b7..49c76b32f79 100644
Binary files a/test/image/baselines/20.png and b/test/image/baselines/20.png differ
diff --git a/test/image/baselines/autorange-tozero-rangemode.png b/test/image/baselines/autorange-tozero-rangemode.png
index ebc57f4d8d2..138d26a311b 100644
Binary files a/test/image/baselines/autorange-tozero-rangemode.png and b/test/image/baselines/autorange-tozero-rangemode.png differ
diff --git a/test/image/baselines/candlestick_double-y-axis.png b/test/image/baselines/candlestick_double-y-axis.png
index 077f3b8fab0..34d4f43bab1 100644
Binary files a/test/image/baselines/candlestick_double-y-axis.png and b/test/image/baselines/candlestick_double-y-axis.png differ
diff --git a/test/image/baselines/candlestick_rangeslider_thai.png b/test/image/baselines/candlestick_rangeslider_thai.png
index f40e1cdd0ef..345a3e4dab5 100644
Binary files a/test/image/baselines/candlestick_rangeslider_thai.png and b/test/image/baselines/candlestick_rangeslider_thai.png differ
diff --git a/test/image/baselines/legend_scroll_beyond_plotarea.png b/test/image/baselines/legend_scroll_beyond_plotarea.png
index 677421dd0ff..51ecafd947b 100644
Binary files a/test/image/baselines/legend_scroll_beyond_plotarea.png and b/test/image/baselines/legend_scroll_beyond_plotarea.png differ
diff --git a/test/image/baselines/legend_visibility.png b/test/image/baselines/legend_visibility.png
index e80069a9c02..bbdb2156d96 100644
Binary files a/test/image/baselines/legend_visibility.png and b/test/image/baselines/legend_visibility.png differ
diff --git a/test/image/baselines/mult-yaxes-subplots-stacked.png b/test/image/baselines/mult-yaxes-subplots-stacked.png
index 5aac4b389cd..855dcde1bf3 100644
Binary files a/test/image/baselines/mult-yaxes-subplots-stacked.png and b/test/image/baselines/mult-yaxes-subplots-stacked.png differ
diff --git a/test/image/baselines/multicategory_series.png b/test/image/baselines/multicategory_series.png
index dfbe24abe2e..7e4b0c8edf0 100644
Binary files a/test/image/baselines/multicategory_series.png and b/test/image/baselines/multicategory_series.png differ
diff --git a/test/image/baselines/range_slider_legend_left.png b/test/image/baselines/range_slider_legend_left.png
index 9eb5c4457ff..d35f8c99b28 100644
Binary files a/test/image/baselines/range_slider_legend_left.png and b/test/image/baselines/range_slider_legend_left.png differ
diff --git a/test/image/baselines/yaxis-over-yaxis2.png b/test/image/baselines/yaxis-over-yaxis2.png
index 175f1c39adb..6d3398ef7aa 100644
Binary files a/test/image/baselines/yaxis-over-yaxis2.png and b/test/image/baselines/yaxis-over-yaxis2.png differ
diff --git a/test/image/baselines/zerolinelayer_above.png b/test/image/baselines/zerolinelayer_above.png
index 10fca3a7e8c..6e4490680da 100644
Binary files a/test/image/baselines/zerolinelayer_above.png and b/test/image/baselines/zerolinelayer_above.png differ
diff --git a/test/image/baselines/zerolinelayer_below.png b/test/image/baselines/zerolinelayer_below.png
index d011848fa65..9e43516c183 100644
Binary files a/test/image/baselines/zerolinelayer_below.png and b/test/image/baselines/zerolinelayer_below.png differ
diff --git a/test/image/mocks/shapes_layer_below_traces.json b/test/image/mocks/shapes_layer_below_traces.json
index 9b221568538..049b66b9c4c 100644
--- a/test/image/mocks/shapes_layer_below_traces.json
+++ b/test/image/mocks/shapes_layer_below_traces.json
@@ -103,7 +103,8 @@
     "yaxis2": {
       "gridwidth": 2,
       "side": "right",
-      "overlaying": "y"
+      "overlaying": "y",
+      "tickmode": "auto"
     }
   }
 }
diff --git a/test/plot-schema.json b/test/plot-schema.json
index 86964d4f5e9..5ae14291f41 100644
--- a/test/plot-schema.json
+++ b/test/plot-schema.json
@@ -14867,7 +14867,7 @@
           "valType": "number"
         },
         "tickmode": {
-          "description": "Sets the tick mode for this axis. If *auto*, the number of ticks is set via `nticks`. If *linear*, the placement of the ticks is determined by a starting position `tick0` and a tick step `dtick` (*linear* is the default value if `tick0` and `dtick` are provided). If *array*, the placement of the ticks is set via `tickvals` and the tick text is `ticktext`. (*array* is the default value if `tickvals` is provided). If *sync*, the number of ticks will sync with the overlayed axis set by `overlaying` property.",
+          "description": "Sets the tick mode for this axis. If *auto*, the number of ticks is set via `nticks`. If *linear*, the placement of the ticks is determined by a starting position `tick0` and a tick step `dtick` (*linear* is the default value if `tick0` and `dtick` are provided). If *array*, the placement of the ticks is set via `tickvals` and the tick text is `ticktext`. (*array* is the default value if `tickvals` is provided). If *sync*, the number of ticks will sync with the overlayed axis set by `overlaying` property. When no other tick info is provided, overlaying (non-categorical) axes default to *sync*, while other axes default to *auto*.",
           "editType": "ticks",
           "impliedEdits": {},
           "valType": "enumerated",
@@ -16146,7 +16146,7 @@
           "valType": "number"
         },
         "tickmode": {
-          "description": "Sets the tick mode for this axis. If *auto*, the number of ticks is set via `nticks`. If *linear*, the placement of the ticks is determined by a starting position `tick0` and a tick step `dtick` (*linear* is the default value if `tick0` and `dtick` are provided). If *array*, the placement of the ticks is set via `tickvals` and the tick text is `ticktext`. (*array* is the default value if `tickvals` is provided). If *sync*, the number of ticks will sync with the overlayed axis set by `overlaying` property.",
+          "description": "Sets the tick mode for this axis. If *auto*, the number of ticks is set via `nticks`. If *linear*, the placement of the ticks is determined by a starting position `tick0` and a tick step `dtick` (*linear* is the default value if `tick0` and `dtick` are provided). If *array*, the placement of the ticks is set via `tickvals` and the tick text is `ticktext`. (*array* is the default value if `tickvals` is provided). If *sync*, the number of ticks will sync with the overlayed axis set by `overlaying` property. When no other tick info is provided, overlaying (non-categorical) axes default to *sync*, while other axes default to *auto*.",
           "editType": "ticks",
           "impliedEdits": {},
           "valType": "enumerated",