Topic: brake caliper piston question

[88blkiroc]

When I got my 74 cb750k it had a dual front disc setup on it. The calipers were stuck so I took them apart yesterday. One of the caliper pistons looks like the other ones I have seen before. Flat bottom and open on the end where the pad sits. The other piston looks different. All the dimensions are similar except that on the end where the pad sits instead of being open the piston has a convex steel cap on it. I looked and it appears that the cap part and piston are too separate pieces but with I could not get them to separate. I don't want to try too hard and break something. Does anyone know why this piston is different? The calipers appear identical otherwise and the pistons are both very clean and in good condition. On the "normal" looking piston the pad sits nice and flush on the piston. With the other since it is dome shaped the pad doesn't sit flush and rocks around a bit. Thanks for the help. P.s. where is a good place to buy pads at? I need two sets and the local honda dealer doesn't have them.

[LesterPiglet]

That closed piston sounds like my 550 one. Mine has a nylon ring on that piston.

[88blkiroc]

No nylon ring on this one. Ill try and get a picture and post it.

[88blkiroc]

Ok here is a picture

[LesterPiglet]

Nope not the same as mine.

[88blkiroc]

Anybody?

[scottly]

My old K1 pistons had the domed insert like the piston on the right side of the pic. My guess is the OP left the domed part off the other piston. They were a loose fit in the piston. The later K7 pistons have a "washer" staked into the open end of the piston, with a small raised area in the center, and the plastic ring.

[grcamna2]

I believe it's best to make both pistons match as close as possible, mainly on how they  make contact with the pads.

[88blkiroc]

Well the domed part is attached pretty firmly to the piston. It isn't loose at all. Any suggestions on what route to go with this? Would a 74 normally just have open top pistons or the domes and if so where do I get another one? Or should I just try and remove it and run it open like the other side?

[scottly]

None of the 750 pistons I've seen have an open top, but I only have seen K1 and K7 pistons. I do know that 550 pistons are quite similar to K7 750 pistons, and the phenolic pistons that a member makes are open top. Confused yet?

[88blkiroc]

Yes, severely confused. I don't want to be wrong on brakes. If you can't go that's one thing but if you can't stop that's a much bigger problem. I am ordering new pads tomorrow but I don't even know where to look for one of those dome things.

[scottly]

Honestly, the only reason I can think of for the dome is to limit heat transfer from the pad to the piston. The K7 also had a small contact point, but it was surrounded with the plastic ring, perhaps to prevent the pad from getting cocked in the caliper housing?

[bryanj]

Open top IS NOT original but has had the washer removed

[MoMo]

That dome comes off and when it does both pistons seem as though they are identical in size. If you have a brass mallet tap the sides of the dome to break loose the corrosion that is probably in there.  I lost one of those dome pieces-wasn't an easy part to find...Larry

[88blkiroc]

So are you saying just run the pistons open and it should be ok?

[70CB750]

Out of the three calipers i opened K0 and K3,4 all of them had lid on. It was always rusted in place but gave in after small effort. I dont see any problems running without it, maybe Hondaman will pitch in here. I dont think you would feel the difference with one side lidded and the other not- the pad will establish itself in the same distance from the disc - thats given by the square rubber ring.

[88blkiroc]

Anyone have one of those caps they want to sell?