brake problem

crooser · Post by **crooser** » 20 Feb 2004, 23:14

the brakes on my xm are seized solid and it's not the calipers.when i release the pressure in the system the correct way and then press the brake pedal a few times the brakes release and the car moves.however when i tighten the pressure release screw and build the pressure back up the brakes lock on again even though i haven't touched the pedal at all.does anyone have any ideas because it's got me foxed.

jeremy · Post by **jeremy** » 20 Feb 2004, 23:45

sounds as though the doseur valve is sticking open. (Is the pedal moving freely?, Is any adjustment of the pedal/linkage correct? Has something failed (spring?) and got between the linkage and the valve piston?
Jeremy

crooser · Post by **crooser** » 21 Feb 2004, 00:06

jeremy,the pedal moves freely and normal.do you have any idea where the doseur valve is on an xm estate?if this is the only cause of the problem i can replace it.i presume that it cannot be serviced.thanks for replying

Dave Burns · Post by **Dave Burns** » 21 Feb 2004, 00:22

If it has ABS there could be a fault there, do all the brakes lock on or is it just one wheel, if it was a single wheel it would be the abs, if fitted of course.
I cant see any way for the doseur valve on its own to maintain high brake pressure without outside interference, nor can I see anything that could break and cause this, what could do it is dirt or swarf entering the valve and getting down the side of a piston and seizing it.
Something else that could cause it would be partially blocked return pipes, this would only cause a low build up of pressure though or the pipes would simply blow off or burst, so are they on solid or just dragging heavily and are they all doing it.
Dave

crooser · Post by **crooser** » 21 Feb 2004, 01:18

dave.the car has abs and all 4 wheels lock solid.even with full power from the engine the car will hardly move.no work has been done on the brakes or hydraulics but once the pressure has been completely removed the brakes are free,start the engine and they lock solid again.the car had been standing for 6 months but the brakes were fine when i drove it home.

noz · Post by **noz** » 21 Feb 2004, 01:58

crooser,
The problem's dead simple, and very common too although not well reported in these forums.
The most common cause is the linkage between the pedal and the master cylinder. The right hand drive cars didn't have enough room to mount the master cylinder(brake valve) behind the pedal so they mounted it up top under the scuttle panel at the bottom of the windscreen. Unfortunately the joints in the linkage are open to the elements and rust/sieze over time.
It's very easy to check. Just remove the scuttle to expose the brake valve and linkage next to the wiper motor. With the brake pedal released, pull the linkage up. If there's more than 5mmm movement it means that the return spring pressure isn't enough to overcome the friction caused buy the corrosion.
If so, undo the bolt through the top linkage union and withdraw. Sandpaper and grease all the components and reassemble. The joint should be free and the return spring should permit enough travel to fully release the brake valve.
Sometimes the stickyness is so slight that you don't notice. The only sign may be premature wear of pads and discs. If it get's worse it'll eventually fry the grease in the wheel bearings and they'll fail too. All in all a very expensive exercise.
Of course if the brakes are dragging it won't do much for the old fuel consumption figures.
Take a tip and check this today. It costs nothing, it's very easy to do and could save you a fortune in the long run.
If you wan't to know the consequences of not checking this read here:
http://club-xm.com/forum/viewtopic.php?t=26
http://club-xm.com/forum/viewtopic.php?t=43
http://club-xm.com/forum/viewtopic.php?t=15
happy motoring
cheers
noz

crooser · Post by **crooser** » 21 Feb 2004, 02:02

well noz, how come it didn't tell me that in my posh new xm cd?only joking,thanks norrie.

AndersDK · Post by **AndersDK** » 21 Feb 2004, 02:12

Crooser -
Year & mileage of this XM would be nice to anticipate likely problems due to age/wear.
Brake doseur valve = master valve = pedal valve.
It's located directly behind the pedal - bolted on to the bodysheeting - protruding the engine bay right down there between engine and footwell wall. Not easy to access [:(] - especially on RHD export models [xx(]
Either the pedal by some fault are resting against the valve - releasing system pressure to the brakes - or the valve itself is at fault. This could be the valve's internal return spring - or the rubber bulb which receives the moving contact from the pedal.
The inertia of a moving heavy car (XM 1.2 - 1.3 ton) is much higher than the engine power available to make the brakes start slipping. Thus the needed brake force to stall the engine is not very high.
As I read your indications - it seems clear you're facing a brake valve replacing.

noz · Post by **noz** » 21 Feb 2004, 02:15

sorry crooser, didn't recognise you with the hat & glasses on !
a manual it may be, but a magic wand it aint

take care
noz

AndersDK · Post by **AndersDK** » 21 Feb 2004, 02:15

ooops [:I][:I]
Just read Norrie's posting - the valve is in fact located odd on RHD's [:o)]

crooser · Post by **crooser** » 21 Feb 2004, 02:34

thanks anders and noz i have a good days work tomorrow.the car by the way is a 95 2.0 turbo vsx estate.i paid 100 for it because the guy had given up.it needs tlc and with the aid of this forum things will always look brighter.my own car is a 2.5 vsx estate and the trouble i've had with it is another very long story.

crooser · Post by **crooser** » 21 Feb 2004, 15:07

well noz and anders, done the job it took about an hour and it all works fine now.there are some very knowledgeable people about thank the lord.

noz · Post by **noz** » 21 Feb 2004, 20:34

crooser,
when you got to the link did it seem like it was sticky?
Presumabley brakes are all freed off now?
You should see a marked improvement in performance and fuel consumption now.
cheers
noz

crooser · Post by **crooser** » 22 Feb 2004, 02:45

noz.when i got to the link i used a crowbar to force it back and low and behold the brakes freed off i removed the bolt cleaned it up,dunked the whole lot in oiland it is now as it should be, brakes ok.economy is a bit premature as i have a lot of work to do on the car,mainly as a result of it standing in a wood for months.our other 2 xm's show similar symptons,my wife's 2.1 had the offside front nearly seize once and i thought it was the brake pads.when i take my foot off the brake on a slight slope in my 2.5 it,s a minute or more before it starts to roll so i suspect the same cause.more work,but after all, it is a citroen

noz · Post by **noz** » 22 Feb 2004, 14:33

crooser,
It never ceases to amaze me how much grief this must be causing on all RHD XM's. The strange phenomenon is that the sticky linkage affects the offside front firs, then the nearside front and finally the rears together. It can only be the very slightly different positions of the machined ports in the doseur valve. The ports must be exposed progressively in the order above.
As I said, if you don't tackle it soon enough, the heat goes for your wheel bearings, which is not a nice job, I know

Take heed all XM owners. This is a very easy problem to check and fix. Probably takes less than an hour in total and that includes making the coffee. Even if you're not in the habit of doing your own maintenance this is a must.
cheers
noz