Master Cylinder Brake & bleeding problem

[djscoutmaster]

im bringing this 1980 gs750e back to life. This doesn't look like the original master cylinder. I need help identifying it in case i need a rebuild kit. I bleed the front brakes because there was no fluid in the master cylinder when i bought it. The liquid seems new and clear and no air is coming out and i still cannot get a firm brake. wondering if i need to rebuild the master cylinder. Any Ideas?

[jwhelan65]

im bringing this 1980 gs750e back to life. This doesn't look like the original master cylinder. I need help identifying it in case i need a rebuild kit. I bleed the front brakes because there was no fluid in the master cylinder when i bought it. The liquid seems new and clear and no air is coming out and i still cannot get a firm brake. wondering if i need to rebuild the master cylinder. Any Ideas?

Are they new lines? keep bleeding there is air in there somewhere if you can't get the lever firm.

[Big T]

Nope, that's not the original MC - it should have a round plastic reservoir with a screw cap on it

If you're reviving this bike, did you take the brake components apart to see what is inside?

That's likely the source of your problem - goo or solids from old brake fluid

[djscoutmaster]

more questions

No i didnt take them apart. They are stainless steel lines. I will take them apart and inspect them. i will inspect and clean them and if that doesnt work i was going to re-build the master cylinder.

Can i just spray brake cleaner through the lines to clean them?

What master cylinder it that in case i have to buy rebuild parts?

What is the best method of bench bleeding a master cylinder and the proceeder for a brake system that is opened up/ bleeding from scratch?

Is the proceedure different with dual front brakes?

[Suzuki mad]

Stick an elastic band around the lever and walk away for 24 hours. You must still have air in the system.
There's no leaks on the callipers by any chance?

[djscoutmaster]

elastic band

i did the elastic band trick for 24 hrs with no change... it didn't do anything. no leaks on the calipers. does that mean the master cylinder is bad?

[Nessism]

My suggestion is to take apart both the master cylinder and the calipers. Clean out all the grunge that's likely to be present in the system. Inspect the master cylinder for corrosion pitting in the metal and replace the master if necessary. Same goes for the brake caliper pistons. Consider replacing the caliper piston seals and master cylinder plunger as as matter of course since the rubber is 30 years old. That master looks stock to me, I'm not sure why Big T says it's not the original. You can order rebuild kits and such from any dealer part source such as Part Shark. If the lines are teflon/stainless I'd reuse them as is. Oh, and make sure to grease the caliper sliding pins with high temp. caliper grease.

Good luck and hope this helps.

[djscoutmaster]

brake inspection

i know its not the original one because the last owner mentioned the stock one had a plastic reservoir.

the outer boot on the master cylinder seems torn and contributes to a noise when the lever is pulled. would this also cause my issue?

Will a stock rebuild kit fit this master cylinder or will i need the rebuild kit from a different year..

[cowboyup3371]

You will need the rebuild kit that is for that master cylinder. Do some investigation and you'll be able to figure it out.

Honestly, whether the lines look good or not, clean that master cylinder for sure to include the return port hole. From my own experience and from watching others on here, failure to do so WILL result in an accident at the worst or failing to move at the least.

[djscoutmaster]

Then I will check out my master cylinder and caliper and go from there. I'll post again if I get stuck

[GS Jim]

i did the elastic band trick for 24 hrs with no change... it didn't do anything. no leaks on the calipers. does that mean the master cylinder is bad?

My bike wasn't braking well until I bit the bullet and went thru the whole system. Here's a tutorial on how to rebuilt the calipers.

http://members.dslextreme.com/users/cbsaunders/gs/79-Brake_overhaul.pdf

[djscoutmaster]

Master cylinder looks good. Callers look great too. Now I can only hope the rebuild kit I ordered will work for this mystery master cylinder.

[1_v8_merc]

You try using a Mighty Vac yet?

I had an extremely stubborn brake system on a cb900, which had a twin piston brake setup. I had the EXACT problem you're having.

Hooked it up....problem gone.

----

If you want to test the MC real quick.
Disconnect the main brake line at the top, where it meets the MC.
Now plug your finger over the hole, and start pumping the lever a buncha times until you start building pressure.
(assuming there is plenty of fluid in the reservoir.)
After the pressure builds, you should be able to let off the hole and get fluid coming out.

If this works, the problem must be Air in the lines or calipers....

Remember, air compresses, so don't be surprised to find some air bubbles causing your problem.

[djscoutmaster]

Bigger Problems

I got one of my parts back. This is the oem part for the master cylinder i though i had. Its the rubber seal. Its not right. so now i know i dont have a master cylinder for a 1984 gs1150. Can someone help me. ive ordered the rebuild kit from this bike and i assume when i get it, that it will be wrong too.

am i going to have an easier time getting a whole new master cylinder?

the picture show the new seal next to the cap. its too long and narrow

I belive this is the master cylinder i thought i had

http://cgi.ebay.com/ebaymotors/89-Katana-GSXF-750-Front-Brake-Master-Cylinder-9A-_W0QQcmdZViewItemQQhashZitem20ba779770QQitemZ140567353200QQptZMotorcyclesQ5fPartsQ5fAccessories#ht_2236wt_981

[Nessism]

How about posting a photo of what the inner components look like? I might be able to help you id what you need. The 1980 master uses a different plunger than the '82 for example.