Car: 1978 Datsun 280z

Problem: When the brakes are slightly applied, they do not engage. After continual pushing it finally catches and nearly locks up the brakes. (Catches about half way from the floor from the original brake pedal position.)

After telling my shop teacher my problem, he immediately said it was the proportioning valve that needed to be replaced; and never told me why even after I asked him. Why would this be the proportioning valves problem? It feels as if it's the front brakes that are doing this because after the brakes actually engage, the front of the car violently dips. I have inspected and cleaned the rear drum assembly and all seems to be well in it's place. When it comes to the front left caliper assembly, I took a look at the drum and it seems as the right side of the drum was in brand new condition. I'm guessing the piston isn't functioning. I doubt that would be the reason to my problem though.

Other than removing and spraying lots of brake cleaner all of the brake assemblies, I haven't flushed the brakes or done any other work to it. Can anyone diagnose my problem? :stupid:

Jayson

Either the brake system needs to be bled, or I'd check the reaction disk. There could be other causes, but those are probably the most likely.

I had similar simptoms on my 76. After removing the master brake cylinder and the brake booster, I found half a quart of brake fluid in the booster. The master cylinder leaked, damaging internal booster seals. I had to apply the brake pedal to the floor before they got enganged. The calipers in the front had brand new pads, the disc rotors were evenly worn (the PO replaced them before I bought the car). I would have never guessed what caused it. There were no visible leaks. So in my case it was a combination of the leaking master cylinder and a damaged booster.

I am at the stage of replacing some brake lines, front calipers, rear cylinders and drums.

Good luck with your project.

Thanks for your replies. Helped a ton. Tomorrow I will remove the master vac and hopefully will find my problem. I'll let you know how it goes.

Jayson