1988 Toyota Pickup WEIRD brake problem

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 snipped-for-privacy@sympatico.ca

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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:

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

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