Major brake failure

[the_welfare_wagon]

So I’m posting this because I have no idea what to do next. I’m not brake expert and need opinions.

Went down to OBX this weekend and had pretty decent brakes on the way down. (I have the TBU) I had also just adjusted the rear shoes. However on the way down I hit some pretty hard bumps and I noticed my brake pedal started sinking to the floor. It still grabbed but didn’t catch till it was just about on the floor. I figured maybe it was some air that the bump had moved around so I went into ABS to see if that would move it around. The brakes instantly felt way better and were back to mostly normal. They stayed good for the 3 days I was down in OBX then on the way home in WV they went to floor again and kept getting worse. Nothing I did fixed it including ABS. I finally had to stop before someone got hurt and checked the rear brakes. The rear wheel cylinder maybe moved the shoe 1/8th of an inch. The shoes were well adjusted so that is not an issue. I had it towed to an autozone where I swapped the master and bled all 4 brakes twice. The pedal was much better however it only lasted for maybe 15 miles and the same issue started to come back. Any ideas what to do next?

The pedal pretty much sinks all the way to the floor and only has any braking effect at the last inch or so of travel and even then it’s barely enough to stop the car

Things I’ve done:
Changed master(Duralast gold new)
Check brake booster pin(moves instantly)
Master was properly bled
Brake fluid is all new at this point
NO loss of brake fluid at all
Getting a decent amount of fluid at each wheel during the bleed


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[brillo_76]

Does the pedal like stop then creeps to the floor. Or just goto the floor to stop the rig.

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[3bears]

brake booster check valve or hose going to it ? Ive only had the check valve malfunction in the opposite...meaning ridiculous hard pedal to push...but maybe it and or the hose can also do what your finding....I dont know...just guessing
how old are your rubber brake hoses....again...just thinking

 

[the_welfare_wagon]

Does the pedal like stop then creeps to the floor. Or just goto the floor to stop the rig.

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There is slight resistance as it goes down to where it grabs. But once it hits where it grabs it really doesn’t go any lower


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[3bears]

sounds like a pressure related issue... you replaced master already...and your not loosing fluid anyplace ?

 

[the_welfare_wagon]

brake booster check valve or hose going to it ? Ive only had the check valve malfunction in the opposite...meaning ridiculous hard pedal to push...but maybe it and or the hose can also do what your finding....I dont know...just guessing
how old are your rubber brake hoses....again...just thinking

See I thought that as well but immediately after I replaced the master the brakes were pretty much fine for about 15 miles. So that tells me it is working. The brake lines are probably factory so 25 years old? I don’t think they are the issue cause like I said once I replaced the master the brakes were great for ~15 miles or so


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[the_welfare_wagon]

sounds like a pressure related issue... you replaced master already...and your not loosing fluid anyplace ?

None whatsoever that I’ve seen. I’m going to trace all the lines tomorrow to rule that that out after driving 500 miles home I’ve noticed no difference in the level of fluid


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[brillo_76]

There is slight resistance as it goes down to where it grabs. But once it hits where it grabs it really doesn’t go any lower


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As that's how you rule out a master cylinder. Mostly they will hold you still and a stop light as your pedal creeps to the floor while waiting slowly.

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[brillo_76]

Being it's a 1996. What happens when you pull the abs fuse? Does anything change or everything the same?

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[the_welfare_wagon]

Being it's a 1996. What happens when you pull the abs fuse? Does anything change or everything the same?

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I’m gonna pull it tomorrow and let you guys know what happens. I do know that when I go as hard as I can on what’s left of brakes it will NOT ABS. My tires will lock up first. I should also note that the ABS pump does work on stuff like sand but on dry pavement it will not ABS


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[PlutosT4r]

Does it seem like you have any rear brakes? Are your front brakes getting extremely hot?

I recently fixed a brake issue with mine, but the way you describe it, yours sounds way more dramatic and odd (where it "grabs" all of a sudden). Doesn't sound like brake fatigue due to no rear brakes. That is a more gradual effect as the rotor gets molten hot.

 

[the_welfare_wagon]

Does it seem like you have any rear brakes? Are your front brakes getting extremely hot?

I recently fixed a brake issue with mine, but the way you describe it, yours sounds way more dramatic and odd (where it "grabs" all of a sudden). Doesn't sound like brake fatigue due to no rear brakes. That is a more gradual effect as the rotor gets molten hot.

So going down the mountain pass my friend behind me said he smelled my brakes. I couldn’t get the right side drum off as the shoes were too tight on it. However the drum wasn’t hot and I checked it about 10 mins after I stopped the car. From what I saw the back brakes aren’t doing anything. When I pushed the pedal to the floor the wheel cylinder moved the shoe maybe 1/8th of an inch if even that much


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[PlutosT4r]

Brakes get hot, so it's hard to say what is normal. Once you reach a certain temp, I'm told the fluid "boils" and there's just too much heat for the pads to be effective. You will feel the heat and smell it from inside the car. Tire pressure might be up 15+ psi. When I didn't have rear brakes, my wheels would lock up without abs kicking in, just like yours. Again, yours sounds a little more fishy though. Hope you find a solution, I'll be following.

 

[brillo_76]

This could also be the flex lines. The 2 front and the one rear. These rubber lines can fail and act like check valves instead of letting the fluid flow like they should.

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[PlutosT4r]

... From what I saw the back brakes aren’t doing anything ...

Sorry, I missed this part. You may in fact be having the same issue I had. I'm just a YouTube connosuer
(sp?) So can't be certain. Check the function of both your parking brake and bell cranks. Easy to tell if one crank is frozen. A frozen bell crank could, eventually, cause issues on the opposite end, too. Don't ask me how, but it can. It can also limit the piston's effectiveness on the frozen end. Typing from my cell phone.

 

[the_welfare_wagon]

Sorry, I missed this part. You may in fact be having the same issue I had. I'm just a YouTube connosuer
(sp?) So can't be certain. Check the function of both your parking brake and bell cranks. Easy to tell if one crank is frozen. A frozen bell crank could, eventually, cause issues on the opposite end, too. Don't ask me how, but it can. It can also limit the piston's effectiveness on the frozen end. Typing from my cell phone.

I’m sure my back brakes are shit but what doesn’t make sense to me is why everything was working fine up until it failed. Then replacing the master it all worked fine again for a short time. However I’m gonna play a little devils advocate here and ask a question that’s been on my mind the whole time. I have the TBU and so does my friend who was with me. His brakes damn near can put us through the windshield. Shouldn’t the front brakes alone be enough to stop the car? Especially being the TBU? It seems to me that whatever is happening is affecting all 4 brakes


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[Bad Luck]

Quite the puzzle you have. My first thought was master cylinder internal leak but you replaced the master. A bad booster/check valve/vacuum hose will cause a stiff pedal. A leaking brake line/hose will cause a soft pedal, but obviously a visible leak as well. A failing/failed brake hose could cause a soft or hard pedal depending on how it fails. I’m not sure how a bad abs pump would cause a soft pedal, but I can’t rule it out completely either.

The rear wheel cylinders don’t actually move much in order to apply the shoes to drums. Technically the pistons don’t move much when you apply the brake pedal either. The master cylinder only moves a couple tablespoons worth of brake fluid in a full stroke/application when working properly.

You said you adjusted your rear brakes if I remember correctly. Did you adjust the shoes to where the drum is slightly dragging on the shoes when the brakes aren’t engaged? Do the bell cranks operate correctly and move freely?

EDIT: I wonder if your problem is in the modulator portion of the ABS pump. The modulator acts similar to a proportioning valve and distribution block for brake fluid.

 

[PlutosT4r]

The front brakes are plenty to stop the car, I drove with little to no rear brakes for hundreds, maybe a thousand miles. Reading your OP again, it's odd it happened after hitting a bump. Many others have offered their suggestions here, you can check on all that, starting with the easiest and cheapest.

What/where is OBX?

 

[the_welfare_wagon]

Quite the puzzle you have. My first thought was master cylinder internal leak but you replaced the master. A bad booster/check valve/vacuum hose will cause a stiff pedal. A leaking brake line/hose will cause a soft pedal, but obviously a visible leak as well. A failing/failed brake hose could cause a soft or hard pedal depending on how it fails. I’m not sure how a bad abs pump would cause a soft pedal, but I can’t rule it out completely either.

The rear wheel cylinders don’t actually move much in order to apply the shoes to drums. Technically the pistons don’t move much when you apply the brake pedal either. The master cylinder only moves a couple tablespoons worth of brake fluid in a full stroke/application when working properly.

You said you adjusted your rear brakes if I remember correctly. Did you adjust the shoes to where the drum is slightly dragging on the shoes when the brakes aren’t engaged? Do the bell cranks operate correctly and move freely?

EDIT: I wonder if your problem is in the modulator portion of the ABS pump. The modulator acts similar to a proportioning valve and distribution block for brake fluid.

I adjusted the rears to the point I almost couldn’t get them on. When I checked them at the point I stopped driving the one side was probably about 1mm off from the surface of the drum. The other side wouldnt come off without tools and unfortunately I had none to check. When I adjusted the rear brakes I discovered the adjusters were almost seized but I could still move them with a little effort from a flathead screwdriver but the arm in the drum definitely couldn’t adjust them automatically. New hardware didn’t come in time for the trip and the brakes were grabbing great when I left so I was comfortable leaving for the trip despite that. I have read that someone swapped the ABS pump with a junkyard one and it instantly fixed brake pedal travel so I’ll have to look further into that. But the whole not losing fluid is really throwing me off


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[the_welfare_wagon]

The front brakes are plenty to stop the car, I drove with little to no rear brakes for hundreds, maybe a thousand miles. Reading your OP again, it's odd it happened after hitting a bump. Many others have offered their suggestions here, you can check on all that, starting with the easiest and cheapest.

What/where is OBX?

Seems to me like pressure isn’t reaching any of the brakes but they all bled very nicely and we’re getting decent amount of fluid so idk what gives. OBX is North Carolina’s outer banks; Cape Hatteras/Ocracoke area

But yeah your totally right, start small and work your way up to find the problem


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