1989 pickup/ brake problem/ need advice

recently bought my 1989 toyota pickup from the original owner. its been well loved. at 217,000 miles, the v6 still runs strong. sadly, the brakes started acting up. here's the symtoms. excessive pedal travel, to the floor. no fluid lost. no blown wheel cylinders. no leaking calipers. for starters, i bled the entire system twice, including the self proportioning valve and the master cylinder. after bleeding the brakes worked great. for about 10 minutes. then failed again. its as if air is entering the system from somewhere, but no fluid is leaking out. how is this possible? and more importantly, is there a way to pin point where air is entering the system from? i'd like to locate the culprit. help.

Reply to
torque
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Reply to
Handyman

Sounds like a bad master cylinder. When the seals inside get worn they allow the brake fluid to go around the edges of the seals and no pressure build up occurs. This also causes brake fluid to leak out the rear of the master cylinder were it attaches to the firewall or brake booster. If you can find no leaks in the system and the pedal goes to the floor I would replace the master cylinder first. Be sure to bench bleed the new master cylinder, if required, as it will save much time bleeding the brakes on the vehicle.

Reply to
Mike

Brake master cylinder. Either replace it or get the rebuild kit.

Reply to
Ernie Leimkuhler

I _think_ you are describing the symptom of a leaking Master Cylinder (mc).

Try this test ... Drive to the corner, or anywhere, and bring the truck to a normal stop. Holding your foot _normally_ to prevent creep during a normal traffic light stop, does your foot slowly fall to the floor? Can you bring the pedal pressure back up by pumping the pedal a couple of times, only to have the pedal fall again as you wait for the green light?

If the answer to these questions is yes, you have a leaking mc.

The master cylinder has chambers and an internal piston. What you are noticing is that the piston's seals are worn, and the piston (connected tot he pedal) is able to move past the fluid. The master cylinder can develop internal leaks, and these leaks will never be apparent from the outside -- there is no visible fluid leak that can be seen.

If you elect to replace the mc by yourself, you MUST perform a procedure called Bench Bleeding. If you want to know more about bench bleeding, just ask.

Reply to
Jeff Strickland

thanks.

torque

Handyman wrote:

Reply to
torque

thanks. can you elaborate on "bench bleed?"

Mike wrote:

Reply to
torque

thanks. can you elaborate on bench bleeding? also, do you know a "reputable" toyota online parts dealer? i want to replace the gasket between the booster and the mc. hopefully, without having to buy a new booster.

Jeff Strickland wrote:

Reply to
torque

Bench Bleeding is a procedure that forces brake fluid into all of the cavities within the MC before the MC is mounted on the vehicle.

No, I do not know a Toyota Parts source online. I do not think that this project demands Toyota parts, all you need is a quality name brand.

When you buy the new MC, you also need to pick up a kit containing a hose or two, and some fittings. You screw the fittings into the side of the MC where the brake pipes normally connect. Connect the hose to the fittings, and route the hoses back into the reservior. Fill the reservior with brake fluid, and activate the piston with a suitable tool that will push the piston the full length of its travel. Air bubbles will come out of the hoses, then fluid will be sucked back through the hose to fill the cavaties. Repeat several times to be sure the air bubbles stop forming. Leave the hoses and fittings connected and the reserviors filled, and mount the new MC to the firewall where the old MC was mounted. Remove one of the hoses and its fitting, and attach the brake pipe to the MC. Repeat for the other hose and plastic fitting. The caveat is that you must connect the brake pipes before the reservior drains. As a practical matter, you could probably do lunch before the reservior drains.

Brake pressure demands that there be no air anywhere in the system. Once the system is filled and installed, any air that might remain is next to impossible to get out because the brake pedal does not move the MC piston for its full length of travel. You can get the full length of travel on your bench, hence the term, bench bleed. There is a school of thought that says if the brake fluid reservior is ever drained, the MC should be removed and bench bled.

Reply to
Jeff Strickland

Just like it sounds - although I would do the 'bench bleed' after the Master is mounted on the car to avoid spills and messes.

You take two short lengths of brake tubing with the metal fittings that fit the output fittings of the MC, and bend them so they loop from the output ports back into the filler cap hole of the fluid reservoir. Then you pump the pedal till you get all clean fluid flowing up and back into the reservoir.

(To tell you how long it's been since I did this last, I only needed one line - my International Scout didn't have split brakes...)

After the master is internally bled, you quickly remove the bleeder loop line and pop in the vehicle line and tighten it down. You still have to do a final bleed of the vehicle lines, but it won't take nearly as long.

It will drip brake fluid - Place rags to catch all the drips, and then dispose of the rags. Put any fluid soaked tools in a strategically placed pan or bucket so the brake fluid doesn't get tracked or spilled anywhere. Clean the tools before they go back in the toolbox.

WARNING: CAUTION: "Danger, Will Robinson! Danger!": Read This!:

DOT-3 brake fluid is a really good automotive paint remover, and the exterior or underhood paint with brake fluid spilled on it will bubble and soften over a period of a few hours and then fall off leaving bare metal. You MUST be VERY careful to keep brake fluid off all painted surfaces, and MUST clean up IMMEDIATELY with an appropriate brake solvent if it gets spilled or splashed.

And furthermore, if you ruin the paint on her car the wife will kill you very dead. This isn't a guess, this is a fact.

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Reply to
Bruce L. Bergman

Reply to
torque

once again, thanks.

Jeff Strickland wrote:

Reply to
torque

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