Doseur

[Phil Peters]

Hi all,

I suspect "Maurice" has a leaky doseur as the brakes are not as sharp as they were 12-18 months ago and there is a noticeable sinking of the rear end under braking with the car correcting its height at traffic lights and junctions. There is also an accompanying hiss or whoosh when the brake pedal is pressed which may or may not be normal behaviour; perhaps a more experienced BXer can comment on this?

Since the car has been 100% reliable and cheap as chips to run over the past year including recently passing MOT with no advisories, I was prepared to stump up the money for a new doseur and also order the relevant parts to rebuild the existing doseur at my leisure, most likely once we've moved house later this year. I've got a spare weekend coming up later this month where I plan to change the doseur, clean out the LHM reservoir filter, replace the LHM and give the brakes a general check over.

Thanks to the ever helpful forum, I went down to my local Citroen dealer this lunchtime armed with all the relevant part numbers except the part n° of the doseur itself. The lad at the parts counter had never even heard of a BX and I actually had to point the car out to him on the forecourt before he understood what I was talking about. Even then, he said he'd never seen one before in his life. My mention of the doseur of course resulted in a similarly mystified expression but nevertheless we began to look up the parts in the database.

For those of you who are interested, here's the current availability of the parts required to overhaul the later 3 piston doseur as of March 2014:



No 2 - Locator ring for rubber knob (5 424 455). Still available. £3.88 ex. VAT each.
No 3 - Rubber actuator knob for doseur (95 640 067). Still available. £7.18 ex. VAT each.
No 11 - Large o ring seal for later 3 piston style doseur (95 638 813). Still available. £1.95 ex. VAT each.
No 12 - Teflon seal (95 495 759). Still available. £1.66 ex. VAT each.
No 13 - Rubber O Ring (79 03 065 984). Still available. £1.04 ex. VAT each.

The parts are on order and should be arriving mid-week. I will be keeping an eye out to make sure part n° 79 03 065 984 is the correct size as mentioned here.

One area of concern was the doseur unit itself. According to the parts dept lad, this part is no longer available. I asked him for the part n° and was given 95 650 892. Is this the correct part n° for the 3 piston doseur and if so, has anyone else had any luck getting hold of one recently?

Cheers,

Phil

[Defender110]

Hi all,
I suspect "Maurice" has a leaky doseur as the brakes are not as sharp as they were 12-18 months ago and there is a noticeable sinking of the rear end under braking with the car correcting its height at traffic lights and junctions.

This is often just the brakes needing bleeding, they can collect gas in the brake lines from leaking suspension spheres, If one or more of your spheres has leaked nitrogen it goes into the LHM system and can get captured in the brake lines.

[Phil Peters]

Thanks for the tip Kevan. The LHM is due for a change so I'll do that and then bleed the brakes to see if that makes a difference before attacking the doseur.

I changed the accumulator sphere about 6 months ago but the other 4 spheres were last done by the previous owner in May 2010 so perhaps some gas has leaked out of them in that time.

Cheers,

Phil

[Defender110]

I had the same symptoms on my TGD with it rising at the rear after I had stopped at traffic lights before lowering itself again. Bleading the rear brakes cured the problem.

[RobC]

The car is meant to appear to stay reasonably level at the rear during heavy braking - that's the built in anti-dive that all hydraulic cits since the DS had, due to the rear brakes being fed from the rear suspension. In fact I notice when I'm carrying heavy loads that the anti-dive is even more noticeable. However when you're sat at lights for a while holding the car on the brake pedal, there is no momentum from heavy braking 'raising' the rear of the car for the anti-dive to counteract, so eventually it starts to sink slightly at the rear as the suspension forfeits its pressure for the more critical brakes: the brakes are a 'number 1 priority' in the hydraulic system. Then when you lift your foot off the brake the rear jumps up as hydraulic pressure floods back into the rear suspension, before the height corrector does its job and sets it at the right level.

Mine has a brand new doseur fitted and it sinks at the back when holding the brake pedal at traffic lights.

Sinking fast after the engine's off at the rear also doesn't mean the doseur's necessarily worn - BXs even brand new, have always done that within a few hours anyway. So I think that's a bit of a myth, though happy to be corrected. The only thing that seems to prevent BXs sinking within a few hours is brand new LHM and/or knackered rear arm bearings!

Someone's going to come along and put me completely straight on this... haha! This is my understanding of it all anyway.

[adamskibx]

I think the anti dive has more to do with the rotational forces escaping from the centre point of the rear wheel bearings and transferring to the rear arm bearings, and also, when you have your foot on the brake you are preventing the wheel from turning while stationary, thus preventing the car from getting longer or shorter, and thus preventing it from rising or falling. The fluid dynamics might contribute to these positive characteristics of the car but I think the main advantages come from the trailing rear arm dynamics.

[B-Hive]

All of my BX's are currently in hiatus, but before this my daily (the GT), had started to intermittently flash the STOP/Brake warning light. As the brakes felt fine, I put this down to shorting pad wear wires.

Not long after, like as described here, the brake pedal was losing its sensitivity and felt a bit numb. Correspondingly the rear now sinks quite quickly after shut down, AND I'm getting the classic sinking whilst at traffic lights..and then the pressure warning light comes on.

I guess my point being here that maybe it is not your dosier if you're not getting a warning light as well. In my case I do think it is the dosier, and similar to the OP, since the GT to date has cost nought to run, I will transplant one of my donor bits, and then rebuild the original with the kit..

BTW I do have a fresh accumulator fitted..

Good luck with the job..