No luck bleeding brakes

[gavin]

Little back-story.... last winter'ish, I wanted to try and flush all the old brake fluid out. Rear calipers were fine. Got to the front, and found bleeder valves were frozen. Replaced both calipers and bled. Never could get that stiff brake pedal back.

This summer, I replaced both my axles with the ones I re-geared. Shortly after, I decided to replace the rear calipers (just because, really).

Last weekend, I decided to try again to flush out all the old brake fluid with fresh stuff. Ran about 64oz brake fluid through, between all 4 calipers. Was still getting some air out, but ran out of fluid.

So... buy more brake fluid, and trying to bleed my brakes.

I have currently run ~96oz brake fluid (3 qts), through one caliper; the pass rear. I'm still getting air?!

I'm using a Motive Products power bleeder.

How can I still be getting air after that much fluid is pushed through?

I thought maybe air was getting "pulled in" through the bleeder valve threads and pushed back out through the nipple; nope. Just barely cracked the valve and still air bubbles. I have not been losing any brake fluid, so I don't see how it can be a leak anywhere.

what gives?
ideas/opinions/suggestions/etc?

 

[OneLever]

My first guess is that tool you are using. It could easily be introducing air into the fluid if not completely sealed and vented properly. I would use the cap and tube assembly and attach it to a container with a hole at the top to gravity feed the master cylinder. This will allow any bubbles that form to escape and prevent them from being formed via a vacuum above the fluid within the container. If you aren't losing fluid anywhere they you aren't gaining air anywhere except for the two openings you made at the master cylinder and bleeder valve.

 

[budwich]

If you didn't take any "precautions" during your caliper replacement in terms of "air-ingression", then you will likely have an issue trying to bleed your brakes because they are ABS based and you need to "exercise" the ABS system to get all the air out of the system.

 

[gavin]

My first guess is that tool you are using. It could easily be introducing air into the fluid if not completely sealed and vented properly. I would use the cap and tube assembly and attach it to a container with a hole at the top to gravity feed the master cylinder. This will allow any bubbles that form to escape and prevent them from being formed via a vacuum above the fluid within the container. If you aren't losing fluid anywhere they you aren't gaining air anywhere except for the two openings you made at the master cylinder and bleeder valve.

I have seen no air bubbles get "pushed" into the master cylinder. There are air bubbles in the hose from the tank to the master cylinder, but this is normal. The master cylinder is also completely full, up to the cap. And considering all the reviews and what-not I've read of it, while there is always the possibility, I don't see this as being probable.

If you didn't take any "precautions" during your caliper replacement in terms of "air-ingression", then you will likely have an issue trying to bleed your brakes because they are ABS based and you need to "exercise" the ABS system to get all the air out of the system.

My master cylinder has never went dry. Even still, with the ABS pump not activating, I should still be able to get all the air out of the lines. With the pump not activating, any air that may be in the HCU will stay in the HCU until the ABS system is activated. Right?

 

[gavin]

ok... so, embarassing, it may have been the hose I was using.

even though it was a tight fit on the bleeder nipple, I found some more hose that hadn't been used for anything. Not seeing all the air bubbles.

hose, or coincidence? I'm not sure... it did look like the bubbles were coming through the bleeder, but I s'pose it is possible it was getting between the hose and nipple?

edit: nope, that wasn't it. Finally stopped getting air bubbles out of the rear calipers, made it to the pass front. Several ounces went through clean. Crawled under to check on it, and saw a bunch more air bubbles come out for a consistent ~5 seconds or so; with the new hose.

 

[OneLever]

So just a ton of air in the system then? How many quarts did you eventually go through?

 

[gavin]

So just a ton of air in the system then? How many quarts did you eventually go through?

for how my brakes were working, I honestly don't see how there could have been that much air in the system.

I got the point of re-using brake fluid, since I knew it was all new stuff and I didn't have over a dozen bottles.

After I finally finished, I want to say I cycled.... about 13-15 quarts worth of fluid?

no way in hell there could have been that much air in the system. If there was, my brakes would have been virtually non-existant.

 

[OneLever]

Hmmm you're right.

There are air bubbles in the hose from the tank to the master cylinder, but this is normal.

Can you please explain that better? I don't understand why there would be bubbles flowing up from the master cylinder to the pump tank. Was the pump tank above the master cylinder the whole time? I could see bubbles forming if it was below the master cylinder and pressure wasn't being applied continuously. If the bleeder valve was left open and the pump tank wasn't being worked continuously the pressure would eventually decrease enough to allow the fluid to split apart in the tube. If at some location the tube was above both the master cylinder and pump tank.

Other than that possibility the only other entry point for air into the system was your bleeder valve right. The reason I'm so interested is I'm thinking of doing a flush this week myself.

 

[gavin]

Hmmm you're right.



Can you please explain that better? I don't understand why there would be bubbles flowing up from the master cylinder to the pump tank. Was the pump tank above the master cylinder the whole time? I could see bubbles forming if it was below the master cylinder and pressure wasn't being applied continuously. If the bleeder valve was left open and the pump tank wasn't being worked continuously the pressure would eventually decrease enough to allow the fluid to split apart in the tube. If at some location the tube was above both the master cylinder and pump tank.

Other than that possibility the only other entry point for air into the system was your bleeder valve right. The reason I'm so interested is I'm thinking of doing a flush this week myself.

well I don't know physics and all that good stuff... lol.

but according to Motive, this is normal as it's the displaced air from the master cylinder. Due to the length of the hose and the way it angles, the air can't actually "escape" anywhere so it "sticks" inside the hose.

The air stays in the "high spots" of the hose. It doesn't appear to matter whether the pressure bottle is higher or lower than the master cylinder (Motive does not state); but in my case, it was above the master cylinder.


edit: I suppose if I flipped the bottle upside down and made sure it was higher than the master cylinder and the hose was relatively straight, then the air would be able to "escape" into the bottle.

 

[OneLever]

Interesting. I think I'll stick to a gravity bleed thanks for the feedback.