Yes - hah you got in before me, thank you though. Could be a winner.
Intermittent random brake failure
- Thread starter BUDFORCE
- Start date
Yes - hah you got in before me, thank you though. Could be a winner.
Yes, after 1 pump it was fine.
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.
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.
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.
Soldato
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It's not a warped disc or bearing issue. You have a hydraulic issue and it needs to be fixed ASAP.
Classic signs of a failing master cylinder (seals are probably on their way out) or perhaps air moving around the system.
I would disregard the other forum thread; you don't know what was done or what parts were used, necessarily, and in many cases some workshops carry out very odd diagnosis and repair procedures that often lead to them going around in circles or overlooking the obvious.
Classic signs of a failing master cylinder (seals are probably on their way out) or perhaps air moving around the system.
I would disregard the other forum thread; you don't know what was done or what parts were used, necessarily, and in many cases some workshops carry out very odd diagnosis and repair procedures that often lead to them going around in circles or overlooking the obvious.
You've basically tested your brake servo, it's fine, the pedal has done what it's supposed to do before and after you start the engine etc.
This ^
Funnily enough, I dont know what a break booster looks like either,
And I have been a professional mechanic for over 40 years!
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)
Soldato
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Funnily enough, I dont know what a break booster looks like either,
And I have been a professional mechanic for over 40 years!
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)
https://en.m.wikipedia.org/wiki/Vacuum_servo
This article mainly refers to the mechanical device in the context of a brake power booster or vehicular braking-system assist. The term "vacuum servo" is actually a generic term for any device which uses a vacuum to amplify/boost the mechanical effort of a device by use of a vacuum in an assisting chamber
Funnily enough, I dont know what a break booster looks like either,
And I have been a professional mechanic for over 40 years!
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)
Thank you for this post.
Soldato
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Got absolutely nothing to do with your issue, though.
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.
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.
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.
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.
Don
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Had anyone actually bled the system since the brake work was done?
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.
Soldato
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If you can find the part number it'll probably be far easier to find; you'll probably discover that the same master cylinder is used in several Mitsubishis. I occasionally can't find parts for my Subaru Forester but, if you cross-reference the part number, you get countless alternatives from the Impreza/Legacy range – all of which are infinitely easier to find.
You might be able to get just a seal kit, too; don't forget to ask Mitsubishi directly.