I realise that ‘anchour’ is an archaic form of ‘anchor’ , but as it could
be said that a drum brake is archaic when compared to a disc, I’m going to go with it ! This article then is about the drum brakes on the 1972 GT750 – and more specifically the front one.
The front drum brake as used on the 1972 GT750 is a twin leading shoe (2ls) drum brake having two brake drums, one on either side of the hub, and four brake shoes in total with each one separately actuated. The idea is that the servo effect of having the 2ls will increase stopping capability – in one direction. Note that when backing a bike off a trailer for example, the brake doesn’t work very well at all in reverse and can lead to unpleasant surprises !
Recall that I had put a front drum aside to be dealt with later as it was badly corroded (photo above on the right – just click for a larger image) . I had both the front and rear drums cleaned at Top Gun Coatings here in Calgary who used a vibro-polishing process. This is perhaps not quite as good as vapour blasting, but it does give a very nice finish which is close to the factory original. On inspection, it was clear that while the front drum would be usable, it did have a few cosmetic issues. The gouges in the spoke flang
e on the left side were deep enough that I didn’t want to try to polish them out as it may have weakened the flange, but the ding in the edge of the drum (which can be seen in the photo above and to the left) needed to be addressed. Art, who is a friend of mine here in Calgary and who teaches welding at SAIT, managed to do a small repair on the edge that makes it look a lot better as can be seen in the photo on the right.
The brake shoe cams are handed, having a slight rounded trailing edge on the edge that lifts the end of the shoe when the arm is actuated. Consequently, you do need to install them on the correct sides. The rear brake cam (which is a conventional drum brake) and mounted on the right side of the drum, is the same part number (54440-11002) as is used on the left hand side on the early, pre-frame number 18325 bikes. The right hand cam (54430-31000) for the front is specific to the 2ls brake as used on the GT550 and the GT750.
At frame 18325 the cam design changed, with the new part numbers being 54430-31001 for the right hand cams, and 54440-33000 left hand ones. The difference between the new and the old cams is the thickness of the pivot block which was increased from about 7mm to be about 10mm. The difference is clearly visib
le in the photo to the left, with the original style on the left and the updated version on the right. Note the rear drum stayed with 54440-11002 which changed to 54440-11003 and was used on many models (T20 rear wheel, T305 rear, all years of T500 front drum brake, and all years of GT750 rear drum brake, plus others).
I had most of the steel fasteners and speciality parts re-zinced by Wespen here in Calgary. On the GT750 J (and K and L) there are quite a number of chromed parts which on later models were left in zinc. In some cases the parts cleaned up like new just by having a good soak in Evapo-rust so that is an obvious first thing to try before sending items out to be re-chromed. The air vents (parts 36 and 37) are in two parts with a under grill which I left in zinc, and a top louvred grill which I had re-chromed. The actuator levers cleaned up well enough to re-use as is. There are a lot of parts in these brakes – I’ve included a parts diagram to the right. The lock tabs (part 42) I ordered from Ian Beardsley in the UK who supplies them in stainless steel. You can find them at this link.
As previously mentioned, I had Suzuki Canada reactivate the part number for the front brake shoes. I still smile whenever I look at the packaging as I’m not sure why they think they can charge the full price for used shoes (it says they are all factory tested ) but no matter. They work and based on the experience with the Oily Purple I built last year, I have to say they do work better than I had expected.
I am still in the process of final assembly. One thing I will need to source are the rubber air vent caps for the side plates. There are five of these (54676-31000) and many of mine have perished from sun and weather damage. I see that Eric of the Knalnaarpotz shop in The Netherlands has these available for about a Euro each. I have bought from him previously and recommend him, but first I will take a look through a couple of local hardware stores to see if they have anything close.
Once I have the wheels mounted and a rolling chassis, the next item on the agenda is the engine !