Author Topic: Mk5 Gearchange Mechanism  (Read 3502 times)

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Offline elaine

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Mk5 Gearchange Mechanism
« on: 17 Aug 2009 at 14:41 »
Hi everyone.
I am overhauling a MK5 gearbox and the gearchange mechanism is giving me problems. I am not able to select all gears.  There is wear on knockout pins 29617/17.  Would this prevent gear changing? Also, is there a specific setting up method for the ratchet 29312/17?
Any help would be much appreciated.

Offline Chris

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Re: Mk5 Gearchange Mechanism
« Reply #1 on: 17 Aug 2009 at 17:32 »
Hi Elaine
    Wear of the selector pins is a very common problem on the Mk and D'Fly gearboxes which will have an impact on gear selection. There have been various "cures" suggested involving building up the wear with weld, drilling out and inserting new pins etc. but care has to be taken not to destroy the heat treatment properties of the selectors. Also the thickness of material in the selectors limits the strength of any inserted pins. The most satisfactory solution I have found is to carefully set up the selectors in a four jaw chuck ensuring that the centre of the worn pin is running true and then to machine the diameter sufficiently to just clean up the two flats that are normal indicators of wear. Sleeves of the correct diameter can then be made to be a good fit on the turned pins. These can be secured by soft soldering which will not affect the heat treatment or even by sticking them on with a suitable grade of Loctite.
     It is necessary to "time" the kick-start mechanism and this is described in detail in pages 56 and 57 in the Maintenance Manual under the section of Re-assembly of the kick-start mechanism.
Replica copies of the Maintenance Manual and the Spare Parts List may be obtained from John Withers. Details elsewhere in the Forum.
     On a recent gearbox restoration after fixing the pins and replacing bearings and worn parts I still had difficulty finding the correct gears only to find after extensive investigation that the gear change quadrant, as the result of a crash, had  twisted relative to its shaft. It was only a few degrees out but was critical. Chris

Offline eddie

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Re: Mk5 Gearchange Mechanism
« Reply #2 on: 17 Aug 2009 at 20:22 »
             Even with the gearbox correctly assembled and adjusted, all gears will not necessarily engage with the internals at a standstill - it is usually necessary to rotate the shafts while changing gear. Wear on the knockout pins can be rectified by turning the pins half a turn. Wear on the selector pins is caused by the 'ramps' on the selector camplate, but doesnt actually affect the depth of engagement as the unworn part of the pin contacts the camplate when a gear is selected. If 2nd or 3rd gear is not engaging correctly, then the layshaft may need shimming either backward or forward - but remember, deeper engagement of one gear will mean shallower engagement of the other. If top gear is not engaging properly, this can be overcome by shimming back the input shaft - this requires the input shaft bearing to be removed from the front cover and the shim inserted first - then the square retaining plate needs a similar thickness shim before tightening the four countersunk screws.