diff --git a/src/routes/dashboard/+page.svelte b/src/routes/dashboard/+page.svelte
index 02bbfbe..d53a504 100644
--- a/src/routes/dashboard/+page.svelte
+++ b/src/routes/dashboard/+page.svelte
@@ -48,6 +48,7 @@
   let personnel = [];
   let goodsManagers = [];
   let filteredGoodsManagers = [];
+  let filteredVehicles = [];
   let formError = "";
   let formSuccess = "";
   let isSubmitting = false;
@@ -65,6 +66,13 @@
     notes: ""
   };
 
+  function setFormField(field, value) {
+    if (formData[field] === value) {
+      return;
+    }
+    formData = { ...formData, [field]: value };
+  }
+
   $: displayPendingSlips = pendingSlips;
   $: displayHistorySlips = approvedRejectedSlips;
 
@@ -167,6 +175,7 @@
       if (vehiclesRes.ok) {
         const vehiclesData = await vehiclesRes.json();
         vehicles = vehiclesData.vehicles || [];
+        await syncVehicleSelection(formData.unit_id);
       }
 
       if (unitsRes.ok) {
@@ -208,6 +217,7 @@
       notes: ""
     };
     syncGoodsManagerSelection("");
+    syncVehicleSelection("");
   }
 
   function getGoodsManagersByUnit(unitId) {
@@ -221,7 +231,7 @@
     filteredGoodsManagers = candidates;
 
     if (!unitId || candidates.length === 0) {
-      formData.goods_manager_id = "";
+      setFormField("goods_manager_id", "");
       return;
     }
 
@@ -231,13 +241,56 @@
     );
 
     if (!hasCurrent) {
-      formData.goods_manager_id = candidates[0].id.toString();
+      setFormField("goods_manager_id", candidates[0].id.toString());
     }
   }
 
-  function handleUnitChange(event) {
-    formData.unit_id = event.target.value;
-    syncGoodsManagerSelection(formData.unit_id);
+  function getVehiclesByUnit(unitId) {
+    if (!unitId) {
+      return [];
+    }
+
+    const normalized = parseInt(unitId);
+    return vehicles.filter((vehicle) => vehicle.unit_id === normalized);
+  }
+
+  async function syncVehicleSelection(unitId = formData.unit_id) {
+    const candidates = getVehiclesByUnit(unitId);
+    filteredVehicles = candidates;
+
+    await tick();
+
+    if (!unitId || candidates.length === 0) {
+      setFormField("vehicle_id", "");
+      return;
+    }
+
+    const hasVehicle = candidates.some(
+      (vehicle) =>
+        vehicle.id.toString() === (formData.vehicle_id ?? "").toString()
+    );
+
+    if (!hasVehicle) {
+      setFormField("vehicle_id", candidates[0].id.toString());
+    }
+  }
+
+  $: if (formData.unit_id && filteredVehicles.length > 0) {
+    const hasVehicle = filteredVehicles.some(
+      (vehicle) =>
+        vehicle.id.toString() === (formData.vehicle_id ?? "").toString()
+    );
+
+    if (!hasVehicle) {
+      setFormField("vehicle_id", filteredVehicles[0].id.toString());
+    }
+  }
+
+  async function handleUnitChange(event) {
+    const value = event.target.value;
+    setFormField("unit_id", value);
+    syncGoodsManagerSelection(value);
+    await syncVehicleSelection(value);
   }
 
   async function handleCreateSlip() {
@@ -1252,14 +1305,19 @@
                           id="vehicle_id"
                           class="form-select"
                           bind:value={formData.vehicle_id}
+                          disabled={!formData.unit_id || filteredVehicles.length === 0}
                           required
                         >
-                          <option value="">Araç Seçin</option>
-                          {#each vehicles as vehicle}
-                            <option value={vehicle.id}
-                              >{vehicle.brand}
-                              {vehicle.model} ({vehicle.plate})</option
-                            >
+                          <option value="" class="s-jZJiUkwef1J0">Araç  Seçin</option>
+                          {#if !formData.unit_id}
+                            <option value="">Önce birlik seçin</option>
+                          {:else if filteredVehicles.length === 0}
+                            <option value="">Bu birliğe kayıtlı araç yok</option>
+                          {/if}
+                          {#each filteredVehicles as vehicle}
+                            <option value={vehicle.id.toString()}>
+                              {vehicle.brand} {vehicle.model} ({vehicle.plate})
+                            </option>
                           {/each}
                         </select>
                       </div>
@@ -1310,9 +1368,9 @@
                         >
                           <option value="">Personel Seçin</option>
                           {#each personnel as person}
-                            <option value={person.id}
-                              >{person.rank} {person.full_name}</option
-                            >
+                            <option value={person.id.toString()}>
+                              {person.rank} {person.full_name}
+                            </option>
                           {/each}
                         </select>
                       </div>
diff --git a/src/routes/fuel-slips/+page.svelte b/src/routes/fuel-slips/+page.svelte
index 739ae23..61df4e4 100644
--- a/src/routes/fuel-slips/+page.svelte
+++ b/src/routes/fuel-slips/+page.svelte
@@ -7,18 +7,19 @@
 </svelte:head>
 
 <script>
-	import { onMount, onDestroy } from 'svelte';
+	import { onMount, onDestroy, tick } from 'svelte';
 	import { goto } from '$app/navigation';
 	import { io } from 'socket.io-client';
 
 	let user = null;
-	let vehicles = [];
-	let units = [];
-	let personnel = [];
-	let fuelSlips = [];
-	let approvedRejectedSlips = [];
+let vehicles = [];
+let units = [];
+let personnel = [];
+let fuelSlips = [];
+let approvedRejectedSlips = [];
 let receivingPersonnel = [];
 let filteredReceivingPersonnel = [];
+let filteredVehicles = [];
 	let loading = true;
 	let error = '';
 	let showCreateModal = false;
@@ -30,18 +31,25 @@ let filteredReceivingPersonnel = [];
 
 	// Form değişkenleri
 	let formData = {
-		date: new Date().toISOString().split('T')[0],
-		force_command: '',
-		unit_id: '',
-		vehicle_id: '',
+	date: new Date().toISOString().split('T')[0],
+	force_command: '',
+	unit_id: '',
+	vehicle_id: '',
 		fuel_type: 'benzin',
 		liters: '',
 		km: '',
 		personnel_id: '',
-		goods_manager_id: '',
-		notes: ''
+	goods_manager_id: '',
+	notes: ''
 	};
 
+	function setFormField(field, value) {
+		if (formData[field] === value) {
+			return;
+		}
+		formData = { ...formData, [field]: value };
+	}
+
 	onMount(async () => {
 		const userData = localStorage.getItem('user');
 		if (!userData || JSON.parse(userData).role !== 'fuel_manager') {
@@ -89,6 +97,7 @@ let filteredReceivingPersonnel = [];
 			if (vehiclesRes.ok) {
 				const vehiclesData = await vehiclesRes.json();
 				vehicles = vehiclesData.vehicles || [];
+				await syncVehicleSelection(formData.unit_id);
 			}
 
 			if (unitsRes.ok) {
@@ -141,30 +150,76 @@ let filteredReceivingPersonnel = [];
 		return receivingPersonnel.filter(person => person.unit_id === normalizedUnit);
 	}
 
-	function syncReceiverSelection(unitId = formData.unit_id) {
+function syncReceiverSelection(unitId = formData.unit_id) {
 		const candidates = getUnitPersonnelByUnit(unitId);
 		filteredReceivingPersonnel = candidates;
 
 		if (!unitId) {
-			formData.goods_manager_id = '';
+			setFormField('goods_manager_id', '');
 			return;
 		}
 
 		if (candidates.length === 0) {
-			formData.goods_manager_id = '';
+			setFormField('goods_manager_id', '');
 			return;
 		}
 
 		const hasCurrent = candidates.some(person => person.id.toString() === formData.goods_manager_id?.toString());
 		if (!hasCurrent) {
-			formData.goods_manager_id = candidates[0].id.toString();
+			setFormField('goods_manager_id', candidates[0].id.toString());
 		}
 	}
 
-	function handleUnitChange(event) {
+	function getVehiclesByUnit(unitId) {
+		if (!unitId) {
+			return [];
+		}
+
+		const normalized = parseInt(unitId);
+		return vehicles.filter((vehicle) => vehicle.unit_id === normalized);
+	}
+
+	async function syncVehicleSelection(unitId = formData.unit_id) {
+		if (!unitId) {
+			filteredVehicles = [];
+			setFormField('vehicle_id', '');
+			return;
+		}
+
+		const candidates = getVehiclesByUnit(unitId);
+		filteredVehicles = candidates;
+
+		await tick();
+
+		if (candidates.length === 0) {
+			setFormField('vehicle_id', '');
+			return;
+		}
+
+		const hasVehicle = candidates.some(
+			(vehicle) => vehicle.id.toString() === formData.vehicle_id?.toString()
+		);
+
+		if (!hasVehicle) {
+			setFormField('vehicle_id', candidates[0].id.toString());
+		}
+	}
+
+	$: if (formData.unit_id && filteredVehicles.length > 0) {
+		const hasVehicle = filteredVehicles.some(
+			(vehicle) => vehicle.id.toString() === formData.vehicle_id?.toString()
+		);
+
+		if (!hasVehicle) {
+			setFormField('vehicle_id', filteredVehicles[0].id.toString());
+		}
+	}
+
+	async function handleUnitChange(event) {
 		const value = event.target.value;
-		formData.unit_id = value;
+		setFormField('unit_id', value);
 		syncReceiverSelection(value);
+		await syncVehicleSelection(value);
 	}
 
 	function resetForm() {
@@ -181,6 +236,7 @@ let filteredReceivingPersonnel = [];
 			notes: ''
 		};
 		syncReceiverSelection('');
+		syncVehicleSelection('');
 	}
 
 	function openCreateModal() {
@@ -424,17 +480,28 @@ let filteredReceivingPersonnel = [];
 								required
 							>
 								<option value="">Birlik Seçin</option>
-								{#each units as unit}
-									<option value={unit.id}>{unit.name}</option>
-								{/each}
+									{#each units as unit}
+										<option value={unit.id.toString()}>{unit.name}</option>
+									{/each}
 							</select>
 						</div>
 						<div class="form-group">
 							<label for="vehicle_id">Araç</label>
-							<select id="vehicle_id" class="form-select" bind:value={formData.vehicle_id} required>
-								<option value="">Araç Seçin</option>
-								{#each vehicles as vehicle}
-									<option value={vehicle.id}>{vehicle.brand} {vehicle.model} ({vehicle.plate})</option>
+							<select
+								id="vehicle_id"
+								class="form-select"
+								bind:value={formData.vehicle_id}
+								disabled={!formData.unit_id || filteredVehicles.length === 0}
+								required
+							>
+								<option value="" class="s-jZJiUkwef1J0">Araç  Seçin</option>
+								{#if !formData.unit_id}
+									<option value="">Önce birlik seçin</option>
+								{:else if filteredVehicles.length === 0}
+									<option value="">Bu birliğe kayıtlı araç yok</option>
+								{/if}
+								{#each filteredVehicles as vehicle}
+									<option value={vehicle.id.toString()}>{vehicle.brand} {vehicle.model} ({vehicle.plate})</option>
 								{/each}
 							</select>
 						</div>
@@ -474,9 +541,9 @@ let filteredReceivingPersonnel = [];
 							<label for="personnel_id">Teslim Eden</label>
 							<select id="personnel_id" class="form-select" bind:value={formData.personnel_id} required>
 								<option value="">Personel Seçin</option>
-								{#each personnel as person}
-									<option value={person.id}>{person.rank} {person.full_name}</option>
-								{/each}
+									{#each personnel as person}
+										<option value={person.id.toString()}>{person.rank} {person.full_name}</option>
+									{/each}
 							</select>
 						</div>
 						<div class="form-group">
@@ -494,7 +561,7 @@ let filteredReceivingPersonnel = [];
 									<option value="">Bu birliğe kayıtlı personel yok</option>
 								{/if}
 								{#each filteredReceivingPersonnel as person}
-									<option value={person.id}>{person.rank} {person.full_name}</option>
+									<option value={person.id.toString()}>{person.rank} {person.full_name}</option>
 								{/each}
 							</select>
 						</div>