1976 900A4 dual disc

I'm collecting parts to put my 900A4 back together. Frame,swing arm, triple tree and other small parts are back from powder coat. I'm investigating the possibility of doing a dual disc front brake set up but want it to be as close to the factory option as possible. I've been looking for a Right hand caliper with out any luck. Can the LH be reversed? I have read a lot about the thicker and thinner rotors, seem to be reading a lot about issues with the thinner rotors. Sense this bike wont be ridden a lot is there that much advantage of the thinner rotors and the potential problems or will the thicker one work?

The caliper can be reversed but the mount bracket can't. You will not notice any difference whilst riding by using the thicker discs.
You will notice the difference not using the twin disc master cylinder as single disc master doesn't give sufficient pressure to generate enough pad pressure for two calipers.
You will also need a twin disc splitter.
Know that many 650 discs, calipers, splitters and masters are the same as twin disc 900 parts so you can broaden your search with higher chances of success.
Alternatively all the parts you need are available as repops from the usual culprits.

Right hand calipers come up on ebay fairly frequently, although I haven't seen any recently. If you're trying to keep it original you will need the correct date code on the disc.

Here is my twin disc conversion. I used KZ650 rotors and calipers. I put the calipers behind the forks only because I like the look. I originally used the dual rotor 5/8" MC but didn't like the feel. It had a really hard feel wooden like and I had to really pull hard to get the brakes to work so I went with the single rotor 14mm MC, that works great. The pull is nice and it's two fingered stops now. You can't swap the calipers side to side due to the bleeder screws. If you run a left one on the right side and visa versa the bleed screw is at the bottom not the top where it's supposed to be. You'll never be able to bleed the air out.

I have a 77 650 custom parts bike with dual disks, it's nice to know they probably would fit on my 77 1000 project
Are there any differences ?
I know the 5/8 master looks the same.
Dual discs were always thinner and I have never had problems warp-age on 2 bikes so far, I think it's a good idea to make them lighter and they make a big difference in stopping with a heavy load :blush: :blush:

Warren3200gt wrote: The caliper can be reversed but the mount bracket can't. You will not notice any difference whilst riding by using the thicker discs.
You will notice the difference not using the twin disc master cylinder as single disc master doesn't give sufficient pressure to generate enough pad pressure for two calipers.
You will also need a twin disc splitter.
Know that many 650 discs, calipers, splitters and masters are the same as twin disc 900 parts so you can broaden your search with higher chances of success.
Alternatively all the parts you need are available as repops from the usual culprits.

Warren, thank you it sure looked like the caliper would work on the RH side, wasn't sure about the bracket. I'll keep an eye out for a RH set up. I have a dual disc set up that I will be using on the next build. That build will be a franken bike made up of all the left over parts I have laying around. I wont care about date codes or crossing over to parts from any other CC size bike. but this A4900 I want as original as I can get it... thank you for the advice.

hardrockminer wrote: Right hand calipers come up on ebay fairly frequently, although I haven't seen any recently. If you're trying to keep it original you will need the correct date code on the disc.

HardRock. Thank you. yes I'm looking for the correct date code. The LH disc is a 0L date code Late '75. My bike was built in November '75.

Baldy110.
Beautiful Build. I'm setting up that type build next. I know I have enough parts to build a bike. It will be similar to yours. Parts from different years and CC's that make it functional and rideable.

Baldy110, are those NOS rotors or did you have them resurfaced? I looked locally here to find someone that could resurface the rear rotor on my '78 1000 B2 without any success. It squealed and I want to resurface it. Not have any luck I just put in new pads, but its already making noise. any recommendations?

Are you retaining the hard brake line, as original, or using the soft line? Caliper RH brackets can be sourced from various KZ models using the same spacing bosses on fork lowers. Here is a RH rebuilt/refurbished assy that had the correct "hard line" for KZ900 and Early KZ1000. A photo of what I refer to as soft line used on later KZ models. Getting closer to getting the gauges started!!

Be aware that the KZ650C and KZ650D dual disk setup use smaller rotors than the dual disk on the KZ1000, they are NOT a straight swap. The KZ650 C&D use a different fork lower than the kz1000, kz750 and kz650B, this allows the caliper to be mounted closer the the axis of the rotor.

Also note that depending on the model the bore of the caliper piston will differ. Cant remember which are which off the top of my head but you can end up with a 38mm caliper piston or a 41. this will have a direct effect on the Master-cylinder to caliper ratio and should be taken into account. as two 38mm calipers will create a a different feel than two 41mm calipers.

with two 38mm single piston calipers and a 5/8" MC that would put the ratio at 11.46 /1 - on the edge of ideal - firm
with two 41mm single piston calipers and a 5/8" MC that would put the ratio at 13.5 - closer to ideal - soft

check out vintage brake for more info on MC ratios
www.vintagebrake.com/mastercylinder.htm

I have dissembled "dual disk" setups to find one of each caliper piston size.