brveagle

My vehicle: 1999 4Runner SR5 4x4 w/ ABS.

Well I had a leaky rear axle seal that I had a local shop replace. Once i got my 4 runner i went ahead and ordered new drums/shoes for the rear as some leaking fluid had got on them.

While i was in the rear brakes I also replaced both wheel cylinders. However during this, I believe i let the master cylinder run dry. No biggie right? Just bleed everything out.

Long story short, I've got through two large containers of fluid and my brake pedal still sinks to the floor. If i pump the brakes 2-3 times i get a nicer feeling pedal, and the truck will stop.

I've bleed the master cylinder, used a minivac bleeder, gravity bleed, pump and bleed method, and tried every trick in the book. I've bleed them with the truck running, with it off, and with the key in the ON position. Still no luck. The rear shoes are adjusted correctly and the front brakes only have maybe 300 miles on them. No leaks anywhere (i have been checking).

What are my other options? I'm at the point now that I think i may have blown the master cylinder.... Anything else I can check before i start replacing parts?

Thanks in advance.

J2F42C

Usually when one has the master cylinder run dry, the only remedy I have seen work is to remove the MC and bench bleed it with a full amount of brake fluid in the reservoir, then reinstall it. Works maybe 50% of the time in removing trapped air. But if you seals dried out, a new MC is probably in order.

When you bleed each cylinder, do you get bubbles in the fluid at each one or just the rears?

brveagle

The master cylinder wasn't left empty very long. Maybe a hour? It was when i was replacing the wheel cylinders, i lost a fair amount of fluid and didn't think to check the m/c.

I am not getting any air while bleeding from any caliper/wheel cylinder. Fluid is coming out nice and clean (obviously) with no air bubbles.

This isn't my first rodeo, just the first time the bull has thrown me for a ride. LOL

BajaRunner

So did you bench bleed it or not?! I'd probably get a power bleeder and set it up. Sometimes that is the only way to get all the air out. :/

You would know as good as anyone, a brake system is simple as it can get. Something is obviously wrong, and I doubt anything broke. I bet you just have air trapped in your system that is causing the problem.

brveagle

I have not bench bleed it, I guess i could give that a go before ordering a new m/c.

I should have mentioned, i did use a snap on power bleeder. It moves alot of fluid fast, but still didn't improve anything.

Nelsonmd

I had the same thing happen to me when I last pulled my brake lines off. the way I managed to fix it was to put some speed bleeders in and pump really hard and fast for a bit. That seemed to flush the bubbles out before they could rise back to where ever they were sitting. After that, the pedal tightened up very nicely. I wasted a ton of fluid though.

brveagle

Just a followup, installed a reman master cylinder, and all my problems went away. Now granted it could have been air in the old master cylinder, but after running 2 giant bottles of fluid through it, I doubt it.

blake.nemitz

i would double check your shoes in the back, and set them the right way with the parking brake. it sounds like they are not adjusted rights since you said you have to pump a few times to grab. i would start there before you go ripping apart the master again