Endless brake bubbles

[Diesel Weasel]

I just replaced the front rotors/calipers (+ hard lines to the calipers)/pads on my BJ60. The calipers were sticking occasionally and the rotors had some damage to them, however, the brake "feel" was normal--the MC was fine, no leaks or damaged brake lines.

After I finished installing the new parts, I decided I would do a full bleed of the brake system with new fluid. So, I went to the LH rear wheel cylinder and proceeded to bleed using the FSM technique with an assistant. There were air bubbles, quite a few of them, but that was fine because I had disconnected the lines to the calipers, so I continuted bleeding. 1.5-2 hrs later on the SAME wheel cylinder, I still had @(#@($*#@ bubbles coming out.

I ran approximately 2.5 litres of fluid through the system over this time. I've bled brakes (not on this truck) and clutch cylinders before and have not ran into this. WTF is going on here? I'm feeling like a newb.

 

[WES1977]

How did you get an assistant to last that long? i'm not sure how the FSM technique is but i've done it with one of those pump bleeders and had it bubble for a non-stop. I did it the old fashion way and it worked perfect.


Can I ask how you performed it?

 

[lovetoski]

I just did a 4 runner front brake upgrade. Bled the calipers extensively...still was getting bubbles. Then pushed the brake pedal down while both bleed screws were tight to seat the pistons...voila, bubbles went away in just a few pumps.

In my case, I'm sure the deal was that there was air in the cyclinder (behind the piston) and this was the source of the bubbles. As soon as I filled the cyclinders with brake fluid, I was able to get all the air out.

In your case, I would do it in a two step process. Do the fronts first, to get all the air out. Then do the rears, then do the fronts again (just to be sure).

 

[Diesel Weasel]

How did you get an assistant to last that long?

She is well trained

Can I ask how you performed it?

I start with a clear hose attached to the bleeder. The hose goes into the jar with brake fluid. I use a 10mm flare-nut wrench to open and close the bleeder.

1. Bleeder closed
2. Assistant pumps 3 times and holds down
3. Open bleeder 1/4 to 1/2 turn -- fluid and bubbles come out
4. Close bleeder
5. Assistant releases and the process starts again.

In your case, I would do it in a two step process. Do the fronts first, to get all the air out. Then do the rears, then do the fronts again (just to be sure).

I forgot to mention that I did do the fronts after and was able to get them clear with no bubbles. I'm only getting bubbles in the rear.

 

[rover67]

master cylinder may be toast.. is it dripping from the rod under the dash?

 

[Diesel Weasel]

master cylinder may be toast.. is it dripping from the rod under the dash?

That was my thought too, so I disconnected the line from the MC to the rear and routed it into the reservior using an old hard line I had laying around. My assistant pumped the brakes many many times and the bubbles kept coming. I ordered a new MC and will put that in tomorrow--hopefully that is my problem. I'll report back.

 

[oldwineo]

You should always start with the farthest wheel first and work to the master cyl. I think on a 60 that is the drivers rear due to line routing.

It sounds like something is loose (fitting or line).

How do the brakes work? Try a skid test to see if the rears are doing any work and no pulling to one side.

Does the hose you are using fit tight on the bleeder screw? It could be the source of your air.

I have a cheap tool that works well for one person bleeding. Available at any auto parts store. Its a clear hose with a inline check valve. just drop it into a jar with a little fluid in it and pump the brakes 4 or 5 times. Refill the master and repeat.

Ken

 

[Diesel Weasel]

It sounds like something is loose (fitting or line).

How do the brakes work? Try a skid test to see if the rears are doing any work and no pulling to one side.

Does the hose you are using fit tight on the bleeder screw? It could be the source of your air.

The brakes are soft but consistant, I can stop quickly if I really push hard. When I push all the way down I can hear a slight noise like I'm hitting metal, like I've gone too far down.

A loose fitting is what I looked for too.. During my work I replaced 2 hard brake lines to the calipers--that's it. All of the bleeders are tight and not leaking.

The hose I have attached to the bleeder is one that I've used many times on various bleeding projects and it fits tight--I know this because when I pull the hose from the container it is sitting in to dump the excess fluid, the fluid in the hose does not drain out, meaning, the seal is tight and no air is getting back in.

Just today I tried teflon taping the bleeder threads to ensure that no air was getting past the threads, no change. I don't see how it would matter if air was getting past the threads in the bleeder though, as it's only open on the down stroke anyway.

I'm still hoping that the MC will fix it... Keep the suggestions coming

 

[Texx]

Did you bench bleed the master?

 

[Diesel Weasel]

Problem solved! The master was at fault. I took the old one off and right away I could see the fluid out the back of it. Put the new master in and bled the whole system in 15 minutes

Rock hard brakes!