Brake Pedal Travel

[Jonc]

Was driving on an A road at speed and needed to slow down, however, the car did not slow down as it should and literally had to press the pedal till it would go no further. The car eventually slowed to a stop right up behind the car in front waiting at the round about. He must have thought I was trying to park in his boot!! Never experienced brake fade like that and drove very carefully to my destination. I have since changed the brake fluid to Halfords "High Performance DOT5.1" fluid. It was the only thing I could get at the time. Completely bled 2 litres of fluid through the system to get rid of the old fluid through all 4 brakes using a "eazibleed" pressure bleeding device and made sure the brake reservoir always had fluid to prevent air getting into the system.

After doing this, I can still press the pedal all the way to the bottom/stop. If I give it a few pumps with the car turned off, the pedal then goes hard. However on starting the car the pedal goes "soft" again and can press all the way to the stop. Braking is now back to normal and can stop with no problems activating the ABS at low to moderate speeds. Also performed a number of emergency stops, which have also improved the bite a little, perhaps de-glazing the pads. When doing these stops, I never reach to end of the brake pedal travel as sufficient pressure is applied to stop the car. Question is, is it normal for me to be able to press the pedal all the way to the stop/end of the travel when the car is stationary? Just don't want ever reach the end of the travel or have a reduced margin of travel during brake fade when I *really* need to stop.

 

[BenG]

Close call !

The brake pedal should not go all the way to the end of the travel when stationary. It sounds like you have air in the system for the pedal to hit the floor.
Ive never bled brakes on a car before but when I do the brakes on my bike I have to 'de gas' the fluid before I bleed the brakes, you cant just pour the fluid straight from the bottle into the brake cylinders etc as Hydraulic fluid absorbs air very easily. Im guessing the same must be done for cars due to it being the same type of fluid ?

 

[g40steve]

Pumping pedal during bleeding can add air also :shock:

Pedal should not go to floor at all, only had that happen after spirited drive down fav roads with lots of heavy braking.

Boiled fluid even with everything uprated :roll:

 

[Jonc]

I didn't quite cack my pants, but yes, it was a close one. I can't see how air could have got into the system. Even before the fluid change, when the car was parked up the next morning, I could still push the pedal to the floor, but again the after a few pumps the pedal was hard to push unti the car was started. I admit that I've never had cause to test the brake pedal like this before the brake fade incident though so can't say for sure that it has always been this way. Neither could I say the brake fluids have been changed before I took ownership of the car, so this could be the first change in 3 and a half years (manual says change every 4 years). The brakes are completely OE standard.

Last night, I bled through another half a litre of fluid with the easibleed device, but this time pumped the pedal about 10 times expelling any old fluid that might still be in the master cylinder. Again always ensuring that the brake reservoir was topped up with fluid to prevent air getting into the system. Initially theres's no change, the pedal being soft as before. Took the car out to do some brake testing at various speed. Now the brakes feel a little more firmer to push, but still its possible to push it to the bottom. Could it be that the pad material is soft? They were changed last summer with Renault items made by Ferodo. After testing the brakes they were hot and the discs now have a tint of blue but there was no degradation in braking performance and no brake fade though. With that in mind, I'm inclined just to leave them as they are and accept that its a characteristic of the car.

Incidently, how do you "de-gas" brake fluid before putting it into your car?

 

[shiftspark]

Could be a master cylinder or servo thats at fault ? are you loosing fluid?

 

[Jonc]

What do I need to look for if there's a fault in the master cylinder or servo? I don't see any leaks and level in the reservoir seems fine, plus there are no signs of a leak on the driveway.

 

[Cue]

this will be different from the time i experienced something similar up at croft. Going into the tight right hand bend at the end of the main straight.... pressed the brake pedal all the way to the floor and nothing - using the gears i managed to get it down to around 85 for a 60mph bend, to this day i don't know how i got around the bend.... that was because i thought i could get one more track day out of the oem brakes.

I judged it wrong, disks were shot, pads were 100% gone - you could see the backing plate had actually stopped the car when i got into the pits and the fluid had boiled.

needless to say a few hundred pounds later with new everything the braking was drastically improved.

 

[Jonc]

this will be different from the time i experienced something similar up at croft. Going into the tight right hand bend at the end of the main straight.... pressed the brake pedal all the way to the floor and nothing - using the gears i managed to get it down to around 85 for a 60mph bend, to this day i don't know how i got around the bend.... that was because i thought i could get one more track day out of the oem brakes.

I judged it wrong, disks were shot, pads were 100% gone - you could see the backing plate had actually stopped the car when i got into the pits and the fluid had boiled.

needless to say a few hundred pounds later with new everything the braking was drastically improved.

You're godlike driving skills must have got you around that bend (tupw)

My pads only have a couple of thousand "easy" miles on them and theres a lot of meat left on them, the discs are OK but will need a change soon. What brake setup do you have?

 

[tractor]

If youve bled the system like you say it's unlikely to be air in the system. The next two things i would look at are the master cylinder and then flexible brake lines.

Master cylinder: The seals inside the cylinder could be slightly worn. Instead of the piston pushing the fluid down the line and pressurising the brakes, the fluid could be leaking past the seals on the piston - hence pedal to floor.

Brake lines: One of the brake lines could have a rupture. Fluid can expand the hose instead of pressurising the brakes.

Be careful bleeding the brakes by pumping the pedal, corrosion inside the master cylinder can tear the seals if the pedal is pushed further than the normal point.

It definatly sounds like a hydraulic problem rather than a mechanical problem ie discs/pads/friction.

 

[BenG]

Does the pedal just hit the floor without any force or does it just feel very soft and spongey ?
At least 'some' of the fluid should be de-gassed before putting it in the system, you cant see the air in the fluid but when you put the fluid into a plunger and block off the end, if you pull the plunger down air will just appear as if from nowhere out of the fluid. It is this air in the fluid which will cause the pedal to feel spongey/soft.

BTW. when the cars ignition is off the brake pedal will go solid after a few pumps, this is normal.

 

[Jonc]

The pedal feels soft and spongy. It does get progressively harder through the travel requiring only moderate force to reach the end of the travel, say a little more force than when pushing the clutch in. If there is a leak in the master cylinder, where does the fluid leak too? The brake lines are internally braided so should be OK. I can see no evidence of any leaks externally, plus the pedal does go solid after a few pumps when the ignition is off, so the system can hold the pressure. As I said, the brakes now stop the car quite effectively, activating the ABS on a dry road, when the car has fully stopped, I can get a further inch of travel too the end. Are the brakes over servo'd?

 

[hoolio]

This is a test for servo though not sure if it will work for clio. Pump pedal to get firm whilst keeping pedal slightly depressed start engine, pedal should give a little. Keep engine running for couple of mins then turn off. Depress pedal 4/5 times, should hear hiss then if servo is ok should return to normal. Like I said this is old school so may not be the same.

 

[Dsturbed]

how much travel should there be before the pedal stiffend then, i get the sound of air compressing (by the pedal) and a good 2" travel before pedal firms up (engine on).

 

[BenG]

how much travel should there be before the pedal stiffend then, i get the sound of air compressing (by the pedal) and a good 2" travel before pedal firms up (engine on).

2" is about right, as long as the pedal is firm they are fine. It depends on how much fluid is in the system and how new the pads are, when the pads wear down the pedal will have to be depressed slightly further that It would originally when the pads were new. The air compressing noise is normal.

 

[Jonc]

Been out again to test the brakes, still no fade and no problem with the ABS, the brakes were literally smokin'! I never reach full travel when doing these extreme braking tests though. Pedal has firmed up a little but I can still push to the end of the travel when the car is stationary but this time requiring more effort. Time will tell if this improves. The brakes seem to work fine so I'm just gonna leave it as it is and put it down to "they all do that sir." May be an upgrade due, hopefully firming things up a bit.

 

[Dsturbed]

ben - i got new pads, discs, lines and fluid, so 2" travel before they firm up is still nothin to worry bout then? they just dont feel as instant as my transit and berlingo.

sorry for hijack.

 

[BenG]

Yeah thats fine mate. My pedal travels 40-50mm before anything happens after that its nice and firm. I find the brakes to be pretty instant, however, a while back I drove my old 1.2 clio and hit the brakes and nearly went through the windscreen, they were very sharp. I much prefer the brakes on the Trophy