Bad Brake Booster?

[ajla]

So over the past two weeks I've noticed that my rear brakes are "squawking" occasionally on stops and that my brake pedal was kind of soft and stopping distance seemed just a little longer. Nothing major, but I was noticing it. I figured either the shoes were worn out or my brakes needed bleeding

In a futile effort to save myself some free time I took it to a mechanic to check the brakes. He calls me up and says my brake equipment at the wheels are fine but my master cylinder and brake booster are bad. And he wants $800 to fix it. I decided to politely decline that offer. So DIY it is.

Now master cylinder I sort of get, but I've never heard of a brake booster failure causing a soft pedal. I've always thought that was a hard pedal condition. I also don't have any "hissing" when I brake. I don't know why the mechanic would make stuff up, I can't imagine he thinks someone rolling in an '89 Bonneville is flush with cash. Plus I was already all set to pay for the rear brake service.

I don't mind replacing the booster, but I'm not too keen to replace a functioning part. Then again I'd rather not put on a new master cylinder just to have to tear everything apart again to replace the booster. Is there any way to test the booster or master cylinder?

My current plan of action when I pick up the car tomorrow is to inspect the rear brakes myself and bleed them to see where that puts me. I just wanted to know if anyone had any thoughts.

[rustyroger]

A look at the rear shoes will quickly tell you if you have worn shoes, a leaking or seized (frozen) cylinder.
A bad booster will hiss if it is leaking, if it isn't working using the brake pedal will feel like standing on a brick.
Have a look at the front pads as well, you might be surprised that a noise apparently from one part of the car actually comes from somewhere else.
A soft pedal particularly if it creeps to the floor under sustained pressure is symptomatic of a bad master cylinder.
Actually it's a cheap and easy fix, I replaced the master cylinder on my '87 Olds 88 a couple of years ago, a new one was less than $100 from Carquest, an hour to do the job and a litre of brake fluid was all that was required. And someone to help bleed the system when it was done.

Roger.

[crash93ssei]

I would also agree. I have had a few boosters fail on me and it is like hitting the brakes without the engine running, very hard to push and you have to practically stand on it to get it to stop.

[ajla]

Well, I checked it out. The shoes looked fine to me and no leaks from the wheel cylinders.

I cleaned the drums up a bit and bled the brakes too. That seems to have solved the issue, no more noise and the pedal feels much better. For now that is all I'm going to do. If the pedal gets soft again soon or I notice a fluid level change I'll swap out the MC. I'm about 90% sure that my booster is fine though.

[MattStrike]

If you have a close U-pull junkyard, grab a complete rear drum setup from a '96-'99 H-body (for next time?). The auto-adjuster is not as finicky as the '86-'89 H-body setup is. And everything will bolt on. I have had nothing but problems on the '86-'89 rear brakes because of that silly mechanism.