KD4315

The video below shows whats going on. I've already run about 12oz of brake fluid through the rear passenger side and it's brand new clean brake fluid coming out. When I first turn the nipple I get a solid flow of break fluid for about 20 seconds then a steady stream of huge bubbles. Is air getting in as I'm bleeding them? There can't be that much air in the system. I replaced the calipers a few days ago and I'm using the motive power bleeder at 20 psi. I have ABS so that's why I'm bleeding it while it's running. 98 Limited

There are huge air pockets in the tube from the power bleeder to the master cylinder. Could that be causing this?

View My Video

RTorrez1

Just tossing out some ideas. Are you sure that the cap is on tight on master cylinder and you're not pulling in air? You may want to check all of the brake line to see if you have any other leaks.

Radi

Back it down to about 5psi and see what happens. I think you are injecting air into the fluid itself. Are you using synth/silicone fluid?
If so, it seems to hang on to air bubbles longer than the older stuff.

KD4315

Yes I'm using synthetic brake fluid. I backed it down to 5 psi and the fluid moved slower but the bubbles still came and they were much longer than at 15-20psi. I think air is getting in but I don't know where from.

DFlintstone

I'm not familiar with the power bleeder, or the ABS system. I have bled at least 100 brakes though, (in various ways).

Recently I did my fronts by simply running a (clear vinyl), tube from ACE right from the bleeder, into the cab, and doing it with my finger on the end of the tube and a coffee can! Six feet worked just fine for that.

NurpleXJ

Take a plastic bottle with a lid, drill a hole in the lid of the bottle big enough to run a small piece of rubber hose into the bottle. The tubing must be long enough to reach the bottom of the bottle. Fill the bottle with about 2" of brake fluid. Put tubing on the bleeder screw and loosen it. Pump away at the brakes. It wont pull in air because it's in the fluid in the bottle. Just keep the master cylinder reservoir full and the bottle from running dry. Start with the RR, LR, RF then the LF. Good luck!

Radi

That sometimes doesn't work...with the bleeder left open, there is nothing forcing the cylinder to pull new fluid from the MC instead back out of the can. Air bubbles further up the lines can just see-saw back and forth instead of being expelled.
Closing the bleeder between pumps makes it act as a one-way checkvalve, keeping the fluid moving from the MC through the lines and eventually out the bleeder.

Radi

Try it the old-fashioned way. Fill the MC, enlist a helper to pump the brake and hold pressure on the pedal while you crack the bleeder. Once it stops spitting, close the bleeder and release the brake pedal. Repeat until no more bubbles.
Then move to the next wheel, etc. Or you could try Dflintstone's method if you can't find a helper.
Synth likes to hold air in suspension if it gets mixed in there...shake a bottle of it and you'll see what I mean. I'm suspicious your power bleeder is somehow mixing air into the fluid and it's staying there as it gets pumped through the lines.

DFlintstone

Napa used to sell a little check valve that made the "hose in a jar" direction work allot better. I don't know what's available now. (I still have 9 good fingers though!)

Radi

Speed Bleeders. About $12 for a pair and they do work.

KD4315

I'll give the old fashioned way a try. It only happens in the rear though. I don't get the steady stream of bubbles from the front.

DFlintstone

Radi's approach should work. Of course air won't come IN, if you know the fluid is under pressure. (I have the helper press, then I open the bleeder). Then I have it closed while they let up. I usually ask them to tickle it a little while it's up. Maybe a personal problem, (lol!) or maybe I've seen it bubble a little there. (in the res)

Air bubbles coming into a stream....would be like a siphon leaking....Your lines up at the Master cylinder weren't messed with. got me.

cdn_xj

I've only ever bled brakes manually as there's generally less apparatus that can fail. The only time I had excess air in the lines was when I accidentally bled the rear brakes dry and then did not properly fill up the reservoir.

The rear brakes and front brakes are on separate hydraulic circuits to provide redundancy in the event of fluid loss south of the reservoir. While the reservoir feeds both circuits IIRC there is a partition within the reservoir that allows one circuit to maintain fluid supply should the other circuit be depleted. This partition is quite high inside the reservoir and when this happened to me I had to raise the fluid level almost to the point of overflowing before the fluid started to fill the rear circuit again.

Note that the partition for the rear brake circuit is quite small as most of the braking is done by the front brakes.

Now, I've never used a power bleeder before so I could be way off, but I would think that the use of one would prevent you from running either circuit dry.

That said, if you are seeing air in the line from the power bleeder to the MC I would investigate that first.

A general comment about brake fluid:
I'm pretty sure everything up to and including DOT4 is synthetic these days. The odd one out is DOT5 - it is SILICONE based and was created to combat "regular" brake fluid's affinity for moisture. The problem is that silicone dissolves rubber. Aaaaand I'll give you one guess as to what most brake piston and wheel cylinder seals are still largely made of. Yep, rubber. So, WHILE DOT5 is great for racing applications because the brakes are generally rebuilt, or at least VERY thoroughly inspected, after each race; its use on a street vehicle is a choice I would classify as "less than advisable".

In other words:
DO NOT USE DOT5 BRAKE FLUID ON ANY VEHICLE YOU PLAN TO DRIVE WITHOUT REBUILDING THE BRAKES AFTER EACH USE.

One more thing: Speed bleeders are awesome! I highly recommend them.

NurpleXJ

That does make sense. I had success with brand new everything on my mustang doing it that way. Guess I got lucky.