Dual piston for single piston caliper Seca

I just won a pair of 1985 Fj600 dual piston calipers from ebay for $15. I would love to make them fit my Seca 650 with late 70s style calipers. I have my doubts that they will work, but for $15 I figure I can't lose too much.
Anyone ever try something like this??????

 

It's done fairly often on race bikes and Harley's. You will need an adapter plate at the least and quite possibly another master cylinder. It is highly unlikely that you will find a plate on the market that is suitable and so it would need to be custom made. Not a hard job, but it does take some knowledge and experience. It has to bolt on to the fork and to the new caliper, be shaped to put the caliper in the right position and may need to be bent or machined for any differences in offset or changes to the offset that were caused by the plate itself, and it has to be stiff. Without seeing the calipers its really hard to say how much is involved in that.

There are a number of after market master cylinders available including some that can be adjusted. That would take a bit of knowledge or a little trial and error to get right. The stock one might work. It would depend on how much of a change in piston area there is with the new calipers.

Good Luck,

 

Here is a picture of the calipers. (if it works)

 

Well today they arrived and i found that the Seca disks are a little too large in the outside diameter. I'm wondering if the FJ or non us XJ600 disks might be smaller and a little less offset. There must be an easier way to replace the 70s type calipers to something a little more modern. These 82 Seca 650 calipers were first made in 76.

 

I apologize for not responding earlier but I've been real busy. I'm glad you had an opportunity to put the parts up to the bike and check them out. I have a sticky note somewhere on this desk that lists the rotor diameters from the various XJ's and I'm having trouble finding it, but if I recall correctly the Seca 650's had the smallest size.

You would definitely need an adapter plate to install those on the bike based on what you've said, and if you went to that much trouble I would consider larger diameter rotors as well. You are into some fairly specialized custom work here and giving advice without being able to be there and match parts up and take some measurements would be difficult.

I understand what you are trying to do and I looked for a long time for info on this kind of project. I couldn't find anywhere that had info for our bikes. The closest thing that I found were references to changing out the whole front end on smaller bikes like the 650's with one from the larger sizes. There were not many details on that though. There's loads of information on messing with Harley brakes out there.

Good Luck,