Z1 dual disc conversion with KZ900 wheel

Years ago I changed the front fork lowers on my '73 Z1-900 to those from a KZ650 because they permitted me to use '76 and later KZ front disc brake calipers. In fact, the calipers from the '79 and '80 have larger diameter caliper pistons than earlier calipers. This made for a great improvement in braking along with the use of those 4-bolt 4.5 mm rotors. Then I upgraded to Race Tech cartridge emulators and Race Tech front fort springs which helped even more. All this went very well with wider rims and radial tires.

Bohicabob: As I recall I read one of your replies to this subject quite a while ago where you discussed the difference in piston sizes. I made sure the "kit" that I bought had the same diameter as the one on the bike. May or may not have made a noticeable difference but I didn't want to upset the apple cart.

My intent throughout the rebuild process was not to restore the bike as I like the way it looks. Hats off to those that restore a bike to like new, but that just isn't for me. As I found out there are far too many variables to truly restoring a bike, OEM parts availability being just one of them. I did strive for using OEM parts whenever I could do so, but within reason. Anything labelled "Z" or "KZ" meaning 900cc or 1000cc, is becoming gold now. I was able to find all new OEM brake pads front and rear for the bike and that's what I installed. Surprisingly for me the front brake isn't touchy in the least or overly sensitive. If you grab a handful of brake it will lock up (no weight shift) or if you are overly progressive on the brake lever and simply go too far it will lock up too. Both scenarios are to be expected. Years ago I swore I would never ride a bike without ABS because I am a true believer in it, but the brakes on my KZ work very well, but I have remind myself no ABS.
Rick H.

david richard wrote: hi rick ,yes very nice and a good update with 2 disc ,what brake pads do you use up front to be able to lock it up if a bit quick to to react ,its a lot of weight to pull up ,,i guess any new pad is way better than 40 year old material ,thanks ,david

Using stock pads on my 1977 KZ650-C1 the only time I locked up the front was when I had Michelin Macadam tires on the bike - not a good feeling considering the reason I hit the brakes so hard was because a fire engine came through a stop sign. After switching to Pirelli Sport Demon tires I cannot lock up the front tire. Instead the bike comes to a VERY quick stop. This is s good thing. My point in describing this is to make the point that when it comes to locking up the front tire a lot depends on the stickiness of the tire. For me even though the front brake is in exactly the same condition the Pirelli tire brings the bike to a very quick stop where the Michelin Macadam tire skidded on clean, dry blacktop. Tires matter a lot. Ed

I decided to go with dual disks after having a real close call with my wife on the back and a full pack to boot, about a 400 pound payload.
I grabbed all the front brake I could and had the back tire locked up skidding sideways thinking I was going to have to T-bone a car that pulled out on us ,
luckily he saw us in the last moment and stopped leaving us a 4 foot window between his car and a on coming truck going at least 55 mph :woohoo:
the bike now has heavy Progressive shocks, fork springs, heavy fork oil and dual disks and she rides/ stops much better.

here we go- from Jeff.saunders in 2011, also sorry to call you out, but that name carries some clout. anyways there were other threads I found when researching but I haven't found them right now, but all of it was on kzriders actually:


On a Z1, the double disk setup is crazy heavy. Each disk rotor 7mm thick and weighs 10lb. On the later models, they reduced the thickness to around 5mm and drilled the disk to drop the weight.

I've ridden a Z1 with double disk, and actually prefer the single disk setup. Cosmetically the double disk gives a nice balanced look, but I didn't like the increased shock coming up through the bars.

The double disk setup will give a little more stability to the front wheel - the centrifical weight will help keep it pointed forwards - and reduce the likelyhood of wheelies..."

Well for some reason I want the stock shock lowers but I'm lacing different sized rims on them and changing a bunch of other stuff, trying to improve what I can.. The stock Z1 lowers just are so Z1.

I worked at a bike salvage yard in the early 80's. I had bought Lester mags but the front wheel was for a KZ 900/1000 so the Z1 disk wouldn't work. I took the disk off a wrecked KZ900 I had, found a matching one, found two H2 calipers and a GPZ duel disk master in the pile of dead bikes. Even found good brake lines to boot. :woohoo: Put it all together and ran it until 14 when I found some later model drilled disks on eBay. You hear all this about unsprung weight but I didn't notice much difference really. I have to admit the drilled ones look much cooler but either way the bike stops RIGHT NOW. Maybe too good. :whistle:
The Lesters were destroyed in the wreck so I have the old KZ900 wheels on it now.
Steve

I like the drilled disks because I think it helps eliminate brake squeal due to dust.

Hi BohicaBob,
I think I asked you about your bike on here years ago. It is still one of the best ones I have seen, in my opinion. I am finally getting around to doing some of the stuff I want to on mine. I am planning on the racetech fork treatment, haven't done it yet. I am just trying to get a running road worthy bike then more will come when time allows.

Hi Swest,
thanks for the reply, it is good to hear from someone with experience. I am anxious to get to the part where I am trying everything I have done and not just looking stuff up on the computer. Life happened and I sold my perfectly running bike, now I am working on getting one going again so I can actually get out and ride.

Here are some infos about the Z1 dual disk conversion kit.

Thanks Scirocco for posting the info on the conversion kit. I have never seen that before. So unless I am wrong the disc rotor in the kit was the same rotor that would have been on the bike both being the wide rotors. If that is true then I have to wonder how much difference there really was in using the two wide rotors versus two thin ones. Obviously the calipers can accommodate either. If weight was of any concern I would expect Kawasaki would have included two thin rotors in the kit or a replacement set of fork springs to replace the stock single disc fork springs. One can discuss the additional weight for days of the of the twin disc conversion, but any effect must have been minimal at best and did not concern the factory. As these conversions go I think the most important factors are using the larger 5/8" master cylinder and using the same size calipers as pointed out in earlier discussions.
Rick H.

When I installed my duel disks in the early 80's I used the stock master cylinder. The brake worked fine but I had the opportunity to get a master off a wrecked GPZ with duel disks so I did that. Glad I did.
Steve