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Rear brakes lock up under hard braking

6K views 24 replies 7 participants last post by  Steevie 
#1 ·
Car just got inspected and told shop under hard braking the rear drums lock up on my 02 sable with 100k. I asked to adjust them and they said they couldn't lock them up so wasn't necessary. After I pick up the car, I drive a lil and slam on them......I'm Goona say it's not an instant lock on but maybe half a second after it begins slowing down both rears lock. Let my foot off and they instantly release. I'm only concerned because this will be my wife's car and don't want any issues in the rain and snow. The abs doesn't kick in on the front wheels. I drive about 10 seconds after locking them up and try again and the pedal is fairly stiff but if I push hard they still lock. Casual driving pedal has no issues.

Is it worth attempting to adjust before sending to another shop? Saw in another post you turn the star until the shoes are barely touching the drum.

Replace rear rubber hoses?
 
#5 ·
On my '03 Sable I had rear lockup on a hard stop. Rear drums also.
Both my front brake hoses were restricted internally. Changing both hoses solved my problem after going through the fronts and rears. Nothing was worn or leaking. In fact this was when I first bought the car from a widow with 110k miles on it. Front pads and rotors were fairly new.
First time I ever had both hoses bad at the same time.
My ABS did not kick in on the fronts either, not even on dirt road testing.
Your pedal stiff comment describes my "hard pedal" description on how they felt. It took a lot of pedal pressure to get the car to slow down in a quick stop. Didn't notice the hard pedal on light stops until after changing the front hoses.
Most braking is on the fronts and with the restricted front hoses it puts more pressure to the rear causing premature lock up.
If nothing is worn, binding or leaking in the rear then the front hoses is where I would go. That's what my experience was on my car.
Bad master cylinder would have a mushy feel to it, not stiff.
 
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#8 ·
Yes you'll need a helper to push the brake pedal to bleed them unless you have the self bleeding equipment. That's what buddies, wife's and GF are for... LOL
DO NOT let the master cylinder reservoir run out of brake fluid when changing hoses. As long as reservoir is full it will not let air into the ABS pump so bleeding it will not be a concern. Just bleeding the line and caliper will be the task at hand. Do one side at a time and don't leave connections open a long time so system drains down and you'll be fine.
Get the big bottle of brake fluid, it's cheap.
 
#9 ·
So repairman my hopes were high since your issues were identical to mine, but unfortunately after both front hoses were replaced and bled, same issue. Test drove and it is acting no differently than before I did the front lines. Any other ideas? Brake fluid was used looking, but u could barely see the bottom of the reservoir so not terrible. Metal lines can't really get clogged up correct? I did forget to mention that I just did rear struts on the car, so rear metal lines were bent about an inch or so to make things easier and get them off the strut. While the car was on stands I did put the jack under the drums and raise the strut up into the 3 holes on top. Thoughts?
 
#10 ·
So repairman my hopes were high since your issues were identical to mine, but unfortunately after both front hoses were replaced and bled, same issue. Test drove and it is acting no differently than before I did the front lines. Any other ideas? Brake fluid was used looking, but u could barely see the bottom of the reservoir so not terrible. Metal lines can't really get clogged up correct? I did forget to mention that I just did rear struts on the car, so rear metal lines were bent about an inch or so to make things easier and get them off the strut. While the car was on stands I did put the jack under the drums and raise the strut up into the 3 holes on top. Thoughts?
" I did put the jack under the drums.."

You might want to put new drums on the rear. No weight ever is to be put on a drum.

-chart-
 
#11 ·
I also forgot to mention I am unaware if they locked up before I was back there doing anything . I bought the car and babied it cause I knew a spring was broke. I only put the jack under one of the drums not both cause it was getting dark, and I only put enough weight on it to compress the strut most of the way....I didn't raise the vehicle at all by the drum. Is that still enough to damage a drum
 
#13 · (Edited)
The car was inspected less than a week ago. Rear drums were 4/32 and if a wheel cyl was remotely leaking it would have failed. I doubt the valve is apart of inspection. I really wish I had tested brakes before I did the struts....how do I test or inspect the valve. also replacement instructions if anyone reading this has done one before
 
#15 ·
On a PA inspection they only just pull a wheel to check pad thickness and shoe thickness if they pulled a drum.
You could have binding caliper pins, sticking calipers, etc. in the front. Your gonna have to recheck everything yourself.
If nothing binding it could be the master cylinder BUT your gonna have to inspect every wheel yourself.
PA inspection is just lining thickness and obvious leaks, I know, have a few friends and relatives living in PA and that's how they do it.
Your in salt country, lots of parts like to freeze up from the winter. I just had to free up the rear caliper pins in my wife's car yesterday.
 
#16 ·
The fluid level sensor won't affect braking, it just turns the idiot light on.
The drums are probably ok. Pulsing in the pedal would be noticeable during light braking if they are out of round.
It's normal without ABS for the rears to lock first so steering isn't lost. Is the ABS system working? Under hard braking a pulsation should be felt in the pedal.
As pointed out, reduced front braking from rusty caliper pins or restricted front hoses will cause rears to lock first. Overly tight rear shoe adjustment too.
Regarding the rear ride height valve, it may have been tinkered with in the past. Final thoughts:Installing new struts/ springs raises the rear ride height and will change braking feel too, especially if the front struts are worn, weight transfer to the front will be out of wack, another possible issue.
 
#17 ·
update: I'm fairly intimidated by drum brakes simply because of all the little parts. I took it to another shop who did the following

-rear shoes look brand new, is it possible they have the wrong shoes on this car?
-remove both rear drums, loosen and readjust shoes. found one was possibly a little too tight, while the other had a seized adjuster.....unseized adjuster and lubed.
-inspected all lines and other brake components for leaks, found no other issues
-no leaks at proportioning valve
-free spun wheels while on lift and both spun freely noise free with no rubbing

here are my thoughts

already bled entire brake system and installed new front hoses, will be doing rears this weekend with little hope that it will do anything.

Don't know how to properly diagnose a booster, master cylinder, or proportioning valve, but there shouldn't be any leaks in the system........with the key off, after about 3 brake pedal pushes, pedal gets firm but i can still push it down about an inch before pedal is super firm. keep pressure on the pedal for over 10 seconds and the pedal still stays put. feels identical to my 200k taurus.

the rear struts don't sit higher as others have suggested, the actually are sitting exactly the same height as the front.

while driving, after i hit the pedal hard.....drive for about 10 seconds, when i then again try another hard brake, the pedal is still fairly firm and is now a little harder to stop the vehicle.......but i can still get the rears to lock.....about how much time should it take for a pedal to soften up after a 50-0 panic stop? is 10 seconds not giving it enough time? I'm about ready to say screw it and just give myself a cushion while driving. Again, i still can't get the fronts to abs or pedal pulse.....may because before they get to that point the backs are locked and I'm letting off.
 
#18 ·
The pedal should be firm on the first application of the brakes, not after 3 strokes. There is still air in the system causing this. The 1inch drop in pedal is air compressing within the fluid.
The booster can be tested by pumping the pedal a few times wirh the engine off to relieve any vacumm in it. Press down on the pedal moderately and start the engine. The pedal should drop about an inch as vacumm builds up. If this doesn't occur, the booster isn't working.
 
#19 ·
2X
Air in the fronts will cause the rears to lock up as fronts are not working
 
#20 ·
A quick and dirty, literally, way to check ABS is to get one side of the car on dirt or gravel, the other on solid pavement and mash the pedal. If there's no pulsation, abs isn't working. Here in MN, we do that all the time in winter on icy roads, although it's usually not planned. We have an '03 SE wagon with ABS (I think it may have been an option, traction control was, are you sure your car has ABS?) and it pulls down from 60 mph on dry pavement with brakes to the floor no problem, no pedal sag, obvious pedal pulsations all the way to a stop. I've done that repeatedly and it's exactly the same every time, the brake system is really good. The pedal isn't super hard, but it's not supposed to be. It should not be spongy though, sink during steady hard braking or be different from stop to stop.

If it definitely does have ABS, pad differences rotor runout, etc won't really have any unbalancing effect but likely will reduce overall braking power; the system works by comparing wheel speed to maintain even braking. I had a rear pad debond once and the system still worked but made a wild grinding sound. One new rotor later...

We had a '94 SE sedan with discs front, drums rear that did something similar to what you're describing. It didn't have ABS but did have a level sensing proportioning valve in the rear activated mechanically by a rod that biased the back brakes more in proportion to increasing rear load. Except on very slick surfaces, it was impossible, I mean you couldn't, lock the front brakes, but the back ones would lock under very hard braking or on slippery surfaces. It was a scary car under hard braking, seemed like everything happened in slow motion with your foot through the firewall!

Anyway, at 140,000 miles, the brake lines rusted out and I replaced them. Since all the fluid ran out during the repair, the brakes were bled and I had to do it 2-3 times to get a hard pedal. The weird brake bias mostly disappeared and the car stopped much better afterward until we sold it a year later. I know I bled the brakes when the front pads and rear shoes were replaced at 80K, but just enough for the black stuff in the fluid to go clear and that didn't change the poor braking or pedal feel, only repeated bleeding did the second time.

I tend to agree that there's still air in the system. At least eliminate that possibility before going deeper because it can mask lots of other things. If you decide to bleed again, be sure at least the amount of fluid estimated to be in each line is purged before moving on and the bleed fitting is really tight before you say "Up"; your helper takes their foot completely off on "Up" and holds the pedal tight to the floor with no movement on "Down." Wait until you hear them push to open the bleeder. Have a quart of new fluid, it's cheap and allows for mistakes.

Ask your helper what they're doing once in a while, all this may sound silly, but to most folks bleeding brakes is like watching paint dry; it's easy to get mesmerized hearing "Up/Down" over and over and accidentally lift the pedal a little when the bleeder's open.
 
#22 ·
I'd also like to add my taurus same year higher miles has a very similar pedal feel in all aspects as this sable does, and the taurus stops hard every time. Never had rear brakes lock up, pedals pulse before that happens. I'll re bleed again and do rear hoses and post back
 
#23 ·
With the engine off, after a few pumps, the pedal goes down maybe 2 in and is very hard. Not totally sure on the distance, my wife has the car at the moment, but it's much less than with the engine running and vacuum working. About the same as what you'd see in any car with power brakes.

It you're spongy in that situation, I'd be almost certain there's air in the system. A leak severe enough to cause sponginess with the engine off would be obvious on the garage floor and the reservoir level would drop fairly quickly.

I think bleeding will fix the problem, ABS is pretty simple; if a major fault develops the warning light should go on. Not sure the hoses will make a difference, but may as well change them. When you do that, bleeding should be done more fastidiously since the system was opened in the middle pushing much more air into the pistons than you'd likely get with a typical bubble.
 
#24 ·
So hers another update

Did rear hoses, new rear drums, and sanded the surface of the shoes hopefully removing any debris.......I bled each wheel about 8-10 times....to the best of my knowledge everything is bled ok......also you can hold the pedal down with the car off and I'm Goona say it goes down about halfway until it gets fully hard. You hold it there for 30 seconds and it stays put doesn't go any. I tried driving on a dirt road, the front wheels do lock up and no abs kicks in.....I may have some air in the system but this abs system needs to be diagnosed. Even if there was air in the system I don't know why the rears would be locking up. The car still stops pretty hard. One other thought....when I jacked up the car to put stands under I lifted the rear up by that center spot on near the gas tank. The center support has like 2 panhard bars going to it.....could this have affected my proportioning valve somehow? I'm Goona start up an abs thread as well hoping to solve that issue too. Thanks for all the replies.
 
#25 ·
You work fast! Seems like bleeding should be OK; there would be a spongy pedal if enough air was present to noticeably affect braking. I just checked my pedal travel engine off and it agrees with what you found, halfway down which is about 2 in for me. My wagon, to the best of my knowledge doesn't have a proportioning valve; I traced the lines from the back to the master cylinder. Definitely doesn't have the spring/rod/lever system in the rear center that my '94 had.

Our wagon has disc brakes in the rear, the suspension is different than sedans, no struts; inboard springs and separate shocks with a forged upper control arm instead of the strut/ stamped tracking link sedan design. It's quite a bit different from the disc/drum sedans, but braking systems are at least conceptually similar.

Just some advice on jacking: the side rails are the best location, they're reinforced at each end and will support the vehicle without bending, except in the middle. It's nice to be able to jack one end, but there are few good hard points for that. If you damaged the proportioning by jacking from the center, I'd think it would be visible; the car can be lifted with both wheels hanging with no problems although there are threads here with the actuator rod pulling off from one wheel full up and one full down.

The ABS should keep the wheels from locking regardless of road surface; hopefully your new thread will turn up something. :)
 
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