I have just encountered a most unusual problem with my Bx turbo diesel estate. Its been off the road for circa 6 months, and whilst taking it for a sneaky test run the other night I discovered to my horror there is no front braking effort.
Its fitted with ABS, and I have got as far as removing the pipe from the ABS block which comes fro the dosuer valve and would be for the front brakes if there were ABS fitted, and there is no flow from the open end of this pipe when the brakes are applied.
It all points to the doseur valve, but this was an item I recently had reconditioned by Pliedes as the old one had the usual trait of allowing the back of the car to sink down rapidly. I used a Pliaedes item due to the agro factor of changing it out and needing it to be right first time.
The rear brakes are operating normal and I have bleed them out and a good flow of LHM is observed, also the hydraulic low pressure light goes out immediantly when the car is started and the car rises to the normal ride height quickly.
Any advice appreciated as its due an MOT on Monday.....
Help urgent advice needed, front brakes not working......
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DLM
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I'd be checking front caliper pistons to see if stuck myself - does the handbrake work? IF it does then they're fine. Suspect ABS light would be coming on & staying on if any prob at ABS valve block....
Had no brake system diags in front of me, and didn't know where in hydraulic system ABS comes in relation to front brakes, but have just retrieved Haynes from the boot & can see where you're coming from. Some questions:
Have the front brakes worked since Doseur changeover?
Is the car post-doseur changeover model (after OCt 1988 ) - when Citroen swapped positions of some of the ports on the doseur valve?
Was the old doseur new or old-type?
Is it possible that the doseur was incorrectly connected (you should only be getting full back brake operation if the back is heavily loaded)?
Did you fit the doseur yourself or did Pleiades do it, and what reference was used to determine connections to the ports?
Apologies if any of these suggestions/questions seem self-evident or have already been covered in step-by-step debugging.
Had no brake system diags in front of me, and didn't know where in hydraulic system ABS comes in relation to front brakes, but have just retrieved Haynes from the boot & can see where you're coming from. Some questions:
Have the front brakes worked since Doseur changeover?
Is the car post-doseur changeover model (after OCt 1988 ) - when Citroen swapped positions of some of the ports on the doseur valve?
Was the old doseur new or old-type?
Is it possible that the doseur was incorrectly connected (you should only be getting full back brake operation if the back is heavily loaded)?
Did you fit the doseur yourself or did Pleiades do it, and what reference was used to determine connections to the ports?
Apologies if any of these suggestions/questions seem self-evident or have already been covered in step-by-step debugging.
Back on two wheels and pedal power for the moment.
DLM, thanks for the quick reply.
In response to your diagnostic questions:
The handbrake works well on both calipers - so not the calipers
There is no ABS check light other than the normal few seconds upon initially turning on the ignition - so not the ABS valve block.
The doseur valve was changed approx 18 months ago and worked perfectly for the 12 months the car was in use for.
The vehicle is H registration making it 1991.
The dosuer valve was a reconditioned Pliaedes item, which I fitted myself. The connections were put back as they were found when I changed the doseur valve myself.
Further tests I have just tried:
I have disconnected the priority valve high pressure line at the point where it goes into the doseur valve and run it into a bottle with a piece of flexible hose on the end, and there is excellent flow, confirming the doseur valve has a high pressure LHM flow into it.
Upon reconnecting it, I tried the same thing for the doseur output pipes at the point where they screw into the ABS valve block, the supply to the rear had good flow, whereas the supply to the front brakes was flowing but it could be stopped by putting your thumb over the end of the open pipe. The only difference this time was the suspension was in the highest setting. Before it was just a dribble on the lowest setting.
I am as sure as I can be that the doseur valve is at fault, does this sound reasonable ???
In response to your diagnostic questions:
The handbrake works well on both calipers - so not the calipers
There is no ABS check light other than the normal few seconds upon initially turning on the ignition - so not the ABS valve block.
The doseur valve was changed approx 18 months ago and worked perfectly for the 12 months the car was in use for.
The vehicle is H registration making it 1991.
The dosuer valve was a reconditioned Pliaedes item, which I fitted myself. The connections were put back as they were found when I changed the doseur valve myself.
Further tests I have just tried:
I have disconnected the priority valve high pressure line at the point where it goes into the doseur valve and run it into a bottle with a piece of flexible hose on the end, and there is excellent flow, confirming the doseur valve has a high pressure LHM flow into it.
Upon reconnecting it, I tried the same thing for the doseur output pipes at the point where they screw into the ABS valve block, the supply to the rear had good flow, whereas the supply to the front brakes was flowing but it could be stopped by putting your thumb over the end of the open pipe. The only difference this time was the suspension was in the highest setting. Before it was just a dribble on the lowest setting.
I am as sure as I can be that the doseur valve is at fault, does this sound reasonable ???
Sounds to me like front and back brakes swapped over!
Doseurs don't really go wrong - just leak internally and maybe allow the back of the car to drop. Search this board and see how few problems there are.
To get a decent flow at the back for bleeding - the back suspension must be placed on high. Try opening a FRONT nipple with the car set high and see if the flow improves.
Be careful with high pressure LHM in contact with your skin. The pressure can be enormous and will easily power LHM through your skin - which isn't to be recommended.
Doseurs don't really go wrong - just leak internally and maybe allow the back of the car to drop. Search this board and see how few problems there are.
To get a decent flow at the back for bleeding - the back suspension must be placed on high. Try opening a FRONT nipple with the car set high and see if the flow improves.
Be careful with high pressure LHM in contact with your skin. The pressure can be enormous and will easily power LHM through your skin - which isn't to be recommended.
It does sound like the back and front pipes are transposed. I think I'm right in saying the rears don't usually work much unless there is a weight in the boot or passengers in the rear or both. So I would have thought by adding extra weight to the front (?) this might cause the front brakes to work. Or would you still have to put weight in the rear?
Worth a try anyway just as a quick test.
Worth a try anyway just as a quick test.
Dave.
2004 C5 Exclusive Estate 2.2hdi automatic.
1990 Bx TGS automatic.
2004 C5 Exclusive Estate 2.2hdi automatic.
1990 Bx TGS automatic.
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tom
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Hold on. The whole principle of dual circuit braking is that if one end fails, the pistons in the master cylinder, or in this case the doseur will cut off the flow to that end. Apply high pressure to a doseur with no load, and I expect that it should cut off the flow. No, This is probably a red herring.
You have good flow from the security valve and doseurs are not prone to jamming at random so I would try putting the pipe back and bleeding both calipers. I'm more inclined to think that the fault lies in seized calipers and I'd be looking for leaks before removing the pads and cleaning and greasing all the bits that slide around and seize up after a few months disuse.
You have good flow from the security valve and doseurs are not prone to jamming at random so I would try putting the pipe back and bleeding both calipers. I'm more inclined to think that the fault lies in seized calipers and I'd be looking for leaks before removing the pads and cleaning and greasing all the bits that slide around and seize up after a few months disuse.