The Sensible Guide to Yamaha Calipers
The brakes on the Yamaha triple were considered to be state of the art in the mid-1970s. Twin discs up front and one at the rear was about as good as it got back then – and many road tests of that era were quite complimentary about the braking performance.
They really aren’t that good by modern standards though. All Japanese manufacturers at that time were using variations on a single-sided brake caliper design (possibly to avoid infringing US and European patents on disc brakes) and the bikes were also getting to be quite fast and relatively heavy compared to earlier models. All this, plus decades of neglect and modern traffic conditions, means you really want to restore your brakes to something like their original state if you want to stop your bike without stopping your heart.
Here’s what I did to rebuild my calipers. I’m only showing one here, but they are all pretty much the same (the bracket is different at the back, as is the direction of the bleed screw, but these changes aren’t significant for rebuild purposes).
Disclaimer: I’m not a qualified brake expert so this instruction is for illustrational purposes only. Only attempt to rebuild your brakes if you know what you are doing and are prepared to take responsibility for the consequences.
With the disclaimer out of the way, I’m going to start with a stripped-down and painted caliper and bracket. I had these blasted and stove enamelled but I’m not sure I would go that route again. The stove enamelling is ultra-resistant to solvents (e.g. brake fluid) but it is quite brittle and chips easily. If you care about a tough long-lasting finish I reckon powder coating might be better. Anyway the important point is, you really need to have everything scrupulously clean. Really, really immaculate and grease free, no hair or dust anywhere. Clean your hands before starting work too.
I’ve cleaned out all the threads with suitable taps and cleaned the groove inside the brake cylinder with a rotary brass wire brush on a Dremel. The brake cylinder itself doesn’t have to be mirror-smooth but it’s very important to get all the corrosion out of the groove where the seal will go.
Here are the parts I’m going to fit first. I got a double sealing kit for the pair of front calipers from Partsnmore but there are many other places that sell them. I’m also fitting a stainless steel piston, which is a very good upgrade because the original mild steel versions tend to corrode badly and then seize into the cylinder. I’m not sure where this one came from, but they are now available from Yambits and other places.
Here’s the sealing ring from the seal kit and a can of silicone spray, which is an essential item when rebuilding hydraulic cylinders or other parts with rubber fittings. Don’t use a petroleum-based lubricant here because it will attack the rubber parts and will also contaminate brake fluid. Silicone spray is ideal because it’s both slippery and inert.
So with a little silicone lube, you can insert your sealing ring like so:
And then insert the piston. If the piston and cylinder are clean, the piston will slide in like a dream.
If it doesn’t, then something is wrong and you should take it apart and investigate. Assuming all is well though, you can push the piston all the way home and put the dust protection boot on:
Next fit the retaining clip. This can be quite fiddly because you can’t easily see the back of the retaining clip, so check it carefully. When it’s on it should look like this one (shown next to the disc pad kit).
This disc pad kit was an eBay find – I chose this type because it comes with the spring clips and retaining screws, which not all kits have. Here’s the kit opened up, with the metal protection plates fitted to the mounting bracket already:
Those protective plates are essential because they prevent the pads from wearing away the soft alloy in the mounting bracket. Next fit the retaining spring and pad retaining screw to the caliper as shown, but don’t turn the screw all the way in yet. Note the little finger on the retaining spring goes nearest the piston (there’s a groove for it):
Now fit the sliding pivot, with its rubber boot. I got a new boot from Mikes XS because the old one was a bit crispy after 30+ years of brake action.
Silicone spray helps a lot here, but it’s still fiddly. The trick is to slip the pivot sleeve half way into the boot, then insert the boot into the caliper and then slide the sleeve all the way in:
When it’s done, you can fit the pivot bolt – I applied a little smear of copper grease to the shank, just to prevent it corroding in future:
At this point, fit the pads loosely in the mounting bracket and bring the caliper and mounting brackets together. Be very careful not to get any grease or silicone spray on the faces of the disc pads when you are doing this. I also used a little medium strength thread locking fluid on the pivot bolt:
This is what it looks like, squeezed together with the pivot bolt and the pad retaining screw tightened:
And from the other side, showing the bleed nipple and dust cap:
Once you’ve done all this, fitting them to the bike is quite easy – there are just 2 mounting bolts, each with a spring washer and a plain washer. Hopefully now your bike will stop reliably for years to come.