Bleeding rear brakes

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Bleeding rear brakes

Post by odedn » 05 Apr 2017, 19:33

Hi friends, 

I have to do this process after replaceing the brake regulator.

After reading the Hynes manuel I don't understand why I should take off the wheels and push up the arm to get "inlet" situation.

Selecting the upper mode is enough to open rhe corrector valve.

I would like to know what is the simple way and what steps are needed for bleeding the rear brakes.

I would appriciate your comments.
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Re: Bleeding rear brakes

Post by Hell Razor5543 » 05 Apr 2017, 19:41

It would help a lot if you could let the forum know what make and model the car is. Then those with the relevant knowledge will be able to advise you.
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Re: Bleeding rear brakes

Post by odedn » 05 Apr 2017, 20:09

Citroen gsa 1982
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Re: Bleeding rear brakes

Post by Stonehopper » 05 Apr 2017, 21:34

Due to the rear brakes being regulated by the weight of the car upon the wheels, the rear end can only be bled correctly through fooling the rear suspension into believing it has a load on the rear end. This is done by jacking up the car; removing the wheels; then jacking the wheel arm up to simulate a load on the suspension. Only then will sufficient hydraulic fluid enter the rear braking system to allow the rear brakes to be bled. If this is not done, almost nothing will leave the bleed nipple when opened, and the brakes will not be bled of air.

PS: A bit of guesswork here - Using the 'high' setting on the ride height will cause too much pressure in the system as a whole, and so no good may come of it.
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Re: Bleeding rear brakes

Post by odedn » 05 Apr 2017, 21:54

Thank you Derek, 

Jecking up the wheel arm will transfer fluid to the suspension and the arms will go down and force the car to rise, isn't it ?


It is not clear to me..
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Re: Bleeding rear brakes

Post by myglaren » 05 Apr 2017, 22:02

odedn wrote:Thank you Derek, 

Jecking up the wheel arm will transfer fluid to the suspension and the arms will go down and force the car to rise, isn't it ?


It is not clear to me..


Yes - as I discovered after re-piping my GS and bleeding the brakes. Pushed the arm up that a second or so later started moving down and almost took my arm off.

Learned the hard way to be very wary of hydraulic Citroens.
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Re: Bleeding rear brakes

Post by Stonehopper » 06 Apr 2017, 09:04

Right, it's complicated. The fronts are easy, the rears are not.

To quote a book in part:

Once you have got the car on stands with the suspension ride selector lever in normal ride position, slacken the screw on the pressure regulator (by the main regulator sphere under the bonnet). Then return the ride selector to the high position and wait for the vehicle to sink down, just the front will of course if you have just the rear up on stands. (Haynes is is confusing around this point).
The front should now be on the deck, and the back on the stands.
Take the rear wheels off, and with the aid of a jack, lift one (or both if two jacks available) rear wheel arm(s). The rear suspension regulator will then be in the open position as if the car was loaded.
Prepare your bleed pipe and container. Here's where you need a second person.
Open the bleed valve and press the brake pedal down hard. With the brake pedal pressed down hard, tighten the pressure regulator valve and start the engine. This will cause fluid to run out the bleed valve until they are free from bubbles. Repeat for the other wheel arm.
Close the bleed valve when free of bubbles and release pressure on the brake pedal - this is the time that pressure will build up in the system and wheel arms will begin to move - keep fingers and limbs away from any such arcs of movement!

Edited to add: WARNING, THIS IS VITALLY IMPORTANT:
Make absolutely sure that the car cannot move off the stands when pressure returns to the arms with any jacks beneath the arms themselves, as it is possible the car will lift off the stands and the weight taken on jacks alone. If the car is not positively located by front wheel chocks or a full set of stands there is a danger of it toppling off the jacks ending in disaster and maybe death by Citroen!!


It is a bit of a faff, but that's how it gets done. I don't think I've missed anything, other than check for leaks by applying pressure to the brake pedal, re-fit wheels, set ride to high, remove stands and lower car to the ground. Job done.
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Re: Bleeding rear brakes

Post by RichardW » 06 Apr 2017, 12:28

Surely that's unnecessarily complicated?

4 wheels on the ground, select high, wait for car to stabilise. Engine off, jack up one side of rear, re-start engine, wedge down the brake pedal, bleed the brake. Wheel back on, drop it back, repeat for the other side. Least that's how it's done on later cars.... The only requirement to jack the arm up is if you have it wheels hanging with no suspension pressure, then it will not pressurise the suspension, which is a problem when taking it off stands - you have to wait till it builds suspension pressure or it drops to the floor!
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Re: Bleeding rear brakes

Post by Stonehopper » 06 Apr 2017, 16:15

You may well be right. It's not a method I have used before, but it should work. Certainly saves the faff.
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Re: Bleeding rear brakes

Post by myglaren » 06 Apr 2017, 17:26

Richards method was the one I adopted after scaring the living daylights out of myself.
This was my first Citroen and I was clueless with regard to hydraulic suspension, and most other things too.
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Re: Bleeding rear brakes

Post by odedn » 06 Apr 2017, 20:09

Hi, 

Thank you all,

Today I looked at the rear suspension and to my opinion there is enough space to reach the valve brakes without taking off the wheels,

Another thought...I think maybe it would be better to bleed both valves in parallel to avoid air movement...or maybe it is not necessary if the system is continuosly under pressure (engine run and brake pedal down) while bleeding both sides.

I will try it tomorrow morning.

Thanks,
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Re: Bleeding rear brakes

Post by odedn » 08 Apr 2017, 16:01

Hi
Ashort update ;
The valve brake is located on the end of the rear arm.
Selection the upper situation makes the arm goes down and the car rises. At this position there is clearly a direct approach to the valves with open spaner.
It would be easyer to close & open the valves by taking off the wheels and to approach it from the side but it is not worth the burden. The only disadvantage doing it that way, is loosen small amount of LHM by that the transparent pipes for short time while closing the valves being at front that them.
In my case after bleeding I noticed that the wheels still rotate while the brake pedal is pressed. I found out that one piston brake in both calipers are jammed.
I looked for easy job and found myself deep deep in it...

By the way after searching for rear caliper repair kit 30 mm, I realized that the BX seals share the same dimensions (although the code number are different) which I assume make it more available.
I will check with the local Diller tomorrow.
There is a slight chance to locate it at short time.
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