Brakes failed

[190]

Maybe they failed or maybe I've just discovered another daft design feature about modern cars.

Parked the car in the garage after doing the weekly shop and 20mins later decided I would give it a wash. The garage floor slopes gently towards the door and my driveway slopes gently out to the road so rather than start the car giving the steering lock one more excuse to fail I thought I'd just release the parking brake and roll it out. Once out of the garage I applied the brakes. Nothing !!! the pedal went to the floor with no braking effect whatsoever. I knew there would be no servo assistance but this is a gentle slope and wouldn't have been a problem with my old car.

I stopped the car with the parking brake so no harm done but is it normal for the pedal to go right to the floor when the engine is not running.

What happens if the engine fails out on the road, do the brakes still work, I guess they would but for how long.

Brakes were fine when I started the car to put it back in the garage.

 

[renault12ts]

No, this should not have happened.

 

[190]

That's what I thought.

I'll take a look at the brake fluid level tomorrow although I imagine there will be a sensor that would have warned me if the level was low.

 

[leef44]

Actually that's what I would expect to happen with the servo brake assistance. I've found this the case with all the recent cars I've had. I'm no expert on this subject but I assumed it was something to do with a pump keeping the hydraulic pressure, run by a belt when the engine is on.

I don't actually think there is anything wrong with your brakes

 

[renault12ts]

The fail safe position should be a hard pedal...and brakes that work, not what the OP experienced...I can't think of anything more dangerous.

 

[merc85]

I think on a mot the brake pedal is messured for creep by pressing it then starting the engine , in ur case I'd have thought going to the floor would be a mot failure.

 

[190]

I'm going to try them again tomorrow and I won't be driving the car on the road if there is a problem. The car doesn't get used during the week anyway so there is no rush.

 

[MancMike]

If your fluid is low, a bubble could have gotten in, and has since worked it's way out with the fluid flow when the pump's running?

 

[a111r]

Nothing to do with bubbles. Air in the system results in only a spongy feel, the brakes still work.

What you have here is a seal failure or a rusted out brake line / damaged flexi.
If there's fluid on the ground...calliper pistons or the above.
If not, master cyl. internal leak.

 

[190]

Well I checked everything today and there was no fluid loss as the master cylinder reservoir was at max. I checked all the pads and they were fine. I had a good reason for doing that as I've had a similar experience before due to a pad failure. Back in the 80's I had a pedal go to the floor while driving. The pedal pumped up eventually and the brakes worked OK but became noisy after a few miles. An Inspection at the side of the road showed that the friction material had sheared of the backing plate and the residue of material/adhesive worked until it wore away. This was Sunday evening with no prospect of getting replacement pads until Monday so I drove home very slowly knowing the brakes would work after a fashion but with metal to metal contact on the affected wheel.

Anyway back to the problem. I can't explain how the pedal would go to the floor without fluid going somewhere and yet the level was OK.

There is another possibility. It's a manual transmission so maybe I hit the clutch pedal by mistake although it didn't feel like the clutch pedal but then it wouldn't because you don't depress the clutch with the right foot so it would feel different. If it turns out that was what I did then my apologies for wasting your time.

I'm going to have garage look it over later in the week just to be sure.

 

[martyz]

I have had the same experience,a runaway merc,jumped in hit brake,pedal straight to
the floor,immediately hit the parking brake and stop,no harm done either(v close )

I get out, think to myself,check car,all good...only explanation I could come up with
and I am happy to accept it is,I hit the clutch pedal

That's if yours is a manual gearbox.

 

[a111r]

When I bought my 240td, I lost the brakes driving it 10 miles home on the A406.
72 bhp... so the hand brake did us fine.
That was due to a seized front calliper piston, boiling the brake fluid. The car had stood for a while. When it cooled down, all appeared normal on the brake pedal, which is a good indicator.

 

[st13phil]

so maybe I hit the clutch pedal by mistake

Absolutely the most likely explanation.

As others have said already, this is not a power brake system, it's a power assisted brake system. In the absence of vacuum for the servo (generated by the engine running) you would have a very hard, high brake pedal that you have to push on incredibly hard to get any stopping power. It is also a dual circuit brake system which means that it has two, independent, hydraulic circuits. The chances of both circuits failing simultaneously and then recovering simultaneously are so vanishingly small that it didn't happen.

 

[GordonTarling]

I think you said that the steering lock was still engaged? If that's the case, then the ignition wouldn't have been on and I would have thought it was this that might have disabled the brakes. But then again, it could be that you hit the clutch pedal.