Such a long time since I was building Uno based kit cars. Have just renewed rear calipers, discs etc. My query is the operation of the self adjusting mechaniscm. Once the piston has engaged with the pin on the back of the pad, how can the piston adjust for pad wear as it is locked to the pad and therefore cannot turn on the handbrake helical screw rod? If the piston is screwed all the way in and the slack taken up by pumping the brake pedal, how does the slot in the piston "find" the pin on the back of the pad? My senior moments are on the increase!

fiatdonor said:

Such a long time since I was building Uno based kit cars. Have just renewed rear calipers, discs etc. My query is the operation of the self adjusting mechaniscm. Once the piston has engaged with the pin on the back of the pad, how can the piston adjust for pad wear as it is locked to the pad and therefore cannot turn on the handbrake helical screw rod? If the piston is screwed all the way in and the slack taken up by pumping the brake pedal, how does the slot in the piston "find" the pin on the back of the pad? My senior moments are on the increase!

Click to expand...

As long as you turn the piston to the right place it will locate to the pad pin, There is not enough space to it to turn away if the pads are new.

SteveNZ said:

As long as you turn the piston to the right place it will locate to the pad pin, There is not enough space to it to turn away if the pads are new.

Click to expand...

Steve, I think the question is more how does the self-adjustment take place (as the pads wear)? Given that the piston is not free to rotate (the pad pin prevents rotation, obviously). I think, like me, fiatdonor was more concerned with how it works rather than how to replace the pads.

I'm not sure myself but I believe it has something to do with the lever attached to the handbrake cable. I think something normally turns when the lever operates, and this turning (of the screw thread the piston is on) takes up the pad clearance before another part of the lever pushes on the piston to actually give the handbrake braking illusion (I mean, "result"). Is this right?

I do know that the self-adjustment seldom takes place properly unless the handbrake cable is really slack first (the levers need maximum 'throw' to adjust themselves). Winding the pistons in seems easier with the handbrake slackened, too. I found all this out by trial and error, rather than by any understanding of the mechanism

-Alex

I dont know how the Uno caliper works. It either does not adjust or works on some sort of self adjusting, maybe a ratchet type setup. Most of the time you need to adjust up the handbrake cable as the pads wear.