Totally Baffled: loss brakes on 1987 pickup

[thebigdog]

Totally Baffled: loss brakes on 1987 pickup

The truck is a 4X4 pickup with a 22RE engine, and an automatic transmission.
A few weeks ago I noticed very infrequently that my brake pedal kept slowly sinking.

This only happened sometimes, while I was waiting for the traffic light to change.
The brakes always stopped perfectly and this symptom soon disappeared.
Today after a month past by, it happened again and I totally loss all brakes.
If a pumped the pedal 5 – 7 times, it briefly gets pressure again but disappears again almost immediately.
Luckily I was near the house, and inched my way back home with massive brake pedal pumping.

It seemed a little like there is air in the lines, but I’ve never seen anything this bad in any other vehicle.
I can find no brake leaks at all and the brake fluid level is full to the top.
This past Spring I had preformed a full brake system overhaul, which included the following:

Every entire steel brake lines, all rubber brake hoses, master cylinder, brake proportioning valve,
Rotors, calipers, drums and shoes (only thing left original was the vacuum booster.

I am totally stumped – re-bleeding the master cylinder and all the wheels has no improvement.
The front brakes are just as bad as the back brakes (basically NOTHING).
The parking brake will still engage, but nothing at all from the hydraulics…

Has this ever happened to anyone at this forum?
Can anybody suggest any kind of help?

Help Please…

 

[KLF]

My first suspect is the master cylinder. Where did you get the "new" one? (Please don't say AutoZone or O'Reilly's)

 

[Jukelemon]

Totally Baffled: loss brakes on 1987 pickup

The truck is a 4X4 pickup with a 22RE engine, and an automatic transmission.
A few weeks ago I noticed very infrequently that my brake pedal kept slowly sinking.

This only happened sometimes, while I was waiting for the traffic light to change.
The brakes always stopped perfectly and this symptom soon disappeared.
Today after a month past by, it happened again and I totally loss all brakes.
If a pumped the pedal 5 – 7 times, it briefly gets pressure again but disappears again almost immediately.
Luckily I was near the house, and inched my way back home with massive brake pedal pumping.

It seemed a little like there is air in the lines, but I’ve never seen anything this bad in any other vehicle.
I can find no brake leaks at all and the brake fluid level is full to the top.
This past Spring I had preformed a full brake system overhaul, which included the following:

Every entire steel brake lines, all rubber brake hoses, master cylinder, brake proportioning valve,
Rotors, calipers, drums and shoes (only thing left original was the vacuum booster.

I am totally stumped – re-bleeding the master cylinder and all the wheels has no improvement.
The front brakes are just as bad as the back brakes (basically NOTHING).
The parking brake will still engage, but nothing at all from the hydraulics…

Has this ever happened to anyone at this forum?
Can anybody suggest any kind of help?

Help Please…

OK, first things first.

Did the brakes ever work right? If so, then you have a failure somewhere so the fact that everything is new is moot.

Is the MC a Toyota MC?

Did you run over anything?

What you describe is usually a very clear example of 1- air in the lines or 2-failed MC.

 

[kore]

sounds like a typical screwed MC. undo the bolts that hold it to the booster and look behind it, if its all wet back there the MC is screwed. rebuilt mcs are known to be trouble.

 

[thebigdog]

Guys, thank you very much for the help.
Everybody so far seems to think it's the master cylinder.
Yes - I unfortunatlly did buy it at AutoZone...

I can alway's get the next one at CarQuest, and give it a try.
Does anyone suggest any special brands on the MC?
I would hate to finally fix this, and have the same crap happen again.

QUESTION: Is there anyway for a backyard mechanic like myself to check and verify that this master cylinder is indeed bad?

Like trying to block the holes where the brake lines connect to it, shouldn't this give me some soret of pressure at the brake pedal?

I'm assuming no pressure and the MC being 100% bad.
Having pressure would eliminate the MC as being the guilty party?

 

[thebigdog]

1) I assume no - it's from autozone.
2). Aside of what I mention above - The brakes work working perfectly.

3). No dodn't run over anything - this is 100% street truck.

As for air in the system:
I would assume if air got inside, some fluid had to had leaked out.
Everything is perfectly bone dry.

Thanks for the help, the hunt continues...

OK, first things first.

Did the brakes ever work right? If so, then you have a failure somewhere so the fact that everything is new is moot.

Is the MC a Toyota MC?

Did you run over anything?

What you describe is usually a very clear example of 1- air in the lines or 2-failed MC.

 

[KLF]

Like many other people, I had to learn my lesson the hard way on AutoZone parts. Sounds great that they are "guaranteed for life", doesn't it? It's a good thing they are, because it'll take you that long to find one that works for any length of time. I went thru 3 master cylinders from them in less than a year, I finally gave up and bought a Toyota one.

The best brand to get is genuine OEM Toyota. Yes, it will cost more. But how much fun it is swapping them out?

What usually fails on master cylinders is the cups on the piston inside. Toyota also sells a rebuild kit with new cups and a bunch of other parts, you could get a brake hone and do that, see if it fixes it. The Factory Service Manual has a detail procedure on how to rebuild them.

 

[Jukelemon]

1) I assume no - it's from autozone.
2). Aside of what I mention above - The brakes work working perfectly.

3). No dodn't run over anything - this is 100% street truck.

As for air in the system:
I would assume if air got inside, some fluid had to had leaked out.
Everything is perfectly bone dry.

Thanks for the help, the hunt continues...

It could be leaking in places you do not see/have not seen yet. But yes, you are correct: in a closed system, there must be a leak in order to introduce air.

Generally speaking, a MC is NOT something you want to buy at any other place except Toyota. I have my original and it has lasted 180k+ miles just to give you a perspective.