In with the old - out with the new

Just exactly how does a broken gearbox become as good as new? H L Smith Transmissions explain the process they use to transform old gearboxes at their West Midlands Re-manufacturing plant.

Remanufactured service exchange components including gearboxes have long been a lifeline for UK operators. In return for your old gearbox, you have a rebuilt one, saving on downtime and with the reassurance of a warranty. And at a fraction of the price of a new one.

At HL Smith, the process starts when the gearbox comes into the plant. Each gearbox is allocated both a stock number and a location number which is logged on to the computer. This location number is critical and may change as the gearbox progresses through the plant. It is also essential in keeping track of low-volume older gearboxes – at the rear of the plant is a veritable Aladdin’s cave of potential core stock. That’s where older type gearboxes are kept. Some are simply casings that have had their working parts stripped out. They might be needed if for example, an old vehicle is involved in an accident and the casing needs to be replaced.

A 16-speed gearbox takes around a day and a half to rebuild, so ensuring there is enough stock of the most popular gearboxes takes planning.

Your vehicle off the Road? Try the fast replacement parts service from H L Smith.

The company has off-the-shelf rebuilt units for the most popular current models. “If a customer has a VOR, you have to be able to respond fast.” For the same reason, HL Smith also keeps a stock of partially rebuilt units and of new units. The partial rebuilds may be awaiting replacement parts and partially rebuilding them speeds up the completion time when they are required.

Once in the plant, the gearbox goes through a predetermined process to ensure quality levels remain high. It is first degreased and washed and then all worn parts are stripped off and discarded. “A quality rebuild depends on replacing all worn parts such as gaskets and bearings automatically,” explains managing director Russell Smith. “There are no short cuts, especially if, like us, you want to be able to offer a 12-month warranty on rebuilt manual boxes and 24-months on automatics. The gearbox is then carefully rebuilt using new components where appropriate.

On the rig

Once the unit is rebuilt, function is checked on one or two test rigs.No gearbox leaves the plant without undergoing a full function test.“It’s a vital quality control check,” explains Smith. “Some functions you can only check with the transmission under load.” The rig can handle a variety of gearbox types thanks to inhouse test turrets the company has designed for various gearboxes and even, where necessary, the bell housing.
The rig is run for 20 to 30 minutes to get the gearbox to normal operating temperatures and then it is tested to OE specification parameters.

Finally...
The main checks are to demonstrate the synchronisers work, that there are no oil leaks, noise levels are acceptable and to check the gear change is functioning. The synchronisation test, is done by placing the gearbox under load and then interrupting the drive. Without a clutch to do this, the synchronisers have to take over. The retarder function can also be tested on the rig as it will also put the gearbox under load. 

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