Horrendous trouble bleeding brakes

[Foeux]

Dear All,

I just did a 3000 mile charity drive around Europe in my LS400. It was excellent and incredibly fast. I wont do any 'willy waving' but we were all startled.

Anyway, going really fast means some serious stopping at times. Unsurprisingly, we warped the discs (3rd set) and cooked the fluid needed changing. With pals, it was jacked, and bled (furthest from master cylinder first) like any other car. Pedal felt rock solid. Engine turned on and the pedal goes straight to the floor.

So I consulted the interned and found that there is an 'ignition on/ignition off' protocol. Did it this way, pedal felt rock solid, straight to the floor. tried activating abs on gravel. no real improvement.

When discs and pads were changed, they were very very clean and the pistons in the calipers all pushed back in with moderate thumb pressure. It has had over 1.5l of fluid, some air has come out and fluid expelled on each corner is now crystal clear.

 

What am I doing wrong and how do I fix it? Usualy a competent DIY mechanic but this has me (and the lexus dealership in bristol stumped.

[steve2006]

When you pushed the pistons back in the calipers did you first loosen the caliper bleed nipples? Reason I ask is that if you didn't you mat have turned a seal inside out in the master cylinder resulting in no brake pressure, this would be confirmed if there are no obvious signs of fluid leaks and the reservoir level remains constant.

[Foeux]

Ah...

 

I took of brake res cap but did not loosed bleed nipples. How easy is MC seal to 'flip'?

 

Thanks for replying so swiftly.

[TigerFish]

I see this being mentioned about seals in master cylinders, but never in all the years I've done brakes have I ever undone the bleed nipple or flipped a seal. It would seem very odd for seals to be so slack they could flip under such small back pressures. The pressure of applying the brakes would be massively greater and should flip the seal if it was that way inclined surely?

Sent from my Iphone using Lexus OC

[steve2006]

Unsure myself just a snippit of info picked up from reading car magazines over the years, the seals are directional and have to be fitted the correct way around, reversing the fluid flow direction could I guess flip the seal.

I would imagine that the only true test would be to disconnect the 2 pipes from the Master cylinder, fit blanking plugs and then see if the pedal still hits the deck when pressed.

Another possible is air in the ABS block located under the airfilter housing, there is also a bleed nipple on this.

[steve2006]

If it is the Master Cylinder, I have a known good one you can have for the cost of the postage.

[plexus914]

Damaging the master cylinder can happen when pushing the pedal to the floor. Most common fault when bleeding the system via brake pedal. Never push it all the way!

[Foeux]

On 06/02/2016 at 7:26 PM, steve2006 said:

Unsure myself just a snippit of info picked up from reading car magazines over the years, the seals are directional and have to be fitted the correct way around, reversing the fluid flow direction could I guess flip the seal.

I would imagine that the only true test would be to disconnect the 2 pipes from the Master cylinder, fit blanking plugs and then see if the pedal still hits the deck when pressed.

Another possible is air in the ABS block located under the airfilter housing, there is also a bleed nipple on this.

Had a look for nipped. Wasn't one sadly...

On 06/02/2016 at 7:27 PM, steve2006 said:

If it is the Master Cylinder, I have a known good one you can have for the cost of the postage.

If shot, I'd love to take you up on offer.

 

As it is brakes a lot better now. ABS working and good power again. Odd. Will replace hoses and report back. Also going to stick some more serious brake pads in it.

[steve2006]

No problem always glad to help another member if I can as other members have helped me in the same position.

[runsgrateasanut]

On 04/06/2016 at 6:22 AM, plexus914 said:

Damaging the master cylinder can happen when pushing the pedal to the floor. Most common fault when bleeding the system via brake pedal. Never push it all the way!

I read this thread and thought thats not the way I used to understand the procedure.  Checked in my old "AA Book of the Car"

and comment says "press the Brake pedal to the Floor and let it return".  Pretty certain thats what I did many many Moons ago if I had to bleed brakes.  Did once have to replace a Master cylinder on my Austin Ambassador (wedge shaped very comfortable Car) which failed whilst driving it, fortunately with no incident occuring as handbrake still operational.

Will bear your advice in mind should I ever want to get my hands dirty again - (unlikely!!)