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Discussion Starter #1
I've had this 1981 CB900C project bike for almost two years now, it's just about done. When I got it, it came with a beat up fairing kit that made it look like a gold wing, but I chose to take it off and make it stock again. In case anybody is wondering, undoing the wiring harness and making it back to original wasn't as bad as it seems. You just have to crimp new connections on a lot of the wires, and remove a few vampire connectors.

The only thing that's left is getting new calipers. The ones that came with the bike were damaged/corroded beyond repair. Before I order new ones, I noticed that the 1982 models had dual piston calipers instead of the single piston ones that I had. I called up the guy who was selling them and he told me that they wouldn't work on my 81 model because the mount brackets are different. He also seemed to think that the bottom ends of the forks were different too.

Can anyone confirm this about the forks? I'd prefer to go with dual piston calipers as long as I don't have to change the ends of the forks. I also think they look better too.

PS:The exploded view on bikebandit.com seems to be identical for the 81 and 82 models.
 

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Rather than give you an answer I am going to teach you how to (parts)fish so you don't have to rely on "maybe" from forums.

Go here: Sale on Motorcycle Parts, ATV & UTV parts Honda, Kawasaki

go to the part where you look up parts OEM parts fiche and look up the parts for a lower fork leg for a 1981 cb900c:
1981 Honda CB900C A FRONT FORK | PartsFish.com

as you can see the part number is:
51521-461-771

Take that part number and go back to partsfish and enter it in the section where you can look up by parts number and hit search:
OEM Parts for Honda


If you click on "where used" it will tell you the bikes that use that same lower fork leg.

so 1981 and 1982 cb900c's use the same lower fork slider.

However, your question is about brakes and the dual piston caliper. So do the same thing and look up the part number for the dual piston caliper assembly part number:
1982 Honda CB900C A FRONT BRAKE CALIPER | PartsFish.com

the part number is:
45100-461-752



and the bikes that used this caliper and bracket are:
Assemblies where 45100-461-752 is used


so that tells you that a complete assembly off those two bikes will work for your motorcycle. But...what about mix and match?

ok look up the number for the caliper body itself:
45101-MA3-006


and it turns out all these bikes used the same exact caliper:

now look up the bracket that mounts the caliper to the fork legs:
45110-MA5-006


and all the bikes that used that part:



and what you have now is a broad list of bikes from which you can grab the caliper and bracket from and you are not married to hunting for a complete assembly off a 1982 cb900c. In otherwords this kind of knowledge helps you get it cheaper.

Now this is all the information for how to do the left caliper, you can do the right one on your own. But you have your answer - yes you can use the dual piston caliper on your 1981 cb900c - you just need to get the correct mounting bracket that mounts to the fork leg.
 

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Holy cow, that was super helpful. That was hands down the most important thing that I've read on this forum so far. You sir, are awsome. I will definitely be using that method A LOT, from now on.
 

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your welcome. I was much in the same place till a buddy at a honda dealer showed me how they do it.

Now I get questions all the time like why does one bike use both the bracket and caliper yet the assembly is not shared? well there could be a couple of reasons, but most often it is due to different hardware or spacers being used. In this case an example of this is the 1982 FT500a which uses both the caliper and bracket but oddly not the same bolts. What this means is that you always need to check and test fit the parts you buy if they are not from a bike that uses the same assembly. It might be the difference is minor or they might not fit till you get the correct bolts.

Since we are talking about the DOHC dual piston swap I also recommend the rotor you use be one of the later ones with vents milled into the braking surface. the bikes they came on are listed below:

these rotors prevent warping normally associated with these brake setups. The left and right use the same part number so it should be super easy to find a pair.
 

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Discussion Starter #5
Cool, I'll check those out.

I find it funny how on ebay, some people list the part name and bike model, while others only use the part number and "fits most models". Guess i have to search for both now!
 

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Geeto's posts need to be put in a thread titled "Teach a man to fish..." And stickied in this section. I don't know how many times I have used that method to determine compatible parts for various bikes. What parts fit various R6 models, it's how I determined my fork swap would fit my front rim, etc.
 
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