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Honda Gearbox - no drive

25th June 2017

This post is about the drive gearbox that honda fit to a lot of their pedestrian lawnmowers and the usual fault is a lack of drive although the drive belt is good and the pulleys are in fair condition, clutch cable is adjusted so that the spring is slightly stretched when fully engaged.

I have had many of these machines in for the same problem and always the dealer answer is a replacement gearbox which yes in some instances is the only option. So if the machine is in reasonable condition and not run into the ground I would generally strip out the rear axle and remove the gearbox, this can take over an hour if the bolts refuse to undo, or more likely the captive nuts start turning in the plastic! 

Anyhow once out, splitting the gearbox invariably reveals a complete lack of lubrication and some metal filings, as below.


This gearbox works by a lever connected to the clutch cable pressing onto a thrust bearing which in turn presses 2 cones together to jamb the brass gear onto the axle shaft and therefore transmit drive to the wheels.


When the gearbox runs out of lubricant what seems to happen is the mouldings which the axle passes through seem to melt with the increased heat produced by the now dry thrust bearing, the owner then tightens the clutch cable further increasing the pressure and therefore heat untill they have no drive at all because the fixed part of the thrust bearing has melted its way into the moulding, as below.


The fix I have found for this (no internal parts are available for this box), is to restore operation by fitting shims onto the moulding to make up the lost distance, there is no excact procedure to this it is trial and error, slightly too tight and the drive won't release, too loose and it won't drive, its then filled with heavy gear oil, or if the seals have been visibly leaking I would use a grease oil mix, the idea is to keep the lubricant in the box for as long as possible. 

Apply silicone sealant around the mating surfaces and reasemble the box, test it works on the bench and if all is well refit it to the mower and you have just saved yourself about £200 for the new gearbox and fitting.  

Some customers machines are still going strong after 3 years from having this done!