couple of probs with my 5/71 240Z

[ZmeFly]

first one is how can you tell if the master cylinder or booster is bad. what happens is the brake pedal has a lot of free travel the bang brake and its hard too.

ive bled them several times using a vacumn bleeder and the pump and release method. still same thing. nothing lot of free travel the hard hard pedal like im at the end of the cylinder as far as it will go the brake.

sometimes its good brake sometimes not. also the engine revs up then back down inbetween where i start to feel brake for a sec and when it hits full brake

second. what would cuase the speedometer to stop working all of a sudden. i mean this literally. drove around for about 25 minutes no problem. stopped to get some gas, started it up went out of the parking lot of the station and now no speedometer. i have put it on the lift yet but out of nowhere its gone.

from looking under the car everything is still hooked up. didnt do anything under the dash where the cable hooks up and i can see its still attached.

what gives.

thanks for any help anyone can give. if on the brakes its the booster it figures that was the only part i didnt save off of my 72:disappoin

also if its the speedo cable just went bad the thats the second bad thing cuz i just cut it when i pulled the 5 speed out of it:tapemouth

[Datzun76]

My master cylinder went out on me and I had no pressure at all to the brake pedal itself. All the way to the floor. Might want to make sure none of your brake lines are leaking. Another mechanic told me the booster/big round cylinder? attached to the master cylinder was bad but so far it has had no effects on my brakes since the master cylinder and brake lines were replaced. I also had a leaky brake caliper which might also be the source of your problem.

[grantman240z]

have u tried bleeding the master cylinder yet...that too could be a source of your troubles

[driftmunky]

i have the same problem with my brakes...the pedal goes all the way to the floor before it starts to work....i don't think anything is leaking in my car either cuz i always check my brake fluid level and it always stays at the same level....any ideas?a mechanic told me it could be my brake booster...what and where is that?

i have a 71 240Z

[Datzun76]

driftmunky - there is a good chance it is a bad caliper since my car was doing the same thing. Sometimes you are not able to detect it unless you actually remove the wheels and look at the brakes. Do you have to keep putting brake fluid in the car or is the master cylinder always full?

[Datzun76]

oops my bad you did say it was staying full. Might have a bad master cylinder. Would be my first guess more so than the booster.

[2ManyZs]

Usually the first place to look would be the master cylinder if you have a soft pedal after a thorough brake bleeding. While you are bleeding them, be sure to inspect all the lines for leaks. If you suspect a brake caliper, take the pads out and have someone very lightly depress the brke pedal to make sure both pistons are free. Be careful not to pop the pistons completely out. Just a very light pressure on the pedal is all you need since you have no resistance.

ZMeFly, one thing you should check is your vacuum likes to the brake booster and the check valve. It sounds like you may have a slight vacuum leak that is causing the idle fluctuation. As far as the speedo goes, you either broke a cable, or it has slipped out of the lug in the back of the speedo. Take it loose at the tranny, use a small cordless drill attached to the end of the cable, and push it back up in the housing, then trun it with the drill and see if it works or not. If not, cable probably is busted.

[wilby34]

the brake booster is a vacuum chamber thing that aids in braking so you dont have to be a 300 lb football player to stop your car. it is the black canister thing behind your brake master cylinder.

[ZmeFly]

i did have leaks at the line fixed those no help. still gets the eratice idle. i tried using the vacumn gauge that you use for bleeding brakes. i could get no vacumn at all from the booster.

looks like the booster is bad. when i push the breaks the pedal goes straight to the spot where the piston seems to stop in the master cylinder then the front brakes i can feel this grab immediately and harshly.