21 Turbo G788 WUD

[Andyquadra]

The ABS light should come on when the ignition is turned on and then go off.
You can't bleed the rear brakes with the back of the car jacked in the air. You need to lower the car onto axle stands to open the brake compensator

 

[DaveL485]

How I do it:

Support car on trailing arms so suspension is loaded (be careful!)
Fill reservoir
Attach eezibleed and pressurise
Open bleed nipple on NSR and let it flow until no air comes out, tap caliper a few times
Close bleed, disconnect bleed and top fluid up
Repeat for OSR
Then I do NSR again and OSR again. You should get a steady, slow flow of fluid with about 20psi pushing through the master. Dont let the fluid run out, better to have too much and syringe some out after.

The accumulator isnt part of the bleedable system as such, it self bleeds when it pressures up. Make sure its running, make sure it goes off after a few moments. Pump the pedal and it releases accumulator pressure and the pump should start up again.

I dont bleed with the ignition on or pump running.

 

[Ben12345]

Using the pressure bleeder is the only way I can get flow to the rear brake line it seems. The pedal is hard even with the brake pipe leading to the rear of the car disconnected. So I was looking more at the brake pump yesterday, as that doesn't seem to be working as it should.

I can bypass the pump relay, and the pump does run. Initially, it sounded like it was working hard and pressurising, but after 30 seconds or so, the motor sounded like it didn't have much load on it.
I take it that the pressure switch (pressostat) is the horizontal sensor that's almost impossible to get to that's screwed into the pump housing? Looking at the wiring diagram, measuring between pin 85 of the pump relay and ground, I should see continuity for the pump to run, but it's open circuit. So it actually appears that I either do have pressure that's caused the high pressure part of the switch to open, or the switch or plug to the switch is bad.
Maybe I didn't make a good flare when I replaced the high pressure pipe that's between the accumulator/pump and the brake master cylinder/abs block? I'll have to crack it open again to see if anything comes out.

I am getting power to the ABS module next to the passenger seat, the main relay and aux relay seem to be doing their business. The two fuses under the cover are OK, as is the single fuse in the fuse box.

Anyway, more work on it this morning while the wife is out.
Cheers

 

[Ben12345]

Right, Making some progress on the ABS.
I cracked open the joint between the flexi and the pipe at the accumulator/pump end and a load of froth came out. Did it back up and then the pump runs with the ignition on, but continues to do so.
Undid the same fitting completely, ran the pump, and initially, nothing came out. After a few more seconds, the pump primed, the tone changed, and we had fluid! Reconnected the pipe to the flexi. Cracked the other end of the pipe, under the master cylinder, ran the pump some more until fluid came out, and retightened.
Now, turn on the ignition, and it actually sounds like the pump is working rather than just whining. After 30 or so seconds, the pump cuts out. Great I though, but still a hard pedal!? And no amount of pumping the pedal will depressurise the system.


Edit: Ok, after today we have the following conditions:

*Pump/pressostat works. Proven by releasing pressure by opening the high pressure line.
*Rear brakes bled by using eezi bleed. Compensator cable tied open.
*Pedal does not actuate rear brakes. Can crack open the line before the compensator/delay valve and fluid only drips out by gravity... no gush when pedal applied.
*Pumping the pedal does not release pressure from the system and pedal is hard.
*Front brakes work OK.

It's like the clutch master all over again!

Any thoughts?

 

[DaveL485]

Any thoughts?

Its good that the accumulator pressures up and turns off.

We need to figure out why there is no pressure being fed to the rear, obviously. Can you crack the brake line to the back at the master, and see if if flows out of the union? I'd start at the master and work my way along the car toward the back to see where the flow stops. Possible corrosion, blockage?
When you say a "hard" pedal do you mean normal hard or a bouncy, not so good hard?

 

[Ben12345]

The fluid flows from the master when the union is opened up. It dribbles out from gravity or squirts with the eezi bleed. Pressing the brake pedal doesn't make any more dribble out though.

The pedal is a normal hard, like you would expect the brake all to be bled and working but with no assist. The front's are bled and working. The union feeding the rear brakes can be open, and the feeling of the pedal doesn't change.

Sounds like the master/abs valve block is shagged to me. I thought one of the solenoid valves feeding the rear could be sticking, but i've actuated each one several times and the master valve but no joy.

 

[DaveL485]

The union feeding the rear brakes can be open, and the feeling of the pedal doesn't change.

Oh...thats very odd... @Red21 any thoughts on this one?

 

[Ben12345]

Not Renault specific, but I found this Jaguar document, with a little bit more information and hydraulic schematics.

After reading through description of operation, it appears that the 'control valve' must be causing the symptoms I have. Either it's not being operated, or the port in the valve leading to the accumulator is blocked.

I wonder if the Renault unit has what appears to be an inspection plug above the control valve in the diagrams?

 

[Red21]

Try this,

 

[Ben12345]

Tried that already. Fluid just drips out. I will however, give it another go after manually emptying the stored pressure again, just to check it's not me being stupid.

Sent from my SM-G900F using Tapatalk

 

[Red21]

Emptying the accumulator pressure by opening a union can allow air to enter the system and when you switch on the ignition it will have to purge that air before any effect on the master cylinder.
I'll ponder for a few hours whilst I sleep and I might have a idea.

 

[DaveL485]

Tried that already. Fluid just drips out. I will however, give it another go after manually emptying the stored pressure again, just to check it's not me being stupid.

Sent from my SM-G900F using Tapatalk

Empty the accumulator by pumping the pedal 20 times with the ign off. You'll get the horrid hard bouncy pedal I mentioned above.

So, make sure its full, bled and working, then empty it with the above method, do not undo any unions.

 

[Ben12345]

I can't empty the accumulator by pressing the pedal. That's why I must undo the unions. Pressing it way more than 20 times with the ignition off doesn't do anything to the pressure.

 

[DaveL485]

I can't empty the accumulator by pressing the pedal. That's why I must undo the unions. Pressing it way more than 20 times with the ignition off doesn't do anything to the pressure.

Something is very wrong there then, if you use the brake pedal a few times with the ignition on, does the Accumulator start up again?

 

[Ben12345]

Nope, pumping the pedal with the ignition on doesn't start the pump either though. Only opening the high pressure line starts the pump back up, which made me think it was something internal to the master cylinder/abs valve.
Its really been one think after another with this car, lol. Good thing i'm not in a rush!

 

[Red21]

Just double check the actual pedal is free and not seized on its pivot and MC clevis pin.

 

[DaveL485]

Nope, pumping the pedal with the ignition on doesn't start the pump either though.

Thats a problem for sure then. There's a lot of pressure behind it (pump cuts in when pressure drops to 1650psi, cuts off at 2150psi) so something has gone wrong somewhere. Ill have a look at home tonight and see if I can find an internal schematic of the master cylinder.

 

[Red21]

I've been doing some more thinking about this problem and the only things I can think of is either a blocked low pressure return pipe but if the actual pipe is restricted that bad it would have burst at 140Bar operating pressure which runs on the HP side and if it didn't pop you would get some brake servo assistance.
The other item besides the previously mentioned seized pedal it would have to be the mechanical shuttle valve which shuts off the the HP before entering the servo section.
If this is stuck pressure would build up but would not open up to provide servo assistance and thus a constant hard pedal with no flow to the rear brake circuit.
This stuck valve event is unusual from my own experience and the only way to confirm is to strip the unit. How ever looking at some pictures there may be an access plug on top which could give a small view of the valve to see if it moves.

 

[DaveL485]

Interesting! Every day is a school day

 

[Ben12345]

Hi,

The pivot and clevis on the brake pedal are all free, so it's definitely got to be something amiss in the master cylinder.
Yes, the Jaguar document that I uploaded refers to this shuttle valve as the control valve, this was also my thought after looking at the internal schematic of the master cylinder hydraulic circuit.
My plan is to remove the whole unit from the car over the weekend and have a look to see if I can see what's going on through the top access port. Hopefully find something stuck or a blockage. If not, i'll have to have a go at stripping the unit further and go from there.

Cheers.