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Diagnose if your gearbox is at fault


  • Engine must be switched off and operating cable must be disconnected before servicing work is carried out.
  • A suitably qualified person should only carry out all servicIng work.
  • DANGER : Hot oil causes burns.

No drive in either shift position could be a result of low oil pressure, a broken drive plates or failure of the inputs or output shaft.

Before assuming the worst, check the oil level, leaks and oil condition. Operate the gearbox directly from its shift lever checking the shaft coupling is not at fault. Next check the shift controls & cables operation at the gearbox end for cable end movement.

Take all precautions to avoid hot oil splash and harm from moving parts. Having checked oil level is correct, discolouration of the oil or an acrid smell would almost certainly indicate a fault is occurring and servicing is required. 

Inspection plates on the box, such as prm,  can determine non rotation of the input shaft assembly which may indicate a broken drive plate or damaged splines.

An intermittent loss of power or lack of increase of drive is often a result of low oil pressure. A suitable gauge needs to be installed to monitor this on all shift positions, to indicate where the fault lies.

A lack of oil delivery due to oil leaks, defective cooler or a failing pump will lead to overheating because of reduced oil flow through the cooler. At this stage damage is occurring throughout its components, therefore complete overhaul of the box is required. Slow engagement on Hurth/ZF mechanical boxes requires immediate workshop repair so to avoid further damage.

Should neutral not be able to be found, it’s likely a clutch is seized or dragging. Inspection of the clutch plates is necessary.

If evidence of a gearbox fault is found, always assume that the oil circuit is contaminated and hoses and coolers need to be cleaned thoroughly. We would recommend cooler replacement with regards to future gearbox warranty.  

We're happy to help. Call +44 (01273) 410025

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