Bad master cylinder, or re-bleed needed? (new booster fixed)

[LeSabre in Buffalo]

The calipers weren't acting like this a week ago. The inner pads aren't worn more than the outers, they're both worn pretty evenly. When I had everything apart, the calipers got new rubber pieces for the pins, and I cleaned up the slide pins thoroughly. Everything slide-related was greased very liberally with that black brake grease. The pins were black with grease going in.

This thing is driving me nuts right now. No daylight or enclosed space to work on it either.

[renchjeep]

Maybe the brakes are somewhat "on" all the time, like the mc is not bleeding pressure back? I think I remember you stating that you had replaced all the rubber brake hoses. I had a wierd brake problem on my 67 Chevelle (4-wheel drum brakes) years ago, she would pull right a bit while driving down the road, and swerve left when the brakes were applied. Turned out to be a bad brake hose on the RF (or was it the LF?). Apparently, the hose collapsed internally, creating a "one-way" valve type of issue. I replaced both front brake hoses, and problem solved. You may have the same type of issue on a "main" rubber brake hose, if you have that sort of setup. Not sure where your car has metal or rubber lines.

Of course, this does not explain your low pedal. For that, I would be looking into rear brake adjustment. Be sure to check the backing plates on the rear drum brakes, assuming you have rear drums, for grooves worn into the backing plates. These grooves can either hold your rear brakes on, or keep them from working properly. I always "gently" grind the backing plates smooth at the shoe contact points, and lube with high-temp anti-seize compound.

OK, I'm done with my rant...............for now, at least.

Let us know what you find, please.

[LeSabre in Buffalo]

Parts replaced in the past year:
Wheel cylinders
Rear brake shoes/hardware
Front rotors/pads
All 4 rubber brake hoses

Brake lines are rust-free, as they were replaced a little over a year ago.

The whole braking system is basically new. Not to say a faulty part isn't lurking somewhere. Or that the new rubber hoses are any better than the ones they replaced, or that both calipers are sticking.

[Jrs3800]

He is starting at the Booster as it hisses when he is on the Brakes... He gets the Woosh from the Booster followed with Hissssssssssssssssssssssssssssss as long as he is on the brakes..

[renchjeep]

He is starting at the Booster as it hisses when he is on the Brakes... He gets the Woosh from the Booster followed with Hissssssssssssssssssssssssssssss as long as he is on the brakes..

I get that part, but would a bad booster cause a low pedal? Or the quick heat generation?

I hope the booster fixes it. This is quite interesting............

[Jrs3800]

I am not certain this will fix the issue... But the Booster leaking is a problem..

This could very well be a bad Master cylinder out of the Box... I have had it happen before..

Almost makes you wonder if the master cylinder isn't letting the fluid flow back into the master cylinder... Generally if the booster is bad you can get a lot of pedal feedback, like the car is trying to push back...lol.... Or Little to no power assist...

I am perplexed...

Step 1) New Booster

Step 2) possible Master Cylinder

[renchjeep]

I am not certain this will fix the issue... But the Booster leaking is a problem..

This could very well be a bad Master cylinder out of the Box... I have had it happen before..

Almost makes you wonder if the master cylinder isn't letting the fluid flow back into the master cylinder... Generally if the booster is bad you can get a lot of pedal feedback, like the car is trying to push back...lol.... Or Little to no power assist...

I am perplexed...

Step 1) New Booster

Step 2) possible Master Cylinder

100% in agreement.

[LeSabre in Buffalo]

So I disconnected the booster today, and got 4 mpg better on my commute. Also didn't have as much KR with that giant vacuum reservoir disconnected. The most I got was 3-4* when accelerating at low speed from a stop, no giant 11-12* spikes like has happened. I'm thinking the booster's bad.

The brakes were still scorching hot getting home today after commuting. I may have pooched my calipers too. Or it could be a bad MC from the box. The heat is affecting all the brakes, even the rear drums. I know brakes get hot, but it's 25*F out right now, and the car was driven gently for a few minutes after the hard braking slowing down from the highway. Please tell me I'm paranoid!

Did I mention the horrible noises the front end of the car is making right now? At highway speeds it sounds like wheel bearings from the pads contacting the slotted rotors.

The car stops just fine with the booster disconnected, FYI. And the pedal is rock-hard at the end of its travel to even with the gas pedal.

Booster's in Buffalo now. Should be on my doorstep tomorrow.

[LeSabre in Buffalo]

Link to video of front-end noises. Listen for the rhythmic noise, that's apparent later on in the video.

http://s207.photobucket.com/albums/bb19 ... G_0199.mp4

[renchjeep]

Video didn't work for me. But noises from the front end are not a good thing. Still should not affect the brakes, unless something is almost literally falling off of the car.

[1oldman]

the only thing I can tell you is do what I would do. Start over and take everything apart again and give it a really good going over. Wish you the best and find the trouble soon. - BC

[LeSabre in Buffalo]

The booster got in today. I'm replacing that in a heated garage later tonight. I also ordered new calipers to be picked up beforehand in case those are shot, too.

Will update with results later.

[LeSabre in Buffalo]

Found this link. Fits my symptoms all too well: http://www.ehow.co.uk/list_7181284_sign ... oster.html

[LeSabre in Buffalo]

Update:

New remanufactured booster installed. Brr, that was cold! Took me 2.5 hours and breaking a bunch of stuff to do it. Use an impact and wobble/swivel joints to get the bolts off of the firewall, there's zero clearance with the steering shaft. And, good luck with the top left bolt, it's a bear. Getting the darned thing back in is a challenge, too. Getting the booster out meant taking off the strut tower brace and shoving the master cylinder as far forward as possible, moving the air box and engine harness to do so.

Long story short, it was probably the problem. Pedal feel is still non-existent. The brake pedal does stay off the carpet, and I only have to press down to the gas pedal to get strong brakes. I'll test it a bit more tomorrow after work.

My long-term fuel trims, which were around 4 to 7 with the old booster (16 at idle with no booster, lol) went back down to 2 to 3. I'll keep monitoring the trims to see if they zero out.

Here's hoping that booster was the problem all along...

[LeSabre in Buffalo]

Bringing this to a conclusion:

After a day of driving the car around town and on the highway, it was the booster. Installing the new booster gave the car its brakes back. The pedal is still feather-light, but it clamps the brakes on hard right when it reaches the gas pedal, or where it should be. And, under heavy braking, it is still 3/4" from the floor. Plus, the car is back to coasting for forever now with my food off the gas, and my fuel trims are back to normal. The car stops very quickly with all the new brake parts that are on it. It's surprised a few folks with how fast it slows itself.

So, I replaced a perfectly good master cylinder, and the faulty brake booster. Along with the new rotors, pads, brake fluid, and hoses, I've poured $400 in parts and many hours of my labor into my brakes in the past month. Ow, my aching wallet!

[spoiledred94]

Congrats! I got a little farther into the brakes on these cars.

[J Wikoff]

Does a new booster come with a new check valve? What's the basic procedure to do the job?

[LeSabre in Buffalo]

Does a new booster come with a new check valve? What's the basic procedure to do the job?

Yes, it does. It also says don't remove it in order to have a valid warranty.

Basically, one has to take down the little kick panel under the dash, and using some deep sockets, wobble joints, and lots of extensions, undo the 4 bolts holding the booster to the firewall. Undo the little clip attaching the pushrod to the brake pedal with a flat-heat screwdriver. Undo the master cylinder, the strut tower brace, and the airbox. Move the throttle and cruise control cables out of the way, and shove the MC as far forward as possible. Get a rag underneath it to catch any spilled brake fluid. Then take out the booster. It's a tight fit, but doable with all that other stuff out of the way. When you're installing, make sure to put on the new gray rubber boot onto the pushrod heading into the cabin. Otherwise your feet will get cold from the draft under there. Then basically get everything aligned, and wiggle it back in there. It helped me to start one of the lower bolts to hold the booster in place, then get the others aligned and shoved in. Tighten everything back down, replace everything you removed, and it's good to go.

If the MC is only shoved forward, there's no need to re-bleed the brakes after.

[spoiledred94]

tight write up. I hope I can find it when I do my 94.

[LeSabre in Buffalo]

Update: Several hundred miles later, and all systems normal. OMG, the brake pedal is feather-light still, but watch out, it's easy to slam them on. Pedal height is equal to the gas pedal with the brakes at full clamp, so that's back to normal. Plus my ScanGauge was a full gallon high for my last fillup, so my gas mileage has gone back up to where it should be for this time of year.