What happens when a gearbox is removed and refitted?

Many repairs depend on taking the gearbox out of the vehicle, even if the problem is not in the gearbox itself. Clutch, flywheel, rear engine seal and gearbox repair work all begin the same way.

This guide explains the steps in plain language, so that you know what you are paying for when We Fit Any Clutch Cornwall removes and refits a gearbox.

Why does a gearbox need to come out?

The gearbox bolts directly to the back of the engine, with the clutch sandwiched between them. To reach the clutch or flywheel, the two have to be separated. To repair the inside of the gearbox, it has to be out on a bench.

That is why a clutch replacement is mostly a gearbox removal job, and why labour is a major part of the cost on many vehicles.

What is disconnected first?

Preparation comes first: securing the vehicle, disconnecting the battery where needed and draining the gearbox oil if required. Then the mechanic disconnects the gear linkage or cables, the clutch cable or hydraulic line, electrical connectors, the starter and exhaust parts that are in the way.

Driveshafts or the propshaft are separated, depending on whether the vehicle is front, rear or four-wheel drive. The engine is supported so it does not move once the gearbox is unbolted.

• Battery and electrics
• Linkage and clutch controls
• Driveshafts or propshaft
• Starter, exhaust and mountings

How does the gearbox come out?

Once everything is disconnected and the engine supported, the bolts joining gearbox to engine are removed. The gearbox is heavy and awkward, and it has to be slid straight back to clear the input shaft, then lowered carefully. A gearbox support jack is normally used to control the weight.

On some vehicles the engine and subframe must be lowered or the gearbox is removed from above. The method varies a lot between makes.

What is checked while it is out?

Access to the back of the engine is a rare opportunity, so the mechanic looks over the clutch, flywheel, rear engine seal, gearbox input shaft seal and the release mechanism. Leaks, worn splines and damaged parts are identified.

This is the ideal moment to renew anything borderline, because refitting the gearbox again later means paying for the labour a second time. You should be told what is found before extra work is done.

How does this differ between vehicles?

Front-wheel-drive cars usually need driveshafts released at each side, often with suspension parts moved aside. Rear-wheel-drive vehicles have a propshaft to remove. Four-wheel-drive and automatic vehicles add transfer units, cooler lines and electronic connections.

Vans can be heavier and more cramped. That is why the mechanic needs your exact vehicle details before talking about the time involved.

How is it refitted and tested?

Refitting is the reverse, with care. The input shaft splines are lightly lubricated, the gearbox is aligned and drawn onto the engine without forcing it, and bolts are tightened properly. Mountings, driveshafts, linkages and electrical connections are restored.

Oil is refilled to the right level, the clutch and gear selection are tested, and the vehicle is road tested for noise and smooth drive. Any final adjustments are made before you get the vehicle back.