Caliper Piston Operation

[Daniel]

Evening all, currently got no forks and decided to clean up the front calipers while they were free. I removed the speed sensor, pads, pad pins, retaining springs and brackets. I left the lines attached.

Cleaned them both with soapy water and toothbrush and then focused more on the pistons, pulling the brake lever to expose more of the piston and only 1 moved at a time. I carried on depressing the brake lever and eventually the other moved instead, neither moved simultaneously, only independently about 3mm at a time. If I put my thumb against one it would not move though, only the adjacent one.

Which brings me to my query, is this correct? Should only 1 move at a time? It was the same with the other caliper. To me it seems wrong but they move very smoothly, are very clean, not used hard and have little over 10,000 miles of use.

 

[Brammers]

Mine does that too. As did the front twin pot caliper on my cb500 (1997).

You didn't say which piston moved first?

J

 

[Daniel]

Mine does that too. As did the front twin pot caliper on my cb500 (1997).

You didn't say which piston moved first?

J

Thanks that's reassuring then, felt like something was a-miss. Can't remember which moved first, may have been the lower one? As seen when mounted.

 

[Brammers]

I think it does that so the pad "scrubs" the disc, then the second piston bites as the pressure evens out behind them both.

 

[ADIOS600]

Did you lube the pistons before pushing them back ?

 

[Daniel]

Yeh, only with a little brake fluid as per service manual.

Separate question, this red substance in the image, it's on fork pinch bolts and caliper mounting bolts but no mention of applying anything in the service manual. Anyone know what it is?

 

[Brammers]

Looks like thread lock. I use the blue stuff (non permanent version) on all those bolts, just to be sure.

 

[Daniel]

Smashing 👌 as I suspected. Thanks for your help.