ZL900 clutch issue

[Blue-Grass-Tornado]

Just picked up an 85 ZL900, bike has been off the road for approximately 10 years. Dead clutch when I got it, took off the reservoir cover to find a substance with the consistency of peanut butter, a real mess! Anyway, I was able to clean it all up, clean out the reservoir, fill it back up with DOT4 fluid and the clutch came back to life. Now here's the issue. I rode the bike just a few miles, and now the clutch feels like it's really spongy, it comes and goes though. For a few pulls, it's fine, then on the 4th of 5th pull theres almost nothing there, I decided to bring her home tonight and bled the line some more, and took it back out. Same thing. Just wondering where to start the troubleshooting, I'm guessing a bad seal somewhere, but it's not leaking either. What would you replace first? I guess the master cylinder would be easiest, or maybe just rebuild it? Maybe the slave cylinder? I've got the fluid coming out clear, it was pretty dark and nasty after I first starting bleeding it, but I think I got all the old stuff out. Any help would be greatly appreciated!

 

[lowlife]

If it is inconsistant I might start with the M/C. Might also be the slave leaking air intermally though I would still start with the M/C.

 

[lowlife]

How did you clean it? Mineral spirits, just a rag etc?

 

[Blue-Grass-Tornado]

How did you clean it? Mineral spirits, just a rag etc?

I normally use carb cleaner but was plum out, so I used some rubbing alcohol, just moistened a rag with it and wiped it out. Bad idea???

 

[lowlife]

No just curious, Not sure if rubbing alcohol will cause problems or not but I don't think so.Recommend sticking to mineral spirits though.

I'm rusty on my brakes, but if memory serves me correct there is a compensation port in the master that could be dirty or your rubbers could be leaking once in a while. (Don't even go there you sickos!!)

I will try to simplify this from memory. I haven't built a M/C in 100 years of so. So the theory is there just cloudy.

As you squeeze the lever it captures fliud and forces it down to the slave cyl. It s possible that eith it isn't capturing it or it isn't holding it. I would google something like master cylinder design so you can see for yourself. Car snowmobile , motorcycle. they will all be similar. the slave if it were leaking air shoud also leak some fluid as well.

Also make sure that yo are getting all the air out, I suspect you are as it would be consistant at least. I built and sold a devise on ebay for kart racers that pressurized the system. i was thinking of modifying one to fit the bike.

 

[zlMark]

I have this same problem. I did rebuild mine using an Ebay kit. It's much better now but still not perfect. I suspect the bore of the m/c is worn or rough or the cup seal is aftermarket crap. If it was the slave the fluid would be leaking externally and you would see it.

 

[Blue-Grass-Tornado]

I will try to bleed a little more today just for the heck of it, but I'm pretty sure I've got all of the old stuff out of there. Like I said, there's no sign of leakage anywhere, it's gotta be air coming out somewhere, you can feel it while you're pulling on the clutch lever, it's got pressure and then all of a sudden it just "releases", and you can feel it in your grip. Anyway, I can't ride the bike this way, even though it has come back with the next squeeze of the lever, I'll probably start with the M/C and go from there, in fact, I bet I have one from a Honda I can slap on there temporarily to see if it fixes the issue, they look almost identical to me. Thanks guys!

 

[lowlife]

Does it pump up with repeated squeezings or is it hit and miss?

 

[wuputt]

I would start with the master. They can be a mother to get all the air out. I get someone to pour fluid while I pump the clutch and run a cup full before I quit. Only takes a air bubble the size of a BB to mess it up.

 

[Blue-Grass-Tornado]

Does it pump up with repeated squeezings or is it hit and miss?

It's hit or miss. I bled it some more today and rode it about 10 miles, it's getting a little better, but not completely gone. Maybe after I get the cobwebs out of this thing it will work its way out!

 

[furchin]

have you checked to see if both tiny holes in the bottem of the master cylinder are open. run a small wire into them to insure that they are open. if I remember correctly you should not have any air bubbles emitted from these holes while squeezing the lever. cap off to check for air.

 

[lowlife]

Furchin does remember correctly , he jogged my memory as well. Ahhh I wish i could remember what I used to know.

 

[Kawasaki-krazy]

have you checked to see if both tiny holes in the bottem of the master cylinder are open. run a small wire into them to insure that they are open. if I remember correctly you should not have any air bubbles emitted from these holes while squeezing the lever. cap off to check for air.

Top up the master cylinder and sqeeze the lever repeatedly VERY gently (lever should not be pulled all the way back to the bars). Look for those 2 tiny holes that furchin is on about. When starting from scratch you will see a stream of bubbles from those 2 holes. Make sure ALL the bubbles have stopped at the master cylinder before bleeding in the normal way.

Works for me

Hope this helps.

KK

 

[Blue-Grass-Tornado]

The last time I had the lid off to add fluid, I pulled the lever in and fluid actually shot up and into the air! Is this normal? I didn't see any bubble, just fluid, but this was a full grab mind you, not a "gentle" pull!!!!!!!!

 

[Kawasaki-krazy]

The last time I had the lid off to add fluid, I pulled the lever in and fluid actually shot up and into the air! Is this normal? I didn't see any bubble, just fluid, but this was a full grab mind you, not a "gentle" pull!!!!!!!!

Yes...that's normal. If fluid is squirting back out of the master cylinder, then that shows there is no air in the system. The only other thing that could be wrong then is fluid passing the seals. Replacements required I'm afraid.

KK

 

[Blue-Grass-Tornado]

If fluid is passing the seals, wouldn't there be a leak somewhere? Are you talking about the seals in the M/C or the slave cylinder? Both?

 

[Kawasaki-krazy]

If fluid is passing the seals, wouldn't there be a leak somewhere?

No not necessarily. The fluid will be staying within the cylinder, but just getting from 'in front' of the seal to 'behind' it.

Are you talking about the seals in the M/C or the slave cylinder? Both?

On bikes this age I would do both. I wouldn't think they would be too expensive.

KK

 

[Blue-Grass-Tornado]

I've already got a master cylinder on the way, I'll change that out first due to ease of installation, and if that doesn't fix it, I'll be attacking the slave cylinder next! Thanks for the info guys, great website!

 

[zlMark]

what was the final fix?

 

[Blue-Grass-Tornado]

Just the master cylinder, that and a good bleed job, and it works like new!