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Discussion Starter #1
So, as it happens a lot, I have these great ideas that don't work out so good in practice or completely won't work at all.

So I have this pitted brake piston, and it is completely unavailable NOS or aftermarket (some CB750K caliper), but the caliper is in otherwise great shape. I should mention I'm a cheap bastard.

I was mucking about soldering some stuff the other day and I thought "hey, I could fill in the pits with brazing or solder!"

So I did. It came out beautifully, the pits all filled and flush, you can hardly tell there were even any pits except for some minor color differences. When I got done, you couldn't even feel where the pits were.

And then this morning, I was brushing my teeth, and I thought, "hey, brake calipers get really hot, don't they?"

Then I thought, "wonder what would happen if the solder melted and then re-solidified in my caliper under heavy braking?"

So, I need a new brake piston anyway. Don't try this! You'll be even dumber than I am because I warned you first!

I figured for as much as I give out shit here I figure reciprocation is deserved :D
 

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My guess is that they wouldn't get hot enough to melt the solder...not without melting the seal on the piston first.

But...I also think the solder, as smooth as it might appear, is not perfectly round or smooth and would tear the seal up anyway.
JohnnyB
 

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I typed you a really long answer and then hit escape right before I posted them by accident. Fuck!

anyway if it is a cb750k caliper then you can order one from honda or wait for the stainless steel ones to come around on ebay again.

most old bike aftermarket phenolic or stainless steel pistons are larger pistons that someone cut down on a lathe. My advice is to find a motorcycle piston with decent thickness that is close and take it to a machine shop to be cut down to the proper size.
 

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Discussion Starter #5
The problem with the caliper I have is that it is apparently just not available. I think the phrase I keep hearing is "for frames up to CM30151". When I looked through the parts fiche for my piston (based on the model of cb750 the guy I got the caliper from told me), the caliper that matched mine just doesn't have an available piston that I could find, so I assume the frame was beyond that frame number.

I found this piston today on CBXman.com, it is very similar:

79-80CBX Front Caliper Piston (1047cc 6cyl.) (OEM Part #45107-415-006)

I sent them an email asking for the piston dimensions, if it matches maybe I'm in luck.
 

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I have a piston that came out of a cb750K5. It looks to me to be in fine shape. It is all yours if it will help.

Mut
 

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Hey guys, don't know if this will be of use to you, but one of the guys on the VRRA site posted the following just today:

I just got my RZ350 FII calipers back from a local caliper rebuilder.

The guy is absolutly amazing.

I brought him my calipers and he popped out the pistons in seconds and sandblasted them for me, gave them back and I took them home to paint with PJ1 Brake caliper paint.

Brought them back to him the next day and he rebuilt them with BRAND NEW seals (He can get seals for everything) on both sides and pressure tested them and even put new bleed screws and gave me new copper banjo washers.

Because I did the painting myself, he only charged me $40.00 per caliper. If you want him to paint or powdercoat he can do that too.

The guys name is Galvin and he knows his shit. He does tons of stuff for vintage car guys all over North America so he's used to recieving stuff in the mail and sending them back out.

Midwest Caliper
140 Midwest Road, Scarborough, ON M1P 3B3
Telephone : 416-751-3660

http://yellowpages.ca/bus/Ontario/Scarborough/Midwest-Caliper/1062356.html?adid=13520512ac
 

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It does not have the groove in the piston. I imagine that is for the seal? The seal on my brake was in the calliper wall. The piston does not have that grove.
 

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quote:Originally posted by Geeto67

post a pic of the caliper - you have piqued my interest....
knowing the proper use and spelling of piqued is kinda gay...impressive, but gay. like james dean.
 

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Just in case any of you are jumping to conclusions, please do not assume that Geeto is gay just becuase he used the word "chequer" with the effeminate British spelling, instead of the more masculine American spelling ("checker"). It is entirely possible that Geeto recently moved to England and has obtained British citizenship. His use of the word "chequer" may therefore not be proof of gayness at all.
 

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the caliper really shouldn't ever get anywhere near hot enough to melt good hard solder

unless the bike melts down in an inferno
 

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solder melts at around 375 degrees. brake pads catch fire at around 1200 degrees. most race pads are good to around 1000 degrees. street pads are better under 600 degrees. i've MADE a cb750 make it home when it didn't want to. and i lost a few brake pads in that battle.
i wouldn't use solder in other words. just have a machine shop make a piston for your. it might be the easiest thing they make all week.
 

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Discussion Starter #17
I believe this is the correct caliper (image too big to inline):

Picture here

The thing doesn't even have a name on the parts page and if you call anywhere they tell you it's not available or discontinued: part number 45107-425-003
 

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Probably a dumb question but rather than have a machine shop make a caliper piston at $75 an hour labor (or labour to m'lord Geeto) plus the cost of the stainless, why not pick up a four piston modern caliper off ebay and hack out a plate aluminum bracket to fit it to your bike? I've seen plenty of nissen and tokico calipers go for $25-35 on ebay.

Or at the very least, look for a different CB750 caliper you can get a piston for and swap for that....

Jim
 

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Discussion Starter #19
that is a good idea, but I don't have the first idea what four-port calipers could even be adapted, whether my current master cylinder would work, or what details I need to know like offsets and angles and disk thickness...plus I'm cheap.

I found a set of cb750f ss calipers cheap, and if the pistons are good I'll use those. mount points are the same.
 

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77-78 cb750F calipers do not have the same mounting points or rotor thickness and offset as the K bikes.

That caliper does not look like any cb750 K caliper I have seen. Actually it looks like one of the old lockheed calipers they used to sell for the cb750.
 
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