brake pedal is like a brick - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 21 (permalink) Old 04-20-2017, 11:14 AM Thread Starter
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brake pedal is like a brick

So I just got my 73 240z running after its been sitting for about 15 years but the brake pedal wont push in at all so no brakes! There is fluid in the reservoirs. Would you guys just think that the booster is bad and I need to replace it? It appears to not be the stock one so I think it was replaced before I got the car 20 years ago.


The pedal just wont push in hardly at all.


Hoping someone has had a similar experience and can offer advice..


Thanks
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post #2 of 21 (permalink) Old 04-20-2017, 12:37 PM
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Booster is trashed

Last edited by 510doc; 04-20-2017 at 07:35 PM.
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post #3 of 21 (permalink) Old 04-20-2017, 06:11 PM
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Yup, master cylinder or brake booster. Most likely master cylinder frozen.
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post #4 of 21 (permalink) Old 04-21-2017, 01:20 AM
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make sure the vacuum line going to the booster is intact and the check valve in it is working properly

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post #5 of 21 (permalink) Old 04-21-2017, 12:58 PM Thread Starter
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Thanks, ill check all of this this weekend
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post #6 of 21 (permalink) Old 04-27-2017, 01:32 PM Thread Starter
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So after the car has ran for a while, the pedal is now pushing in. The not moving at all "brick" is gone and it goes in fine but now I don't have any pressure or stopping power.


When I do press the brakes, it seems like I can hear a vacuum sound (leak?) down at the pedal and the engine will idle up and down.


Do you guys think the booster is still trash? How do I check the the check valve in the hose? Should I try to bleed the system?


I feel like I should mention that my car has a 4 barrel carb conversion on it. It has a Holley 390 that has just been rebuilt and tuned.


The vacuum hose to the booster runs right from the corner of my carburetor...
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post #7 of 21 (permalink) Old 04-27-2017, 07:45 PM
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Quote:
Originally Posted by dcooper23 View Post
So after the car has ran for a while, the pedal is now pushing in. The not moving at all "brick" is gone and it goes in fine but now I don't have any pressure or stopping power.


When I do press the brakes, it seems like I can hear a vacuum sound (leak?) down at the pedal and the engine will idle up and down.


Do you guys think the booster is still trash? How do I check the the check valve in the hose? Should I try to bleed the system?


I feel like I should mention that my car has a 4 barrel carb conversion on it. It has a Holley 390 that has just been rebuilt and tuned.


The vacuum hose to the booster runs right from the corner of my carburetor...
Try to bleed them. Sitting for 15 years will do a lot to a system. its likely gunked. The noise you are hearing is probably the booster itself.

Make sure there is adequate fluid in the master cyl and bleed away. Go until you see new fluid on all 4 sides. If at this point you have no pressure still, make sure you don't have a leak draining your fluids, then check your master cyl for operation, then if all else fails check the booster.

If you do have pressure after bleeding them, but no brakes, check the brake pads and such.

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post #8 of 21 (permalink) Old 04-28-2017, 11:38 AM
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If that vehicle has a carb conversion on it, one possible problem is low vacuum due to the carb setup, or a conversion that omitted the check valve between the carb and the booster.

I like the brake bleed idea, because you have to do it anyway after a car has been sitting that long. If you're in an environment with any humidity, it's also possible that there's corrosion in the wheel calipers preventing the pistons from moving.

Bleeding will tell you whether you're getting brake line pressure to the corners, but if you have pressure and the brakes aren't grabbing, you'll need to check the calipers.
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post #9 of 21 (permalink) Old 04-28-2017, 10:28 PM
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Mr.Cooper:

Possible food for thought...

Still a question or two (diagnostically speaking) unanswered:

1) Are the calipers/shoes moving at all?

2) Pedal movement: how does it end; "normal" point of maximum pressure or bottoming out in the M.C.?

3) Stock or not, can you see a bore dia. on the M.C. casing?

4) What dia. vacuum line is run out of the carb? Between the carb and the vac booster is there an intervening device (about the size of a stack of 8 or ten quarters with a bracket to the firewall; this is the one-way valve) in the vacuum line? Keep in mind that the stock vac line is like 3/8" I.D., and a smaller line will not charge the booster properly.



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post #10 of 21 (permalink) Old 05-01-2017, 10:34 PM
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Quote:
Originally Posted by dcooper23 View Post
So after the car has ran for a while, the pedal is now pushing in. The not moving at all "brick" is gone and it goes in fine but now I don't have any pressure or stopping power.


When I do press the brakes, it seems like I can hear a vacuum sound (leak?) down at the pedal and the engine will idle up and down.


Do you guys think the booster is still trash? How do I check the the check valve in the hose? Should I try to bleed the system?


I feel like I should mention that my car has a 4 barrel carb conversion on it. It has a Holley 390 that has just been rebuilt and tuned.


The vacuum hose to the booster runs right from the corner of my carburetor...
Here is a possible answer to your brake problem. Found it on CTZCC website. Good luck.
This is what I found wrong with mine when I got it back:
In the brake booster vacuum line (btwn the manifold and the booster), the previous owner had reversed the One-Way Valve and put the hoses back over it. That prevented access to manifold vacuum so the power assisted brakes had no assist at all except both my feet. I reversed the valve and the first time I pressed the pedal it about threw me thru the windscreen.

You might not even know that valve exists; it hides completely on your firewall, under a hold down clamp. The hose btwn the booster and the manifold is two-piece and the valve lives at the junction, but the clamp holding the hoses to the firewall conceals the junction.

The valve looks identical on both ends so novices often install it backwards, but one end is slightly smaller than the other. It only allows air to flow in one direction (hence the name) so you can blow thru it to determine which way the air flows. Try reversing it then try your brakes again (carefully) .

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