You need to weld a small piece of metal to hold the piston in place.
That is also with the pads in the auction.
No, you do NOT weld anything to the pads, and you should never weld anything anyway as the heat will damage the pad material and bonding.
You need to understand why that small pip is on the back of certain pads.
The piston on the rear caliper MUST be fitted with the bleed point inside the piston at the highest point, to allow the calipers to be bled properly. Since you cannot see that bleed point, they machined a groove across the piston and then made a smaller parallel groove to one side of it. When that groove is horizontal with the smaller groove to the top, the piston bleed point is correctly in the highest position.
The pip on the back of the pad when fitted fits in that groove, but is offset from the centre of the piston. That means that if the groove was not horizontal, and therefore the piston was not in the right position, you could not fit the pads. So it forces the person fitting the pads to make sure the piston groove is horizontal. However, they could have the piston 'upside down' with the smaller groove at the bottom, so it is not 100% foolproof.
If you find some pads without the pip on the back AND they are the right pads, then you can still use them. But you must make sure the piston is fitted correctly with the groove horizontal and the smaller groove to the top. If you do that everything will work as it is supposed to. (assuming everything else is good!)
Some people think the pip is to stop the piston rotating in use. That is total nonsense!! Just think about it for a moment. If you have ever fitted new pads or overhauled the calipers you will know how much effort is required to rotate the piston when you need to, to wind it back in to fit new pads, or when re-assembling after overhaul. So the piston will never rotate on its own at any time. Second, when applying the brakes, the force of the piston on the pads and the disc is sufficient to ensure no rotation could ever take place at that time owing to the friction and forces involved. So the piston will NEVER rotate at any time either on its own or when being applied.
So the pip has no other function than to ensure the groove is horizontal and if it is not present, as long as the piston groove is horizontal, the pads and brakes will be fine.
One further thing about brake pads. I am finding that most pads these days are coming fitted with aural reminder buttons, to warn you when the pads are getting low. A good idea that is far more reliable than the electrical wire system. However, I don't think the manufacturers of the pads understand what these buttons are for!
They are fitting them on the wrong side of the pads! :-)
The button is a soft material and is supposed to be fitted so that it contacts the disc and makes a lot of noise but without damaging the disc, when the linings are nearly worn out. As there is one button on each pad, it doesn't matter which pad wears first or even if one wears rapidly as the caliper is sticking, you will get a warning before the material is all worn out. But not if they fit them on the wrong side!
When you get the new pads, you need to punch these buttons out and fit them on the correct side, so they can do the job they were designed for. If you punch them out with a small pin punch in the centre of the riveted side, it should retain the material so that when you push them in again from the correct side, there will be enough sticking through to re-rivet them in again. I have done this numerous times so I know it works fine. All was explained in our club magazine with diagrams.
Roy
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