GS1100 Front Master Cylinder Rebuild Woes

[denydog]

Put the calipers back on the front, bleed them, but the master cylinder still won't build pressure.

I'm at a total loss now. I'm going to be making ebay offers for a used master cylinder.

I know it's frustrating, but I wouldn't give up. Many of us have been in your exact situation. How are you going to feel when you get a new/used master cylinder, and it won't build pressure either?

I've been through this not too long ago. Pumped on that limp lever for two hours! I think you've seen all the tips, and have read this thread. http://www.thegsresources.com/_forum...ht=bench+bleed

I followed the advice of rustybronco in post #12 with good results one time. It's kind of like bench bleeding a master cyclinder, but that sounded too messy. I could feel the fluid pressure on my finger as I held it over the hole. Then I just had to re-attatch and bleed the line(s).

If you keep at it, I bet you'll eventually get it working.

BTW- I think even if you had that seal reversed, the master cylinder would still work, but maybe tend to leak just a slight amount.

[arveejay]

The U shape opening faces the direction it will travel when engaged. If the seal is backward it will not build pressure. Make sure both holes in bottom of reservoir are open or it wont work. If you had crap in the mc you will have crap in the holes and if it can't pull fluid when retracting it can't expell the air. If it's working correct the fluid will run out of the bleeder with no lever action and you keep putting clean fluid in till it runs out clear. Another trick is to compress the brakes with a c clamp or big pliers before bleeding and don't let the reservoir run dry when bleeding.

[AOD]

:?

After rebuilding the front master cylinder for my 1980 gs550, I also found it to be impossible to get pressure in the lines. I found a great trick by accident: I had a hand pumped syphon thingy and I hooked the "suck" end to the bleeder valve. Next I pumped it until there was a mild vacuum in the pump, then I opened the bleed valve and closed it again after about 2 seconds. I repeated this a few more times and when I got back on the brake lever... WOW! Like magic, I finally had brake pressure! I figure by sucking the fluid thru the lines instead of just pushing it the bubbles get sucked right out. Good luck!

I will try try try try try again to bleed the master cylinder. I did the above method many times...in fact I've now put an entire small bottle of brake fluid through the front!

I used my mighty-vac to create 5 PSI of vaccum then I crack the bleeder valves and watch it suck fluid through. I can get it to a point where there is no air coming out of the bleeders....but the brake lever is still soft!

I did notice that as a pump the lever I get a small 'fountain' from the master cylinder holes. I think the smaller one is pushing fluid up....and if I remember right, it did this last year when I bled the brakes, prior to my rebuild.

This is just damn frustrating.

~Adam

[AOD]

Hey guys, update here. I came home today and found fluid sitting on the ground under the master cylinder and wheel area. I tightened up the banjos and didn't see any leaks. Left again for a bit this evening, come back and more fluid under the master cylinder area.

There's a machined hole on the bottom of the master cylinder, near the brake switch area. It's wet...it makes a bubble / air noise when I pull the lever. What is this hole??? :? :?

~Adam

[AOD]

http://www.thegsresources.com/_forum/showthread.php?t=98258&highlight=master+cylinder+hole

Interesting post Deny, you had some of the same questions as me!

The only thing I see wrong is the diagram from Alpha Sports shows #7 BEFORE #6 on the piston. Both you and me have it the other way...

http://alpha-sports.com/spst/1982%20GS1000S/25.gif

~Adam

[AOD]

Update! I had an older wiser friend stop by tonight and we went through my master cylinder. Since it wasn't building any pressure and it was dripping out the hole in the bottom of the unit, I prety much narrowed it down.

My error came in that I had the spring and seal unit #2 and #3 installed backwards. I had the rubber seal pushed in first...which meant it was not doing anything.



What we decided was that part #7 installed into part #6 with the cup facing inward. The Suzuki service manual shows the cup unit as one assembly and when #6 is installed into #7 it fits perfectly.

The result...my front brake built pressure in a hurry and is really solid now. I have the lever tied back and the cap loose tonight trying to work any bubbles upwards.

Thanks to all who helped on here with this. If anyone reads this in the future and needs help, don't hesitate to send me a PM or email. I'll help how I can.

~Adam

[denydog]

Congratulations!!! I told you you wouldn't need a new MC :-D

[chef1366]

Yay!!!!!!!!!!!!!!

[AOD]

Congratulations!!! I told you you wouldn't need a new MC

Yeah...you guys were right. I'm headed home now to finish bolting things on and take it on a shakedown ride!

~Adam