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MC Piston and Cup assembly

tas850g

tas850g

Forum Mentor
Hi All,

I've been trying to bleed my brakes on the gixxer for 2 days and I am having problems. I installed new SS lines, cleaned, painted the MC, and threw in a new rebuild kit.

I want to make sure I have the kit assembled correctly.

Currently, I have the cup and piston assembled like this:

cuppiston2.jpg


The ribbed part of the cup is facing in the direction of the spring:

cup2.jpg


But when I work the brake lever I can hear some suction going on as if there is not a good seal. The piston slides in and out without any catching.

Should the cup be in this position instead?

cuppiston1.jpg


I'm not sure if you can see the difference in the orientation of the cup in both pictures.

I am able to get fluid coming out into the mightvac if I stick the banjo bolt from the MC into the brake fluid container. However, I cannot get any fluid to come out of the MC when I try bleeding the brakes with the banjo attached to the MC.

I've read the writeup on Cliff's site so I think I have the process down as far as priming the MC.

The pictures you are seeing is the kit from for my '79 850 but believe it or not the rebuild kit for the gixxer and the gs are the same. Got them for Z1 and it is a K & L kit. Thought I was getting OEM but we'll see how the aftermarket kit works.

Its been a couple of months since tearing this down so I thought I disassembled it with the cup in the above mentioned position but there never was any suction type noise before the rebuild.
 
Howdy

I have an OEM rebuild kit here that looks the same as yours and the rubber part you are having issues with is already installed from the factory. On mine it is installed per your first image with the smallest part of the taper against the flange.
P1010059.jpg


P1010057.jpg


Hope it helps
 
tas850g said:
The pictures you are seeing is the kit from for my '79 850 but believe it or not the rebuild kit for the gixxer and the gs are the same. Got them for Z1 and it is a K & L kit. Thought I was getting OEM but we'll see how the aftermarket kit works.
Click to expand...


I looked up the piston cup sets for both your bikes at alpha-sports & it doesn't appear they are inter-changeable??

Maybe you have the wrong rebuild set? I only use OEM stuff for my MC rebuilds, lots of members here have reported issues with the K&L parts.
 
I found the old cup and piston and the the K & L kit I got matches everything that came out of it. Unless the PO installed the wrong one.

Also, the cup was on the piston as haggishbasher has his. Still having issues with bleeding.

Let's try day 3 and see if I can make any progress on bleeding.
 
I had looked at the exploded views for each MC on PartsShark & they didn't look similar, nor where the p/n's cross-referenced with each bike...

Oh well, you never know I guess.

Are you certain that little hole down the MC bore is free & clear? I know I've had trouble bleeding brakes in the past too...

Good luck - new day, better results perhaps!
 
Both holes are clear, I shined a light and could see it coming thru both holes.

In had one blessed off and squeezed the level and fluid was squirting out so there must be pressure building up.

I've got the lever tied down to the bar right now to see if that makes any difference.
 
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