Can't get air out of my lines

[first timer]

i was just about to make the same recommendation. Back bleed it and see if that works. You can get big syringes from the local pharmacy. I think they are used for irrigating things or ememas or something. Mine came with my KTM clutch slave kit...

Also look into the reservoir and make sure all the little holes in it are cleared. Clogged ones can trap air.

[wymple]

"I've tried ziptying my lever overnight with no effect."

I've not seen this fail on a functional system. You have something wrong bleeding all that air out and still getting more in.

[mmattockx]

I watched some youtube videos and have kind of a stupid question: Why it is that the fluid can just get pushed up through the line and into the master cylinder without any actuation of the piston. Is there some kind of one way valve that lets the fluid get into the MC somewhere?

There is a small hole that lets fluid bleed back into the reservoir from the MC bore when you release the brake lever. It is what allows the pistons to retract a bit into the calipers so the pads aren't dragging all the time. When you fill it from the bottom air is pushed out of this hole until the fluid fills the line, then fluid will begin to run out into the reservoir when the lines are full. I just realized that you may not know to leave the cap off the reservoir while filling from the bottom. Leave the cap off (or very loosely sitting on the reservoir) to let the air out as you fill the lines. As TxGSrider says, wrap a rag around the reservoir to catch any fluid that bubbles out and protect all the painted surfaces.


Mark

[sam000lee]

So I drained my MC + lines and then filled up the system from the bottom using the syringe. I sucked out the fluid in the MC after it was full and then kept pumping fluid up to make sure all the bubbles were out. Still NO pressure in the lever. If I roll the bike and hit it I can see the forks absorb something but only for an instant. When I pull the lever a cloud of tiny bubbles comes up through the fluid. I have it zip tied right now so I'll check tomorrow to see if anything improves.

I did notice that the bolt area holding the lever is wet with fluid (didn't spill any) so I'm thinking that the seal on my MC piston is bad. I think I'm going to try and source a whole new used MC assembly.

Does anybody know what other models' MC would be compatible with the GS750?

[hannibal]

A rebuild kit should fix the MC. I believe the kit you need is part # 59600-33810 (33811). See this thread: http://www.thegsresources.com/_forum...r-rebuild-kits

I have a -33811 kit new in the unopened package. Let me know if you're interested.

[sam000lee]

A rebuild kit should fix the MC. I believe the kit you need is part # 59600-33810 (33811). See this thread: http://www.thegsresources.com/_forum...r-rebuild-kits

I have a -33811 kit new in the unopened package. Let me know if you're interested.

Just PM'ed you.

[sam000lee]

So I got a rebuild kit for a 1977 GS750B. It's part number 59600-33811 http://www.partsoutlaw.com/oemparts/...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?

[sam000lee]

Here's a picture the right clip/rubber thing are from my rebuild kit and the clip is certainly smaller so I guess I have a different MC. The top of the piston is also smaller if you can see that in the picture.

Anybody know what bike my MC might be from?

[sam000lee]

Does anybody know the thread pitch of the banjo bolt for the master cylinder?

[Gorminrider]

Mine is very similar (http://www.partsoutlaw.com/oemparts/...linder-model-x) all I can say. IT needs (M) 10mmx1 pitch...the finer thread.

[limeex2]

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]

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!

[sam000lee]

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?

[mmattockx]

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.

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

[sam000lee]

Okay thanks - Anybody have experience sanding and baking the pads. Was just doing some internet searching and that seems to be something people do...