Brakes worked fine for months then suddenly spongy. Only fronts work? No leaks. Help!

[DeadlySteve]

Hello all!

I have a 1994 limited.

A couple months ago I had my front and rear brakes changed out in the middle of a 1000 mile trip. Everything worked fine there and on the way back. No problems.

A week ago my pedal started going almost to the floor (as if I were bleeding the brakes). When I hit the pedal, the car slows down a little, but it isn't until it gets almost completely to the floor that it really catches.

I expected to open my hood and have the brake reservoir completely empty from something exploding. That wasn't the case at all. My brakes have always leaked a little (We're talking having to top it up once or twice a year-ish)... but now the brake reservoir isn't at the usual fill line; its over-full without me filling it.

What's odd is that if I have to stomp on the brakes, the truck will stop but the front tires will actually lock up trying to stop the explorer as if the rears aren't working at all.

I did notice that one of my vacuum lines on the vacuum tree had been unplugged a few days prior to having this issue. It wasn't going to anything regarding the brakes, but could this be involved?

The weather is FINALLY gonna be higher than zero degrees, so I'm getting ready to look at it this week. Any suggestions on what I should be lighting on fire... er.. I mean fixing?

Thanks for the help guys!

 

[FR-425]

Your master cylinder is gone ca-puts.

It's bypassing the rears.

 

[DeadlySteve]

Thank you for the FAST reply FR! Besides bleeding the master cylinder before installing it, is there any tips you'd have for someone who hasn't replaced one specifically before?

 

[FR-425]

Na, it's really straight forward,

er, uhm, Oh; Use a "line" wrench, don't want to be rounding off those flare nuts. (they are metric BTW)

Other than that it's like 30 min. job.

 

[FR-425]

Oh and buy one with a new reservoir; put'n the old one on a new master just never made sense to me.

 

[DeadlySteve]

Thanks for the update. For whatever reason, do you think it could also be a brake booster problem?

 

[cgbier]

Nope, not the booster. If that was the case you just needed more force, but the pedal wouldn't fall through.

 

[cgbier]

Be careful though. If you don't see any seepage in the outside of you break cylinder, the break fluid might leak into the booster. That fluid is highly corrosive and might also lovemake up the booster's membrane.

 

[DeadlySteve]

Well, I just finished swapping out the new master cylinder.

The old one was not leaking in the back. I haven't bled the brakes yet (I did bench bleed the MS first), however I drove it down the street and its EXACTLY how it was with the old master cylinder. I know there will be a bit of air in the system but the pedal is still going almost completely to the floor before it engages.

Is there anything else that could be causing this, or do you really expect it to be that much of an amazing difference after I bleed the brakes?

Btw, in case anyone finds this in the future; the line wrench you need is 13mm metric. You'll also need a 13mm metric to undo the first nut holding the brake line support bracket. Then you'll need a 14mm metric to undo the two nuts holding the master cylinder to the brake booster.

Thanks for the help guys!

 

[kbsmith_48]

I know this is going to sound crazy, but check the self adjusters for your rear brakes. I had one fall out of place when driving. Was a loud pop then straight to the floor. Had master cylinder replaced and bleed brakes multiple times. Still no help. Then took to a mechanic and he found that the adjuster was just laying inside the drum. Brakes work pretty good now.

 

[DeadlySteve]

Update!

Today I bled the brakes and oh my god! The brake fluid that came out was completely BLACK and it would take 7-10 full pedal presses at each wheel to get anything but air to come out. I pumped a good 36 oz. of brake fluid through the system.

Probably close to a year ago I was supposed to have had my brake lines flushed at a mechanic... something tells me I got ripped off big time.

But anyway, after bleeding the brakes, I have solid brakes again! Yay! However, I'm gonna still take a look at the rear brakes because I don't think they're adjusted very well. It still doesn't feel like its stopping quite enough toward the rear.

Thank you SO much for the help guys! ^_^

 

[FR-425]

Cool.

All the black junk was from the failed master. (eroded rubber plungers)

The 4 wheel ABS system on the 94's hold a truck load of fluid.

 

[BKennedy]

There is a specific bleeding process for the ABS controller on the 1994 Explorer. You need a special bleeder. If you start experiencing a soft pedal after repeated use, you need to get it bled at a shop because there is air trapped in the controller/pump. I changed out the master on my 94 several years ago. It all seemed fine until I was on a difficult 4x4 trail on a hot day at high altitude. My brakes faded out. Took it to a shop that had the bleeder and all was fine.

 

[DeadlySteve]

I read in another couple of threads that if you think you have air in your ABS, you can lock up your tires and engage the ABS a few times on a gravel road. That'll get the air out of the ABS unit and into your lines. Then you can just re-bleed your lines. People seemed to think that did indeed work after trying it.

 

[FR-425]

Yes, that will work.

I have a trick I use, to "simulate" the gravel road method.

I have a spare rotor with some of the ABS signal vanes broken off.

I put that on and drive along slowly with light pressure on the brake pedal; the dead spot activates the ABS pump every revolution. Makes quite a noise, Thump, thump, thump

Knocks the air out in about 100 ft. of that. Then put the good rotor back on, and bleed the normal way to chase the air out of the rest of the brake lines.