Rear Brake Line Replacement

BX Tech talk
Dytie
New Member
Posts: 9
Joined: Mon Jan 17, 2022 10:29 pm
Location: South West Angleterre
My Cars: BX 16v
x 2

Re: Rear Brake Line Replacement

Post by Dytie »

LHM fluid has started to come through the replaced brake line to the bleed nipple but it’s not a constant flow (stuck about 2 inches from the nipple). I think you’re right, sounds like there’s a major airlock somewhere. I’ll try opening the bleed valve on the other side to see if that helps.

And yes, I remembered to do up the pressure relief bolt.

It’s a bit of a nightmare.. as the car is stuck half in and half out of the garage

User avatar
white exec
BXpert
Posts: 682
Joined: Sat Sep 12, 2020 4:04 pm
Location: Sayalonga, Malaga
My Cars: 1992 BX19D Millesime
- LHD, NA, AC, RP_5800
1996 XM 2.5TD Exclusive
x 69

Re: Rear Brake Line Replacement

Post by white exec »

Yes, try another bleed nipple to see whether there's any flow there.
Also try some firmer pressure on the brake pedal.
Also open the pressure relief bolt (1.5 turns) with engine running, to let fluid pump straight back to the reservoir, to give the pump a good flushing through. :!: Support the car securely at the front when doing this.
Chris

Dytie
New Member
Posts: 9
Joined: Mon Jan 17, 2022 10:29 pm
Location: South West Angleterre
My Cars: BX 16v
x 2

Re: Rear Brake Line Replacement

Post by Dytie »

It’s beaten me!! I’ll have another go next weekend.

I loosened off the bleed nipple on the other side and the flow rate was also pretty much non-existent. I managed to squeeze a bit out with some vigorous pumping of the brake pedal but even that stopped working after a while.

The front still goes up and down and the steering feels assisted so hopefully it’s just an air lock.

I tried undoing the pressure relief bolt on the accumulator with the engine running but was worried about undoing it too much. It’s not particularly accessible so I’ll mark the bolt next time so I can be more precise about the number of turns I’m doing.

xantia_v6
BXpert
Posts: 295
Joined: Wed Dec 16, 2015 6:13 pm
Location: here and there
My Cars: Peugeot 308 CC
Citroen XM V6 ES9
Citroen Xantia V6
Jaguar XJ-S V12
x 35

Re: Rear Brake Line Replacement

Post by xantia_v6 »

It may be that there is something amiss with the height control adjustment. If you jack up the rear hubs, does the car try to lift itself? (be careful, it may lift itself off of the axle stands).

User avatar
white exec
BXpert
Posts: 682
Joined: Sat Sep 12, 2020 4:04 pm
Location: Sayalonga, Malaga
My Cars: 1992 BX19D Millesime
- LHD, NA, AC, RP_5800
1996 XM 2.5TD Exclusive
x 69

Re: Rear Brake Line Replacement

Post by white exec »

Relief bolt just needs to be slackened a tad. 1 to 1.5 turns approx . . . just don't remove it, or a ball bearing behind it can be lost.
As steering is assisted, and front goes up/down ok, then the pump etc is doing its stuff.
Try putting the rear wheels back on, to see whether rear end lifts/lowers the weight of the car normally. Mike made similar suggestion.
The rear brakes are fed from the rear suspension (rear braking force increases with rear end load), so we need to know that the rear suspension is working ok.
Chris

thorter
New Member
Posts: 17
Joined: Fri Feb 29, 2008 9:18 pm
Location: Edinburgh, Scotland
x 2

Re: Rear Brake Line Replacement

Post by thorter »

A problem with both BX and Xantia hydraulic suspension can be that the height corrector spool valve does not reach the expected state, or takes a very long time as a result of the damper built into the height corrector. The manual height lever setting and the axle height feedback are mechanically added or subtracted (they act via torsion springs), and the result sets the spool valve. The manual lever ought to win when set to highest or lowest positions, but this sometimes does not work.

Particularly with the rear arms hanging on the rebound stops, the height corrector “thinks" the suspension is fully up and does not need pressurised, and putting the manual lever high fails to make it open. Sometimes you need to lift one or both arms enough to encourage proper operation. It is yet worse on an anti sink Xantia, an extra slew of difficult to fathom complication!

User avatar
white exec
BXpert
Posts: 682
Joined: Sat Sep 12, 2020 4:04 pm
Location: Sayalonga, Malaga
My Cars: 1992 BX19D Millesime
- LHD, NA, AC, RP_5800
1996 XM 2.5TD Exclusive
x 69

Re: Rear Brake Line Replacement

Post by white exec »

Interesting. If so, can this be got over by raising the car to max height while still on its wheels, then removing the wheel (to bleed), after lifting the trailing arm/crosstube/RR subframe with a jack to allow the wheel to come off?
Chris

Dytie
New Member
Posts: 9
Joined: Mon Jan 17, 2022 10:29 pm
Location: South West Angleterre
My Cars: BX 16v
x 2

Re: Rear Brake Line Replacement

Post by Dytie »

Unfortunately I can’t physically get the rear wheels back on as there isn’t enough room between the wing and the hub to slide the wheel into position. I’m going to try supporting the rear hubs and lowering the car on to them so they take the load to see if that resolves the issue.

thorter
New Member
Posts: 17
Joined: Fri Feb 29, 2008 9:18 pm
Location: Edinburgh, Scotland
x 2

Re: Rear Brake Line Replacement

Post by thorter »

I assume you have the car on axle stands, but it is probably not high enough for the wheels to clear the ground with the suspension on high. The best thing would be to try to get it that high, but perhaps easier said than done. If that is not possible, the slow response of the suspension makes manipulating the clearances tedious, and also risks trapping the wheel and bending the bodywork. It does seem you have successfully discharged the pressure if the wheels can foul the bodywork.

Here are some general thoughts.

I had three BXs, all estates, and this problem rang a bell. It’s a long time ago, but I recall that working on the (mainly rear) suspension, there was often difficulty at one or other extreme of suspension travel (the suspension is very trouble free in normal use).

I suspect the cause is that the manual lever has just enough total travel to override the control loop at both limits, but if the setting is offset slightly then there may not be enough at one or other limit. Also, after high mileage, the pivot points can be worn, which will waste some of the manual travel range. I recall on one car improving matters with a piece of nylon tube that took up the wear.

However, it is not a good idea to start adjusting things unless you are 200% confident you know exactly what you are doing. Rather, try to find out what is going on. I recall being able to push slightly on the linkage at the height corrector, and hear the hiss of fluid that should have happened automatically. To check the hydraulic pressure is completely discharged, the hydraulic cylinders should feel slightly loose. They are not rigidly clamped.

Remember that with both rear arms hanging there is no force present to lift them, so you may need to jack an arm, It is not always easy to find a good place to jack, but once lifted as high as possible, put a block under one or other side and the anti-roll bar will keep the other wheel up. Bear in mind it also takes time for the fluid to flow back to the tank. Levering with a wooden batten to raise the arm is another possibility. The best thing in the future is to jack the car so that the wheels are definitely clear of the ground.

The delay to prevent too rapid a height response is due to the fluid volume in the height corrector rubber end caps in conjunction with fine nozzles leading to the return outlet. These can become gummed up leading to excessively slow response. I successfully cleaned them on the car by flushing with petrol. I made a rig with two electrically operated air valves and a one-minute timer switch to alternately fill and dump air pressure. This controlled pressure from a tyre (perhaps one bar) and pressurised a small container of petrol. A second tube was connected instead of the height corrector return (plug this pipe!) forcing petrol in and out by bulging the rubber caps. Leave operating for a while, and proper operation is restored without removing the height corrector.

Dytie
New Member
Posts: 9
Joined: Mon Jan 17, 2022 10:29 pm
Location: South West Angleterre
My Cars: BX 16v
x 2

Re: Rear Brake Line Replacement

Post by Dytie »

Houston we have lift off!

Thanks for all the replies and suggestions. I supported the rear swinging arms and lowered the car onto them so they were taking the load and voila. The back of the car lifted and LHM started flowing from the calliper bleed nipples.

Now onto the next job which I’ll start a new thread for

User avatar
white exec
BXpert
Posts: 682
Joined: Sat Sep 12, 2020 4:04 pm
Location: Sayalonga, Malaga
My Cars: 1992 BX19D Millesime
- LHD, NA, AC, RP_5800
1996 XM 2.5TD Exclusive
x 69

Re: Rear Brake Line Replacement

Post by white exec »

Great news!
It should have done that by just putting the car on Highest, which has the same effect as putting weight on the rear wheels... #-o .
Anyway, you provoked it into action, so good stuff.
Chris

rutter123
Over 2k
Posts: 2582
Joined: Sun Sep 02, 2012 9:54 pm
Location: South Lincs
My Cars: 90 Bx Tzd turbo ven red 295k
74 D Super 5 black
05 Volvo V50 2.0d 180k
65 Peugeot Boxer work van 280k
x 110

Re: Rear Brake Line Replacement

Post by rutter123 »

A lot of the time it's just trial and error getting the rear end to work and behave itself after bleeding it down, usually just a case of a few lows and mids and let the system repressurise and settle in normal ride height then try a few highs, the system pretty much bleeds itself (except the brake lines) providing your not still leaking on the high pressure side.
90 BX Tzd turbo 294k SORN undergoing major surgery
90 BX Tzd turbo estate 46k awaiting surgery
65 Peugeot Boxer Van the new workhorse
52 Toyota Rav4 180k Bulletproof Jap reliability