No se pueden eliminar capas con clústeres en leaflet.js

Estoy usando el leaflet cluster plugin to map out a bunch of crashes. When you load up the page, I map out all crashes (stored in a GeoJSON file). I also have buttons that load up a different geoJSON file for each year.

The problem I am running into is that removeLayer() isn't actually removing the layers. So when I remap a new GeoJSON file, it's just stacking all the crashes on top of each other.

These are my two functions that fire when you click a button. marcadores var is defined in the global namespace, seen below (maybe this is part of the problem)?

var markers = L.markerClusterGroup({spiderfyDistanceMultiplier: 1.3});

//Lay new data on map
function buildMarkers(yearData){
        var crashLayer = new L.geoJson(yearData, {
                onEachFeature: function (feature, layer) {
                    layer.bindPopup(feature.properties.year);
                }
        });
        markers.addLayer(crashLayer);
        map.addLayer(markers);

    }

//Remove ALL data on map        
function removeClusters(){
        map.removeLayer(markers)
    }

//AN example of a button
$("#twelve").click(function(e){
        e.preventDefault();
        $('a').removeClass('selected');
        $(this).addClass('selected');
        removeClusters();
        buildMarkers(twelveCrashes);
    });