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    Can't get air out of my lines

    Just replaced the front brake line on my GS750 (single caliper) with a stainless steel one and I'm having trouble bleeding them. I'm bleeding via:

    open bleeder, squeeze + hold, close bleeder, release, repeat

    and have gone through a bottle of brake fluid and am still getting lots of tiny bubbles coming out of the bleeder with no pressure in the lever.
    The brake system had been weak and upon investigation, the brake lever wasn't springing back (i.e friction/resistance in piston) until I soaked it in some penetrating oil. I'm wandering how likely it is that air is getting into the system via the MC or if I am somehow bleeding incorrectly.
    1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
    1977 GS550
    1977 GS750 - Cross country trip thread

    #2
    Originally posted by sam000lee View Post
    Just replaced the front brake line on my GS750 (single caliper) with a stainless steel one and I'm having trouble bleeding them. I'm bleeding via:

    open bleeder, squeeze + hold, close bleeder, release, repeat

    and have gone through a bottle of brake fluid and am still getting lots of tiny bubbles coming out of the bleeder with no pressure in the lever.
    The brake system had been weak and upon investigation, the brake lever wasn't springing back (i.e friction/resistance in piston) until I soaked it in some penetrating oil. I'm wandering how likely it is that air is getting into the system via the MC or if I am somehow bleeding incorrectly.
    Try this: bleeder closed, pump up pressure several times and hold, then open bleeder slowly, closing before full travel of the brake lever is lost.
    Larry

    '79 GS 1000E
    '93 Honda ST 1100 SOLD-- now residing in Arizona.
    '18 Triumph Tiger 800 (gone too soon)
    '19 Triumph Tiger 800 Christmas 2018 to me from me.
    '01 BMW R1100RL project purchased from a friend.

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      #3
      the bubbles MIGHT be coming from the bleeder threads, try some teflon tape on them....
      1983 GS 1100 ESD

      Comment


        #4
        Your technique is OK, but I have to ask: after using penetrating oil on the piston, did you replace the seals?

        Most of the "rubber" parts in a brake system are only designed to withstand brake fluid. Any other chemical tends to degrade them.

        Also: did you "bench prime" the master cylinder? Two variations I have seen include removing the line, holding your finger over the outlet, squeezing the lever while looking for some pressure. Allow a little fluid to come past your finger, but clamp down while releasing the lever. If that does not give good results, there might be an air bubble stuck at the top of the bore. Remove the M/C from the handlebar (with the cap on), hold it vertical so the outlet is at the top and squeeze a bit to force any air out. Be sure to block the outlet with a finger when you release the lever or you will just suck more air back in.

        Have you put any Teflon tape around the bleeder threads? I used to get a lot of air bubbles while bleeding until I started using tape. Now, the only bubbles I see are ones that were actually in the fluid, not what snuck in around the threads.

        .
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          #5
          Teflon tape on the bleeder threads and a Mighty Vac are your friends.
          MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
          1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

          NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


          I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

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            #6
            I haven't been using teflon tape or the other bleeding method but will do both tonight. There isn't any pressure in the line so I'm not sure pumping several times and then opening bleeder will be effective. I'll try the bench prime thing tonight, too!

            Thanks for the quick responses - I just got the carbs sorted after doing the valves and fresh oil and it's running awesome so I just need to make sure my brakes are working well before I'm on the road!
            1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
            1977 GS550
            1977 GS750 - Cross country trip thread

            Comment


              #7
              Pump the lever a dozen times or so, and holding it down, tie it there. I use a zip tie. Leave it set that way overnight and the air will all bleed out.

              Comment


                #8
                You may need to crack the banjo bolts to release air that can get trapped there. Everywhere there is one. Just wrap a shop towel to catch the fluid that will come out with the air. You may have to do this a couple of times. I also flick the lever quickly to work the air out of the master. You don't want to apply pressure doing this, just pull back about half way and let it go. The quick shock works very small bubble back into the reservoir. It may look like foam. I usually do this first, so I'm not forcing air into the lines. I'm talking around 20-30 flicks or until the tiny bubble stop releasing into the reservoir.

                One of the benefits of modern master cylinders on sport bikes is a remote reservoir and a bleeder valve at the master, but even with both of those improvements, I still often need to crack the banjo bolts to get all of the air out. Last resort I use the tie off method mentioned, but then still crack the banjo at the master. Just remember when you cut the zip tie, release the lever very slowly.
                GSRick
                No God, no peace. Know God, know peace.

                Eric Bang RIP 9/5/2018
                Have some bikes ready for us when we meet up.

                Comment


                  #9
                  I use a hand vacuum pump with a reservoir after a good bleed/flush. Attach the line to the bleeder zerk, make sure you keep your master cylinder full and double pump. takes about 2-3 minutes to get all the air out and fill the line.

                  Comment


                    #10
                    I added teflon tape to the bleeder and am still getting loads of tiny bubbles coming out. Gone through 2 bottles of brake fluid at this point.

                    Originally posted by gsrick View Post
                    You may need to crack the banjo bolts to release air that can get trapped there. Everywhere there is one. Just wrap a shop towel to catch the fluid that will come out with the air. You may have to do this a couple of times. I also flick the lever quickly to work the air out of the master. You don't want to apply pressure doing this, just pull back about half way and let it go.
                    When you say crack the banjos do you mean crack them and then bleed or just crack them and then retighten after a couple flicks?

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

                    I'm getting essentially no pressure at the lever. What are peoples experience with MC rebuild kits? Good source?
                    1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
                    1977 GS550
                    1977 GS750 - Cross country trip thread

                    Comment


                      #11
                      Originally posted by sam000lee View Post
                      I added teflon tape to the bleeder and am still getting loads of tiny bubbles coming out. Gone through 2 bottles of brake fluid at this point.
                      Since you are still fighting it, it might be time to try more severe measures. You can fill the lines from the bottom up using a large syringe through the bleeder nipple. That pushes the air towards the top and usually cleans it out through the MC reservoir. You would normally fill from the bottom with an empty system, so drain your lines first or you will end up sucking a lot of fluid out of the MC reservoir. If you don't want to do that then get a vacuum bleeder, they typically work great and can be operated by one person without help.



                      Originally posted by sam000lee View Post
                      When you say crack the banjos do you mean crack them and then bleed or just crack them and then retighten after a couple flicks?
                      You use the same procedure as with the bleeders on the calipers. Pump the lever a few times, hold pressure and crack the banjo bolt to let any air out. Tighten it back up before the lever bottoms out on the bar. Rinse and repeat. I have found the banjo bolt on the MC will often hold a bit of air depending on how it is oriented. I can't say on the rest of them, I always switch to a 2 line system because they are so much easier to bleed than the typical OEM Rube Goldberg set up.


                      Mark
                      1982 GS1100E
                      1998 ZX-6R
                      2005 KTM 450EXC

                      Comment


                        #13
                        Originally posted by sam000lee View Post
                        That's not a vacuum bleeder, it is just a fancy catch can to simplify handling everything. This is what you are looking for: https://www.princessauto.com/en/deta...it/A-p8050832e

                        The syringe works great for pushing the air out the top but you may still need to bleed it a bit depending on how the system is configured if it traps pockets of air. Going slow and careful when filling from the bottom helps minimize that problem, though. The vacuum bleeder works great for getting those last bits of air out of the system, especially if it is trapped in your calipers or the banjo bolt into the calipers. I can't say one is better than the other, they are more complementary. Considering how cheap the syringe is I would try it first. If you do you will want to drain all the fluid from the lines and MC reservoir, then fill using the bleed nipples on the calipers.

                        Nobody answered you question about MC rebuild kits, so I will say that the best way to go is to buy the parts from your dealer. You can still get the piston and cup set for most GS's and you can't beat OEM for the quality. Yes, it may cost a bit more, but considering how safety critical brakes are I would say they are a bad place to save a couple $$.


                        Mark
                        1982 GS1100E
                        1998 ZX-6R
                        2005 KTM 450EXC

                        Comment


                          #14
                          Thanks for all the help, Mark. I'll have some time tomorrow so I spent the extra $4 to get 1 day shipping on the syringe and will see how that goes before buying a vacuum bleeder or new parts.

                          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?
                          1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
                          1977 GS550
                          1977 GS750 - Cross country trip thread

                          Comment


                            #15
                            Ive got a KTM motored atv with a hydraulic clutch, and I you can bleed it all day in the traditional way (top to bottom) and it wont work. But if I use a syringe or squeeze bottle and a piece of vacuum hose and "reverse bleed" it (pump the fluid in from the bottom) it takes just a few seconds and works perfect. Just be sure you use a towel around the reservoir and don't squeeze the handle at all while youre filling it that way.
                            (I have used an injector syringe from a deep fryer injection kit with the neede cut off)
                            Last edited by TxGSrider; 05-31-2017, 03:27 PM.
                            1982 GS1100E "Jolene"

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