Gearbox Internals

The synchroniser for that gear is worn. Its blocker ring should drag against a cone on the gear and match speeds before the sleeve engages, and once the friction surface glazes or the teeth on the ring wear, the sleeve arrives before the speeds have matched and you hear the gear teeth clash. It shows up first on fast changes and while the oil is cold. The cure is the synchroniser and often the gear it works with, listed here individually rather than as a unit.

Because something has stopped holding the sleeve engaged. Inside, the usual causes are worn engagement teeth on the gear and sleeve, which develop a taper that pushes them apart under load, a worn selector fork, or a weak detent. Outside, worn powertrain mounts can let the drivetrain move enough to pull a linkage partially out. Check the mounts and the linkage first because they are far cheaper, then plan a strip if the fault sits in one gear under load.

No, and the pattern tells you which. A whine present in every gear and also in neutral with the clutch up points at an input or countershaft bearing, because those turn whenever the shafts turn. A whine present in some gears and absent in others points at the gear pair for those ratios. A noise only in neutral that disappears when the clutch is pressed is usually the input shaft bearing. Working out which before you strip means ordering the right parts once.

Look at the debris. Fine grey paste on the magnet is normal. Metal flakes, broken teeth or a filter element packed with material mean contamination has reached every bearing and every gear face, and a partial rebuild will fail. Where the fault is confined, a worn synchroniser, one noisy gear pair or a single bearing, a rebuild using the individual parts listed here is far better value. The strip tells you which case you are in, which is why parts are ordered afterwards.

Order the obvious ones and wait on the rest. Seals, dust covers, the filter element and gaskets are needed regardless and can be bought in advance. Bearings, shims and specific gears cannot, because bearing preload and endplay are set by measurement on assembly and the grade required is only known once the shafts are in the case. Buying a full assortment in advance wastes most of it. Strip, measure, then order the exact references.

Look outside the casing. A stretched or seized selector cable, worn cable end bushes, or a loose linkage at the lever produce imprecise selection, long throws and occasional refusals to engage while everything inside the gearbox is perfectly healthy. Powertrain mounts contribute too, since a drivetrain that moves takes the cable with it. Gear selector cable assemblies are listed here, and replacing one is a fraction of the cost and effort of opening a gearbox.

More than most people assume. Synchroniser friction depends on the oil, and a lubricant with the wrong additive package makes a healthy gearbox baulk on cold changes even though nothing is worn. Use exactly what the manufacturer specifies, in the correct quantity, and change it at the stated interval. If a gearbox has developed a cold change problem after a service, the oil is the first thing to check before anything is dismantled. Lubricants sit in their own category on the site.

Washers, dust covers, filter elements and seals sit right at the bottom of the range. Bearings and selector cables are modest. Individual gears, mainshafts, countershafts and complete shaft assemblies cost considerably more, and rear cases sit near the top. The live minimum and maximum are shown in the band at the top of this page. Because a rebuild is a list of small items plus one or two large ones, it is worth quoting the whole list at once.

No, and it is worth saying plainly. A battery electric drivetrain uses a single speed reduction gearset that is permanently in mesh, with no synchronisers, no selector forks and no gear changes to make, so nothing in this category applies to it. Its gears, bearings and housing sit under the reduction gear and e axle listings instead. The parts here belong to combustion and hybrid vehicles in the catalogue that use a conventional manual transmission.

It is possible with the right equipment and unforgiving without it. You need a press for the bearings, a dial indicator to measure endplay, the correct shim grades available, a clean bench and the manufacturer's tolerances. The mechanical steps are logical. The measuring is where rebuilds succeed or fail. Photograph every stage, keep each shaft's components in order, and expect the job to take longer than planned. Where the measuring tools are unavailable, hand the assembly to a specialist and supply the parts.

Only where the numbers agree. Gear sets change with ratio, and manufacturers revise ratios, tooth counts and bearing sizes within a single model run without announcing it. A gear that looks right and has one tooth more will not mesh with its partner. Read the numbers from the parts you remove, match them exactly, and where a reference returns nothing, send it through the quote form so the factory catalogue is checked rather than approximated from the model name.

Yes. Individual gears, synchronisers and selector forks move in very small numbers, so most of them are handled by enquiry rather than shown with a figure. Send the reference and a current price comes back. Two pieces of advice for this category. Order the bearings, circlips and the case gasket at the same time as the failed component, because they are needed whatever the strip turns up. And have the endplay checked while the box is open, since a gear replaced in a case with worn bearing seats will not last the season.