Major brake failure - Page 2 - Toyota 4Runner Forum

the_welfare_wagon · 06-07-2022, 10:25 PM

Quote:

Originally Posted by PlutosT4r

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 · 06-07-2022, 11:09 PM

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 · 06-07-2022, 11:10 PM

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 · 06-07-2022, 11:23 PM

Quote:

Originally Posted by 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.

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 · 06-07-2022, 11:25 PM

Quote:

Originally Posted by 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?

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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pluton · 06-08-2022, 12:13 AM

Can the metal brake lines rust out, develop holes? (I see NY in your sig)
BTW, check those rubber brake hoses. 25 years---if true---is way too old to be in use on the car. They'll be stiff and with a cracked surface if they are that old.

the_welfare_wagon · 06-08-2022, 12:43 AM

Quote:

Originally Posted by pluton

Can the metal brake lines rust out, develop holes? (I see NY in your sig)
BTW, check those rubber brake hoses. 25 years---if true---is way too old to be in use on the car. They'll be stiff and with a cracked surface if they are that old.

Yeah I agree they are well overdue for a change. The entire rig is pretty much covered in some sort of factory rust prevention so I doubt a line has a hole. No fluid has been lost either from what I’ve seen

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3bears · 06-08-2022, 12:45 AM

yes please keep us posted on what you find so we can all learn. I would def replace all the rubber hoses. I have seen when one looked good , it swelled to the inside and that wheel did not want to bleed correctly. I dont think that is your problem right now....but should be on your future to do list....I just replaced mine with stainless.( when doing a brake refresh)...as hey....they were 22 years old

toverturf · 06-08-2022, 06:24 AM

I'm going to take a guess and says it's your ABS pump. I had the same issue where you pretty much had to have the pedal to the floor for the brakes to work. Replaced master cylinder, got steel brake lines, bled it a million times, replaced pretty much all the rear brake hardware, and still nothing. Went to the junkyard and got a ABS pump and issue fixed. Had no ABS codes or anything but something was clearly wrong with it.

Jakeepoo3 · 06-08-2022, 07:57 AM

Quote:

Originally Posted by 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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Everything sounds in good order. To me the problem may be a simple adjustment. You mentioned the booster push rod moved instantly. That's good but the you need to check for the proper gap between push rod and master cylinder, especially after changing parts. Your soft brakes would mean the rod needs adjusted out. I had the the opposite symptom of dragging brakes, push rod too far out on my Cherokee. Tiny adjustments make big changes so make note of the rods original position and pay close attention to how much you're adjusting. I started by adjusting in small increments until it was dialed in then verified proper gap.

jgue467 · 06-08-2022, 08:31 AM

Quote:

Originally Posted by the_welfare_wagon

So going down the mountain pass my friend behind me said he smelled my brakes. ...

ya' gotta gear down for engine braking while going down a significant hill or multiple ones, no other way. Even my big boy Tundra will overheat the brakes going down I-70 in either direction west of Denver (Eisenhower/Johnson Tunnel area).

This way you use your brakes less and all is good. BTW, my runner has all original brakes here at 340K and it does I-70 with engine braking like a duck takes to water. Luck.

brillo_76 · 06-08-2022, 10:47 AM

Looking like several possibilities:

1] bad or misadjusted master cylinder.

2] abs pump messed up

3] The original rubber flex lines failing causing a check valve like situation

4] wheel cylinder or caliper pistons seizing [ unlikely]

5] bell cranks seized causing rear brake issues

It's definitely a puzzle that's for sure.

Out of curiosity, which tundra calipers did you use? The 199mm or the 231mm?

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the_welfare_wagon · 06-08-2022, 10:55 AM

Quote:

Originally Posted by jgue467

ya' gotta gear down for engine braking while going down a significant hill or multiple ones, no other way. Even my big boy Tundra will overheat the brakes going down I-70 in either direction west of Denver (Eisenhower/Johnson Tunnel area).

This way you use your brakes less and all is good. BTW, my runner has all original brakes here at 340K and it does I-70 with engine braking like a duck takes to water. Luck.

I was in 2nd gear going down the hill. With a lot of probably pissed off local drivers behind me haha

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the_welfare_wagon · 06-08-2022, 10:58 AM

So I haven’t dived too deep yet however this is what I’ve done so far until my friend arrives to help me out:

Pulled ABS fuse- no change
Re bled all 4 again- MAYBE some air in the right rear but I think I cracked the bleeder too much. Other 3 had none whatsoever
Had both rears up in the air to they could freely spin. Wouldn’t stop spinning till pedal was on the floor. The fronts however stopped the second the pedal was applied despite all the travel.

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Skulking · 06-08-2022, 01:26 PM

Quote:

Originally Posted by the_welfare_wagon

So I haven’t dived too deep yet however this is what I’ve done so far until my friend arrives to help me out:

Pulled ABS fuse- no change
Re bled all 4 again- MAYBE some air in the right rear but I think I cracked the bleeder too much. Other 3 had none whatsoever
Had both rears up in the air to they could freely spin. Wouldn’t stop spinning till pedal was on the floor. The fronts however stopped the second the pedal was applied despite all the travel.

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With the rear in the air, what happens if you spin the wheels and then pull the parking brake? If you have the same behavior with the parking brake I'd check shoe adjustment. If the parking brake stops the rears, then there is a problem with getting pressure to the rear brakes.

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