Brake bleeding problems (dual line) SOLVED

Eus

Eus

New Member
Hi all,
I am a new member, you can all rear read my personal introduction in the 'new member section'!

Last week I reconditioned my rear calipers of my P6 3500/1971/dual line. That job went OK.
However bleeding the system is causing trouble now.
A lot of air is coming through both front calipers, and my rear calibers seem to receive no brake fluid at all.
I suspect the '5 way junction assy' to be causing it.

The procedure that I followed is:
- open all 3 bleed nipples on the calipers ( 2 front, 1 rear)
- start engine
- gently push the brake pedal all the way to the floor several times, wait 5 seconds after each time realeasing the pedal.

My plan is to bring back the piston of the '5 way junction assy' in the centre position (if this is not), and try to lock it there with a pin during bleeding.

Any recommendations?

Thanks in advance
 
Re: Brake bleeding problems (dual line)

Hi Eus,

You have not mentioned as to whether you have self bleeding hoses complete with non return valves attached to each open bleed screw. If you don't, that is why you can't bleed the air out. I would only bleed one at a time also, starting at the rear, then L/H front followed by R/H front. If doing the bleeding alone, you need to use one of the hoses that I mentioned above. If you don't have one, then you will either need to buy one or use a standard hose fed into a bottle with the end submerged within brake fluid. Each time the pedal is depressed, prior to lifting your foot to allow the pedal to return, the bleed screw must be tightened. So you need an assistant to open and close the bleed screw while you push the pedal. Open when depressing, closed before lifting.

Ron.
 
Re: Brake bleeding problems (dual line)

Hi Ron,
Thanks for the reply, what you describe is more or less the conventional way of bleeding.
I assume you have good experience with this procedure with your P6.
I'm going to try after work today.

Thanks!
Eus
 
Re: Brake bleeding problems (dual line)

Hi Eus,

I've done (on my dual and other single circuits) as Ron describes, but never with the engine running. It shouldn't make a difference and petrol isn't spent...

Getting the rears purged is a classic trouble spot, a) because it's a long line and b) because the bleed nipple is lower than the LHS caliper feed line so some struggle getting enough force behind the fluid to get all the air out the back. I also bled at the five-way junction as a first step (by undoing one of the unions), to get the fluid flowing initially. That helped me get started.

I seem to remember that I couldn't get the rears done on my car without having one of the fronts open at the same time, else the pedal jammed hard and nothing came out of the rears at all. But I'm not the best source of reliable methods here and I do have a fault in my dual line booster.

Tor
 
Re: Brake bleeding problems (dual line)

Tor said:
Hi Eus,

I've done (on my dual and other single circuits) as Ron describes, but never with the engine running. It shouldn't make a difference and petrol isn't spent...

Getting the rears purged is a classic trouble spot, a) because it's a long line and b) because the bleed nipple is lower than the LHS caliper feed line so some struggle getting enough force behind the fluid to get all the air out the back. I also bled at the five-way junction as a first step (by undoing one of the unions), to get the fluid flowing initially. That helped me get started.

I seem to remember that I couldn't get the rears done on my car without having one of the fronts open at the same time, else the pedal jammed hard and nothing came out of the rears at all. But I'm not the best source of reliable methods here and I do have a fault in my dual line booster.

Tor
Click to expand...

This makes sense, if you have one circuit open and the other closed, the shuttle moves and restricts the open circuit. The shuttle needs to be fixed at the centre position or you need to pressure/vacuum bleed both circuits at the same time.

Yours
Vern
 
Re: Brake bleeding problems (dual line)

Tor and Vern, thanks for your contribution.
I will try bleed the 5 way junction first and see if this helps
 
Re: Brake bleeding problems (dual line)

I have done the dual brake several times and had no problems maybe i was lucky?? :oops:
My daughter in the car and i at the back under the car . Move brake pedal VERY SLOWLY .
Regards Hans
 
It turned out to be a defective master cylinder (under the foot pedal).
I overhauled it with new rubbers and I was able to bleed very easy.

Also I suspect that pushing the pedal all the way to the floor may not necessairily always be the appropriate way to bleed.
Cylinder is more prone to suck air through the small seal + o-ring seal at the very end of the master cylinder. At least in my case this procedure worked.

5 way junction: I dismanteld it, and analysed the function:
- the small piston will never be able to close one of the passages, front or rear brake line.
- it is practically impossible to suck air through this device because there is never lower pressure than ambient air pressure, if it would leak then brake fluid would come out, air will never enter.
- the function of this device is only to detect brake pressure failure in the rear line because it can only move towards the rear brake line mechanically from the centre position
- if we don't want any additional sources of error, we may just as well take the device out, connect in en out rear brake line, and connect in and (2x) out front brake line.
 
Eus said:
It turned out to be a defective master cylinder (under the foot pedal).
I overhauled it with new rubbers and I was able to bleed very easy.
Click to expand...
Result!
Eus said:
5 way junction: I dismanteld it,
Click to expand...
:shock:
Eus said:
and analysed the function:
- the small piston will never be able to close one of the passages, front or rear brake line.
- it is practically impossible to suck air through this device because there is never lower pressure than ambient air pressure, if it would leak then brake fluid would come out, air will never enter.
- the function of this device is only to detect brake pressure failure in the rear line because it can only move towards the rear brake line mechanically from the centre position
- if we don't want any additional sources of error, we may just as well take the device out, connect in en out rear brake line, and connect in and (2x) out front brake line.
Click to expand...
I'm not sure I fully understand the last sentence here - do you mean connecting the brake lines as they are minus the warning switch?

Eus, I should say thanks for doing this, a great disambiguation exercise! Now that mine have been bled and the shuttle piston correctly held in place, it should connect up to the warning light system without giving me a red light in the dash... :wink:
 
Re: Brake bleeding problems (dual line)

Hi Tor, yes I think we can take the device, it is only meant for (rear) brake failure indication.
And a possible cause for error and fluid leakage.
Agree?
 
Re: Brake bleeding problems (dual line)

Hi Eus,

I think I'll try to reconnect mine as I want the warning circuit to work right, and leave it with the assumption it will never, ever leak... :wink:

Tor
 
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