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Master Cylinder - What am I doing wrong?

  • Thread starter Thread starter GooberPea
  • Start date Start date
G

GooberPea

Guest
Hi all. This is probably something obvious I'm overlooking. '81 850G. Front brakes worked but not great. I got a OEM rebuild kit for the front master Cylinder along with stainless lines. My problem is with the m/c though.

When I put the Master Cylinder together with the new parts and push in the piston no fluid comes out. If I take off the circlip and then push in the piston with my finger fluid comes out. Put the circlip back on, and no fluid again. The difference is that with the circlip in the piston is compressed much further into the bore. More than I can do comfortably with my fingers with the circlip out.

I thought maybe I got the wrong parts but when I compare them to the old ones, they look the same, only cleaner, and it worked before. What the heck am I missing here? Please enlighten me. I've got the factory manual and a Haynes. I've put together lots of Lego sets successfully, so I'm pretty confident that I have the parts in the same orientation and order as the books show;) Thanks,

Craig
 
Make sure the small master bleed hole is open – it’s extremely small. This helps fluid get down to the piston where is can be pumped. After you verify the hole is open, put the master together and install it on the bike. To prime the master you might have to draw fluid down out of the reservoir and into the mastercylinder bore by applying a vacuum to the nipple on the caliper. If you have a long piece of clear tubing you can suck on the tubing to draw the vacuum – the long part comes in for obvious reasons. Once the master is primed it should start pumping.

Good luck
 
Does small master bleed hole = the little hole at the bottom of the depression in the reservoir? By the way, how do you get the reservoir off? I got a new o-ring for it but I can't get it off. I can sort of twist it back and forth a little. Is it just brute force or am I missing something here too?

I'll try the vacuum and post back. That sounds reasonable. Thanks for the advice.

Craig
 
OK. I'm not sure if I'm making progress or not. I used some hose connected to the bleeder nipples and sucked some fluid through both calipers. I've been bleeding for about the last 20 minutes but it doesn't seem to be doing anything. I bled the brakes previously with the old lines and before I put in the MC rebuild kit, and it helped a lot so I'm confident I'm doing in correctly.

I must've squeezed that lever 1000 times and it feels as if there is no resistance whatsoever. When I open the bleeder a little bit of fluid comes out but thats it. I've gone through about half the bottle of fluid and I can still pull the lever all the way back to the grip with next to no effort. Any suggestions? Thanks, I realize you are all out riding tonight so I'll be patient. :)
 
One more tidbit and then I'm done for the night. Too frustrated. I'm still thinking the issue is in the master cylinder because when I squeeze the lever, fluid (I'm pretty sure it's NOT air) is getting squeezed up and out of the little hole at the bottom of the depression in the reservoir. That didn't happen when I bled the brakes with all the old parts on it. Seriously all, it's going to be a beautiful weekend on the shores of Lake Superior and we don't get a whole lot of those:) I'd really appreciate any expertise you could lend. I'll check back in the morning. Thanks again everyone!
 
You need to get more of the air out of the system. Putting a rag over the banjo fitting on the master and then bleeding it there often helps get air out. Also, do the same thing on the junction at the lower triple clamp. Another trick is to hold the lever in and then tap the brake line to work the bubbles up to the master; pull the lever very slightly and you will see bubbles coming up though the small hole in the master.

Good luck and don't give up.
 
other than bleeding at the m/c banjo bolt... if you have the means, try pushing the fluid up from the bleeders at the calipers (connect a plastic bottle to a hose attached to the bleeder nipple)

failing that...
temporarily, put the old parts back in the m/c and see if the results change
if you are doing everything right, i would suspect the piston/seals may be at fault
 
Last edited:
Alright then. Seems the consensus is still air in the lines. I'll go along with that. I just wasn't sure because it wasn't as easy as last time. Of course last time I didn't replace anything. Thank goodness for people with experience. Thanks for the bleeding tips I will give those a try in the morning. It is getting dark here and I am very literally a shade tree mechanic.

Also, maybe I should've mentioned but I bypassed the junction at the lower triple clamp and just ran two lines to a double banjo at the MC. That shouldn't make a difference should it?
 
GooberPea said:
Also, maybe I should've mentioned but I bypassed the junction at the lower triple clamp and just ran two lines to a double banjo at the MC. That shouldn't make a difference should it?
Click to expand...

if anything, it should help as theres one junction less (for the air to get trapped in)
 
Take off the brake lever and push the piston in with a philip screwdriver. This pushes the piston all the way in and gets those pesky bubbles out of the m/c.
 
Air in Brakes

Air in Brakes

GooberPea,
Is sounds as though you still have air in the MC and it is not pushing fluid. Nessism had it right early on when he suggested pulling fluid from the reservoir using a tube. You may have tried the tube on the bleed nipples. Try taking the banjo bolt out of the end of the MC and push the tube into the hole and then draw fluid into the cylinder. That will relieve the airlock in the cylinder and it will now push fluid through the lines. Another way to prime the cylinder is to remove the banjo bolt and press the brake lever and while it is down put your finger over the hole where the bolt was. Release the lever and that should draw fluid into the cylinder. Do this a couple of times until you feel good pressure against your finger. Hook up the plumbing and clean off all the fluid that squirted out and bleed the system. HANG IN THERE!
Lee :)
 
Well I want to thank you all for your advice. I just don't have the knack I guess. I normally don't throw money at problems but it is just TOO nice not to be out on the bike so I went and got one of these pumps from Sears.

That did it! My brakes work so well that now I have to deal with a new problem. Massive dive when I stop. Oh well. That's the fun I guess.

Thanks again everyone.
 
Thanks for this post and all advice.
Just cured my problems after rebuild. Just sucked those bubbles out and it worked like a charm.

JF
 
I was just going to say "go get a mighty vac" they work great if you have a lazy side like me!!:oops:
 
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