Intermittent random brake failure

BUDFORCE

BUDFORCE

BUDFORCE

Soldato
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Before going further, yes I will take it straight to the garage.

However, knowledge is power right?

So, in January had a seized brake caliper, replaced, car was fine for a while. About 3 weeks ago driving on the A1, went to brake, pedal just went to the floor, no pressure, no braking. Fortunately I didnt need to slow down in any major hurry, so after about a second or so, releasing, re-applying pressure, brakes then worked, and continued to do so.

Thought, meh, wierd, but one off, been driving the car 3 weeks no problems.

Today, oddly, (but I doubt related), also driving down the A1, went to brake, same problem, all be it this time the ABS light came on.

Googled and there is little, found two threads detailing exactly the same problem, and she went and had the ABS unit, master cyclinder and brake booster changed, none of which solved the problem. All pretty expensive mitsubishi parts, unfortuantely my car isnt that common for parts.

Now, I pretty much garantee the garage are going to test everything they can, and find no fault.

Ever been doing 90 on a motorway and pushed the brake pedal fore nothing to happen? it's a disconcerting feeling I tell you.

Anyway, can't drive a car that will do that, might kill you, or someone else. I'll give the garage a go, but reckon I'lll need a new car.

Damn annoying, its a Mistsubish Lancer Equippe 07 plate, 110k mileage, which I have had since 30k miles and has otherwise been faultless, and although not worth much now, its a damn good car, real shame if I have have to get rid of it.
 
NoobCannon said:
Sounds like brake booster to me. Altho wierd to be that intermittent

Pedal going straight to the floor is usually air in the system, could be a caliper/seal gone bad somewhere

Does the pedal go straight to the floor or theres still pedal but no immediate breaking?
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No pretty much to the floor with no braking at all, there is no pressure behind the pedal either, like it just goes straight down with nothing/no weight behind it. Almost like if you had no brake fluid at all.
 
NoobCannon said:
And then it comes straight back afterwards?

Do you know what a break booster looks like? Check the vacuum connection to it from what is usually the inlet manifold.
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Yeah pressure comes back after, literally just goes down once, no brakes, let off the pedal, then push the pedal down again and brakes work. It's fine, unless that one random time I need to stop ina hurry quickly the first time, it does it, then that split second to release and put the brake back on is plenty enough to give you a real ****** up day.

As I said, literally done it twice in say, 1000 miles? 500 at least. fortunately both times I didnt need to stop in a hurry.
 
jpaul said:
if the servo assist went it, you have to apply more pressure ?
moreover maybe the fluids old and it's boiled if he's been driving/braking @90 .. but presumably fluid was changed following calliper change.
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Yes, I don't see how you even could change a caliper without changing the fluid, also both times the brakes failed was not following a period of heavy braking, the opposite if anything, driving along probably not using the brakes at all for say 10 minutes of driving.
 
red eye said:
Keep the brake pedal pressed or clamp the hose (not with mole grips) when changing the caliper, stops it leaking and makeing everything slippery.

a fluid change is not a workshop consumable like copper grease, customer has to pay for fluid and labor. Depending on location people don’t like spending £35-40 on brake fluid, even when the fluid looks like something has taken a dump in it.

I’ll bet you an internet beer op hasn’t had a fluid change since 2009
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Hah, incorrect! I did it, hmmm about 3 years ago. I'm not completely inept with cars but I know my limits and what I don't want to mess with, something like this is one of those things.

I did read one thing though which kinda did make a little sense and was to check bearings.

If you think about it, motorway driving, not braking, slight wobble pushes the piston back, right back into the caliper, so when you brake, it has to travel so far your pedal goes right down before you get any pressure, and need a second "pump" for the piston to start pressing against the back of the pad. I will mention that.
 
Munchies said:
Could be the disc the seized caliper was on is warped, and kicking the pads away from the disc, first press brings them back close to the discs, second pump they make contact. Especially if you drove it with a seized caliper.
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Yes - hah you got in before me, thank you though. Could be a winner.
 
So the other thing, I did this test right, pumped the brake pedal with the engine off, it gets hard, so you can hardly press it down anymore.

Turn the engine on with my foot still on the brake, and it goes down.

Then, with teh engine still running, if I pump the brake, it does get harder (a bit) then slowly gets softer again. Also starting the car this moring (its a bit cold) I can hear the engine reving higher when I am pumping the brake, I am guessing to compensate for the power drawn of that vacuum pump (or whatever that bit is).

Apaprently all of the above is a what is supposed to happen.
 
Actually mate of mine Ive been chatting about this with just came up with a really good idea, he said to idle the car for a while, and every now and then test the brakes.

Might help to prove that the problem occurs when the vehicle is in motion, which would further point towards a bearing/warped disc/something similar rather than an issue with the electronics/brake system itself.
 
I ran the car for about an hour, idling on the drive (not actually driving it anywhere) and intermittently tested the brakes, random gaps, no brake failure at all.

Doesn't completely dismiss the cylinder granted.
 
Orionaut said:
Funnily enough, I dont know what a break booster looks like either,

And I have been a professional mechanic for over 40 years!

;) :D

But yes, back to thread. I have come across this sort of thing before with failing wheel bearings.

(Warped disks would produce vibration on braking which might not happen with a wheel bearing issue)

Jack up each wheel, grasp at 6 and 12 o'clock, and see if you can wobble them.

A "Small" amount of movement (IE a mm or two) is acceptable (*Indeed, on older cars it is essential) but anything more than that and you have a problem.

(* this is one of the reasons why the MOT has been scrapped for "Classic" cars. The current MOT is very rule based and things, like hub end-float, that are essential on old type bearings would constitute a fail on a modern car. Tighten a taper roller bearing until there is no wobble/end float and the wheels will fall off! People have actually had major accidents after "Helpful" MOT garages tightened up "Loose" wheel bearings after a supposed MOT fail. This is why the new ruling for older cars came in)
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Thank you for this post.
 
Mechanic spent half a day with it so far, can't find a fault in the braking system itself, surprise surprise.

Couldn't obviously see anything else wrong either.

Is going to check bearings etc tomorrow and get the car moving at speed to see if they can replicate it.

That isn't good news though, the worst possible outcome will be if they can't identify the problem.
 
jpaul said:
.. what did the mechanic say about driving the car in the interim .. can't really see how you can until it's resolved. .. insurance etc.
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Legal issues aside, I'm not going to. Can't drive a car that'll do that. To be honest if they can't find anything I may try another mechanic, maybe even try my nearest Mitsubishi garage, failing that I'll need to get rid of the car, which is really bloody annoying.
 
ron3003 said:
This is almost certainly a failure of the master cylinder seals. If as has been suggested it's a problem with one caliper then you'd still have some brakes due to the way the modern braking system works ie a dual master cylinder system with side one working ns front and the os rear wheel and the second side working the os front and the ns rear wheel.
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Given the number of suggestions I may speak to them and get this priced up. Unfortunately my car isn't that common, so getting hold of one might not be easy. What I am conscious of if spending money throwing parts at it, which is A possibly throwing money away that could be put towards a new car a B not being 100% confident of a fix, with a problem that could potentially kill.
 
So to update, I've decided to get rid of the car. Damn shame as otherwise it's a good car although the mileage is getting on about (110k) , mechanic ain't confident about the master cylinder or servo, nothing wrong with bearings discs everything is aligned.

I just cannot risk replacing parts without being sure it'll fix it, plus it's throwing money at it, which could be put towards a new one.

Sigh..... :(
 
Yea it's a sealed system, air wouldn't cause something like this, plus over time it'll tend to work it's way to the top, the brakes work completely fine, until the two times they failed then it completely failed, with probably 500 miles of completely problem free braking in between.
 
Yea so he said it himself, after lots of braking the fluid heats up, both times this happened I was cruising on the motorway and hadn't been using my brakes beforehand, both times the second pump returned full pressure.

I have been driving my car and being more intensive on the brakes between and all fine, if it were boiling fluid/air this would happen in between under braking, it would also happen to varying degrees depending on how got it got, not join at go from working 100% then complete failure, then back again.

Anyway, might stick the car on eBay under spares and repairs, I could never sell it without making it clear about the fault.
 
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