Reverse bleeding issue

RCinNC

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Yesterday I flushed the brake and clutch fluid using the reverse bleeding method. It's the first time I've tried this; usually I use a vacuum pump. The process worked fine for the clutch, rear brakes, and right side front caliper. However, on the left front caliper, I couldn't push brake fluid through it using the syringe. I thought there might have been some debris on the bleed valve that was clogging it so I removed it to check, and it was fine. Still couldn't push fluid through that caliper. I ended up bleeding the left front using the vacuum pump, which did work. Once I was done, all the brakes and the clutch worked fine. ABS system works fine too. There are no trouble codes or warning lights.

The bleeder valves are OEM; they're not Speed Bleeders. And yes, the bleeder valve was open when I was reverse bleeding the left front caliper.

Any ideas on why I could pull fluid out of that caliper using a vacuum pump, but couldn't push it in using a syringe?
 

RCinNC

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I don't know, Dogdaze. Is that something that exists on other dual caliper front brake systems?
 

Dogdaze

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TBH RC, I was just guessing, some cars have those and as there is a sequence to bleeding the brakes I thought parhaps it had something to the way air needed to be evacuated from the system............... On cars if a brake fails on one side you can still use your brakes and the rest will still work by isolating the 'failed' side.
 

EricV

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It's also possible it has something to do with the linked brake system.

What benefits to you feel the reverse bleeding method has? (just curious)
 

Jlq1969

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I think that the end line of the front brake, is rigth caliper. fluid fills the left caliper and pushes the air to the rigth caliper, where it is purged.
 

RCinNC

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It's also possible it has something to do with the linked brake system.

What benefits to you feel the reverse bleeding method has? (just curious)
For me, Eric, is was as easier process, plus it made more sense from a physics standpoint. Since air bubbles rise in fluid, pushing fluid into a system from the lowest point would make it easier to get any air out, because you're working with an air bubble's natural tendency to rise up through the system to the master cylinder. You're just giving the air a helping hand to do what it naturally does. Plus, there's no danger of accidentally sucking the master cylinder dry and introducing air into the system the way you can when you're pulling fluid out of the system with a vacuum pump. And there's no hassle of trying to get a perfect seal with the vacuum pump on the bleed screw. In spite of zip ties and grease seals, I can never get my vacuum pump to totally seal; there is always air being pulled into the line from outside while I'm drawing a vacuum. That makes for a bad vacuum which makes pulling the fluid out more difficult, and it also makes it impossible to tell if you're actually pulling air out of the brake system or just sucking outside air into the vacuum pump through the bad seal. With the reverse bleed, the brake fluid itself forms the seal on the bleed screw; even if the tubing leaks a little, you aren't drawing air into the line.

For me it was a way easier process (other than the uncooperative left caliper).
 
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RCinNC

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I think that the end line of the front brake, is rigth caliper. fluid fills the left caliper and pushes the air to the rigth caliper, where it is purged.
Maybe that's the reason. I was using a big syringe to reverse bleed the system, and it's possible that I couldn't generate sufficient pressure to move the fluid through the other caliper and back into the master cylinder. Next time I do this, I'll start with the left caliper first and see if that makes any difference.
 

EricV

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Thanks for sharing your POV RC. I use a compressed air vacuum bleeder myself. I get what you're saying, but since I don't need to pump the handle, the air sucked in around the threads has never bothered me. (former auto wrench in the past among other things). The only time I've resorted to pressure bleeding is when doing full brake line swaps in the past. Just a lot easier to get new lines full of fluid that way. On a bike I usually just let gravity do it's thing, no longer being on the clock for that work.
 

RCinNC

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I'll probably end up doing a combination of the two methods in the future, Eric, if the left side caliper remains uncooperative. I actually went old school on the left side once I had flushed the fluid and replaced it; I wrapped a bungee cord around the brake handle, cracked the bleed screw, bled off some fluid, sealed the screw, and released the brake handle. I did that a few more times, just to be sure any air that might be in there was gone.
 
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ballisticexchris

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Maybe that's the reason. I was using a big syringe to reverse bleed the system, and it's possible that I couldn't generate sufficient pressure to move the fluid through the other caliper and back into the master cylinder. Next time I do this, I'll start with the left caliper first and see if that makes any difference.
I'm getting ready to bleed my system for the first time so this helps. I have tried those "Mityvac" pumps in the past and not had much luck. I use the syringe method you describe only when doing my LHRB system. I'm thinking that the back-bleed method is not going to work very well due to the antilock valve. I'm willing to bet there is some kind of check valve in there.

I decided to just do the old school pump and fill as described in the manual. I did it this way on my Beta the last few times and it's worked out great. I put a tight loop in the bleeder hose (to prevent bubbles backing up) and just pump and fill.
 

RCinNC

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It definitely felt like an actual mechanical blockage, Chris. Upon reflection, that's about the only thing that would prevent me being able to move fluid into an open hydraulic system. There was no pressure in the system; the master cylinder was open, so my syringe shouldn't have had a problem moving that small of a volume of fluid into a system with no resistance. I had to put some force into the syringe to move the fluid into the rear and right front caliper and clutch (my guess is because the ports that the fluid passes through are really small), but there was no feeling at all with the left front caliper that any fluid was going anywhere. In fact, I ended up blowing the hose off the end of the syringe while trying to get fluid into the left front. There must be some sort of check valve in there like you said, but I'm no expert on brake systems.
 

Jlq1969

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It definitely felt like an actual mechanical blockage, Chris. Upon reflection, that's about the only thing that would prevent me being able to move fluid into an open hydraulic system. There was no pressure in the system; the master cylinder was open, so my syringe shouldn't have had a problem moving that small of a volume of fluid into a system with no resistance. I had to put some force into the syringe to move the fluid into the rear and right front caliper and clutch (my guess is because the ports that the fluid passes through are really small), but there was no feeling at all with the left front caliper that any fluid was going anywhere. In fact, I ended up blowing the hose off the end of the syringe while trying to get fluid into the left front. There must be some sort of check valve in there like you said, but I'm no expert on brake systems.
There should be no check valve, the repair manual talks about bleed Right, left and rear caliper. Try to remove the left caliper, open the left vent screw, and push the brake pads / or piston brake pads. The hydraulic pressure is much higher reverse. Yes, I know, and the tools for push?:):)
934B0582-F343-4153-B693-D8E392C38A66.jpeg
 

RCinNC

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Fortunately that's the order I did mine in; to my discredit, I never even looked in the manual to see if there was a specific order to bleed them in. As far as the calipers go, I can push the pistons back in with my hands; I've done it in the past on all three calipers when I've done a brake pad change.

When I changed the fluid in the right front and rear caliper, I had to exert some pressure on the syringe to do it; there was a definite feeling of resistance. However, I could tell the fluid was moving, and I could see it filling the master cylinder reservoir. I had the same experience with the clutch master cylinder reservoir. When I tried to pump fluid into the left front caliper, it felt very much like I was pushing against a compressed fluid; there was even the feeling of rebound in the syringe. No fluid entered the master cylinder under pressure. It definitely felt like something was stopping the flow of the brake fluid, and it wasn't just a case of a higher amount of resistance in the left front compared to the right front and rear.
 
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