Why did my brakes stop working?
September 27, 2015 7:17 AM Subscribe
I have an automatic Ford Focus ZX3 from 2003. Yesterday, a friend who really knows cars taught me how to change the oil. We also rotated the tires and filled them to spec (34 psi as indicated on the door). When I left, two strange things happened: my right back tail light was out, and more importantly: my brakes were not responsive.
The brakes on my car have always been kind of crummy, even after having them replaced a few years ago. They squeak and they aren't the most responsive generally. But they definitely work and they get the job done. I've never been in an accident.
Yesterday we changed the oil and it went well. We also rotated the tires from front to the alternate back sides and vice versa. These tires are about six months old. They were at 26 psi when we rotated them and the door says that they should be at 34 so we filled them to 34. We didn't mess with the brakes or the electrical at all.
They live in a rural hilly area. When I left a deer crossed my path. I pressed the brakes and the car slowed down but it didn't feel right. It felt like there was less pressure than usual. I got to the end of the road and stopped at the stop sign. The car stopped but then sort of shuddered and got some extra momentum. It was not on a downhill but I attributed it to the fatter tires. I then was on a straightaway and I tested the brakes a bit. The car stopped when I hit them. But when I got to the next stop sign, where I was to turn right, the car kept rolling. I pulled off to the side of the road and used my e-brake to come to a full stop.
I then slowly returned to my friends house, noting that (of course) it felt normal. We looked it over. The brake fluid was fine. He and I took it out for a test drive and of course it behaved normally. I drove the nervous 40 minutes home and the car was fine.
So my two questions are:
1. What the heck happened?
2. Is my car safe to drive? I live in a high traffic area in the US and being on the road is already stressful enough as is.
The brakes on my car have always been kind of crummy, even after having them replaced a few years ago. They squeak and they aren't the most responsive generally. But they definitely work and they get the job done. I've never been in an accident.
Yesterday we changed the oil and it went well. We also rotated the tires from front to the alternate back sides and vice versa. These tires are about six months old. They were at 26 psi when we rotated them and the door says that they should be at 34 so we filled them to 34. We didn't mess with the brakes or the electrical at all.
They live in a rural hilly area. When I left a deer crossed my path. I pressed the brakes and the car slowed down but it didn't feel right. It felt like there was less pressure than usual. I got to the end of the road and stopped at the stop sign. The car stopped but then sort of shuddered and got some extra momentum. It was not on a downhill but I attributed it to the fatter tires. I then was on a straightaway and I tested the brakes a bit. The car stopped when I hit them. But when I got to the next stop sign, where I was to turn right, the car kept rolling. I pulled off to the side of the road and used my e-brake to come to a full stop.
I then slowly returned to my friends house, noting that (of course) it felt normal. We looked it over. The brake fluid was fine. He and I took it out for a test drive and of course it behaved normally. I drove the nervous 40 minutes home and the car was fine.
So my two questions are:
1. What the heck happened?
2. Is my car safe to drive? I live in a high traffic area in the US and being on the road is already stressful enough as is.
Right tail light - did you replace the bulb and did that correct it? It's possible you haven't noticed and it's been out a while. Did you and your friend notice as you were finishing up, or only when you got on the road? Probably not related.
I'm with Thorzdad - concerned that something happened to a brake line. At the very least, some of it sounds like a brake line or lines losing "prime," i.e. an air bubble forming in a brake line, which can disrupt the consistency of the hydraulic pressure. If a line were dislodged so as to be broken, you'd have lost a LOT of brake fluid, and assuming there was enough left it should have been seen when you parked at your friend's house again.
I'm not a big expert on brakes and it's been years since I touched my own brakes on a car. Usually simply swapping out tires/wheels should NOT have any affect on brakes, but on the other hand a little knock if one of the rims hit something as you were mounting it might have pushed one of the brake shoes, which could (maybe?) have disrupted the line pressure momentarily.
If your friend *really* knows cars (i.e. has done this for a living) and looked over the brakes, ask him about this possibility, and whether perhaps he observed anything like this.
I'd do one of two things depending on how risk adverse you are:
- take it on a long, slow drive on some deserted streets where nothing is likely to require a panic stop. If nothing else happens for SEVERAL minutes, get on a highway and with nobody behind you, do a few slowdowns from speed (nothing crazy, just like 55 miles per hour to 25 miles per hour as if you were slowing for an upcoming red light).
If nothing happened in an hour or so of this, I'd say you had some air bubbles and you're good to go.
- if it's really worrying you, and/or if anything hiccups AT ALL during another test drive, I'd get it to a mechanic.
posted by randomkeystrike at 7:38 AM on September 27, 2015
I'm with Thorzdad - concerned that something happened to a brake line. At the very least, some of it sounds like a brake line or lines losing "prime," i.e. an air bubble forming in a brake line, which can disrupt the consistency of the hydraulic pressure. If a line were dislodged so as to be broken, you'd have lost a LOT of brake fluid, and assuming there was enough left it should have been seen when you parked at your friend's house again.
I'm not a big expert on brakes and it's been years since I touched my own brakes on a car. Usually simply swapping out tires/wheels should NOT have any affect on brakes, but on the other hand a little knock if one of the rims hit something as you were mounting it might have pushed one of the brake shoes, which could (maybe?) have disrupted the line pressure momentarily.
If your friend *really* knows cars (i.e. has done this for a living) and looked over the brakes, ask him about this possibility, and whether perhaps he observed anything like this.
I'd do one of two things depending on how risk adverse you are:
- take it on a long, slow drive on some deserted streets where nothing is likely to require a panic stop. If nothing else happens for SEVERAL minutes, get on a highway and with nobody behind you, do a few slowdowns from speed (nothing crazy, just like 55 miles per hour to 25 miles per hour as if you were slowing for an upcoming red light).
If nothing happened in an hour or so of this, I'd say you had some air bubbles and you're good to go.
- if it's really worrying you, and/or if anything hiccups AT ALL during another test drive, I'd get it to a mechanic.
posted by randomkeystrike at 7:38 AM on September 27, 2015
These tires are about six months old. They were at 26 psi when we rotated them and the door says that they should be at 34 so we filled them to 34.
This would've made the contact area proportionally smaller.
The car stopped but then sort of shuddered and got some extra momentum.
Any chance you hit a patch of gravel or an oily spot? Was the road wet with rain?
posted by jon1270 at 7:55 AM on September 27, 2015
This would've made the contact area proportionally smaller.
The car stopped but then sort of shuddered and got some extra momentum.
Any chance you hit a patch of gravel or an oily spot? Was the road wet with rain?
posted by jon1270 at 7:55 AM on September 27, 2015
I'd guess that a small amount of oil could have gotten on your power brakes belt when you changed the oil, and then burned away.
In which case you should be pretty OK, but I'd like you to look under the hood regularly for the next few days to make sure oil is not spraying around in there somehow.
posted by jamjam at 8:39 AM on September 27, 2015
In which case you should be pretty OK, but I'd like you to look under the hood regularly for the next few days to make sure oil is not spraying around in there somehow.
posted by jamjam at 8:39 AM on September 27, 2015
Best answer: The tyre pressures are a complete red herring. Nothing about 26psi (which is too low) and 34 psi (which is about right) would affect braking performance in this way. Nothing at all. The contact patch changing is snake oil handwavey stuff.
I'd guess that a small amount of oil could have gotten on your power brakes belt when you changed the oil, and then burned away.
This doesn't even make sense.
I suspect you somehow got something on the friction face of the discs - like oil or grease or even dirty water - when you changed the wheels over. If the car has been checked and the car performs normally now, then presumably it burnt off and now the surface is clean again?
Alternatively, and more likely in my opinion, is that the brake surfaces 'knocked back' when the wheels were off. This means the brake caliper pistons relax away from the braking surface a little and so the first few pushes just move the pads back towards the friction surface but not actually pressing it hard against it. All mechanics should press the brake pedal a few times after brake or wheel work to check everything is where it should be. Sounds like this step was missed out.
It felt like there was less pressure than usual.
Clarify this please - less pressure in what way? As in the pedal was easier to press and so moved further (so less resistance to pressure with your foot) or you were pressing the same as you always do and the car just wasn't stopping?
if it is a: That supports the knockback theory, assuming the brakes are back to normal after a few stops.
If it is b: Then it is possible the vacuum booster feed is broken/leaking and you are lacking power assistance. So you have to hit the brakes harder to get the same stopping.
If you have ANY issue with your brakes, you first response to unexpected slowing is to hit the brakes as hard as you can, then come off the pedal and hit them again. Not just hold you foot there and worry about the not stopping. Super hard pressure will overcome a fault booster, and coming off and on again will fix any pad knock off issues. As long as you can manage any locking of the wheels (which is possibly ABS on your car anyway) then this is a safe 'go to' in a panic situation.
posted by Brockles at 9:32 AM on September 27, 2015 [8 favorites]
I'd guess that a small amount of oil could have gotten on your power brakes belt when you changed the oil, and then burned away.
This doesn't even make sense.
I suspect you somehow got something on the friction face of the discs - like oil or grease or even dirty water - when you changed the wheels over. If the car has been checked and the car performs normally now, then presumably it burnt off and now the surface is clean again?
Alternatively, and more likely in my opinion, is that the brake surfaces 'knocked back' when the wheels were off. This means the brake caliper pistons relax away from the braking surface a little and so the first few pushes just move the pads back towards the friction surface but not actually pressing it hard against it. All mechanics should press the brake pedal a few times after brake or wheel work to check everything is where it should be. Sounds like this step was missed out.
It felt like there was less pressure than usual.
Clarify this please - less pressure in what way? As in the pedal was easier to press and so moved further (so less resistance to pressure with your foot) or you were pressing the same as you always do and the car just wasn't stopping?
if it is a: That supports the knockback theory, assuming the brakes are back to normal after a few stops.
If it is b: Then it is possible the vacuum booster feed is broken/leaking and you are lacking power assistance. So you have to hit the brakes harder to get the same stopping.
If you have ANY issue with your brakes, you first response to unexpected slowing is to hit the brakes as hard as you can, then come off the pedal and hit them again. Not just hold you foot there and worry about the not stopping. Super hard pressure will overcome a fault booster, and coming off and on again will fix any pad knock off issues. As long as you can manage any locking of the wheels (which is possibly ABS on your car anyway) then this is a safe 'go to' in a panic situation.
posted by Brockles at 9:32 AM on September 27, 2015 [8 favorites]
I'd guess that a small amount of oil could have gotten on your power brakes belt when you changed the oil, and then burned away.
This doesn't even make sense.
Well, not common, granted, but perhaps not inconceivable:
This doesn't even make sense.
Well, not common, granted, but perhaps not inconceivable:
Although vacuum brake boosters are almost ubiquitous, some vehicles use hydraulic brake boosters, which are powered by hydraulic pressure instead of vacuum. This pressure is provided by a drive belt-driven pump and may be tied into a hydraulic power steering system. In other cases, a vehicle may use a vacuum brake booster that uses a belt-driven vacuum pump instead of manifold vacuum.posted by jamjam at 11:09 AM on September 27, 2015
perhaps not inconceivable
It is completely inconceivable with a car that has a vacuum-based booster system. Like the vast majority of passenger cars and, crucially, the one in question which is easily verified by a simple google search. A bit of research would have saved a completely unhelpful answer being posted, particularly one that used the platitude that "you should be pretty OK" if there is no oil flying around the engine, which is bordering on dangerous advice if you aren't even talking about a relevant system to the car in question.
Please don't guess or throw random suggestions at a question that has a serious safety connotation. Especially if you can't even identify the relevant system in question.
posted by Brockles at 5:06 PM on September 27, 2015
It is completely inconceivable with a car that has a vacuum-based booster system. Like the vast majority of passenger cars and, crucially, the one in question which is easily verified by a simple google search. A bit of research would have saved a completely unhelpful answer being posted, particularly one that used the platitude that "you should be pretty OK" if there is no oil flying around the engine, which is bordering on dangerous advice if you aren't even talking about a relevant system to the car in question.
Please don't guess or throw random suggestions at a question that has a serious safety connotation. Especially if you can't even identify the relevant system in question.
posted by Brockles at 5:06 PM on September 27, 2015
Response by poster: Well, the brakes are back to normal and have been since a few minutes after I started driving the car that evening. Brockles, thanks for the comprehensive answer. I think you're right with the knock back idea.
posted by k8lin at 10:13 AM on October 3, 2015
posted by k8lin at 10:13 AM on October 3, 2015
This thread is closed to new comments.
posted by Thorzdad at 7:28 AM on September 27, 2015 [1 favorite]