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Strange Pop Sound at brake pedal

Old 11-18-2015, 07:39 PM
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Strange Pop Sound at brake pedal

Hey guys/gals

Last time I was scalded for not using the correct lingo, so bear with me this time. I will do my best.:wink

So here's what happened. I was trying to bleed my brakes on my 1972 240z. I had my dad working the brake pedal, which at the time felt pretty stiff. This is the reason we were bleeding the brakes in the first place. So when I opened the bleed valve, and had my dad depress the brake pedal, following standard procedure. But no fluid or air came out of the tube I had hooked up. Essentially, we weren't able to bleed the brakes.:cry

What happened though that is crucial to the discussion is that when my dad pumped the brakes a few times, with all the bleed valves closed, we heard a "pop" or "click" sound at the pedal and then all the stiffness on the pedal disappeared. It was like the pedal wasn't attached to anything-completely free-floating.

The PO figured it would need a new master cylinder. So I ordered one and slapped it on today. I figured this might be the culprit to the problem with the pedal. When I was installing the new M.C, I noticed that the rod that runs from the brake pedal through the vacuum and to the M.C. (I think it's called a push rod) was loose. Is this normal? Or should that rod have been stiff on the M.C. side? I'm looking through the manuals and can't find any information on this, so that is why I am writing up my own post. If the push rod is not the issue, would I be looking at a new vacuum servo unit? I just can't seem to figure out where the disconnect is happening. My lines are good and with the new M.C, I figured that would solve the problem, but that was not the case. I will also add that after installing the new M.C. and pumping the brakes a few times (thinking I might build up regular pressure in the pedal), the fluid level in the rear brake reservoir went down. I tried to bleed the new M.C., but again got no fluid or air through my tube as I should have.

Any suggestions as to what that pop sound was and why I have absolutely no pressure on the brake pedal would be much appreciated! And I am willing to clarify anything, just ask! Thanks!
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Old 11-18-2015, 10:02 PM
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look at your post on zcar.com you still don't know enough to tell what car you are talking about.
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Old 11-18-2015, 10:11 PM
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The rods on aftermarket master cylinders are often too short for your car. I hope you saved the old rod. It can be swapped.
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