Topic: Solid vs Hollow Caliper Pistons (69-76 CB750)

[cyclepsycho]

Is there any reason why I shouldn't use a 78 GL1000 front brake caliper piston in a 69-76 CB750 caliper?
The GL1000 piston is the same diameter and length as the CB750 piston, but it's a hollow cup type, rather than having the steel plug in the end.
The CB750 piston weighs 7.05 ounces while the GL1000 piston weighs 4.35 ounces.

I have a drawer full of new GL1000 pistons and they are inexpensive compared to the CB750 pistons (when you can find them).

What do you think?

[somesuch]

Anyone tried it?

[iya0yas]

You indicated the diameter and length of both pistons are equivalent.  So long as the volume of brake fluid acting on the 'hollow' piston remains the same as that for the 'solid' piston.  Check to make sure the distance both pistons travel within the caliper to make contact with the pad are the same too (i.e., spacers between piston & pad?).  The capacity of your brake fluid reservoir is designed to hold enough 'reserve' fluid so that when your pad material wears down to the pad backing plate you still have fluid available to develop pressure within your brake system and stop the vehicle.

[bryanj]

The overall length is the same BUT the wing one is smaller diameter at the pad end as it has a "Dust" seal as well as the fluid seal.

Having looked closely on a 500 (same piston as 750) with the piston all the way in the top edge of the sealing diameter is down in the seal groove area so in my opinion as long as you are using worn pads it will be OK but New pads might be a problem and with your US style of litigation if you sell the bike and somebody gets hurt because you have "Bodged" it would you be liable?

Dave Silver is now selling pattern stainless pistons cheaper than the genuine plated ones so thats the way i go!!