diff --git a/libraries/cms/installer/adapter/component.php b/libraries/cms/installer/adapter/component.php
index 83e42a6d135bb..97b01ab6eaf0e 100644
--- a/libraries/cms/installer/adapter/component.php
+++ b/libraries/cms/installer/adapter/component.php
@@ -1334,14 +1334,3 @@ protected function _createAdminMenuItem(array &$data, $parentId)
 		return $table->id;
 	}
 }
-
-/**
- * Deprecated class placeholder. You should use JInstallerAdapterComponent instead.
- *
- * @since       3.1
- * @deprecated  4.0
- * @codeCoverageIgnore
- */
-class JInstallerComponent extends JInstallerAdapterComponent
-{
-}
diff --git a/libraries/cms/installer/adapter/file.php b/libraries/cms/installer/adapter/file.php
index f87c811156c24..1341a515c04ba 100644
--- a/libraries/cms/installer/adapter/file.php
+++ b/libraries/cms/installer/adapter/file.php
@@ -637,14 +637,3 @@ public function refreshManifestCache()
 		}
 	}
 }
-
-/**
- * Deprecated class placeholder. You should use JInstallerAdapterFile instead.
- *
- * @since       3.1
- * @deprecated  4.0
- * @codeCoverageIgnore
- */
-class JInstallerFile extends JInstallerAdapterFile
-{
-}
diff --git a/libraries/cms/installer/adapter/language.php b/libraries/cms/installer/adapter/language.php
index b403abec808b1..40efc4a34761f 100644
--- a/libraries/cms/installer/adapter/language.php
+++ b/libraries/cms/installer/adapter/language.php
@@ -703,14 +703,3 @@ public function refreshManifestCache()
 		}
 	}
 }
-
-/**
- * Deprecated class placeholder. You should use JInstallerAdapterLanguage instead.
- *
- * @since       3.1
- * @deprecated  4.0
- * @codeCoverageIgnore
- */
-class JInstallerLanguage extends JInstallerAdapterLanguage
-{
-}
diff --git a/libraries/cms/installer/adapter/library.php b/libraries/cms/installer/adapter/library.php
index a124903438c03..0b6fc0d0c190d 100644
--- a/libraries/cms/installer/adapter/library.php
+++ b/libraries/cms/installer/adapter/library.php
@@ -504,14 +504,3 @@ public function refreshManifestCache()
 		}
 	}
 }
-
-/**
- * Deprecated class placeholder. You should use JInstallerAdapterLibrary instead.
- *
- * @since       3.1
- * @deprecated  4.0
- * @codeCoverageIgnore
- */
-class JInstallerLibrary extends JInstallerAdapterLibrary
-{
-}
diff --git a/libraries/cms/installer/adapter/module.php b/libraries/cms/installer/adapter/module.php
index ecf8a08f9b9bb..d88a86e9fd29f 100644
--- a/libraries/cms/installer/adapter/module.php
+++ b/libraries/cms/installer/adapter/module.php
@@ -775,14 +775,3 @@ protected function _rollback_module($arg)
 		}
 	}
 }
-
-/**
- * Deprecated class placeholder. You should use JInstallerAdapterModule instead.
- *
- * @since       3.1
- * @deprecated  4.0
- * @codeCoverageIgnore
- */
-class JInstallerModule extends JInstallerAdapterModule
-{
-}
diff --git a/libraries/cms/installer/adapter/package.php b/libraries/cms/installer/adapter/package.php
index fbb83761fe0f1..46f999e856b55 100644
--- a/libraries/cms/installer/adapter/package.php
+++ b/libraries/cms/installer/adapter/package.php
@@ -689,14 +689,3 @@ public function refreshManifestCache()
 		}
 	}
 }
-
-/**
- * Deprecated class placeholder. You should use JInstallerAdapterPackage instead.
- *
- * @since       3.1
- * @deprecated  4.0
- * @codeCoverageIgnore
- */
-class JInstallerPackage extends JInstallerAdapterPackage
-{
-}
diff --git a/libraries/cms/installer/adapter/plugin.php b/libraries/cms/installer/adapter/plugin.php
index 1865100ade9da..b723f14180474 100644
--- a/libraries/cms/installer/adapter/plugin.php
+++ b/libraries/cms/installer/adapter/plugin.php
@@ -305,18 +305,9 @@ protected function parseOptionalTags()
 	 */
 	public function prepareDiscoverInstall()
 	{
-		$client   = JApplicationHelper::getClientInfo($this->extension->client_id);
-		$basePath = $client->path . '/plugins/' . $this->extension->folder;
-
-		if (is_dir($basePath . '/' . $this->extension->element))
-		{
-			$manifestPath = $basePath . '/' . $this->extension->element . '/' . $this->extension->element . '.xml';
-		}
-		else
-		{
-			// @deprecated 4.0 - This path supports Joomla! 1.5 plugin folder layouts
-			$manifestPath = $basePath . '/' . $this->extension->element . '.xml';
-		}
+		$client       = JApplicationHelper::getClientInfo($this->extension->client_id);
+		$basePath     = $client->path . '/plugins/' . $this->extension->folder;
+		$manifestPath = $basePath . '/' . $this->extension->element . '/' . $this->extension->element . '.xml';
 
 		$this->parent->manifest = $this->parent->isManifest($manifestPath);
 		$this->parent->setPath('manifest', $manifestPath);
@@ -723,14 +714,3 @@ public function refreshManifestCache()
 		}
 	}
 }
-
-/**
- * Deprecated class placeholder. You should use JInstallerAdapterPlugin instead.
- *
- * @since       3.1
- * @deprecated  4.0
- * @codeCoverageIgnore
- */
-class JInstallerPlugin extends JInstallerAdapterPlugin
-{
-}
diff --git a/libraries/cms/installer/adapter/template.php b/libraries/cms/installer/adapter/template.php
index b24ae7431e092..df53a44564706 100644
--- a/libraries/cms/installer/adapter/template.php
+++ b/libraries/cms/installer/adapter/template.php
@@ -611,14 +611,3 @@ public function refreshManifestCache()
 		}
 	}
 }
-
-/**
- * Deprecated class placeholder. You should use JInstallerAdapterTemplate instead.
- *
- * @since       3.1
- * @deprecated  4.0
- * @codeCoverageIgnore
- */
-class JInstallerTemplate extends JInstallerAdapterTemplate
-{
-}
diff --git a/libraries/cms/installer/installer.php b/libraries/cms/installer/installer.php
index 07f8730eb4a18..9129223ca9714 100644
--- a/libraries/cms/installer/installer.php
+++ b/libraries/cms/installer/installer.php
@@ -518,7 +518,7 @@ public function discover_install($eid = null)
 		$type   = $this->extension->type;
 		$params = array('extension' => $this->extension, 'route' => 'discover_install');
 
-		$adapter = $this->getAdapter($type, $params);
+		$adapter = $this->loadAdapter($type, $params);
 
 		if (!is_object($adapter))
 		{
@@ -596,15 +596,16 @@ public function discover_install($eid = null)
 	 */
 	public function discover()
 	{
-		$this->loadAllAdapters();
 		$results = array();
 
-		foreach ($this->_adapters as $adapter)
+		foreach ($this->getAdapters() as $adapter)
 		{
+			$instance = $this->loadAdapter($adapter);
+
 			// Joomla! 1.5 installation adapter legacy support
-			if (method_exists($adapter, 'discover'))
+			if (method_exists($instance, 'discover'))
 			{
-				$tmp = $adapter->discover();
+				$tmp = $instance->discover();
 
 				// If its an array and has entries
 				if (is_array($tmp) && count($tmp))
@@ -685,19 +686,18 @@ public function update($path = null)
 	/**
 	 * Package uninstallation method
 	 *
-	 * @param   string   $type        Package type
-	 * @param   mixed    $identifier  Package identifier for adapter
-	 * @param   integer  $cid         Application ID; deprecated in 1.6
+	 * @param   string  $type        Package type
+	 * @param   mixed   $identifier  Package identifier for adapter
 	 *
 	 * @return  boolean  True if successful
 	 *
 	 * @since   3.1
 	 */
-	public function uninstall($type, $identifier, $cid = 0)
+	public function uninstall($type, $identifier)
 	{
 		$params = array('extension' => $this->extension, 'route' => 'uninstall');
 
-		$adapter = $this->getAdapter($type, $params);
+		$adapter = $this->loadAdapter($type, $params);
 
 		if (!is_object($adapter))
 		{
@@ -755,7 +755,7 @@ public function refreshManifestCache($eid)
 			}
 
 			// Fetch the adapter
-			$adapter = $this->getAdapter($this->extension->type);
+			$adapter = $this->loadAdapter($this->extension->type);
 
 			if (!is_object($adapter))
 			{
@@ -812,7 +812,7 @@ public function setupInstall($route = 'install', $returnAdapter = false)
 		$params = array('route' => $route, 'manifest' => $this->getManifest());
 
 		// Load the adapter
-		$adapter = $this->getAdapter($type, $params);
+		$adapter = $this->loadAdapter($type, $params);
 
 		if ($returnAdapter)
 		{
@@ -2216,42 +2216,15 @@ public static function parseXMLInstallFile($path)
 		return $data;
 	}
 
-	/**
-	 * Fetches an adapter and adds it to the internal storage if an instance is not set
-	 * while also ensuring its a valid adapter name
-	 *
-	 * @param   string  $name     Name of adapter to return
-	 * @param   array   $options  Adapter options
-	 *
-	 * @return  JInstallerAdapter
-	 *
-	 * @since       3.4
-	 * @deprecated  4.0  The internal adapter cache will no longer be supported,
-	 *                   use loadAdapter() to fetch an adapter instance
-	 */
-	public function getAdapter($name, $options = array())
-	{
-		$this->getAdapters($options);
-
-		if (!$this->setAdapter($name, $this->_adapters[$name]))
-		{
-			return false;
-		}
-
-		return $this->_adapters[$name];
-	}
-
 	/**
 	 * Gets a list of available install adapters.
 	 *
 	 * @param   array  $options  An array of options to inject into the adapter
 	 * @param   array  $custom   Array of custom install adapters
 	 *
-	 * @return  array  An array of available install adapters.
+	 * @return  string[]  An array of the class names of available install adapters.
 	 *
 	 * @since   3.4
-	 * @note    As of 4.0, this method will only return the names of available adapters and will not
-	 *          instantiate them and store to the $_adapters class var.
 	 */
 	public function getAdapters($options = array(), array $custom = array())
 	{
@@ -2285,7 +2258,7 @@ public function getAdapters($options = array(), array $custom = array())
 				}
 			}
 
-			$this->_adapters[$name] = $this->loadAdapter($name, $options);
+			$adapters[] = str_ireplace('.php', '', $fileName);
 		}
 
 		// Add any custom adapters if specified
@@ -2303,11 +2276,11 @@ public function getAdapters($options = array(), array $custom = array())
 					continue;
 				}
 
-				$this->_adapters[$name] = $this->loadAdapter($name, $options);
+				$adapters[] = str_ireplace('.php', '', $fileName);
 			}
 		}
 
-		return $this->_adapters;
+		return $adapters;
 	}
 
 	/**
@@ -2327,22 +2300,7 @@ public function loadAdapter($adapter, $options = array())
 
 		if (!class_exists($class))
 		{
-			// @deprecated 4.0 - The adapter should be autoloaded or manually included by the caller
-			$path = $this->_basepath . '/' . $this->_adapterfolder . '/' . $adapter . '.php';
-
-			// Try to load the adapter object
-			if (!file_exists($path))
-			{
-				throw new InvalidArgumentException(sprintf('The %s install adapter does not exist.', $adapter));
-			}
-
-			// Try once more to find the class
-			require_once $path;
-
-			if (!class_exists($class))
-			{
-				throw new InvalidArgumentException(sprintf('The %s install adapter does not exist.', $adapter));
-			}
+			throw new InvalidArgumentException(sprintf('The %s install adapter does not exist.', $adapter));
 		}
 
 		// Ensure the adapter type is part of the options array
@@ -2356,20 +2314,4 @@ public function loadAdapter($adapter, $options = array())
 
 		return new $class($this, $this->getDbo(), $options);
 	}
-
-	/**
-	 * Loads all adapters.
-	 *
-	 * @param   array  $options  Adapter options
-	 *
-	 * @return  void
-	 *
-	 * @since       3.4
-	 * @deprecated  4.0  Individual adapters should be instantiated as needed
-	 * @note        This method is serving as a proxy of the legacy JAdapter API into the preferred API
-	 */
-	public function loadAllAdapters($options = array())
-	{
-		$this->getAdapters($options);
-	}
 }