Brake disk switch

I have a 77 KZ 650 C1 and the front disks are solid.

Is it possible to switch out the solid brake disks for ones that are ventilated (gots holes?).

Seems that the ventilated ones would be more effective?

Has anyone ever done this?

a

Provided that the C1 has the same size rotors as the B models (297mm/11.7" diameter) the drilled rotors off a Z1R is a direct bolt on - this is the front wheel I have on my B1:

In addition to the diameter be sure to check the thickness of the disks. I know some models were different than others, but I don't know the details. Ed

650ed wrote:

In addition to the diameter be sure to check the thickness of the disks. I know some models were different than others, but I don't know the details. Ed

The stock 650 rotors are 7 mm thick and have a 6 mm service limit, the Z1R rotors are 5 mm thick and have a 4.2 mm service limit. The difference in thickness didn´t present any problems when I did the swap though.

OnkelB wrote:

The stock 650 rotors are 7 mm thick and have a 6 mm service limit, the Z1R rotors are 5 mm thick and have a 4.2 mm service limit. The difference in thickness didn´t present any problems when I did the swap though.

This is the front brake here, I have to be sure that it is safe. Catastrophic malfunction here could easily be fatal.

Does this bother anyone else? With the disk swap from stock 7-6 mil. to ZR1 5-4.2 mil.? That is a 30 % reduction in brake disk thickness.

Is it possible that the calipers are different as well? If they are different calipers there might be a chance that the caliper for the thicker disk would be out of its service limits with a thinner disk, i.e the 5-4.2 ZR1 disk as opposed to its original 7-6 stock disk.

Does anyone know how often the calipers were changed or upgraded?

How many different calipers exist for any given year on Kawasakis? Did they use the same caliper on a 400 as they did on a 1000?

Does the caliper from a ZR1 have the same/or similar tolerances as the one from the stock 77 650 C1?

If not, I would need/want to change the calipers out with the disks to have piece of mind.

What are the thoughts?

Any disc that bolts up will work just fine. The Z1R rotor was also stock equipment on 1979- 80 KZ1000s and the 1980 650LTD among others. They use the same exact brake pads as the KZ650C. The smaller thickness of the rotor is not a problem as the hydraulic pistons self adjust to the new rotors with a few tugs of the brake lever. These drilled discs wore rapidly a lot of time though, so I wouldn't actually recommend them.

Okay, now my curiosity is starting to get the best of me. The rear disk thickness for my ’77 KZ650C1 is listed as 6.9 – 7.1 mm (service limit = 6mm); the fronts are listed as 4.9 – 5.1 mm (service limit = 4mm). Now I know the active pad on the rear (Pad A = #43050-1006) is different than that on the front (Pad A = #43050-011) but I figure that’s because the rear pad has a notch that slides over a clip in the rear mounting bracket (but I don’t know the purpose of the clip). The “static” pads front and rear are the same (Pad B = #43051-011).

When I compare the 2 front calipers to the rear caliper, they look the same except for the mounting brackets. But here’s the surprise. The part numbers for the front and rear caliper pistons are different. So are the part numbers for the piston seal rings. Is it possible that the differences in these internal parts compensate for the differences in the thickness of the rotors? Maybe the pistons are different lengths? Or maybe the different part numbers are totally unrelated to the rotor thickness. Inquiring minds want to know. Ed

Check the diameter of the front and rear pistons, I think you'll find that the front pistons are larger than the rear.

The front does 80-95% of the braking

On the large fours, the Z1 ('73-'75) with single front disc became KZ900 in '76 continuing with single 6mm thick front disc on US model and adopting dual 4.5mm front discs on UK model and LTD.

Thinner dual disc helped reduce unsprung weight.

Front master cylinder was 14mm bore for single front disc and was enlarged to 5/8 inch for dual front discs.

Reportedly, continuing with the smaller 14mm master cylinder when converting to dual discs (instead of using larger 5/8 inch master cylinder) results in overly sensitive braking, especially in emergency panic stop situations where front wheel unexpectedly locks and causes loss of control and bike turning over.

Best of Luck with whatever is decided.

the dual discs are thinner because the work is shared by 2 rotors so the heat isnt such a big issue.id say as long as both rotors are same you should be fineB)

Plummen,

It is an issue of the drilled disks being thinner than the solid disks.

Come to find out that the drilled disks wear more rapidly, are thinner and lighter, and should bolt right up if bolt patterns match as the pistons will compensate.