BMW Mini drain plug issue

Valeo technical expert and product manager, Stephen Knight visits a workshop to look at the problem

The vehicle in question was experiencing clutch selection problems after having a brand new clutch fitted.

Valeo are aware that the Mini 5 speed gearbox (GS5 65BH) found in the Cooper models (non-S) built between 2001 and July 2004 is referred to as the R65 or the Midland gearbox and was not the preferred choice by BMW Technicians.

BMW had wanted the engine to have a Getrag gearbox, but the original UK engineers put the Midland gearbox instead due to it being more cost effective and more compact.

The Midland gearbox is no longer produced and a BMW dealer will only supply a reconditioned gearbox or replace it with the later.

After July 2004 the Getrag gearbox was put in on the facelift model.

With this in mind Stephen was expecting to help the respective garage remove the gearbox and clutch and find either a fault with the gearbox itself, or a fault with the clutch release mechanism.

What was found however, was something slightly different.

As a leading manufacturer of clutches, Valeo advises to drain and replace the gearbox oil during each and every clutch change.

This however is not standard practice with every garage or clutch fitter.

Transmission fluid, just like engine oil, is a lubricant.

Its purpose is to ensure that the various working parts of the transmission are not subject to damage.

The fluid will keep the transmission both lubricated and cool.

When transmission fluid goes bad, problems will begin to surface.

When the fluid stops becoming effective it loses its viscosity and does not sufficiently lubricate the gears in the gearbox.

This results in metal gears grinding on each other.

When this occurs small pieces of metal, often described as filings, will be produced from the metal on metal contact. In this particular vehicle, this is exactly what was identified.

When removing the gearbox drain plug, it was found to be saturated in metal filings.

As the drain plug is magnetic (which is becoming increasingly more common) the filings are collected at the bottom of the tank so they do not get stuck between the gear synchros.

However, when the magnetic drain plug is completely saturated in metal filings, and can no longer magnetically attract anymore, the metal filings are free to float around inside the gearbox oil.

An accumulation of these filings in a gear synchro can seriously affect its performance. If a gear synchro is not free to turn as required then gear changes will be affected.

Best practice for best results

The manual transmission fluid/gearbox oil should be changed at regular intervals.

Even though Mini calls it “lifetime” fluid there is no filtration system in the manual transmission, only the magnetic drain plugs to capture debris.

It is recommended that the transmission oil be changed every time the clutch is changed and the magnetic draining plugs cleaned of all debris before it circulates causing potential damage to the gearbox bearings and synchros.

It is also equally important to ensure that transmission fluid is kept at the proper level, otherwise it will result in the transmission wearing significantly.

If the transmission oil is low, the wear on the synchro rings and sliders will accelerate significantly as they require a slick surface in order to match speeds when shifting, thus saturating the oil with more debris.

A Mini clutch change takes 5.5 hours.

The bottom line; changing the transmission is a 10 minute job that may stop you having Big problems with a Mini.


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