TOPIC:

I did a full restoration on my 74 Z1 900 from a barn find. It was ruff, but got it looking like showroom, finished last year in August. But I do have an issue with my front single disc brake. The original master cylinder and caliper was really rough. So I order a replacements including lines from Z1 enterprises. But ever since the install, the front brake is almost useless, I only have about 1/4 inch pull before very tight and it does stop the brakes, but not very good. Have been a mechanic all my life, so this has got me a little stumped, was an aviation hydraulic mech, so I understand brakes. It's bleed, I don't really see any adjustment. My thinking is the brake pads that came with the caliper are too wide. Haven't taken them out to check yet. I tore the original parts apart just to check, and the master is rough. I am using the original front disc, it was in good shape, I checked and removed some fluid to see if any difference, but nothing. I did use DOT 3 fluid. I'm using the back brake about 80%. The master and caliper aren't Chinese, so that's out of the equation. Hope many someone has any idea or have had this problem before. I searched the forum, but didn't really find anything. Thanks, Tim  

It sounds like the piston in the calliper is applying the outer pad put the calliper isn't sliding at the point indicated below to apply the inner pad. If you unbolt the calliper from the fork leg and rotate it away from the fork (still engaged with the disc) does the lever now feel as expected ?

 

What size if the piston in the new master?  I've seen ads for some replica masters with a 7/8" (22mm) piston, and that will lead to a completely wooden and hard as a rock lever feel when braking.  

OK, I thought I bought this from Z1(master cylinder), but it's off EBAY, so maybe junk: It says 5/8. I just got my original torn down and the rebuild piston is way bigger that original. I'll try to post pic, even the Kawasaki parts diagram shows a longer piston than mine, don't know if this makes a difference, but logically it would seem that it would. Any thoughts. and thanks guys for the reply, give me more to think about and diagnose.
 

I doesn't look like the photo posted, so the original piston is about half as long as the replacement. even in the parts diagram from Kawasaki, the piston in the diagram matches the rebuild kit part. But the original is literally half the length.

The Z1 manual hosted here says the master bore should be 14mm.  Using a 5/8" bore master will result in increased hand effort and a very solid feeling lever.

Thanks, I saw that in the manual online also for specs, but from what I'm finding, it looks like they have a 5/8 and 7/8 master cylinder only. The one offered on Z1parts.net (which is where I ordered the replacement caliper from, has original replacement of 5/8, they state not made in China also. I do have an EBAY 5/8 master on the bike right now. I initially bought a rebuild kit for original, but when I opened it up it was way rusted out. 
 

OK, thanks to Nessism letting me know about the 14mm bore and digging in deeper. The 14mm(9/16) bore is for single disc and the 15.6 (5/8) bore is for dual disc. I have the single, checked the bore of the piston and rebuild kit for the original are both 14mm. My original is fairly pitted, so will work on cleaning that up, But did a search for 14 mm bore Japaneses master cylinder and found 4into1.com, they do Honda but have replica 14mm for Kawasaki, both the 14 and 15.6 are available. So I ordered one, when I receive this and install it, I will post my results, Hopefully fixes the problem, makes sense so far. Thanks for the help folks!

Nessism wrote:

The Z1 manual hosted here says the master bore should be 14mm.  Using a 5/8" bore master will result in increased hand effort and a very solid feeling lever.

Whilst I understand an extra 1.8mm on the bore size will displace more fluid so reduce "lever travel" and "feel" however given that fluid is still being displaced under pressure I don't understand how this translates into poor brake efficiency (the OP said that the brake works but stopping efficiency is poor ??) can anyone clarify ??
I would suggest before spending more money and digging too deep that you check the calliper sliders as previously suggested (it will take 10 mins and is free)

Wookie58 wrote:

Nessism wrote:

The Z1 manual hosted here says the master bore should be 14mm.  Using a 5/8" bore master will result in increased hand effort and a very solid feeling lever.

Whilst I understand an extra 1.8mm on the bore size will displace more fluid so reduce "lever travel" and "feel" however given that fluid is still being displaced under pressure I don't understand how this translates into poor brake efficiency (the OP said that the brake works but stopping efficiency is poor ??) can anyone clarify ??
I would suggest before spending more money and digging too deep that you check the calliper sliders as previously suggested (it will take 10 mins and is free)

Z1 calipers have one fixed pad and one that moves when the piston moves.  I am wondering if the sealing ring inside the caliper cylinder was replaced?  This is what forces the piston to retract,, and it fits inside a groove in the cylinder.  It needs to be carefully cleaned, as dirt will build up and force the sealing ring to tighten up on the piston.  I usually use a dental pic to clean the groove.  It can take some time to clean completely.

hardrockminer wrote:

Wookie58 wrote:

Nessism wrote:

The Z1 manual hosted here says the master bore should be 14mm.  Using a 5/8" bore master will result in increased hand effort and a very solid feeling lever.

Whilst I understand an extra 1.8mm on the bore size will displace more fluid so reduce "lever travel" and "feel" however given that fluid is still being displaced under pressure I don't understand how this translates into poor brake efficiency (the OP said that the brake works but stopping efficiency is poor ??) can anyone clarify ??
I would suggest before spending more money and digging too deep that you check the calliper sliders as previously suggested (it will take 10 mins and is free)

Z1 calipers have one fixed pad and one that moves when the piston moves.  I am wondering if the sealing ring inside the caliper cylinder was replaced?  This is what forces the piston to retract,, and it fits inside a groove in the cylinder.  It needs to be carefully cleaned, as dirt will build up and force the sealing ring to tighten up on the piston.  I usually use a dental pic to clean the groove.  It can take some time to clean completely.

I am assuming when pressure is applied to the piston the calliper body slides on it's mounts to apply pressure to the fixed pad ?

Wookie58 wrote:

Nessism wrote:

The Z1 manual hosted here says the master bore should be 14mm.  Using a 5/8" bore master will result in increased hand effort and a very solid feeling lever.

Whilst I understand an extra 1.8mm on the bore size will displace more fluid so reduce "lever travel" and "feel" however given that fluid is still being displaced under pressure I don't understand how this translates into poor brake efficiency (the OP said that the brake works but stopping efficiency is poor ??) can anyone clarify ??
I would suggest before spending more money and digging too deep that you check the calliper sliders as previously suggested (it will take 10 mins and is free)

This link does a good job of explaining...www.vintagebrake.com/mastercylinder.htm

I put a 5/8" master on a bike that had a very spongy feeling front brake lever and the result was rock hard feel afterwards.  The brake feel was poor, though.  Wooden feeling, so to speak.
 

Nessism wrote:

Wookie58 wrote:

Nessism wrote:

The Z1 manual hosted here says the master bore should be 14mm.  Using a 5/8" bore master will result in increased hand effort and a very solid feeling lever.

Whilst I understand an extra 1.8mm on the bore size will displace more fluid so reduce "lever travel" and "feel" however given that fluid is still being displaced under pressure I don't understand how this translates into poor brake efficiency (the OP said that the brake works but stopping efficiency is poor ??) can anyone clarify ??
I would suggest before spending more money and digging too deep that you check the calliper sliders as previously suggested (it will take 10 mins and is free)

This link does a good job of explaining...www.vintagebrake.com/mastercylinder.htm

I put a 5/8" master on a bike that had a very spongy feeling front brake lever and the result was rock hard feel afterwards.  The brake feel was poor, though.  Wooden feeling, so to speak.



 

Nessism I get the change in lever action but when you fitted that 5/8 cylinder was the brake efficiency effected or did it still stop ok (albeit with no "feel" in the lever) I am interested to learn ?
PS; good article by the way