Braking and Hissing inside cabin

[KDMatt]

Ok, so I've got a question...

Today while I was driving the Z, I came to an intersection and as I held my foot down on the brake, I started to hear a hissing sound -- my immediate first thought was "brake booster"

.. as I kept driving I didn't notice the sound again (and obviously the brakes still work, otherwise I'd be writing to you from a hospital)

When I got back home I left the car running and knelt down on the ground beside the car to press the brake pedal by hand to see what the story was.

... and oddly enough, the hissing sound is coming from INSIDE the car. I can hear (and nearly feel) the air getting sucked inside of the booster from within the cabin where the rod off of the brake pedal goes through the firewall.

The master cylinder I believe only has around 20,000 miles on it (PO replaced it around 15 years ago I think).

My question is, what has gone bad and how easy is it to fix?

I've got some money saved up, do I bite the bullet and just redo everything?

(I've been considering a disc brake upgrade and a 2+2 booster install).

Thoughts?

[MikeW]

Definitely the booster. The reason you're not in the hospital is that you didn't have to brake really hard in your normal driving. The brakes still work; the vacuum-powered booster just helps you push the pedal with more force. If it's a slow leak and not a total failure it's possible that you're still getting some assist but not full assist. Think of power brakes like power steering. Our cars don't have power steering which you don't really notice in normal highway driving but you do notice pulling into or out of a parking spot. If you've ever had power steering fail on you in a car that really needs power steering you'll know how hard it can be to steer.

[KDMatt]

Alrighty, so the booster's gone bad.

Then perhaps I'll take this opportunity to upgrade to the 2+2 booster.

Without me glancing at my FSM, how hard of a job do you figure this to be?

[MikeW]

I don't know what's involved with the upgraded booster but the standard booster is very easy to replace.

[KDMatt]

I don't know what's involved with the upgraded booster but the standard booster is very easy to replace.

Good to know.

As I'm looking at parts online, I see two options, one is the 8.5 inch diameter booster, the other is the 10 inch diameter booster. Is it reasonable to assume that the 10" is for the 2+2?

[Oiluj]

To install the larger booster you will need to elongate the holes in the firewall. Not hard, but a bit of work.

[KDMatt]

To install the larger booster you will need to elongate the holes in the firewall. Not hard, but a bit of work.

Perhaps I'll do a little research then before I decide. Thanks for the useful tidbit!

[KDMatt]

OK, and correct me if I'm wrong, but it looks like I can remove the booster without having to mess with/bleed any of the brake hydraulics? ... As in the master cylinder can come out of there as one, unmolested unit?

This is just an issue for me because if I have to bleed the system/mess with hydraulics, I need to have another person to help me, but if I can leave all of that alone, it looks like I could "easily" take care of this job by myself.

[Richard Oben]

No need to remove any fluid. Two bolts for the MC. And the stand on you head under the dash to get the 4 bolts on the firewall and the pedal pin. From there the booster will come out no problem. The MC may need to be pushed out of the way a little but no need to undo any lines. HTH, Richard.

[KDMatt]

No need to remove any fluid. Two bolts for the MC. And the stand on you head under the dash to get the 4 bolts on the firewall and the pedal pin. From there the booster will come out no problem. The MC may need to be pushed out of the way a little but no need to undo any lines. HTH, Richard.

Sweet. That's exactly what I needed to hear. :classic:

I have no desire to mess with brake hydraulics, even though, technically the repair manual says you're supposed to pull the brake lines out of the MC.

New booster comes in tomorrow (long story, short: was out of town, it came in while I was gone, and even though I told them to hold it, they sent it back when I didn't claim it... reordered on Sat), so with any luck I'll be sittin' pretty by tomorrow night.

[Jeff G 78]

Just be very careful that you don't bend any brake lines. I'd actually be surprised if you can remove the booster without removing the lines. The MC will have to slide forward quite a ways to clear the mounting studs. Hopefully it can be done. Good luck.

[KDMatt]

Ok folks, update:

Finally got the job done, without removing the MC. This is a job of four-letter expletives, like... all of them... especially when it comes to the retaining spring (piece of mother @#^%in etc. etc. etc.) ...

Anyway, all is said and done now and HOLY ____ ... my brakes have NEVER felt so good in the entire time I've owned the car ... they actually feel... sporty? Jeez, the booster must have slowly been going out because this is incredible, simply incredible. I can't believe how sensitive they feel, I barely have to tap on them to feel stopping power. I'm really impressed. :classic:

Now, time to clean up and enjoy brakes.

In fact... I think I'll fix a snack and have a ... 'brake' ... myself...