In hard braking one wheel locks up, why?

I went to test my breaking ability the other day, only come to a stop and have blue smoke rise from my front left wheel.

First, I don't have (working) anti-lock brakes. However I would expect, and have experienced, multiple wheels locking up at once. In this instance I could barely tell the front wheel was even locked up, so I didn't know to ease off the brakes.

Now, the scientist in me says that not all friction combination are equal, that of the rotor, pad (and caliper pressure), tire, and road surface, thus ONE wheel must break first. However I have not personally ever experienced this before. I'm quite certain I've been able to break harder without a wheel locking up. Also, the other 3 wheels did not lock up, so I don't think I was teetering on the edge of locking all 4 (though I'm sure it wasn't that far away).

Should I be worried? What would cause a single wheel to lock up before the others? The tire doesn't look any worse than the others...

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles




Edited 1 time(s). Last edit at 09/23/2009 04:25PM by Earendil.

The short answer is that the caliper has seized up.
You'll either have to replace it or if you're lucky you may be able to rebuild it.

Before I got my car, one of the previous owners had a seized caliper and the BMW dealer simply replaced the whole unit... $$$

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Archeo-peteriX
The short answer is that the caliper has seized up.
You'll either have to replace it or if you're lucky you may be able to rebuild it.

Before I got my car, one of the previous owners had a seized caliper and the BMW dealer simply replaced the whole unit... $$$

Knowing the visual state of my calipers up front, this isn't surprising. What is surprising to me is that a seized caliper would cause an increase in pressure on the pad/rotor?
I would have thought the brake would either not engage, or would fail to disengage. I don't suppose you know what is happening mechanically?

I'll take my caliper off tomorrow and give it a look over, as well as check for anything else that may be obviously wrong.

Peter, are you sure you don't have some answer like "Obviously the X switch is in the wrong position, just flip it the other way and you're set!". No? Damn... It's just never that simple

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles




Edited 2 time(s). Last edit at 09/23/2009 08:24PM by Earendil.

my theory is that the left/front wheel has the shortest brake duct and that's why it always locks up first. however, i have no proof for this - it's just something i *think*, because i noticed it in almost all cars i've driven

if you have a seized caliper, you WILL notice. you will hear noise, feel it in the steering wheel at some speed and SMELL it. of course, it will happen at midnight, on the highway. ask me how i know

--
A physics truck just turned over outside. There's physics everywhere!

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jaffar
my theory is that the left/front wheel has the shortest brake duct and that's why it always locks up first. however, i have no proof for this - it's just something i *think*, because i noticed it in almost all cars i've driven

if you have a seized caliper, you WILL notice. you will hear noise, feel it in the steering wheel at some speed and SMELL it. of course, it will happen at midnight, on the highway. ask me how i know

Not to shoot a hole in your theory.... But when I said front left brake, what I really meant was front RIGHT brake.
I like your thinking though

I have noticed no unusual smell, noise, or performance change of any kind... accept for the braking of course :undecided:

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles




Edited 2 time(s). Last edit at 09/24/2009 01:25AM by Earendil.

Tyler, Jack the front up so both wheels are off the ground, spin the wheels and see if they both are free; slight drag. Now have a helper push the brakes down hard at the pedal and let off, the wheels should free right up- report back

I (unfortunately) have a lot of experience locking up the brakes in my track car (a 1990 Miata). It does not have ABS, and because I'm threshold braking most of the time, there have been moments when I get carried away and lock them up going into a turn. As you discovered, it is always the front right that locks up first. Why? There are a couple things going on here.

1. Street cars are always designed with a front brake bias, so that the fronts will always lock up before the rears. They're designed that way so that if the brakes do lock up, you'll skid in a straight line. If the rears were to lock up first, all kinds of mayhem happens, usually involving the rear of the car passing the front. Race cars often have an adjustable brake bias, so the driver can control how much braking the rears do. The more equal you make the brake bias, the greater the stopping power, but the greater chances of a spin under lockup. (There's also a personal preference; some drivers prefer more front bias, some more rear bias.)

2. OK, so why the front right and not the front left? Because with only one person in the car, there is more weight on the left side, so the front right tire is less loaded. With less weight on it, it skids first. To verify this, one could see if right-hand drive cars lock up the front left first. I would bet that they do.

Anyway, you should see about getting that ABS fixed. It's nice to have a street cars, and the ABS on our E30s is the best ABS I've ever seen. It's really nice -- smooth and unobtrusive.

__________
Dave
'91 325iX



Edited 1 time(s). Last edit at 09/24/2009 05:03AM by Dave_G.

I can confirm this somewhat, I've had two MB with non-working/non-existent ABS and during experimentation (or fun, I can't remember) I realized that only the front right was leaving black marks. I thought something was wrong until my mechanic (who auto-crosses regularly) told me he experiences the same thing.

i think a lot more factors should be taken into account on this for example, the age of the car, the age of the suspension parts, the fact that the car was driven mostly wth just the driver inside, the type of roads the car has been driven on (for example, if you have REALLY bad roads like we do, the right side suspension parts are broken a lot sooner) etc. all old(ish) cars i've driven lock the front/left wheel first.

i've never liked the e30 abs. in my oppinion, it kicks in way too early and it works very badly. i could control the e30 MUCH better without ABS, and i could also get a lot shorter braking distances. e30 ABS sucks, if you ask me. e36 ABS is a bit better (kicks in when it should, has a lot more cycles) but it still sucks and makes the braking distance way too long. modern ABS seems to be a lot better, even on cheaper cars.

--
A physics truck just turned over outside. There's physics everywhere!

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Earendil
Knowing the visual state of my calipers up front, this isn't surprising. What is surprising to me is that a seized caliper would cause an increase in pressure on the pad/rotor?
I would have thought the brake would either not engage, or would fail to disengage.

More likely, the caliper on the opposite front side is seized, providing less braking on that side. Under maximum braking the good front caliper is doing all the hard work and will lock up first.

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Ferdinand

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Earendil
Knowing the visual state of my calipers up front, this isn't surprising. What is surprising to me is that a seized caliper would cause an increase in pressure on the pad/rotor?
I would have thought the brake would either not engage, or would fail to disengage.

More likely, the caliper on the opposite front side is seized, providing less braking on that side. Under maximum braking the good front caliper is doing all the hard work and will lock up first.

Good point

For its age, the E30 ABS is a pretty good thing. Sure, modern ABS's are better, but for its age it was good.

I quite like the ABS on my new E30.

My old black 86 325e had no ABS and I didn't miss it. My wife's 2002 Subaru Outback has ABS and I detest it with a passion. It is waaaay too sensitive and kicks in way too early, and then it feels like it's not braking at all. I hate it so much that I always pull the ABS fuse on the Subaru before the first snow flies.

The ABS on this new red 1990 325i isn't bad at all though. It kicked in a few times during our Targa week under really hard braking, but without the ABS I probably would have ended up with locked brakes and flatspotted tires.

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Ferdinand
My wife's 2002 Subaru Outback has ABS and I detest it with a passion. It is waaaay too sensitive and kicks in way too early, and then it feels like it's not braking at all. I hate it so much that I always pull the ABS fuse on the Subaru before the first snow flies.

It's not just you. It seems like everyone hates Subaru's ABS. For the record, I've had ABS in an '01 Ford and an '04 Mazda, and the system in my '91 E30 is better than both of them (slightly better than the Mazda, WAY better than the Ford). In fact, the ABS in my E30 is the only one I've personally driven that hasn't been intrusive enough to drive me crazy.

__________
Dave
'91 325iX

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Dave_G

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Ferdinand
My wife's 2002 Subaru Outback has ABS and I detest it with a passion. It is waaaay too sensitive and kicks in way too early, and then it feels like it's not braking at all. I hate it so much that I always pull the ABS fuse on the Subaru before the first snow flies.

It's not just you. It seems like everyone hates Subaru's ABS. For the record, I've had ABS in an '01 Ford and an '04 Mazda, and the system in my '91 E30 is better than both of them (slightly better than the Mazda, WAY better than the Ford). In fact, the ABS in my E30 is the only one I've personally driven that hasn't been intrusive enough to drive me crazy.

I've got chime in here. Janet's car has the ABS working and I really hate it, but I've left it in place because it's gotta help some; for her I want everything in place to help.

For me, I hate it and always disconnect it on my cars; I don't want anything between me and the road. I've locked my car up a few times and both wheels were smoking, Tyler just has a bad caliper/hose or something going on. I gave him a test to tell just what it is that's gone south.

Most cars have portioning valves on the rear brake lines so they don't lock up before the fronts, thirtys do not have these but these cars brakes seem fairly evenly balanced. Its been my experience anyhow

Rick

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rkj

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Dave_G

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Ferdinand
My wife's 2002 Subaru Outback has ABS and I detest it with a passion. It is waaaay too sensitive and kicks in way too early, and then it feels like it's not braking at all. I hate it so much that I always pull the ABS fuse on the Subaru before the first snow flies.

It's not just you. It seems like everyone hates Subaru's ABS. For the record, I've had ABS in an '01 Ford and an '04 Mazda, and the system in my '91 E30 is better than both of them (slightly better than the Mazda, WAY better than the Ford). In fact, the ABS in my E30 is the only one I've personally driven that hasn't been intrusive enough to drive me crazy.

I've got chime in here. Janet's car has the ABS working and I really hate it, but I've left it in place because it's gotta help some; for her I want everything in place to help.

For me, I hate it and always disconnect it on my cars; I don't want anything between me and the road. I've locked my car up a few times and both wheels were smoking, Tyler just has a bad caliper/hose or something going on. I gave him a test to tell just what it is that's gone south.

Most cars have portioning valves on the rear brake lines so they don't lock up before the fronts, thirtys do not have these but these cars brakes seem fairly evenly balanced. Its been my experience anyhow

Rick

The E30 has something called a brake pressure regulator in the rear lines. I don't know if this is the same thing as a proportioning valve or not but it definitely must have some affect that reduces potential rear wheel lock up.

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Archeo-peteriX

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rkj

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Dave_G

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Ferdinand
My wife's 2002 Subaru Outback has ABS and I detest it with a passion. It is waaaay too sensitive and kicks in way too early, and then it feels like it's not braking at all. I hate it so much that I always pull the ABS fuse on the Subaru before the first snow flies.

It's not just you. It seems like everyone hates Subaru's ABS. For the record, I've had ABS in an '01 Ford and an '04 Mazda, and the system in my '91 E30 is better than both of them (slightly better than the Mazda, WAY better than the Ford). In fact, the ABS in my E30 is the only one I've personally driven that hasn't been intrusive enough to drive me crazy.

I've got chime in here. Janet's car has the ABS working and I really hate it, but I've left it in place because it's gotta help some; for her I want everything in place to help.

For me, I hate it and always disconnect it on my cars; I don't want anything between me and the road. I've locked my car up a few times and both wheels were smoking, Tyler just has a bad caliper/hose or something going on. I gave him a test to tell just what it is that's gone south.

Most cars have portioning valves on the rear brake lines so they don't lock up before the fronts, thirtys do not have these but these cars brakes seem fairly evenly balanced. Its been my experience anyhow

Rick

The E30 has something called a brake pressure regulator in the rear lines. I don't know if this is the same thing as a proportioning valve or not but it definitely must have some affect that reduces potential rear wheel lock up.

Really Peter, I've never seen one on mine (1988 325is), maybe on later cars? The 5er's have em.

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rkj

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Archeo-peteriX

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rkj

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Dave_G

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Ferdinand
My wife's 2002 Subaru Outback has ABS and I detest it with a passion. It is waaaay too sensitive and kicks in way too early, and then it feels like it's not braking at all. I hate it so much that I always pull the ABS fuse on the Subaru before the first snow flies.

It's not just you. It seems like everyone hates Subaru's ABS. For the record, I've had ABS in an '01 Ford and an '04 Mazda, and the system in my '91 E30 is better than both of them (slightly better than the Mazda, WAY better than the Ford). In fact, the ABS in my E30 is the only one I've personally driven that hasn't been intrusive enough to drive me crazy.

I've got chime in here. Janet's car has the ABS working and I really hate it, but I've left it in place because it's gotta help some; for her I want everything in place to help.

For me, I hate it and always disconnect it on my cars; I don't want anything between me and the road. I've locked my car up a few times and both wheels were smoking, Tyler just has a bad caliper/hose or something going on. I gave him a test to tell just what it is that's gone south.

Most cars have portioning valves on the rear brake lines so they don't lock up before the fronts, thirtys do not have these but these cars brakes seem fairly evenly balanced. Its been my experience anyhow

Rick

The E30 has something called a brake pressure regulator in the rear lines. I don't know if this is the same thing as a proportioning valve or not but it definitely must have some affect that reduces potential rear wheel lock up.

Really Peter, I've never seen one on mine (1988 325is), maybe on later cars? The 5er's have em.

I'm just going by the RealOEM parts lists. I checked the 325e,/i/ix They call it a regulator...whatever that means.

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Archeo-peteriX

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rkj

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Archeo-peteriX

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rkj

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Dave_G

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Ferdinand
My wife's 2002 Subaru Outback has ABS and I detest it with a passion. It is waaaay too sensitive and kicks in way too early, and then it feels like it's not braking at all. I hate it so much that I always pull the ABS fuse on the Subaru before the first snow flies.

It's not just you. It seems like everyone hates Subaru's ABS. For the record, I've had ABS in an '01 Ford and an '04 Mazda, and the system in my '91 E30 is better than both of them (slightly better than the Mazda, WAY better than the Ford). In fact, the ABS in my E30 is the only one I've personally driven that hasn't been intrusive enough to drive me crazy.

I've got chime in here. Janet's car has the ABS working and I really hate it, but I've left it in place because it's gotta help some; for her I want everything in place to help.

For me, I hate it and always disconnect it on my cars; I don't want anything between me and the road. I've locked my car up a few times and both wheels were smoking, Tyler just has a bad caliper/hose or something going on. I gave him a test to tell just what it is that's gone south.

Most cars have portioning valves on the rear brake lines so they don't lock up before the fronts, thirtys do not have these but these cars brakes seem fairly evenly balanced. Its been my experience anyhow

Rick

The E30 has something called a brake pressure regulator in the rear lines. I don't know if this is the same thing as a proportioning valve or not but it definitely must have some affect that reduces potential rear wheel lock up.

Really Peter, I've never seen one on mine (1988 325is), maybe on later cars? The 5er's have em.

I'm just going by the RealOEM parts lists. I checked the 325e,/i/ix They call it a regulator...whatever that means.

Can you please give me the page Peter?

This is for a 325i; check item #5...
[www.realoem.com]

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Archeo-peteriX
This is for a 325i; check item #5...
[www.realoem.com]

I'll be Thanks Peter

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Earendil
Not to shoot a hole in your theory.... But when I said front left brake, what I really meant was front RIGHT brake.
I like your thinking though

I have noticed no unusual smell, noise, or performance change of any kind... accept for the braking of course :undecided:

Hi,
A friend of mine is an ABS calibration engineer, so I asked him about the whole driver weight = later lockup on that wheel thing. He says there is an effect, they always see slightly lower lock-up pressures on the drivers side, but it's really a small amount. Without ABS, the passenger side should lockup miliseconds later so you shouldn't notice just one wheel locking on its own.

Afterthought: unless the road you were testing on was highly cambered near the gutter?

So I reckon something is not right on your car. No idea what, though, sorry! :embarrassed:

Well, I can't find anything wrong with the system. Brake calipers release my wheel quickly, and none of them are dragging.

I'm wondering now if it wasn't a combination of worn tires and a slicker portion of the road. That would cause a single wheel to lock up before the rest, if it didn't have the same rolling friction as the rest of them. Yet still enough friction to burn rubber

I bet I know what it is! My rotors are warped!

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles




Edited 1 time(s). Last edit at 09/27/2009 08:04PM by Earendil.

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nomis3613
Without ABS, the passenger side should lockup miliseconds later so you shouldn't notice just one wheel locking on its own.

That may be the theory, and while in theory there should be no difference between theory and practice, in practice there is. As I mentioned, over the years I've locked my brakes many times, and in every instance only one (front) wheel locked. In my Mazda MX-5 track car, it's always the front right, as it is on almost all of the other MX-5s on the track. Other cars may lock the other side, but IME it's almost always one wheel.

I will allow that there may be a difference between locking up on the track vs. a typical street car, in that typically a race driver is threshold braking and trying very hard to modulate the brake pedal, whereas in a typical panic stop on the street a driver is just mashing the brake pedal as hard as possible. In that case, in the absence of ABS it may be that both front wheels lock up. (I don't know from experience -- I try to avoid doing that. )

In thinking about this I was reminded of one of my favorite YouTube clips of the epic battle between Gilles Villeneuve and Rene Arnoux at the 1979 French Grand Prix. It's heart-pounding stuff, but in this context I was thinking of all the times that Villeneuve locked up his brakes going into Turn 1. In every single case, only the left side locked up. That's very typical behavior. Have a look: Villeneuve and Arnoux, 1979 French GP

__________
Dave
'91 325iX

Dave,
Great video! If only the Singapore Grand Prix last night was as interesting as that, I might have stayed awake for more than 1/2 of it...

It's strange that Villeneuve's outside wheel locked each time. Normally it's the (unloaded) inside. Perhaps the outside tire was worn far more than the inside, so it had less braking grip??

If there is a reason that causes one side to lock before the other, I reckon it isn't the static weight of the driver.

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Dave_G
In thinking about this I was reminded of one of my favorite YouTube clips of the epic battle between Gilles Villeneuve and Rene Arnoux at the 1979 French Grand Prix....

I still miss that guy. http://www.iprimus.ca/~trauttf/Gilles/

The tires on Villenuve's Ferrari were completely shot by that point, and Arnoux's Renault was running low on fuel and experiencing fuel pick up issues. But neither would give up.

Poor Jean-Pierre Jabouille delivered the turbo Renault team its first ever F1 victory, in it's home French Grand Prix no less. But hardly nobody noticed or remembered that in comparison to the battle for second place.

The engineer in me sez the left front should lock up first (shortest brake line distance from the master cly). but road conditions and how the car is loaded at the time probably has something to do with it too.

Hi Rick,
(apologies to Earendil for hijacking this into an engineering geek-off!)

In theory, yes, the pressure wave will reach the closest wheel first. But the speed of sound in water is 1 484 m/s so a 1m difference in brake lines will cause the far wheel to lock 0.000 674 seconds later!

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nomis3613
Hi Rick,
(apologies to Earendil for hijacking this into an engineering geek-off!)

In theory, yes, the pressure wave will reach the closest wheel first. But the speed of sound in water is 1 484 m/s so a 1m difference in brake lines will cause the far wheel to lock 0.000 674 seconds later!

You may not be aware, but when I ask a technical question, I fully expect and enjoy a technical answer ;-)

I wouldn't think it would be the pressure wave that would cause it. In this case, I was doing a braking test, so I was applying ever so firmer pressure to the pedal. I was not jabbing it down suddenly. If anything, I would think that the shorter line would have less compression, and so would generate more force. I am aware that one of the key characteristics of hydraulic fuel is that it compresses really poorly, so I say this without knowing what the compression difference might be on this small of a scale.

I suspect at this point that there is a much higher chance that the breaking difference has something more to do with imperfection between all the tires/rotors/pads/pavement than it does with the engineering specifications of the braking system its self. The size of the variables associated with just the tire alone are huge, and if we wanted to know "which wheel locks up first" we would need to have every tire as identical as possible.
Can we conclude that, outside of normal ware-and-tear items, there is probably no significant problem with my car?
Don't worry, I won't sue

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

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Earendil
I suspect at this point that there is a much higher chance that the breaking difference has something more to do with imperfection between all the tires/rotors/pads/pavement than it does with the engineering specifications of the braking system its self.

I totally agree!

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Earendil
Can we conclude that, outside of normal ware-and-tear items, there is probably no significant problem with my car?

Yep. Except for that wierd crunch it makes as you shift into forth...