GT750 Speedometer Drive

In the process of putting together the front wheel for my GT750 project bike, I noticed that the speedometer drive housing had a problem. Basically the output shaft to the speedometer cable would not turn when the wheel was spun. These drive units are not intended to be repaired, and no parts are available for order to repair them – they were available only as assemblies. The specific part for the GT750 (54600-34000 or 54600-34001) is no longer be available from Suzuki and has been superseded by a new part number 54600-08C00, and can be bought new for about $84 USD in the USA. This speedometer drive assembly was used on about 25 different models of Suzuki motorcycle between 1973 through till 1982 so used ones should also be readily available on eBay.

At any rate, I’ve had this problem before and I also had a few spare drives so I thought it worth the time to try to overhaul the drive assembly that I had, rather than try and find another one.

The components of the drive assembly are shown in the  photo (just ‘click’ on it to see a larger image).

Taking it apart is not difficult – remove the snap ring on the back, then the space washer and (if it is fitted) the thrust washer – and then what I do is just carefully pull the main gear through the seal. For the speedometer drive itself, the bush and seal unscrew and the output shaft then is free to be removed. Don’t lose the small thrust washer on the output shaft ! There is a seal on the back of the drive housing facing the wheel, as well as a small one in the bush. As yet I have not had to look for a replacement for these.

Referring to the photo – the main gear and output shaft are machined steel and as yet, I have not seen them fail (although I’m sure it could happen). On any of the units I’ve looked at, the problem area always seems to be the two small tabs on the inside of the driven gear which is really just a mild steel washer and that was the case with this one also. The inner tabs mesh with the harder steel of the main gear and eventually just rub away. I was lucky to have a spare part, although I’m also sure a couple of small welds which would then need to be ground down and squared up would work just as well.

When reassembling, I repacked the drive housing with a bit of wheel bearing grease, taking care to ensure the bottom end of the output shaft is greased as it is a blind hole. Some units have the small thrust washer on the back between the drive gear and washer, and some don’t – basically if the snap ring seems loose such that the driven gear does not engage properly, then it needs the additional shim.

Now that its all back together and installed, it seems to work fine – so on the the next item ……

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