Can't get air out of my lines

[TxGSrider]

If the aftermarket master cylinder has a larger bore than the stock one, it can cause the symptoms that you are describing.

[sam000lee]

I matched the bore unless I measured incorrectly. In the picture from post #23 - I measured the diameter of the area in the top left of the pictures where you can see the top of the plunger (kind of underneath the mirror mount) - 15.8mm. Can somebody check to tell me if that is the correct way to measure?

I couldn't verify with the plunger p/n: 59600-33811 (the MC plunger for my bike) since that one didn't fit in the MC.

The caliper piston is 50mm and this is the MC I bought.

[sam000lee]

Okay so I did some math. My caliper to MC piston surface area ratio is:

(pi x 25^2)/(pi x 7.9^2) = 10.0144

which according to the chart on this thread:

http://www.customfighters.com/forums/showthread.php?t=56704

puts my brakes in the `wooden' category. Going down to a 14mm MC bore puts me at 12.8367 which is a more appropriate ratio....

[Gorminrider]

New pads are better than trying to clean old ones. I've tried "cleaning/sanding" just to get a bike to a trial ride but so many have had leaking fork seals before I got them, and I never noticed any improvement whatsoever. The stuff goes deep into the pad apparently. Alcohol and solvents just seem to make it worse. Id expect putting them in an oven would again, make it worse.

Sanding them means that like new pads, they need a little break in to match the discs grooves. It may go some way to explain why pads are made the way they are...to wear in to these quickly.

as to bore size, that's right. ....but If it feels okay at the lever, it is ok. Even if the pads are contaminated, you will feel that you are applying them hard.

[TxGSrider]

From what Ive been able to find, most of the single disc use 14mm master cylinder and the duals use 5/8" (15.875mm).

[sam000lee]

From what Ive been able to find, most of the single disc use 14mm master cylinder and the duals use 5/8" (15.875mm).

I'm starting to think that maybe my MC was replaced at some point with one from a dual disc model.

[TxGSrider]

Also, its possible that it had the wrong master cylinder to begin with as you noted in an earlier that the rebuild kit that shouldve worked was too small and didn't fit.

[TxGSrider]

I'm starting to think that maybe my MC was replaced at some point with one from a dual disc model.

lol- I was posting that when you posted.

Maybe you can "borrow" the one off your 450 and see if it works.

[Nessism]

Single front brake caliper GS bikes should be using a 14mm master cylinder. 5/8" masters are for dual caliper bikes. Using a 5/8" bore master on a single caliper system will result in a very firm lever feel, and require a very firm pull on the lever to generate brake force. Since your bike has a spongy lever that suggests there are other problems. Most likely the caliper piston is sludged up and/or the sliding pins are binding.

Standard protocol for reviving a 40 year old bike includes a full brake system teardown and rebuild.

-Remove the caliper pistons and clean out the grunge
-Replace the piston if pitted and install new OEM Suzuki piston seals
-Grease the sliding pins with heavy black brake caliper grease
-Replace pads as needed
-Replace brake line
-Remove the master cylinder plunger and clean out grunge
-Inspect master bore and replace if there is any pitting
-Dual caliper bikes take a 5/8" master and single caliper bikes use 14mm master
-Bleed the system after first priming the master by pulling vacuum on the bleed nipple

If the lever feels spongy after bleeding that means the caliper piston is binding and not moving close enough to the disc. Tying back the lever overnight after building pressure in the system usually helps in this regard. If aftermarket caliper piston seals are used all bets are off.

[sam000lee]

lol- I was posting that when you posted.

Maybe you can "borrow" the one off your 450 and see if it works.

I was actually considering just migrating the whole system over to avoid any bleeding so I could ride while waiting for parts. On my 450 the brakes are awesome.