Vehicle dies when downshifting to first gear and also makes a squeling noise

Manual Transmission

1. 1
   Park your car with its front tyres touching the curb. Engage 1st and start slowly releasing the clutch pedal without applying any throttle. The engine should gradually fade out and bog down when the pedal is completely released. If the engine just bogs down at some point, or the fading is not gradual, the clutch is damaged. If the gearbox grinds when you try to shift in first from a standstill, there's a damage in the clutch too.
   
   
   
   
2. 2
   Try to pull off in 3rd gear with the front wheels at the curb, and without applying throttle. If the engine doesn't die, it shows a complete clutch failure. In that case, do not drive this vehicle.
   
   
3. 3
   Find a smooth, straight road to test the vehicle. Start from first, and slowly accelerate from second. As you do this use late-shifting, i.e. slightly over-rev the engine (approx. 500-1000 RPM faster than the revs you'd normally shift at). Up-shift to second without using double-clutching. Repeat the same procedure when shifting into 3rd. Now, with your car running at approximately 50 km/h (25 mph) try down-shifting to second without double-clutching. Both the up-shifting and the down-shifting must be done without grinding. Grinding of the gears indicates a gearbox malfunction, most likely in the sync gears ("synchronizers"). To make sure it's the synchronizers, try up-shifting and down-shifting with double-clutching. If the grinding stops, then it's the synchronization.
   
   

2
Shift into drive and hold the break pedal after making sure your brakes work. Press the gas pedal all the way down. The engine should not fade. If it does, it means the transmission (particularly the clutch) does not disengVehicle dies when downshifting to first gear and - 550px-find-out-if-a-transmission-has-gone-out-step-5.jpg/Image:Find-out-if-a-Transmission-Has-Gone-out-Step-5.jpg">

3
Check for smooth shifting. On an even and relatively horizontal road you should be able to accelerate without anyVehicle dies when downshifting to first gear and - 550px-find-out-if-a-transmission-has-gone-out-step-6.jpgunctioned.

4
Check for vibrations. Driving at about 70 km/h (35 mph) switch to Neutral (both auto and manual). There shouldn't be any lateral vibrations. If there are, this is either due to a warping of the drive-shaft, or a suspension damage. Basically, drive-shaft warping is perceived as a vibration in both vertical and horizontal directioVehicle dies when downshifting to first gear and - 550px-find-out-if-a-transmission-has-gone-out-step-7.jpg only one direction (i.e. either horizontally or vertically).

5
Test steering. When trying to enter a corner with approximately 30 km/h (15 mph) there shouldn't be any tangible under-steer. The presence of suVehicle dies when downshifting to first gear and - 550px-find-out-if-a-transmission-has-gone-out-step-8.jpgWD cars. Novice drivers must never try and test their differentials by trying to induce under/over-steer!

• Avoid prolonged driving by slipping the clutch.
• Avoid jerks and jolts while driving.
• Avoid "riding the clutch", i.e. needlessly keeping your foot on the clutch pedal.
• Never use clutch slipping for regulating the speed of a heavy truck!
• Make sure the clutch of a manual transmission is fully pressed when shifting
• Do not use excessive force when shifting a manual.
• For rear wheel drive (RWD) vehicles, avoid driving through places at the minimum of the vehicle's clearance.
  

• Incomplete disengaging is due to the trailing disc sticking to the leading one, e.g. because of mechanical soiling of the friction surfaces or worn out springs.
• Incomplete disengaging in automatic transmissions is felt as a forward jolt when the gearbox changes gears, whereas incomplete engaging is felt as over-revving the engine without any significant change in speed, especially when stepping on the throttle at high speeds (over 50 km/h or 30 mph).
• Automatic transmissions have the so-called "hydraulic clutch". It's basically a combination of a hydraulic pump, driven by the engine, and a hydraulic motor, linked to the rest of the drive-train. This allows for the hydraulic liquid to flow through the motor, even if its load is too big for the engine to rotate it. This eases operation, but results in poorer acceleration, greater fuel consumption and severely decreased ability of the driver to use engine braking, which can be very dangerous on long downward slopes. Hydraulic clutches are easier to operate in urban driving, but become a drawback on long roads
• Gearboxes come in three types: manual, semi-automatic, and automatic
• Malfunctions in a hydraulic clutch include incomplete disengaging (due to old hydraulic fluid, which has become thicker than specified by the manufacturer), or incomplete engaging (most often due to a leak of hydraulic fluid or presence of an air pocket within the hydraulic circuit. These are both dealt with by replacing the hydraulic fluid, bleeding (if necessary) of the hydraulic system, and removing any possible leaks.
• The most common malfunction of a dispatch box is the inability to change its function (e.g. switch between 4x2 and 4x4) If this happens, refer to a repair shop.
• The clutch is designed to smoothly disconnect the engine from the rest of the drive-train.
• The clutch disengaging too low or too high is an indication of a worn out trailing disc.
• There are implements that allow an automatic gearbox to operate in semi-automatic mode, allowing the driver to manually shift gear up or gear down, but w/o using a clutch. These operate exclusively by aids of electronics. This is common in high-class German cars like the S-Klasse Mercedes. Usually the corresponding position of the lever is marked with T or M and the driver selects a gear down by moving the lever to the left, and a gear up by nudging it do the right.
• Semi-automatic gearboxes are combined with a hydraulic clutch. They allow the driver to select a gear up or a gear down. These are most often seen in rally cars, where there are two levers on both sides of the steering wheel. Usually the right one switches a gear up, and the left one switches a gear down.