Description W5x / J160 / R15x gearbox – Internal speedo drive / sensor worm gear wire clip A worm gear and wire retainer clip as fitted inside the rear housing of a gearbox. There is one of these on the output shaft of a gearbox and is used to either drive a mechanical speedo drive or a speedo sensor. Suits various models- Please see the parts compatibility before purchase. These internal worm drive gears can be swapped so as to change which speedo drives / sensor options can be potentially be fitted. While this can be used to let an individual adjust their speedometers reading it is instead suggested to use an external speed correction box as it is a simpler and more accurate method. Instead the more likely use case in swapping this part is for those who have no speedo drive / sensor options with their factory fitted gear. For example if an individual is missing and requires a speedo drive and their gearbox is fitted with an internal 9-tooth worm drive then they have will likely have no other choice as all of the options to suit 9-tooth gears have been discontinued. See also our compatible speedo drive units to suit these. Parts supplied – Brand new worm gear of the chosen type – Wire retaining clip – Not pictured: This small wire clip fits through the inner slot in the gear and has it’s end fit into holes in the output shaft of the gearbox to hold this gear in place. Part Compatibility and Options – Speedo drives / Speedo sensors: When matched to a compatible driven gear these are worm drive gears are compatible with both mechanical speedo drives and electronic speedo sensors. – W5x gearboxes: Compatible with (and possibly fitted as standard in some) W55, 56, 57, 58 and 59 model gearboxes. It is not compatible with a W50 model (Steel case). – J160 gearboxes: Compatible with all variants of the J160 gearboxes. In standard form the early model J160’s were fitted with the 10 tooth (Type#1) gear to suit 31T to 33T (x 10) driven gears. While the later model J160’s were fitted with the 10 tooth (Type#2) gear to suit 34T to 36T (x 10) driven gears. See the next section for further details. – R15x Gearbox compatibility: These are compatible with (some?) the R15x gearboxes such as R151 / R154. However this has not be confirmed to be compatible with all variants. – Gear compatibility: See the section further down on this page. Parts options – 10 tooth (Type #1) / 10 x (31-33): Is compatible with the following gear options: 31:10, 32:10, 33:10. – 10 tooth (Type #2) / 10 x (34-36): Is compatible with the following gear options: 34:10, 35:10, 36:10. General additional information on Internal / external gear compatibility – There are two different variants of each of the 10 and 11 tooth internal drive gears and a single type of 9 tooth option. None of these different variants are cross compatible with any other, even for the same tooth count, for example the 10T:(31-33) variant of the 10 tooth gear is not compatible with the 10T:(34-36) variant. See the chart below to identify which internal gear is compatible with which range of speedo drive gears. – There are different types of internal worm drive gears as used inside of gearboxes. To determine which is fitted remove the existing mechanical speedo drive / electronic speed sensor unit and examine the two different numbers imprinted on the bottom face of the plastic gear. This will show how many teeth are on the current gear and also the amount of teeth on the internal gear. Using this and some research can determine the compatible gears available. The picture below shows an example of a 32:10 speedo gear – as an example if this was previously used then a 31T:(10) or 33T:10 option speedo gear would also be compatible. – If there isn’t an existing speedo drive / speed sensor drive unit to use as a reference and the internal gear isn’t a 9 tooth then the only sure way to identify the internal gear is to visibly look at the engraving on the face of the gear itself. These are tiny characters that are difficult to read. The options are to either use a bore scope with a mirror or if it’s an option to remove the shifter housing for direct visibility. Below are pictures that show a gearbox without the shifter housing and another showing an example of an internal drive gear. (click to zoom) Choosing the correct speedo drive for the correct readout. IMPORTANT NOTE: All of these choices below are dependant on if the gear compatible with the gearboxes internal gear, see the sections further up this page before making a choice. For many people they will need to choice an option that suits what they have and then for any resulting inaccuracy an speedo correction module is suggested. One method is to compare the measured speed from a GPS against the cars reading, work out the percentage of inaccuracy and order the correct ratio correction module to suit. These are available from various sources, one of them being from the “Castlemain rod shop”. Below are the different options of gears as fitted to the speedo drive unit. They are listed in the estimated relation to the diff ratio as used on the vehicle, however this can only be used as a rough guide as it will change pending on the accuracy of the dash speedo unit, rolling tyre diameter and so on. Calculated when using a 185 / 60 / 14″ tyre – rough guide only: 31 (:11 #1) Teeth: Suits a 3.3:1 diff ratio 31 (:10 #1) Teeth: Suits a 3.64:1 diff ratio 32 (:10 #1) Teeth: Suits a 3.7:1 diff ratio 33 (:10 #1) Teeth: Suits a 3.9:1 diff ratio 35 (:10 #2) Teeth: Suits a 4.1:1 diff ratio
