Ex650 Twin Front Master Swap

I bought a used, front brake master on ebay to try out on the 81 Gpz550. The Ex650 (Ninja 650 twin), ABS and non-ABS, from 2009 to 2016 uses a master marked with a "14" on the bottom. Presumably that's a 14mm piston, which seems a little small for a dual-caliper system.

After installing it, my first impression is that it makes the brakes a bit more touchy, and a bit more spongey. I hadn't ridden in several weeks, so it's hard to say for sure. I'll have to compare it to one of the other bikes. However, this particular bike has had some issues for the last few years. With the old master, the lever, for the last several years, felt solid and immediate, which I liked, but I knew it was not normal. I have two other bikes to compare to and they had a lot more lever travel before the brakes would grab. That's how these bikes are when everything is right.

This bike, for the last few years, gave me the feeling the front brakes were not releasing completely, at least not immediately. It felt like the calipers were dragging. This would explain the immediate lever response, if the calipers were not retracting, or if the master was not returning.

But the real frustrating issue is that occasionally I would go to ride the bike and the front would have no brakes at all. No fluid would leak out anywhere, but the lever would travel to the grip with no resistance. This would only happen after the bike sat for a few months. This has happened about 3 times over the last 3 or 4 years.

Bleeding the system would quickly resolve the problem temporarily. Plenty of air would come out. The problem was relatively sudden. The brakes would work 100% solid one day, then a few weeks later, after sitting, there would be 0% brakes.

Over the last 5 years, I've probably rebuilt both calipers twice with new seals etc. Everything looks clean inside, and the condition is as good, if not better, than the calipers on my other bikes.

I've also rebuilt the old master during that time with new piston, seals etc. The old master is the one I've had the longest, and it's been through two crashes, but has always worked fine even after my buddy repaired it with a mig welder (before the internet, getting parts was not easy).

Since replacing the master is easier, that is what I'm trying first. Since I still feel a slight drag, I suspect the problem was not with the master.

I'll post some photos in a bit.

Maybe a long shot but some blathering off the top of my head. I respect your wrenching abilities so these seem unlikely but just say'n...

The two most common reasons I've found for dragging brakes are 1) master cylinder return port plugged and 2) caliper pistons are binding.

The master return port is tiny and can get plugged relatively easily if there are chunks in the fluid and/or if the old rubber brake lines are used and they are full of scale.

Binding pistons can occur if they have corrosion inside the caliper and/or if K&L caliper seals are used.

I've also seen K&L master cylinder plungers that bound up inside the bore too. Needless to say I'm not a K&L fan.

BTW, the EX650 master shown below is 5/8" and has a threaded mirror lug. I'm happy with the unit on my 750...

P1010741 by nessism , on Flickr

P1010740 by nessism , on Flickr

Thanks, I was hoping you would reply.

Those were the first two thought I had as well. Replacing the master did not seem to change anything. The drag is very slight, but noticeable. If I ride a bit without using the brakes, the drag seems to be gone, as if minor deflections of the disk can push the pistons back in. It doesn't even drag after every brake use. Sometimes I'll stop with the brakes, and the drag does not seem to be there (rolling the bike forward and back with my feet while waiting at a stop light etc.).

The way I understand it, when fluid pressure pushes the caliper piston outward, the rubber seal on the piston is designed to deflect into a chamfer when the piston pulls on it. When the pressure is removed, the rubber seal wants to return to its original shape and pulls the piston back slightly. If the piston needs to move more than the seal will allow, the piston slides through the seal, but the seal is still deflected, and will still pull the piston back by a small amount. That way the piston is always compensating for lost pad material, but will still always retract enough to let the wheel spin free.

If the seal is too loose that it does not grab the piston, then it will not deflect and the piston slide outward and stay out. So I think the seal being too loose may be the problem. The brakes stop the bike really well.

I think I've been using K&L rebuild kits on all of the bikes. The other two bikes seem to have no problems.

When I've had the calipers apart they were pefectly clean, which would be expected since they were rebuilt maybe a year before that.

The real puzzle is how so much air can get in with no apparent fluid leak. This is also starting to make me think the seals may be too loose.

The last time I rebuilt them, I don't recall if the pistons went in any easier than normal or not.

So, in the long run, I probably want the earlier, rectangular Ninja-650 master if I keep the stock calipers.
This 2009-2016 master has a diamond shape.. oooh, diamond. I only chose it because it was more recent and with the hashed-out cover, it was cheap.

Here are some crappy in-garage photos.







Now, don't let the old frankenstein master scare you. I stress-tested the shit out of it trying to break it. I wouldn't even let my buddy (he migged it) make it look pretty. I've really enjoyed using this thing for the last 15-20 years. I'm starting to think the problem(s) is not really the master anyway.

K&L kits throw a red flag. Man I hate those things. Most of my experiences are from caliper seals that were too tight. They couldn't allow the piston to move closer to the disc. BTW, I believe you are correct in your assessment about how the seals function.

The master return port is about 1mm diameter so I'd make sure it's open. If you pump fluid with the cover off there should be a little fountain of fluid that shoots out of the return port so that's your confirmation. If that's clear then I'd consider some new OEM caliper seals.

Thanks Ed.
I did always get that little fountain of fluid when pumping the master. (I think everyone finds out the hard way when it spews over onto the fender paint!)

On the up-side, I think the new Ex650 master has a little diverter that stops the fountain from shooting straight up. You can still see it, but it seems to shoot a little sideways. I was in a hurry so I didn't look closely, but it seemed like there was a little piece of casting designed to redirect the fountain.

I'm not sure if there is another option regarding caliper kits. Maybe there is an industrial, square o-ring, or maybe if there is another caliper that uses the same size pistons with a fatter o-ring. Or maybe I will check Kawasaki in case they miraculously still carry it.

I'm not hesitant to just throw on all new calipers from an Ex650, or some other bike, but I'd really rather figure out what's going on with these, just for my piece of mind. I've seen other posts here with people reporting the mysterious no-brakes issue but with no leaks.

My first guess was that if the master cylinder's vent got clogged, and there was a cold temperature change, and no air could get into the master reservoir, it would create a slight vacuum. Then if the caliper piston seals were loose maybe they would let air in.

Seems unlikely, but I can't come up with anything better. Can the seal act in a way that brake pressure won't leak out, but air can get in? It's not impossible.

Either way, I think I'm on a search for seals.

I have K&L kits for the master, and I also have a brand called "Tour Master". I wonder if Tour Master is different, and if they make caliper kits.

The K&L caliper seals seem to work fine on my other two bikes, and I think this problem may have started with original seals in the calipers. Memory is hazy since I'm juggling enough spare parts for 5 or 6 bikes.

All Balls sells master cylinder and caliper rebuild kits. Just recently, I replaced my stock master with a remote reservoir master from a 2003 Kawasaki ZX636. Rebuilt the master before hand, and out came a few chunks of what was mentioned above. I now have an adjustable lever. Works great, and stock brake line bolts tight on.

The ZR550 master cylinder is a direct bolt on but the same year lever will be needed. I had one on my race bike, as it came on a past parts bike. Worked great.

Thanks Corey!
I will look into the All Balls caliper rebuild kits. The sad thing is I have a bunch of the K&L kits already. But that's what's in there now.

www.partzilla.com/product/kawasaki/43049...5323ffe9e4bd0036ce6d

OEM caliper seals are only $6.67 each and guaranteed to be the proper part. Use your "kits" for the dust boots and what have you but not for the piston seal. Even if you still have issues after install, you will know what the problem is NOT.

Nessism wrote: www.partzilla.com/product/kawasaki/43049...5323ffe9e4bd0036ce6d

OEM caliper seals are only $6.67 each and guaranteed to be the proper part. Use your "kits" for the dust boots and what have you but not for the piston seal. Even if you still have issues after install, you will know what the problem is NOT.

Awesome. Thanks. I just ordered two. we'll see if the weather holds out long enough for me to swap them.