Poor brakes

[ghaddon1701]

I may have over estimated slightly with saying a centimeter. I think it says in the Haynes manual what the free play should be. I also belive it is supposed to be different depending on whether you have an early doseur or a late one.

[michaelr]

Going back to the original poster's question, I suggest that there is a fairly clear path to follow in diagnosing the poor braking.

Firstly I read that the main accumulator is suspect. This is a disaster for the entire high pressure system of a Citroen and needs immediate attention. Not only is there a limited reserve of pressure for emergencies, a flat main accumulator puts enormous strain on the pump and pressure regulator and can lead to cracks and leaks in the pump body and high pressure lines.

Second, an inspection of the pads and discs only takes a short time. Worn pads, thin discs or oil contamination requires replacement parts, easily available.

Bleeding the brakes is also easily done. A ruptured or porous sphere diaphragm could have allowed nitrogen to enter the system though as a previous post pointed out this usually results in a delay between pushing the pedal and the braking action. Allowing the system to run low on LHM also introduces air to the system which is not self bleeding for the brake system ( unlike the suspension which has a circuit returning fluid and air to the reservoir)

The discussion of the "spring" in the later systems is not relevant to poor brake performance. It only affects the pedal "feel".

When the DS was released in 1955 it had a very abrupt and hard pedal feel. People were more used to a conventional pedal which responded to distance pushed whereas the Citroen high pressure system responds simply to pressure applied with the foot. The actual valve plunger movement it very short. The DS fitted a rubber mushroom to give an artificial "distance" feel to the action, the early BX I believe had just a rubber block behind a conventional pedal and I read in this post that later BX have a spring included to mimic the feel of a conventional system. All these additions only affect the pedal feel, not the braking efficiency.

PS I am an old bugger and tend to be a bit opinionated.

[Dollywobbler]

Accumulator now replaced. One caliper is new, all seem to be working ok (no probs passing an MOT). Discs are pretty new, pads at the front are brand new (and now bedded in). Front brakes were bled last week. Rears were bled when the arm bearings were done (and a pipe snapped). Throughout all this work, the brakes have got no better or worse.

[citronut]

Ian how quick dies the car rise on starting from fully down and first go of the day,

i would still give it a thorough bleed of the hole brake circuit, might also try bleeding the dosour valve at the same time,

regards malcolm

[benben10]

interesting reading this thread... my bx with abs feels mushy when i compare it to my series 1 cx estate (RIP)
brakes on that seemed to operate on a switch, either on or off. verry little pressure would have you testing the seatbelts.

[Dollywobbler]

Malcolm - at the moment, I'm still having to pull the height lever quickly to max then normal height to get the front end to rise at all. Comes up in stages, but I know I've got at least one sticky strut which probably doesn't help. I really do need to crack on and get a Hydraflush going on. Having had the fluid since November...

Bleeding the doseur - sounds interesting. The pedal actually feels slightly bouncy at times, so I wouldn't rule out air being stuck somewhere. If I really push the pedal, it feels squashy in a way Citroen brakes don't usually. (but nowhere near as squashy as normal servo brakes, just a slight sensation).

[citronut]

when are you this neck of the woods next Ian,

maybe we can spend a bit more time that your lasy flyung visit checking it out

regards malcolm

[Vanny]

So i've been reading the workshop manual (in preparation of resetting the suspension height on the valver tomorrow!) and was reading through the BRAKES section and spotted some images that might expand on some of the topics covered here.

So the pedal spring, these are drawings of the old (Mk1) and new (face lift) pedal clearly showing the addition of the 'spring' unit;



I see its been mentioned above, and frankly i'd forgotten about it, but have you yet tried bleeding the brake valve/dosseur? It's likely something i'll try tomorrow. It's labelled number 7 here;



I'm betting a bit of pedal wiggling would help to replace any air with LHM, and it does look like an air trap. It also looks to me like this could be the cause of poor rear braking effort?

[Tim Leech]

Interesting pictures, shows why the Mk1 Brakes are so sharp!

[MULLEY]

I had no idea that you could blead the doseur, whats the technique?

[citronut]

I had no idea that you could blead the doseur, whats the technique?

so you didnt know were all your nipples were then MULLEY

long time since i have bled this bleeder/point but i think you di the same as a caliper bleed, open nipple clear pipe attached, other end in to hydraulic tank, engine running, press and hold pedal down till you have a good strong flow of citro blood

Vanny
what does it state the air gap should be beween the pedal and doseur????
regards malcolm

[Dollywobbler]

You'll have to forgive my ignorance. Is the doseur in the engine bay then? Trying to work out how to access it. Not something I've had anything to do with but I'd very much like to try bleeding it.

[citronut]

Ian
the doseur valve is in the engine and behind the brake pedal,

in conventional cars it would be the master cylinder

regards malcolm

[Vanny]

Vanny
what does it state the air gap should be beween the pedal and doseur????
regards malcolm

Mk1's (upto R.P. no 2235) J = 1 to 3mm
Mk2's (post R.P. no 2235) J= 0.1 to 1mm


Interesting the technical note also states that to bleed the rear calipers and the brake compensator-control valve (or dosseur) the suspension should be set to max height so that the 'rear suspension circuit is fed'. Doing this when bleeding the fronts will apparently emulfisy the LHM!

If i get chance i'll scan the whole section up, it makes for interesting reading!

[Dollywobbler]

That's a top tip. Does having it on high make the car think there's a high load in the rear then? I guess it probably does. I'm tempted to have another go at bleeding the rear now, though I'll try and do the doseur (and test) first.