Can't get air out of my lines

[sam000lee]

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.

 

[alke46]

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.

 

[Guest]

the bubbles MIGHT be coming from the bleeder threads, try some teflon tape on them....

 

[Steve]

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.

.

 

[chuck hahn]

Teflon tape on the bleeder threads and a Mighty Vac are your friends.

 

[sam000lee]

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!

 

[wymple]

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.

 

[Guest]

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.

 

[Blue Falcon]

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.

 

[sam000lee]

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.

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?

 

[Guest]

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.

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

 

[sam000lee]

Will something like this work?

https://www.amazon.com/ABN-One-Man-...635&sr=1-1-spons&keywords=brake+bleeder&psc=1

or in your experience would the syringe be better

https://www.amazon.com/Karlling-Pla...&qid=1496180870&sr=8-2&keywords=large+syringe

 

[Guest]

Will something like this work?

https://www.amazon.com/ABN-One-Man-...635&sr=1-1-spons&keywords=brake+bleeder&psc=1

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/detail/vacuum-pump-and-brake-bleeder-kit/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

 

[sam000lee]

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?

 

[TxGSrider]

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)

 

[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.

 

[Guest]

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/_foru...S750-master-cylinder-and-caliper-rebuild-kits

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