Rebuilt master cylinder & now no forward motion?

SpkLife

SpkLife

SpkLife
Joined
Jul 30, 2019
Messages
53
Age
59
Location
Jacksonville, Fl
So on my just purchased 1999 ST1100 I noticed the master cylinder was full of orangey stuff so I took it apart and cleaned/rebuilt it. It took awhile to get all the air out of the lines and after some tips from Ashley (thank you!) also purged the air from the master cylinder. Wala - the clutch engaged! I took it on a very short ride a week ago after I had success and all seemed to work fine with the clutch engaging and no slippage. I did notice the clutch seemed to engage way far out much more than before I rebuilt it. Tonight I went for a ride to do some carb idle adjustment and initially everything was fine shifting then... I noticed the clutch seemed to be slipping! Huh!
Before the rebuild and when I bought the bike I really went through the gear "banging" the clutch out to notice if there was any slippage and nada. It hooked up great in each gear and went down the road in quiet hustle. Fast forward to tonight and major slippage and all forward momentem came to a halt with the engine reving and clutch slipping! I got it to about a block from home feathering the throttle and a hot long walk back home (the walk was a nice 95 degree cardio workout!)) and now I'm scratching my head as to whats wrong.

Also, while the bike is sitting ideling with both tires on the ground I can shift through each gear. I didn't try it though without pulling in the clutch handle

Any suggestions? Do I need to clean and rebuild the slave cylinder? New clutch?


Thanks!
 
My guess is that you have a blockage in the compensation port in the floor of the master. You will find a small pressed steel deflector in there, pick that out and you will be looking at a pin-hole sized port. When you release the clutch lever, any residual pressure bleeds out through this hole, and if it blocks you can build up more and more fluid pressure which stops the clutch lifter from releasing, so you get slip.

Best bet would be to disassemble the master and give it a good clean, especially making sure these ports are spotless.
 
Dang John you beat me to the punch once again....
Good call.:thumb:
 
After removing many screws and nuts and bolts just to get to the 3rd bolt behind the header pipe. Much teeth grinding and help from my son who's a mechanic I have success and a good clutch!
 
Mkr64 said:
Here's the problem!
Click to expand...
For those of us who haven't gotten into the master cylinder or clutch much in the past, what is that a picture of? My clutch fluid was very discolored a while back but I thought I flushed it all out fairly well (due for another this off season), but wondering if there's still some gunk left somewhere else deeper down...

(edited after John's post) Slave cylinder!
 
Great video jfheath! The pictures the side facing the engine and it’s my slave cylinder after the master cylinder rebuild. The master had a very fine 1/16” layer of orange “dust” which seemed to be all throughout the system. I’ll try and get a picture of the “inside” of the slave cylinder. Keep in mind i sprayed a lot of brake fluid cleaner through it hoping I wouldn’t have to take it off
 
Well, I thought I had this thing sorted out. While trying to sell the bike to get an ABS model I found the clutch acting very strange and I’ve removed it from selling until I know it’s sorted out.

I think I’m ready to take it to a shop after spending another 3 hours trying to get it working properly. Ugh, it’s got me beat down! Maybe this is rocket science!! I’m in Jax, Fl if anyone’s got a little spare time... :)
 
Mkr64 said:
Well, I thought I had this thing sorted out. While trying to sell the bike to get an ABS model I found the clutch acting very strange and I’ve removed it from selling until I know it’s sorted out.

I think I’m ready to take it to a shop after spending another 3 hours trying to get it working properly. Ugh, it’s got me beat down! Maybe this is rocket science!! I’m in Jax, Fl if anyone’s got a little spare time... :)
Click to expand...
What is it doing?
 
Oh man just maybe! It’s sooooo frustrating!

When I try and bleed the normal way it will pump out kinda weak at the slave for a couple of lever pulls then just peters out and the lever has no resistance. I tried it from the bottom but no fluid goes up to the reservoir whether the handle is pulled or not.
 
Disconnect the the line at the master cylinder just to make sure fluid bleeding upward from the slave is flowing up.
When you cleaned and rebuilt the master cylinder, did you reuse parts? If so were they cleaned with brake cleaner?
Or did you use a new rebuild kit?
 
Good idea I’ll do the disconnect tonight and... I don’t remember exactly but I believe I used the rebuild kits without the brake fluid on the final but...

I did a bench test of the master after going through it again last night and it definitely held pressure and spit fluid all over (I filled the reservoir and primed it) when I moved my finger off. I could also feel the pressure in the lever too. So I don’t think it is the master. Now the slave is a bit harder to remove and check but I did it once...
 
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