Topic: Attention Front Disc Brake Experts: Differences K1 though K8?

[Rainmaker]

I'm shopping for a new disc brake caliper piston for my '78 CB750K.  I see they make stainless steel repops out there....makes sense considering the pits we get with the plain steel ones.  But I was surprised to find out that vendors show a different (and considerably more expensive) stainless piston for the '77-'78 K bike. Now I have a '74, a '76 as well as the '78 SOHC K bike and I can't see any difference in the entire caliper or the piston itself.  I have interchanged the piston them between all three bikes without issues. 

So I need help to figure out which piston to buy for my '78.  Does anyone know if the K7 and or K8 bikes have different front disc brakes or is it, perhaps, a factory anomoly that I have a earlier model front brake on my '78?  Thanks for your response.

[nteek754]

Hey rainmaker the only thing I have seen differant  from the 72 73 74 75 75 to the 77 78 is the pads are a bit differant on  the older ones the pad next to the caliper has a little stud that screws into the top of the pad that fits into a groove in the caliper where as the 77 78s went the other way the groove was in the pad and the peeton (not a stud) is from the caliper hope this helps a bit  Craig in Maine seven fifty four ever

[eldar]

As far as the piston is concerned, I dont think there is a difference. Only the f2/s are different I think.

[Clyde]

The K0 to K6 all use the same early caliper and hence the same piston. There is a change in the caliper arm and the way it mounts to the fork, which occured late in the K2 model.
The 75 F and 76 F1 have a different caliper which uses a normal hex head bolt from the outside or piston side (compared to the K0-K6 caliper which uses an Allen key type bolt bolted from the wheel side. These calipers use a bigger piston to that of the K0-K6 and are certainly not interchangeable. Also the pads are different
The K7-K8 use the same caliper as the F/F1

If you want dimensions/diameters let me know

Good Luck
Clyde

[Rainmaker]

My K8 brake piston measures 1 and 5/16" in length & 1 and (just a hair over) 5/8" in diameter. Picture attached.  My K8 caliper is the same size as my '76 CB750 F model. Both have the hex bolt caliper that is accessible from the outside (left side) of the bike (no allen bolts). 

Can anyone measure a K0-K6 piston for me to see if it is a different size that what I state above.  Thanks for the effort.

[burmashave]

If it helps, the part number for the '78 CB750 K piston is 45107-392-003.

The Honda parts manual lists the same piston (part number) for these model/years.
CB750F '76
CB750A '76
CB750A '77 - '78
CB750K '77 - '78

I picked up a stainless piston for my '77, and I thought the difference is that the later piston is sealed on both sides of the piston cylinder, whereas the earlier pistons were open on one end.  If so, that would help explain the difference in price -- the earlier model would be a simple milled piece.

[Rainmaker]

OKay....well I hadn't heard that one. That must explain the difference.........except the remaining question is....can an old style piston be used with the '77 -'78?  Must be cause that's what I have.  thanks for the info and update.