No rear brakes on '93 Xantia - advice please!

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richiesxantia
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Joined: 07 Jul 2005, 13:16

No rear brakes on '93 Xantia - advice please!

Post by richiesxantia »

Hi folks,
In the process of bleeding my brakes, I've discovered here is no pressure at the rear at all...
Can anyone advise how I might troubleshoot this?
I have tried putting the suspension height control lever to maximum, but there appears to be no change - A few bubbles are evident when opening either bleed screw at the rear, but virtually no fluid escapes at full pedal pressure. The front bleeds fine both sides.
The car is up on blocks with all wheels of the ground.
It is a non-hydractive system.
-----------------
Some background : my regulator does a big hiss about every 5 seconds, and the car sinks in a few minutes with engine off so I recently changed the main acc sphere. This didn't fix the hissing (ticking?) or sinking problem (though sitting on the boot with engine off now does raise once), so I pulled all the return hoses off the lhm tank and found the one from the abs valve block seemed to be leaking even with the engine off (double checked it at the block end), so I changed the valve block. Sadly, the replacement leaks in the same way, and when bleeding the brakes I encountered the problem above. *sigh*
I have no idea if the rear brakes were working before I changed the valve block.
Strangely, with the old abs valve fitted, if I moved the suspension from standard height to max a few times and left it on max for a few minutes, the ticking slowed to about 30-40 seconds. Checking the ABS valve block return leak pipe (also the doseur valve return), it appeared not to be leaking anymore. If I then depressed the brakes, the ticking immediately returned to every 5 seconds and checking the abs valve return pipe I found it was leaking again... I guess the shared return pipe means it could be the doseur valve...
Getting a bit sidetracked there - I guess I have two problems - the pressure loss and the lack of rear brakes -
Any help troubleshooting appreciated!!!
thanks,
Richie
West Wales

dnsey
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Post by dnsey »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">The car is up on blocks with all wheels of the ground.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
That's your problem!
To put it simply, rear brake pressure is designed to increase with loading. You effectively have no weight in the car, hence no brakes :-)
Take the car off the blocks and use axle stands or something under the trailing arms (make sure that the support is safe), and you should have no problems. Do be aware that under fault conditions the suspension could drop to minimum height, and work accordingly (keep hands from between discs and bodywork etc.).

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Mandrake
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Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by dnsey</i>

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">The car is up on blocks with all wheels of the ground.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
That's your problem!
To put it simply, rear brake pressure is designed to increase with loading. You effectively have no weight in the car, hence no brakes :-)
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Unfortunately thats not the case if the height control lever is set to maximum - as there will be full pressure available for the rear brakes whether or not there is any weight on the wheels.
My approach to bleeding the rear brakes is to set the suspension to full height, jack up one rear corner under the suspension subframe (where the crossbar bolts on) remove the wheel, bleed that side, then put the wheel back on, move the jack over to the other side, and repeat.
Regards,
Simon

dnsey
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Post by dnsey »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Unfortunately thats not the case if the height control lever is set to maximum <hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Sorry, missed that bit[:I]

richiesxantia
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Joined: 07 Jul 2005, 13:16

Post by richiesxantia »

Problem #1 solved!
Thanks Mandrake and Dnsey - I think you were both right in a way - unlike the Haynes manual which specifically says to bleed as I did! Ah well - live and learn...
This morning I tried again with the height set to max, but still no action - so I just jacked up one rear swing arm and hey presto, the magic green fluid ran nicely out of the rear brakes...
I guess the height corrector valve needed actuating in order so supply pressure to the rear suspension beacuse even though the lever was on max, there was no resistance in the rear suspension hanging freely at full travel.
A couple of nice tips for anyone else bleeding brakes -
- If you're stuck for a bleed pipe, the overflow/breather pipe from the lhm tank filler cap works nicely...
- Use the leftover fluid in your jar to lube the threads on your wheelnuts - mine were so dry, I had to use a jack on the wheelbrace to budge them! Maybe an apprentice mechanic got over enthusiastic with the rattle gun!
FYI, the new ABS block I fitted seems not to leak, but the doseur (brake actuator) valve does. Sharing the same return line makes this harder to diagnose I guess. Lucky for me I have a donor car!
Let you know how I go with the leak problem.
What a fantastic forum this is!
cheers,
Richie Out

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Mandrake
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Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by richiesxantia</i>

Problem #1 solved!
Thanks Mandrake and Dnsey - I think you were both right in a way - unlike the Haynes manual which specifically says to bleed as I did! Ah well - live and learn...
This morning I tried again with the height set to max, but still no action - so I just jacked up one rear swing arm and hey presto, the magic green fluid ran nicely out of the rear brakes...
I guess the height corrector valve needed actuating in order so supply pressure to the rear suspension beacuse even though the lever was on max, there was no resistance in the rear suspension hanging freely at full travel.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Ok, I was thinking about that as a possibility - basically that means the manual height override linkage (from the console control to the height correctors) is maladjusted, as when it is set to high it should be able to hold the height corrector open even with the wheels hanging down.
I guess thats one reason why my approach always works - one rear wheel still sits on the ground and the weight means that the height corrector must be open to keep the height at full, and even if it was out of adjustment a bit it would just result in the height of the car being a bit lower, but would still be under pressure.
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">
FYI, the new ABS block I fitted seems not to leak, but the doseur (brake actuator) valve does. Sharing the same return line makes this harder to diagnose I guess. Lucky for me I have a donor car!
Let you know how I go with the leak problem.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
A small amount of return leakage from the brake doseur valve is normal - it is in fact the leakiest component in the whole hydraulic system due to its internal design. Judging when the leakage is excessive is difficult though, and leakage from the brake valve will primarily affect how fast the back goes down, not the front.
On non anti-sink models such as yours its normal for the back to go down before the front.
Regards,
Simon

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Mandrake
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Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by richiesxantia</i>
Some background : my regulator does a big hiss about every 5 seconds, and the car sinks in a few minutes with engine off so I recently changed the main acc sphere. This didn't fix the hissing (ticking?) or sinking problem (though sitting on the boot with engine off now does raise once),
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
The regulator shouldn't hiss, except when you're opening the bleed screw, it should only tick normally.
A couple of possible reasons for a hiss - leaking bleed valve or non return valve, (both are ball valves in the regulator) or an air leak in the tank to pump inlet hose - more of a sucking noise than a hissing noise.
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">
Strangely, with the old abs valve fitted, if I moved the suspension from standard height to max a few times and left it on max for a few minutes, the ticking slowed to about 30-40 seconds.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Wait a second, you're saying that at normal height after stabalising the regulator ticks more frequently than every 30 seconds ?
That either means the accumulator sphere is no good, or the bleed or non return valves in the regulator are leaking, or that there is excessive leakage somewhere else in the system drawing on the main supply.
Regards,
Simon

richiesxantia
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Post by richiesxantia »

Doseur valve changed now with one from my donor car, and the 'tshhhhht' noise happens now only now avery 35-45 seconds instead of every 3 to 5s! Much better.
No LHM present at the ABS/Doseur leak return now! Though the PAS leak return (the small one closest to the firewall) is now dripping with the engine off and pouring steadily at idle!!! *sigh* Car still sinks with engine off in an hour or so.
Well 35 seconds will just have to do until I feel like getting coated in LHM again... ;) Wonder if the PAS ram is easy to remove?
The Acc sphere is new (just changed as first step to fixing fast 'ticking' problem). I know it's working 'cause sitting on the boot with engine off will raise back up once which it didn't do before.
I've noticed there are two distinctly different types of noise the regulator makes - a short 'tsht' noise and a longer 'tssshhhhhhhhht' one that lasts for about 1 second at idle usually (this is the one that happens every 35-45 secs), and I think is the same noise as the reg makes when pumping up the suspension.
Is the short one a 'pressure relief' and the longer one a 'pressure increase'?
Never having a cit before, I don't know if my Xant is 'ticking' with the right sound...
A weird car, but fun to play with the hydraulics!
Learning heaps,
thanks all!!!
Rich

richiesxantia
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Post by richiesxantia »

So should this car be making a sound while pumping the suspension up or should it be silent?
I always thought this was a bit odd but it's 'normal' for my car!
Starting engine with suspension flat :
"TSHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH!" 35sec "TSSHHT" 35sec "TSSHHT" 35sec "TSSHHT"
or
"tick........................................." 35sec "tick" 35sec "tick" 35sec "tick"
Maybe there's some obstruction in the pressure reg valve?
Rich

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Mandrake
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Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by richiesxantia</i>

Doseur valve changed now with one from my donor car, and the 'tshhhhht' noise happens now only now avery 35-45 seconds instead of every 3 to 5s! Much better.
No LHM present at the ABS/Doseur leak return now! Though the PAS leak return (the small one closest to the firewall) is now dripping with the engine off and pouring steadily at idle!!! *sigh* Car still sinks with engine off in an hour or so.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Someone else might correct me if I'm wrong, but continuous overflow from the PAS rack while the engine is running is normal.
Your '93 has the single output pump and flow diverter valve, which means the power steering runs off two sources - off the main regulated output of the pressure regulator while the regulator is in cut-in mode, and direct unregulated overflow output from the pressure regulator in cut-out mode.
To prevent the pressure getting too high in the latter case there is a pressure relief valve (its either in the flow diverter or the PAS itself, not sure which) that opens at maximum pressure allowing excess fluid to recirculate back to the tank, much the same as the main regulator recirculates in cut-out mode.
So oil returning to the tank from the PAS while idling is perfectly normal. What matters is how much it leaks when the engine is off. (I'm not sure how much leakage is normal in that situation)
Regards,
Simon

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Post by 406 V6 »

Check this one :
http://www.andyspares.com/discussionfor ... leed,screw
Read well, or you may never find the small steel ball.
Hydracleaning the system is also good for it (what doesn't hurt...).
From memory, that tschhhh you mean seems like the normal heart beat of the system; it's not loud, more like when you're drinking from a straw and you reach the end. "schlurp"[:P]. But you should hear a small ""click-"schlurp"-click"" as the low pressure valve opens, high pressure closes, the pump feeds the acc, then the low pressure valve closes and the high p valve opens the return path to the reservoir(hope i'm not getting confused and confusing), releasing the pump from the effort of filling the system with enough pressure.

alexx
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Post by alexx »

Simon is correct about PAS
In the neutral position of the steering wheel, fluid is just circulating through the PAS control valve with no pressure. Turning the wheel results with closing of the slots in the control valve in proportion to the force applied to the wheel. Overflow is cut and the pressure builds in the hydraulic cylinder. Similar systems are fitted to other cars.
Pressure relief valve is in the flow distributor (models prior to '94) or in the pump (6+2 pump, from '94 on).