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Can't get air out of my lines
- Thread starter sam000lee
- Start date
sam000lee
Forum Mentor
So I got a rebuild kit for a 1977 GS750B. It's part number 59600-33811 http://www.partsoutlaw.com/oemparts/a/suz/50d3ff04f8700230d8b4dd7a/front-master-cylinder-gs750
As far as I know the MC is the stock one since the bike has the stock rotor and I just took off the stock lines to replace with an SS one.
A couple questions:
1. I took out in this order, rubber cap, metal ring, nylon washer, circlip and now don't know how to proceed. The piston/cup are still in there and it looks like there is some kind of other retaining plate. What do I do to get the piston/cup out. On the brake section on Basscliff's site it mentions some kind of wire setup you can use going through the banjo bolt hole but I didn't quite understand what was going on.
2. The end of the piston/cup that I can currently see is wider than the equivalent part of the one on the rebuild kit. It is the correct one for the bike but it looks like it's not going to fit. I have been searching for parts under 1977 GS750B but my bike's manufacturing date is 1976 is listed as an A on the GSR model page. There aren't any GS750's listed under the 1976 years on most sites like partsoutlaw so I've always just used the release year which was 1977 so the `B'. Do I have the correct P/N assuming the MC is the original one?
3. In the rebuild kit there is a little brass disc. Whats that for?
As far as I know the MC is the stock one since the bike has the stock rotor and I just took off the stock lines to replace with an SS one.
A couple questions:
1. I took out in this order, rubber cap, metal ring, nylon washer, circlip and now don't know how to proceed. The piston/cup are still in there and it looks like there is some kind of other retaining plate. What do I do to get the piston/cup out. On the brake section on Basscliff's site it mentions some kind of wire setup you can use going through the banjo bolt hole but I didn't quite understand what was going on.
2. The end of the piston/cup that I can currently see is wider than the equivalent part of the one on the rebuild kit. It is the correct one for the bike but it looks like it's not going to fit. I have been searching for parts under 1977 GS750B but my bike's manufacturing date is 1976 is listed as an A on the GSR model page. There aren't any GS750's listed under the 1976 years on most sites like partsoutlaw so I've always just used the release year which was 1977 so the `B'. Do I have the correct P/N assuming the MC is the original one?
3. In the rebuild kit there is a little brass disc. Whats that for?
Mine is very similar (http://www.partsoutlaw.com/oemparts/a/suz/50d3f2acf8700230d8b4bf0a/master-cylinder-model-x) all I can say. IT needs (M) 10mmx1 pitch...the finer thread.
In my 20 year as a service manager and now working on my own stuff, heres my 2 cents worth. If the previous owner didn't maintain the brake system( regularly change fluids) The mc plunger bore will wear out and rebuilding them is a waste of time. Unless you have to have an original mc, find a nice clean modern new mc. As far as bleeding goes, I made my own bleeder. Back yard as heck but it works great. Took a large glass jar with a lid. (pickle jar) Found clear lines that fit the bleed nipples. Measured o.d. of hose and drilled 2 holes in lid. Put 2 separate hoses into 2 holes. Run one down an inch from bottom, the other an inch from top. Use plumbers putty to seal hoses on both sides of lid. Put one hose on bleed nipple and you can suck on the other. Worked way better than the Miti-Vac I borrowed, and no you do not get brake fluid in your mouth. When done, apply brakes and tape lever tight, leave over night. This has always worked for me. If pressure is still low, bleed all union fittings. ALWAYS use oem parts only. Meticulously clean caliper piston and seal seats must be perfectly clean. I use Volvo brake caliper grease on seals and pistons. My bikes have 2 finger braking.
sam000lee
Forum Mentor
Thanks for the input - I ordered an aftermarket MC last week only to find that the banjo threading was off and that it didn't have a brake switch. Ordered one of those banjo bolts with the pressure switch thats getting here today. I'm hoping the caliper is okay - hasn't been leaking and moves freely so we'll see what happens when I bleed it later on.
I'm supposed to be taking this bike cross country in 3 weeks so am hoping I can get it sorted quickly... otherwise I'm taking my GS450!
I'm supposed to be taking this bike cross country in 3 weeks so am hoping I can get it sorted quickly... otherwise I'm taking my GS450!
sam000lee
Forum Mentor
Got my new MC installed with a fitting banjo + new crush washers. After reverse bleeding the system with my syringe, then pumping the lever a whole bunch I got some good pressure in the lever. I zip tied it for a couple hours, some more pumping and it still felt a little spongy. Then I just did the regular bleeding procedure and the first couple of pump, hold, bleed, close, release cycles let out some air and and then I had clear fluid. Now the lever feels nice and hard. I took it out for a cautious test ride (first time since October!) and it works okay but just doesn't have good stopping power. The lever FEELS awesome but doesn't seem to be stopping hard and definitely not hard enough for me to feel safe.
The caliper piston moves freely so I am trying to think of other things before having to buy a rebuild and having to bleed the system again. There's the chance I dripped brake fluid on the rotor at some point - could that be a culprit for the lack of stopping power? Other suggestions?
The caliper piston moves freely so I am trying to think of other things before having to buy a rebuild and having to bleed the system again. There's the chance I dripped brake fluid on the rotor at some point - could that be a culprit for the lack of stopping power? Other suggestions?
G
Guest
Guest
Clean rotors, fresh pads? If you contaminated a pad/rotor with brake fluid that will result in minimal braking effect. At this point I would be buying new pads and installing them. Clean the rotors with a scotchbrite pad and hot water with dish soap. You will be amazed at the colour of the water when done. Then go do a series of stops, starting with 3 medium effort ones (maybe 60% of max), then 3 harder ones (75%), then 3 very firm stops (90+%). After that your pads should be bedded and working well.
Mark
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sam000lee
Forum Mentor
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.
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.
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sam000lee
Forum Mentor
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....
(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....
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.
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.
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sam000lee
Forum Mentor
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.
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.
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
Forum Mentor
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.
