Something's wrong with my brakes. Help?

[Newai]

'92 Chevy Lumina sedan
3.1L engine

They're really soft. They work, but not like brakes in every other vehicle I've ever driven. When I push down, I have to pump a bit to get to a reasonable level of responsiveness. I can hear what sounds like air squeezing out as I pump. I've replaced everything brake-related I can think of: master cylinder, line, calipers, pads. On a related note, the emergency brake has the same effect. Barely puts any pressure on the wheel; a little gas and the car takes off. My mechanic is out of ideas.

Any thoughts what could be up with this car?

 

[Ms Music]

My mechanic is out of ideas.

Maybe you need a new mechanic.

Definitely sounds like a leak. How is your fluid level?

 

[Newai]

Brake fluid is always fine.

My mechanic has always been very good with my car. Every other problem I've ever had he's handled just fine.

 

[Ms Music]

If fluid level never goes down, then maybe the brakes need to be bled better. Trapped air will make you have to pump your brakes, also.

 

[TurtleMeister]

I agree with Ms Music. Sounds like air in the brake lines. Your mechanic should be using the shop manual procedure for your vehicle to bleed the lines. The procedure is different for different vehicles.

 

[Jimmy Snyder]

Before you help Newai with his brakes, could you please help me with my ripcord. I keep pulling on it but nothing happens.

 

[TurtleMeister]

Before you help Newai with his brakes, could you please help me with my ripcord. I keep pulling on it but nothing happens.

Take your pants off and hold them over your head. Hope I'm not too late.

 

[turbo]

Have you adjusted your rear brakes? You have drums on the rear, I believe, and you can adjust them by backing up at 10-15 mph and hitting the brakes hard. You might have to do this several times. An empty parking lot is probably the best place to do this.

 

[Newai]

Well, we've handled the bleeding very carefully. Though that feels like it's the right area, I believe there's more to it.

No drum brakes at all.

Before you help Newai with his brakes, could you please help me with my ripcord. I keep pulling on it but nothing happens.

My manual strongly suggests placing thumb in mouth and blowing real hard.

 

[Ms Music]

To Newai and any other interested person, I have a tip for bleeding brakes. Well, if I remember right, that is. See, my dad made me take auto shop to buy a car, and since the boy to girl ratio was unbelievable... ;) But that experience was also long before your car was made. So I don't remember all the details.

My dad had this contraption that he made, where you take a small jar and fill it part way up with brake fluid. Find a tube that fits the brake bleed valve (wish I remembered the diameter, but you can find that out easily). Tightly clamp one end of the tube on the bleed valve, and stick the other end into the brake fluid. Then slowly pump the brakes numerous times. You can technically bleed brakes all by yourself this way, although it is much quicker with 2 people.

I had brake issues on my car that I drove in high school (68 Cougar XR7) and wound up replacing the entire brake system, piece by piece. I had to do it the "high school auto shop" way, and my dad's way, depending on where I was working on my car. Bleeding works best with my dad's method, as when you take your foot off the break, there is no air sneaking back into the line.

Might be worth a try.

 

[BobG]

If your car has ABS, then there is definitely a distinct procedure for bleeding the lines, which you have to do if you've replaced the calipers or anything else that opens the lines to air.

It's more complicated than the old non-ABS brakes (and I didn't even like bleeding them, although I was always able to eventually get them bled properly).

Of course, as long as ABS has been around, any good auto shop should be able to bleed an ABS system properly. An experienced home mechanic that relies on his own experience and common sense may have more trouble, but still should be able to bleed the brakes provided he follows the sequence in the manual, etc (it's not that incredibly different than the old brake systems).

The fact that the emergency brake doesn't work well either suggests some other problem or multiple problems, though. Emergency brakes usually rely on cables/levers rather than hydraulic pressure. However, those also have to be adjusted if you replaced your rear brakes.

Edit: Ms Music's method works for non-ABS brakes, but probably won't work for ABS systems.

The real secret is to never open the brake lines. Of course, that's impossible if you replace as many parts as you did.

 

[Newai]

To Newai and any other interested person, I have a tip for bleeding brakes. Well, if I remember right, that is. See, my dad made me take auto shop to buy a car, and since the boy to girl ratio was unbelievable... ;) But that experience was also long before your car was made. So I don't remember all the details.

My dad had this contraption that he made, where you take a small jar and fill it part way up with brake fluid. Find a tube that fits the brake bleed valve (wish I remembered the diameter, but you can find that out easily). Tightly clamp one end of the tube on the bleed valve, and stick the other end into the brake fluid. Then slowly pump the brakes numerous times. You can technically bleed brakes all by yourself this way, although it is much quicker with 2 people.

I had brake issues on my car that I drove in high school (68 Cougar XR7) and wound up replacing the entire brake system, piece by piece. I had to do it the "high school auto shop" way, and my dad's way, depending on where I was working on my car. Bleeding works best with my dad's method, as when you take your foot off the break, there is no air sneaking back into the line.

Might be worth a try.

That is what we've done.

The car shouldn't have ABS since there's nothing on the brake pedal, and he's gone over everything in the car related to that anyway. I also noticed that there is no ALB fuse in the box, if that helps.

 

[AlephZero]

Sort the handbrake out first, because you should be able to put the car on a ramp, take the wheels off, and see what is happening (or not happening) when you pull the lever.

If the handbrake is barely operating the brake pads, quite likely the footbrake has a lot of slack for the same reason.

 

[DaveC426913]

Before you help Newai with his brakes, could you please help me with my ripcord. I keep pulling on it but nothing happens.

:rofl: :rofl:

I always love these 'need diagnosis urgent' threads, but your turn of a phrase is genius!

 

[QuarkCharmer]

Sort the handbrake out first, because you should be able to put the car on a ramp, take the wheels off, and see what is happening (or not happening) when you pull the lever.

If the handbrake is barely operating the brake pads, quite likely the footbrake has a lot of slack for the same reason.

The E-brake on those drums is cable driven to a secondary mechanism. The foot-brake feeds an actuator. Unless there is a huge (and loud) mechanical flaw in the horseshoe-shaped apparatus that applies pressure, it's not likely that both of these systems would fail to work. It's a redundant system, with one low-fail part between them.

 

[KingNothing]

Shot in the dark, but it could be a mis-sized rotor.

 

[edward]

Anti lock brakes were an option on the 92 Lumina Euro sedan. They have to be bled in the correct sequence or they can do weird things.

Pumping the pedal with ABS isn't a good idea.

 

[dlgoff]

I can hear what sounds like air squeezing out as I pump.

What you are hearing is the power/boost(assist) vacuum leaking. It's what the master cylinder is attached to. Between your foot and the master cylinder.

http://www.cardone.com/English/Club/Products/Brakes/Protech/Images/930393e.gif

 

[edward]

What you are hearing is the power/boost(assist) vacuum leaking. It's what the master cylinder is attached to. Between your foot and the master cylinder.

http://www.cardone.com/English/Club/Products/Brakes/Protech/Images/930393e.gif

I think you just nailed it down.

 

[Newai]

Shot in the dark, but it could be a mis-sized rotor.

The rotors are indeed larger than the ones the car came with. That matters?

 

[BobG]

That is what we've done.

The car shouldn't have ABS since there's nothing on the brake pedal, and he's gone over everything in the car related to that anyway. I also noticed that there is no ALB fuse in the box, if that helps.

Are you sure? ABS is standard on the Euro model, which has a 3.1L engine. ABS is optional on the base model, which has a 2.5L engine.

Not a guarantee, since you can swap out engines and the car is nearly 20 years old, but I think you have the Euro model.

http://www.edmunds.com/chevrolet/lumina/1992/

 

[Newai]

Are you sure? ABS is standard on the Euro model, which has a 3.1L engine. ABS is optional on the base model, which has a 2.5L engine.

Not a guarantee, since you can swap out engines and the car is nearly 20 years old, but I think you have the Euro model.

http://www.edmunds.com/chevrolet/lumina/1992/

This car isn't the Euro model. The engine was replaced; I didn't know that the base model was 2.5. Should that be mentioned when I'm getting parts that aren't engine related?

 

[BobG]

This car isn't the Euro model. The engine was replaced; I didn't know that the base model was 2.5. Should that be mentioned when I'm getting parts that aren't engine related?

Possibly. You wouldn't think the brake rotors would be dependent on engine size, but if you just give the parts store the make and engine size, there's a good chance they'll just automatically give you parts for the Euro model instead of the base model.

And you did say the new rotor isn't the same size as the old.

 

[Newai]

Funny thing about that is the dashboard reads Euro because I replaced that, too. My car is so confused.

Okay, so far it looks like mismatched parts and vacuum booster/hose. Otherwise, the car is in really good shape so it might be worth the money.

 

[BobG]

I think you've reached the point where your only solution is to call Car Talk.

http://xkcd.com/582/

Note: I have a t-shirt with this cartoon on it. It encompasses two of my favorite things on one t-shirt: Car Talk and xkcd.

 

[Newai]

I've been looking at some articles and videos on vacuum boosters. Seems to fit my situation. I didn't know what a vacuum booster was till dlgoff described it. I just took my car out and noticed that the brake pedal slowly goes all the way to the floor while hissing.

Alright. Thanks everyone! I'll get on that in the next week or two and let you know how it turned out.

 

[brewnog]

I wouldn't worry. There are plenty of other things (besides your brakes) which can stop you.

 

[BobG]

I wouldn't worry. There are plenty of other things (besides your brakes) which can stop you.

Turning off your ignition isn't one of them. That usually just locks up the steering wheel and eliminates any pressure your brakes might have possibly found.

I wouldn't drive down any mountains, if I were you.

http://findarticles.com/p/articles/mi_qn4191/is_20000102/ai_n9964496/

You're supposed to use a lower gear when driving down Pikes Peak, but, every few years or so, some flatlander rides their brakes until the fluid all boils away and then they get to test how well they make decisions in an emergency. Most try to choose a good location to crash, but even that doesn't help them if they've allowed themselves to build up too much speed. (By the way, the story is wrong about the cause of the accident. The passenger turned the ignition off and eyewitness reported the car rolling silently down the mountain with the terrified passengers crying while peering desperately out the windows.)

The strangest Pikes Peak accident happened last summer. Engineers sent a driverless Audi up the mountain, using GPS to navigate all of the turns. The car made it fine, but the helicopter filming the car crashed at the summit. http://www.kktv.com/home/headlines/103131224.html

 

[Ms Music]

Newai - Best of luck to you! I hope that is the problem, and that it will be over and your brakes work properly.

Also, I want to suggest again... If this is a friend or family, never mind. But if your mechanic is Joe Schmoe down the road at ABC Automechanic, and you are being billed normal rates, I would strongly suggest thinking about my first sentence in this thread again... A good mechanic worth the standard billing rate shouldn't leave you asking for suggestions on a physics forum... No response to me needed.

Again, best of luck.

 

[DaveC426913]

I wouldn't worry. There are plenty of other things (besides your brakes) which can stop you.

Turning off your ignition isn't one of them.

I was thinking he meant such things as other cars, telephone poles, bridge abutments...

 

[erok81]

What you are hearing is the power/boost(assist) vacuum leaking. It's what the master cylinder is attached to. Between your foot and the master cylinder.

http://www.cardone.com/English/Club/Products/Brakes/Protech/Images/930393e.gif

This would have been my first guess as well...but that doesn't explain the e-brake not working well.

Unless one came before the other? Or they both happened at the same time, but that is a bit unlikely.

I may have missed this, but did they both happen at the same time? Or was the e-brake like that before and maybe you didn't notice because the rest of the brakes were working fine?

 

[Newai]

This would have been my first guess as well...but that doesn't explain the e-brake not working well.

Unless one came before the other? Or they both happened at the same time, but that is a bit unlikely.

I may have missed this, but did they both happen at the same time? Or was the e-brake like that before and maybe you didn't notice because the rest of the brakes were working fine?

I've had the car for about four years. They have both always been like that the whole time I've had it.

 

[dlgoff]

This would have been my first guess as well...but that doesn't explain the e-brake not working well.

I've had the car for about four years. They have both always been like that the whole time I've had it.

Well, most emergency brakes I've seen only apply to the rear wheels. And they aren't really meant to stop your car like the hydraulic system is designed to.

 

[turbo]

Well, most emergency brakes I've seen only apply to the rear wheels. And they aren't really meant to stop your car like the hydraulic system is designed to.

Yep! Maybe I'm really used to older vehicles, but most emergency brakes in my trucks/cars were cable-operated tensioners that engaged the rear brakes mechanically. Not really enough to stop you if your vehicle has any momentum, but enough to stall out your engine if you dump the clutch with the EB engaged.

 

[AlephZero]

I've had the car for about four years. They have both always been like that the whole time I've had it.

Doesn't the US have any mandatory safety inspections, like the UK "MOT test". The name is an anachronism now, because the Ministry of Transport doesn't run they system any more - it's an annual inspection of the safety related components for all vehicles, starting at 3 years old.

You wouldn't be able to tax or insure a car more than 3 years old with faults like that in the UK, and if it was picked up by a numberplate recognition camera while being driven untaxed/uninsured you would probably get a visit from the police not long afterwards.