Jump to content


Brake booster & missing brake fluid


Recommended Posts

I searched and found some stuff but don't have a clear answer so here's the situation:

Brakes didn't work when I bought the car due to sitting for years. Replaced master cylinder with unit from rockauto flushed and refilled, worked perfectly for months

Car went to interior shop and sat for a month, brakes stopped working. Front reservoir was empty but it didn't appear to be leaking. I'm not a pro so I didn't know what happened, refilled, bled and ran for another month

Today I'm driving around and hit the brakes. Break pedal is super hard but the car doesn't stop well, hissing sound, motor dies. Obviously the brake booster failed, no apparent external vacuum leaks

So the questions:

Did my master cylinder have shavings in it and kill my booster? Did the fluid end up in the brake booster? Should I replace them both? I also have a 1" MC that i bought at a junk yard, should I rebuild and use that with a new booster?

Link to comment
Share on other sites

I've had a clutch slave cylinder go bad within months of installing. I took the replacement apart before installing and found manufacturing grit inside, which I removed with a brake fluid rinse. So some aftermarket parts don't have the greatest QC on the cleaning side. Could explain the master cylinder going bad. It shouldn't leak, and there's no where for the fluid to go except backwards toward the booster. It could also leak down the face of the booster at the mounting surface.

I also had a booster go bad after already having replaced the brake master cylinder. It was full of old brake fluid (that dripped on my paint when I was removing it), from the bad master that I had replaced. The car had sat for a few years. The fluid isn't kind to any plastic type materials and probably helped the booster disc fail.

So I would say that yes, your master cylinder is bad, and yes that you should replace both. But the 1" master would give you shorter travel on the brake pedal but will require more effort, so you might want to consider that before deciding which master to use. If you get another aftermarket master cylinder take it apart and clean the bore, piston and seals, or flush it out well before installing.

Edit - Forgot to say that the hissing sound and the motor dieing are sings of a bad booster. The hissing is intake manifold vacuum escaping and the motor dies because of it.

Good point on matching part dimensions (below) before installing.

Edited by Zed Head
Link to comment
Share on other sites

You might also want to search for "reaction disk".

As a matter of fact, here's a google search of this site: Reaction Disk Search

Anyway, replace both as mentioned earlier. Oh, and when you remove the old booster, MEASURE how far out the rod extends. (Lord, that sounds bad.) If you don't match it with the new booster, that WILL affect your braking.

Link to comment
Share on other sites

Thanks guys, I know what to do now. last question: Rock Auto and the local auto parts stores dont list a brake booster for my early 1974 260z, however black dragon auto lists one part as fitting from 1973-1978 vehicles. All the regular auto parts stores show brake booster's available for 1975-78 Z's and even list the part as being the same 8.5" size that i have. Can i just buy a brake booster for a 1978 or is there some difference i dont know about?

Link to comment
Share on other sites

Looking at the parts manual, each brake booster superceeded another through part number 47210-N3001. The top end of the date range is 7507, implying that the 260Z and 240Z boosters are essentially interchangeable. Blackdragon Automotive lists the range from 73-78 for their boosters.

You can always return the part...

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy and Guidelines. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.