Brake caliper adapter RD400 for a 297mm TZ brake disc

[stresa]

Hi,
a few years back I had a RD400 with a 297mm TZ brake disc. So there was an adapter for the use of the genuine RD caliper installed. Sadly the bike is long gone.
So my question is. Has anybody a drawing or a STL-file of such an adapter plate?
I would like to build a bike with such a combo.
Regards Uwe

[Dvsrd]

Another alternative is fork sliders from a 1976 XS650C. US market 73-76 XS650 had  a single 298 mm disc, and the same 2x48 mm caliper as the RDs. These 73-76 fork sliders are a little longer than the RD sliders, due to the 19" front wheel, and also a bit thicker and heavier,  but can surely be machined down for more appropriate dimensions for an RD. These XS models had 34 mm fork tubes, like the RDs, but only the 76 had the caliper behind the fork slider, just like the RD400. This way, no caliper adapter is required. I have also seen other custom bikes where suitable caliper mounts have been welded on to fork sliders.

[Dvsrd]

Also, the 38 mm forks from FZR400 and FZ600 have the same C-C measurement on the caliper mounts. But I am not sure what size brake disc those forks, combined with an RD caliper would accommodate. Also, I do not know what offset requirement this would result in.

[stresa]

Hi @Dvsrd,
I am aware of the XS sliders. We tried them many years ago. The length of them is the problem. Under hard brakeing they hit the bottom yoke. So not really a solution.
The 38mm doesn't fit in the rules for the class the bike is in. Maximum 36mm ones allowed.
I know that the mounting lug can be relocated per welding a new one on. A friend will use one for a street used caferacer also. The registration rules in Germany are that strict that no welding is allowed on structural devices. It is difficult enough to get an adapter through it.. But for that we have someone who is certified for to do the calculations and we have a certified shop who could machin such an adapter. It is a bit more difficult here to get a modified bike on the street than in the States.
But thanks for your input
Gruß

[Dvsrd]

What about TZ fork or sliders?

[stresa]

Only sliders won't work. They are for 35mm stanchions up to 1978 or 36mm 1979/80.
Complete TZ fork is just too expensive for the bike we will build.
Background is that our team build a bike out of leftover parts which we will lent newcomers for free. Everybody of the team donated parts which he had lying around. The TZ rotor is not a must, we can always start with a RD rotor but we have it. As a friend builds a RD caferacer with a TZ brake we thought we try to get an adapter. If we don't find one we have to do a drawing or a pattern one ourselves. It is just a shout out to get a drawing or file to make it easier for us.
In the meantime I located my old bike and the owner is capable and willing to make a drawing of the one I used many years ago.

[Dvsrd]

A while ago, I was looking into using a 298 mm disc with the stock RD350 caliper and a RD400 slider (to get the caliper behind the fork) What I found was that a caliper adapter would be quite large and triangular in shape, so I shelved that idea for a while.
That 298 mm disc was an XS650 disc hub that I refurbished, with a custom ordered disc from ISR in Sweden. Sort of a "sleeper setup", but the necessary caliper adapter would stand out too much for my taste.

[stresa]

I agree. It is not best solution optical wise. If it would be my own bike and own decision I would go another route. We have to use a period solution and that is the cheapest option. But it is race bike so optics are behind function.
Myself I would go the Lockheed or Brembo P05 route. I have a RD250 race bike with a Lockheed caliper and EBC disk. It is a good combo. Obviously it need an adapter also.