Urgent Help!: Brake pedal goes to floor after fluid change

[Ash1502]

Hello,

I require urgent help please.

I have a 2004 / 54 reg Rav4 2litre petrol, and the brake pedal goes all the way to the floro with the engine running.

Have just replaced front brake pads, osf caliper as it was seized and done a brake fluid change by pumping the pedal and opening the bleed valve flushing the fluid through. All 4 calipers bled ok, no air bubbles appearing in the bleed pipe. The fluid level is maintaining max level. With the engine off, the brake pedal is rock solid, as soon as the engine is started the pedal goes to the floor when pressed. As soon as the engine is stopped, and the pedal is brought up, when it is next pressed it is hard, but only untill the engine is started again. No signs of external leakage from any of the calipers, brake lines, ABS unit, or master cylinder.

The car did not have this fault before the brake fluid change was carried out. In my experience it feels like air in the system, but having bled the brakes twice now, and having a hard pedal with the engine off, leads me to believe it is something else.

Any and all help greatly appreiciated.

[yossarian247]

It's worth searching similar posts on here, but this is reckoned to be perfectly normal on relatively recent model Toyotas. I've tested it on my Auris and Avensis and they both do it too. 

Chances are your car has always done this but until you bled the brakes you never sat in it pumping the brake pedal before so never noticed. 

[Gerg]

I wonder if the brakes are spongy partly because the new pads need to bed into the old rotors?

The rotors will have worn into a tapered cross-section, as they always do, so the new pads will be working against a disk that they don't match up to, at least for a few hundred miles, anyway.

I sent this post was  to an Avensis owner, I don't know if his brakes got better with use, he's not replied that it did.

 

[gjnorthall]

If the pedal is solid after exhausting the servo system and with the engine stopped - there is no air trapped in the system. It’s normal for the pedal to sink to the floor when pressed and with the engine running. Under dynamic conditions ie whilst driving, the free movement in the pedal will be small even under very hard braking. 

[Ash1502]

Thank you all for the replies although I am not sure you understand exactly what is happening

yossarian247: a brake pedal should never go all the way to the floor.

Gerg: when fitting new brake pads yes the pedal will be "spongy" initially as you have the piston pressed back. Once its pressed once the pedal should be always hard and not go the floor.

gjnorthall: it is NEVER ok for a pedal to sink all the way to the floor when driving. Yes the pedal will move a bit, but not all the way to the carpet. 

A fellow mechanic has sugested it could be an internal leak in the master cylinder, causing the pedal to extend further than it should, hence going to the floor. 

[yossarian247]

If I'm understanding correctly, the pedal will go to the floor with the engine running, but is rock solid when the engine is off? That pretty much rules out any fault with the hydraulics, master cylinder, calipers, brake lines, air in the system etc. If there was it would still give a spongy pedal feel and sink down with the engine switched off too. Do the brakes work correctly under normal driving?

Have a look here:

 

The above suggests it is normal.

Last night I went out to my 2009 Auris, started the engine, held the brake pedal down hard and it sank all the way down to the end of its travel. I stopped the engine and tried it again, the brake pedal then went rock hard.

I then tried the same with my wife's 2012 Avensis, and exactly the same behaviour, the brake pedal sinks right down to the end of its travel with the engine running, switch the engine off and it goes rock hard again.

Both cars have full service history, stop very well, and have never had any issues passing the MOT brake test.

[Ash1502]

Yes that is what it is doing. I have only driven the car a few yards to test the brakes. It stops but only once the pedal is on the floor. It did not do this before the brake fluid change. And no car I have ever driven has its brake pedal on the floor. 

[Ash1502]

And reading that post you sent a link for, people in there also agree that a pedal on the floor is not normal. 

[alan333]

What happens if you start the car, let it idle a min or so, press the brake pedal a few times, let it idle another min or so, then press the brake normally?

[Ash1502]

Hi guys, this evening have put a new master cylinder on it, bled the system through thoroughly, master cylinder bled and calipers bled. There is no air coming out of any calipers. The level is at the max. Still got exactly the same problem.

Pedal is nice and hard with very little travel, start engine and pedal goes to the floor every time. Have road tested the car and the car stops dead, locking the wheels and the abs kicking in, but only when the pedal is nearly at the floor.

alan333, if i start the car and let it idle for a couple of minutes, press pedal, let idle and try again, it is the same every time. Pedal goes to the floor. Once the engine is turned off, the pedal is pushed once to the floor ( as though the pistons in the calipers had been pushed back ), and from then on its a hard pedal.

I would now liken it to when you first press the pedal after fitting new brake pads, when the pistons are all the way in and the first pedal press is long as they have to extend back out to the pads. However it should not be doing this every time you have the engine running.

Attached is a video of the fault.

20180515_194208.mp4

[alan333]

If it's pumping up and staying firm with the engine off it's gotta be something to do with the servo then, since you've exhausted everything else.  Or, I seem to remember reading about filling a system with brake fluid from empty on some vehicle (possibly not a Toyota) where there was a specific procedure for filling/bleeding the ABS pump - msybe there's some relevancy there?

[Ash1502]

I see what you're saying about the servo, as it's the last part left really. But I can't hear any air escaping when engine on/off, and as I never went near the servo or pipes im led to believe it's fine. 

[gjnorthall]

Unlikely to be a culprit but the servo can be eliminated as an issue by testing the car with the vacuum hose clamped or disconnected and plugged at the engine side - taking care, of course, during testing as there will be no servo assistance. Under certain circumstances when the hydraulic system has been opened up - air can be trapped in the ABS pump system and this won't be eliminated by normal bleeding. It's necessary to cycle the unit and signal opening and closing the ABS valves as part of the bleeding routine.

[gjnorthall]

Just to be clear - there was no suggestion in my initial post that it was OK to drive with the brake pedal almost to the floor when braking. I was pointing out that when stationary and with the engine running - a feature of some ABS equipped systems is that the brake pedal can be pushed to the floor - this is not a fault. However when driving there should only be modest pedal movement before the brakes act.

[Konrad C]

When I last changed the brake fluid on my old Avensis, I pressure bled the system using Gunsons Easibleed kit. I am sure the Haynes manual suggested pressure bleeding. I tried a pressure of 15psi, but was not happy with the pedal, so increased the pressure. That did the trick and the pedal. Pumping the pedal alone does not work! 

[Gerg]

1 hour ago, Konrad C said:

When I last changed the brake fluid on my old Avensis, I pressure bled the system using Gunsons Easibleed kit. I am sure the Haynes manual suggested pressure bleeding. I tried a pressure of 15psi, but was not happy with the pedal, so increased the pressure. That did the trick and the pedal. Pumping the pedal alone does not work! 

Hi Konrad, can you remember what pressure you went to for a successful brake bleed?  If I remember correctly, the Gunsons kit has a maximum operating pressure in the instructions (25 psi?), did you go much above that?

Top marks for persistence btw!

[Konrad C]

2 hours ago, Gerg said:

Hi Konrad, can you remember what pressure you went to for a successful brake bleed?  If I remember correctly, the Gunsons kit has a maximum operating pressure in the instructions (25 psi?), did you go much above that?

Top marks for persistence btw!

I think I did go to around 25psi. I was worried about going too high. The higher pressure forced the fluid out quicker, including the any air bubbles. Then I noticed the brake fluid becoming clear, telling me the new fluided had come through. Once I did all four wheels, the pedal was firm and brake feeling was improved. 

As I said in my earlier post, when I first tried to bleed the brakes at 15psi, but the pedal travel was soft. That is when I increased the pressure, which gave the better pedal feel and response.  

[Flatfour]

I would be very careful about pressurising the brake fluid reservoir beyond 15 psi as it is only plastic and have been known to split in these methods of bleeding!

I find a better way to get this job done is to use a vacuum pump to draw the fluid through the system, and if necessary have an assistant pump the pedal as well.

[gjnorthall]

Did you manage to sort out the problem?