Brakes don't "work"

[dvorak]

Hi everyone, I've just taken ownership of a '73 240Z and have started restoring it. I've run into one problem so far though. I can't get the brakes to fully work. I've changed out the rear wheel cylinders due to the old ones being leaky, and some new hard lines in to them. I pulled the MC and thoroughly cleaned it. I haven't done a full proper bench bleed, but I have used a vacuum bleeder on the the MC trying to get most of the air out. also used the vacuum bleeder on wheel bleeders and got the air out of the lines. However i'm still not getting any braking force. With the engine off the pedal is hard to push. when i start it the pedal goes to the floor with almost no resistance. I have to then pump the pedal to get any braking force.

[siteunseen]

When I bought my '72 the previous owner had to replace the brake booster before he could sell it, same problems you're having, no pedal according to him. He said it wasn't a big job?

[SteveJ]

Search here for "reaction disk". You'll find a lot of good information.

[cbuczesk]

What SteveJ said...

Chuck

[Captain_Zeros]

Have you gone through the front brakes too? If the MC and rear cylinders were shot I can about guarantee the fronts were too. Also make sure all the rubber lines are replaced too.

If you pulled the MC apart a bench bleed is recommended, and in fact most people recommend not trying to service it at all because if they have any pitting on the bore they tend to go bad rather quickly anyways (and new ones are readily available for very reasonable prices).

[jcb]

Had same problems. Above suggestions plus make sure the rear shoes are adjusted correctly. Very important!!! I also had reaction disk problems that had to be corrected before I was satisfied with the amount of brake pedal I had.

[John Coffey]

If you have to pump the pedal to build brake pressure you have air in the hydraulic system. Do a proper MC bleed and then properly bleed the rest of the brake system.

[240260280z]

make sure the calipers are on the correct side. Their bleeders should be on the top.

[madkaw]

Like John said and that you admitted of not doing the proper bleeding of the MC. You will be chasing your tail if you don't eliminate that first. There could be many possibilities but always suspect air. If you have been bleeding the brakes by yourself with a vacuum, then get someone to help you do it the old fashoned way-pump,pump,bleed!!

[dvorak]

Sorry for taking so long, with work I really don't get much time to work on the Z, but here's some updates.

I replaced the MC with a new one that came with the car. I properly bench bled it.

Properly bled each brake line with someone pressing the pedal. I would have them hold the pedal down, open the bleeder, close the bleeder, let off the pedal, repeat.

I've found out that the block with the "Brake Line Pressure Differential Warning Light Switch" is leaking, but only when force is applied to the brakes. seems like it's leaking from one of the two ports on the bottom where the MC connects.

When I start the car, the brake pedal goes straight to the floor, but if I pump it, it builds pressure and gets firmer. If I let it run for a a couple seconds after that all pressure is lost and the pedal goes straight to the floor.

Also found a plug unplugged and the "brake warning" light on the dash now comes on when I press the brakes and the pedal goes to the floor. When I pump them and the pedal gets stiffer, the light doesn't come on.

[Captain_Zeros]

Sounds like you're on the right track. Get those leaks sorted out and you'll probably have brakes.

When I got my Z it had been parked for a decade and one by one I ended up having to replace everything in the system except most the hardlines and the proportioning block. Master cylinder, rubber flex hoses, calipers, wheel cylinders, and eventually the booster too (losing your brake booster while driving is pretty exciting, in the bad way)

[dvorak]

well replaced those leaky lines and still no full brakes. While sitting in the drive way running it's still the same symptoms. Pedal goes straight to the floor and "Brake" light on the dash comes on. Pump the pedal and it builds pressure and gets stiffer and no light. let it sit for a couple seconds and it goes to the floor again. Gonna replace the front calipers and flex lines next and see if that helps. Took it slowly around the block too, the car stops just slowly and at the very last bit of the pedal. also the E-brake does't really work while moving, gotta adjust that.