Breaking fault

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Alastair
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Breaking fault

Post by Alastair » Sun May 08, 2016 12:23 am

Hi ....anyone got any thoughts on this? I eventually get round to changing the front subframe on my 1991 turbo after it cracked. The car has patiently waited two years for me to do this standing unused! However..... I replaced front arms and links while I was at it and also two front to rear pipes ( they haven't got mixed up). Well the suspension is fine.... But the breakers are dangerous.... There is a strange delay as I press the break pedal,,,,,, nothing happens then they come on like mad and nearly throw you thru the windscreen. I suspect the rears are hardly working at all..... The discs are/were new. The fronts are nice and shiny...... The rears making progress......and thoughts as to the cause of this dangerous delayed breaking?
Bx turbo diesel 1989
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Jaba
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Re: Breaking fault

Post by Jaba » Sun May 08, 2016 8:35 am

Air in the system would behave this way. Have you tried lots of citaerobics to dispel all air in the system and then bleeding all the front and rear brake lines ?
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Re: Breaking fault

Post by Tinkley » Sun May 08, 2016 8:36 am

Difficult to say exactly what is causing that problem. I suspect I would look at the following. Bleed the hydraulic system with relief valve. Bleed front brakes, and rears to get clean fluid through the brake system. Ensure Accumulator sphere is in good condition. Check calipers are not partially seized, and pedal travel not obstructed. Renew fluid (LHM) if old, it may have become a bit hydroscopic (not as bad as Dot 4 Stuff mind). Finally the FDV may be faulty, it's on or near the nearside rear of the front subframe.

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JayW
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Re: Breaking fault

Post by JayW » Sun May 08, 2016 9:27 pm

The "relief" valve does not bleed anything, it just releases system pressure, IT MUST remain done up when bleeding.

The FDV is bolted to the front of the gearbox with the regulator and does not affect brake or suspension pressure, only the steering. The thing at the back of the sub frame is the safety/security valve.

I would also agree that air in the system or a doseur fault are most likely providing all the pipework went back on properly.
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Re: Breaking fault

Post by Alastair » Sun May 08, 2016 9:31 pm

To up date you for further help! I have bled the front brakes no problem..... Fluid comes out easy...... No fluid however comes out of the rear.... I have even disconnected a pipe at the off side rear caliper..... No fluid! This was done on a garage two poster lift with the engine running, with the wheels suspended if it makes any difference. I have driven the car ( on trade plates) some twenty miles (very carefully) ..... No change..... I have re piped whole bx s in the past with no problem..... Any more ideas?
Bx turbo diesel 1989
Bx 1.9 Rd estate 1989
Citroen Light 15 1952
Bx 17 TZD diesel turbo 1992
Xantia 1.8 16v

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JayW
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Re: Breaking fault

Post by JayW » Sun May 08, 2016 10:25 pm

Bleeding the rears with the wheels suspended can be problematic.

They are fed by the pressure in the rear suspension (the higher the load, the greater the pressure and the greater the braking force), suspending the wheels all but cuts off fluid supply.

You really need to try with the cars weight on them (4 post or pit).

That being said, you should still get SOMETHING through. Sounding increasingly like a doseur issue.
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Re: Breaking fault

Post by rutter123 » Sun May 08, 2016 10:29 pm

I'd go with the faulty doseur valve, not uncommon for them to fail.
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Re: Breaking fault

Post by Alastair » Sun May 08, 2016 11:30 pm

I can look at this tomorrow.......but...... Doseur valve? Where is it located?
Bx turbo diesel 1989
Bx 1.9 Rd estate 1989
Citroen Light 15 1952
Bx 17 TZD diesel turbo 1992
Xantia 1.8 16v

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Re: Breaking fault

Post by Defender110 » Mon May 09, 2016 9:11 am

As said by Jay you can't bleed the rear brakes with the wheels suspended, some even put a heavy load in the back to increase the fluid flow through the load sensing.
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Re: Breaking fault

Post by Tinkley » Mon May 09, 2016 10:15 am

BTW I thought it was meant to be spelt Braking rather than Breaking, the former preferable for a BX rather than the latter... :wink:

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Re: Breaking fault

Post by Pluto » Mon May 09, 2016 2:20 pm

Alastair wrote:I can look at this tomorrow.......but...... Doseur valve? Where is it located?
The doseur valve is mounted low down on the bulkhead in the engine bay. It's on the drivers side (assuming right hand drive). The bolts that hold it in place are actually inside the car behind the brake pedal.

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David
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Re: Breaking fault

Post by David » Sun May 15, 2016 1:42 pm

It still sounds like air in the system to me.

The doseur valve is the Citroen equivalent of the brake master cylinder.
To bleed the brakes properly, you need to press & HOLD the brake pedal down, undo the bleed screws on the front callipers until all the air comes out of them.

It is the same principal for the rears, only you need some weight on the back axle. If you use a 2 post ramp, then you will need a stand (such as a transmission jack) under a rear arm, and then proceed with bleeding. The rears will take longer to bleed as the pipe is in effect, twice the length of the car.
I made the same mistake with the rear brakes the first time I tried to bleed mine, not understanding how the system worked. With weight on the axle it will send LHM out.

Hope that helps.
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Re: Breaking fault

Post by rutter123 » Sun May 15, 2016 3:05 pm

The rear brakes take pressure from the rear spheres as a supplement i.e the more weight you have on the back end the more pressure is applied to the rear brake calipers so effectively wheels off and rest the hubs on blocks of wood (this is how i do it) as if the rear end is "loaded".
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Re: Breaking fault

Post by Alastair » Sun May 15, 2016 3:55 pm

Thanks David.... I have had BXs for 20 years and never had an issue after piping.... But your advice sounds good as does rutter123.... I can proceed along these lines with hope..... Will report back...... Much better than silly Snyd comments about spelling!!!
Bx turbo diesel 1989
Bx 1.9 Rd estate 1989
Citroen Light 15 1952
Bx 17 TZD diesel turbo 1992
Xantia 1.8 16v

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Re: Breaking fault

Post by Tinkley » Mon May 16, 2016 7:05 am

Alastair wrote: Much better than silly Snyd comments about spelling!!!

Oh Dear.... :wink: