Gearbox Replacement Guide

Gearbox part

When you are looking to buy a gearbox to replace your old one it is important to match up the part numbers to be sure it’s the correct one for your car. Get it right the first time – You do not want to purchase the wrong one and then go though the process of finding the correct one all over again.

At Your Car Spares Ltd  – What we test and look for!!!!

When deciding if we should keep the gearbox from an end of life vehicle we look at the history of the car and the mileage it has covered because we don’t want to sell a gearbox only for it to stop working a few weeks down the line. Once we’ve made a decision based on the history and mileage we then test it to ensure everything is working as intended. Our tests involve us testing each of the gears and listening out for any sounds , such as grinding. If the gearbox is in full working order then we will look at the condition of it. We don’t want to keep a gearbox that is badly rusted or in poor condition.

Where to find the Part Number on a Gearbox

The gearbox code can be found stamped into the gearbox or on a sticker on the gearbox. The location and what the code looks is dependant on the manufacturer of the car , some manufacturers put a sticker on the sump whereas others stamp it into the gearbox. The gearbox code is usually a code with a mixture of numbers and letters. Some car manufacturers will put the code into the owners manual. Below we will show you examples of gearbox codes.

Gearbox parts number

Where to find the parts number on a gearbox

Gearbox serial code

Sample of a serial code on a gearbox

Parts number location

Overview of the gearbox parts number location


Close-up view of sample serial code

How does a Manual Gearbox Work?

The crankshaft in your engine is attached to a flywheel and they spin together. Attached to the flywheel is a clutch plate with a pressure plate over the top of it. When the engine is running and and the clutch pedal is up and not being pressed the flywheel and clutch plate spins together , but when the clutch pedal is down the pressure plate releases the pressure on the clutch plate which causes it to stop spinning , allowing the driver to seamlessly change the gear without causing any problems to the transmission. The power from the flywheel goes into the gearbox input shaft. The input shaft is connected through a gear to the layshaft , causing them both to turn at the same time. Above the layshaft is the main shaft and they are connected through their gears , the number of gears on the shaft represent every gear the driver can select through the gear stick. Each gear on the main shaft is a different diameter and rotates at a different speed with the 1st gear being the largest in diameter and rotating slowest whereas the highest gear is the smallest  and rotating quickest thus causing you to go faster as you change up a gear. The main shaft is a splined shaft and in the middle of each pair of gears is a collar which rotates with the shaft as well as sliding up and down the shaft. On the side of the collars are dog teeth which allows the gears on the main shaft shaft to attach to and lock in place.  When you change gear the collar will slide up the shaft and lock onto the gear you select and the power will transfer from the layshaft to the main shaft and then to the gearbox output shaft. Once you’ve changed gears and the clutch pedal is up again the clutch plate is pressured back to the flywheel to receive power.

How does an Automatic Gearbox work?

An automatic gearbox sends transmission fluid into the torque converter and the pressure of the fluid activate clutches and bands which decide what gear the car should be in. A planetary gear set creates the gear ratios that a transmission can produce and there are 3 components to the gear set : a sun gear , planet gears (at least two) and  a ring gear which are all connected together. The ring gear is a big circle gear on the outside with pinions on the inside that the planet gears are connected to and the sun gear is in the middle connected to the planets. The planetary gear set has various ways of working and one example is that when the ring gear turns , the planet gears will ‘orbit’ the stationary sun gear which causes the output shaft (which is connected to the planet carrier) to turn in the same direction as the input shaft (which is connected to the ring carrier) but at a lower speed causing the car to act like it’s in 1st gear. If the sun gear is unlocked but the lock two of the other gears it will make the 3 of them to turn at the exact same speed thus replicating a car in 3rd gear or higher.

Top view of a gearbox spare part

Top view of a gearbox spare part

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