1988 Toyota Pickup WEIRD brake problem

I have a 1988 toyota pickup 4 cylinder 4x4. I have had to replace the front
brakes 3 times and my rear brakes look brand new. I replaced the front pads
and calipers, new master cylinder, wheel cylinders, and proportioning
valve. I adjusted the brake booster pushrod to master cylinder correctly.
I adjusted the brake pedal correctly. I adjusted the rear brakes
correctly. I have bled the brakes all around more than enough and all the
air is out of the system. BUT, the pedal goes all the way to the floor but
the brakes apply about half way down and the brakes are VERY touchy. It's
either all or nothing. I have tried everything I know to do. I have
blocked off lines, reverse bled, and vacuum bled. Please help.

On Wed, 28 Sep 2005 19:36:43 -0500, slngblde <me@nothere.org> wrote:
[color=blue]
>Where are you getting your parts from? autozone or similar discount
>chain? I had similar problems recently with the hydraulic clutch
>system on my 85 truck,i went through 3 clutch master clyinders and two
>slave cylinders from oreillys.I finally gavee up and got my money back
>on their parts and went to napa and their parts worked perfectly the
>first time and were only abou t 20 dollars more than oreillys junk[/color]

On Wed, 28 Sep 2005 20:20:01 -0400, "Codymccui" <codymccui@aol.com>
wrote:
[color=blue]
>I have a 1988 toyota pickup 4 cylinder 4x4. I have had to replace the front
>brakes 3 times and my rear brakes look brand new. I replaced the front pads
>and calipers, new master cylinder, wheel cylinders, and proportioning
>valve. I adjusted the brake booster pushrod to master cylinder correctly.
>I adjusted the brake pedal correctly. I adjusted the rear brakes
>correctly. I have bled the brakes all around more than enough and all the
>air is out of the system. BUT, the pedal goes all the way to the floor but
>the brakes apply about half way down and the brakes are VERY touchy. It's
>either all or nothing. I have tried everything I know to do. I have
>blocked off lines, reverse bled, and vacuum bled. Please help.
>[/color]

Two things - 1) What happens if you blank off the vacuum line to the
brake booser? 2) Does your truck have a load proportioning valve above
the rear axle?

Touchy brakes can come from bad brake hoses that act like one way
valves, letting the fluid through but not back. That may account for
your worn front brakes.

Hope this helps.

Dentman


Training Solutions Group
Box 617,2577 Church St.
North Gower ON Canada
K0A 2T0
(613) 489-2759
[email]dw.tsg@sympatico.ca[/email]

"It's better to be in the race for a second than to spectate forever."

Codymccui wrote:[color=blue]
> I have a 1988 toyota pickup 4 cylinder 4x4. I have had to replace the
> front brakes 3 times and my rear brakes look brand new. I replaced
> the front pads and calipers, new master cylinder, wheel cylinders,
> and proportioning valve. I adjusted the brake booster pushrod to
> master cylinder correctly. I adjusted the brake pedal correctly. I
> adjusted the rear brakes correctly. I have bled the brakes all around
> more than enough and all the air is out of the system. BUT, the pedal
> goes all the way to the floor but the brakes apply about half way
> down and the brakes are VERY touchy. It's either all or nothing. I
> have tried everything I know to do. I have blocked off lines, reverse
> bled, and vacuum bled. Please help.[/color]

If you pump pedal with engine running, does the pedal get higher and brakes
firmer?
The first things I think of are, in this order:
1. Bad or contaminated (water in it) brake fluid.
2. Bad master cylinder.
3. Bad brake booster.

Flush/fill with new fluid and bleed system.
Verify brake action and if brakes are stopping rotation at front wheel and
rear wheel to check master cylinder function.
While sitting still with engine running can you hear a vacuum leak? Push the
brake pedal down and hold it. Can you hear a vacuum leak? If any vacuum
leaks, it's bad.
With engine off, pump pedal until firm. Hold pedal while starting engine, if
pedal drops more than appx 1/4" then booster is bad.
There are other booster checks but these are the two most common checks.
HTH, davidj92

My front calipers are from Auto zone which fixed my pulling to the left
problem. My pads are from auto zone also. My wheel cylinders are from napa
and my master cylinder is a new napa cylinder, not rebuilt. My brake shoes
are also napa. If I vise grip my rear line off going down to the rear end,
with the engine running the pedal does get alittle harder, but not much at
all. It does have a load sensing proportioning valve, I had checked and
rechecked it many times and it seems to be in working conditon. As for my
booster, if I crank the engine and let it run for a few, then cut it off
and pull the vacuum hose off of the booster a "woush" sound is made. If
that makes sense. It is sucking air so I know there are no leaks in the
booster. When I pump the pedal up with the engine off, hold the brakes and
crank it up the pedal goes all the way to the floor. Could this mean I
still have a bad booster. It is about the only thing I have not replaced.
All the brake fluid is new and is DOT 3. Thanks for your help.

Cody

Codymccui wrote:[color=blue]
> My front calipers are from Auto zone which fixed my pulling to the
> left problem. My pads are from auto zone also. My wheel cylinders are
> from napa and my master cylinder is a new napa cylinder, not rebuilt.
> My brake shoes are also napa. If I vise grip my rear line off going
> down to the rear end, with the engine running the pedal does get
> alittle harder, but not much at all. It does have a load sensing
> proportioning valve, I had checked and rechecked it many times and it
> seems to be in working conditon. As for my booster, if I crank the
> engine and let it run for a few, then cut it off and pull the vacuum
> hose off of the booster a "woush" sound is made. If that makes sense.
> It is sucking air so I know there are no leaks in the booster. When I
> pump the pedal up with the engine off, hold the brakes and crank it
> up the pedal goes all the way to the floor. Could this mean I still
> have a bad booster. It is about the only thing I have not replaced.
> All the brake fluid is new and is DOT 3. Thanks for your help.
>
> Cody[/color]

I personally don't like or use Autozone parts.
They have a high failure rate, even on new parts.
None of the retail shops I network with in this area will install Autozone
parts for you at any price (well, maybe at some price) :-)
NAPA is a good choice for parts if you don't use OEM.
You've eliminated the possiblility of bad fluid.
The whooshing you hear when you remove the vacuum line means the check valve
is working. It's function is to hold vacuum in the booster so if you have
engine failure while driving you should still be able to stop. You could
still have a bad booster even though it holds vacuum.
Since it seems you rear brakes aren't working correctly I would not replace
the booster at this point.
While you were bleeding brakes did you push pedal all the way to the floor?
You can damage a master cylinder by doing this and a new cylinder could be
bad. You may also have gotten air in the load proportioning valve and it's
preventing the rears from working correctly. Look for a way to bleed at the
valve, not sure how it's constructed so I can't advise on how.
I don't advise using vice grips or any other type of pliers on brake hoses,
it can damage the inner liner of the hose and cause problems.
You need to verify visually the brake components are working, both front and
rear, when you push pedal. On front is easy, on rear you can pull drum off
just enough to be able to see brake shoes work and verify they will stop the
rotation of drum. I suspect your problem is the rear not applying and
causing the fronts to take more work and wear faster than normal.
HTH, davidj92

I don't think my master cylinder is the problem because I have put 4 on it
and every one does the same thing. The proportional valve has a bleeder
screw on it and I have bled it thoroughly. When I take the drums off and
mash the pedal down, the rear brakes only go out a very little bit and
then you can push them back in with your hands. Thanks for your help.

Cody

Codymccui wrote:[color=blue]
> I don't think my master cylinder is the problem because I have put 4 on it
> and every one does the same thing. The proportional valve has a bleeder
> screw on it and I have bled it thoroughly. When I take the drums off and
> mash the pedal down, the rear brakes only go out a very little bit and
> then you can push them back in with your hands. Thanks for your help.
>
> Cody[/color]

Could it be something like a damaged brake hose not holding under
pressure. You know, acting like an aneurysm in a blood vessel...
--
Tom - Vista, CA