Brakes have a mind of their own !

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rookie
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Re: Brakes have a mind of their own !

Post by rookie »

Yes, it has ABS but not esp.
I did think about something bouncing up and down, it even crossed my mind that it was the brake pedal bouncing up and down ever so slightly, but then, why would it not release the pressure when the pedal bounced back up again ?

I have not had chance to have another look at the vehicle as dam work seems to always get in the way, but, something someone mentioned earlier keeps sticking in my brain. I was asked if the car had a remote braking system.

The brake pedal, obviously is on the offside but the master cylinder is on the nearside. Without looking as yet, I am assuming there is some sort of actuating bar that travels across the front bulkhead from the pedal and presses the master cylinder on the other side of the car. Could there be anything on that bar which could creep the brakes on ?

Also noted that the Master Cylinder has been recently changed, could a mixed up connection of the brake lines tot he master cylinder cause an intermitent brake lock on yet still allow normal brake activity for the majority of the time?

God I wish it was the weekend so I could get my hands on it.

Thanks chaps
citronut
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Re: Brakes have a mind of their own !

Post by citronut »

rookie wrote: The brake pedal, obviously is on the offside but the master cylinder is on the nearside. Without looking as yet, I am assuming there is some sort of actuating bar that travels across the front bulkhead from the pedal and presses the master cylinder on the other side of the car. Could there be anything on that bar which could creep the brakes on ?

Thanks chaps
yes thats correct,

i have seen an AX years ago the brakes kept locking up all round,

turned out to the linkages behind the servo were seized up, so when the pedal was pressed the linkage stayed in the brake on position,

nout that a good doss of duck oil didnt fix
Regards, malcolm.

current ride a BX 1.7 TZD estate
1986 MK1 BX 1.9na D Auto(in Mothman Andy's stable )
layed up roppy 1.9TD XANT estate, now gone to meet her maker
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Re: Brakes have a mind of their own !

Post by Old-Guy »

Thinking out loud: if the brakes are rubbing slightly, and the brake fluid is contaminated with dirt, air and moisture, then if dirt prevents the master cylinder from releasing, pressure will build from the air expanding and eventually the moist brake fluid in the cylinders will generate steam! I'd start by thoroughly bleeding the brakes and seeing what comes out - I know there won't be much evidence left, but that's to the good.
2011 Grand C4 Picasso VTR+ 1.6HDi in Kyanos Blue
1995 Xantia Estate SX 1.9TD in Vert Vega "The Green Lady" - after 11 years now owned by XanTom
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rookie
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Re: Brakes have a mind of their own !

Post by rookie »

Hi Old Guy

Thanks for the reply. I take note of what you say, and today have finally found the time to have a look at the problem.

What i did notice was that the clutch (hydraulic operated) only had about an inch of movement at the bottom of it's travel (though the car did still go into gear ok).
I filled up the brake system and bled it through until I had a solid feel on the pedal.
I then decided that given the clutch problem I would bleed the clutch (BIG MISTAKE !!!!)

Only a very small amount of fluid came out of the clutch and the pedal sprung to the floor.
No matter how I tried I could not get the clutch master cylinder (fastened to the pedal) to accept any fluid from the shared brake master cylinder.

So I came to the conclusion that either the master cylinder (clutch) or slave cylinder were knackered. Ordered new ones from that well known website and await their delivery.

Then I started to think about the clutch and brake sharing the same reservoir.
Is there any way that a fault in the clutch master cylinder could cause a pressure in the brake system ?

If the seals in the clutch master cylinder are passing (which they clearly were), could that have caused fluid under pressure (when the clutch was pressed) to pass the seals and travel up into the shared Brake Fluid Reservoir ?

Or am I talking out of my rear end ?

:-)
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Re: Brakes have a mind of their own !

Post by Peter.N. »

I wouldn't think the two could be connected but if the clutch cylinder is old enough to fail, likely the brake one will to. What used to happen many years ago is the rubbers would swell due possibly to oil contamination, the rubber on the fluid feed end would swell and cover the return hole - had it happen on a Morris Oxford.

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Re: Brakes have a mind of their own !

Post by citronut »

looks to me there are toooooo many ideas rattling around now,
and you need to focus on one thing at a time,

check and triple check one idea until you are 200% sure before moving on or trying to find other possible causes
Regards, malcolm.

current ride a BX 1.7 TZD estate
1986 MK1 BX 1.9na D Auto(in Mothman Andy's stable )
layed up roppy 1.9TD XANT estate, now gone to meet her maker
purple and lilac metalic 2CV(VIOLET)registered to her in doors
1972 DS special been layed up aprox 31 years
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Re: Brakes have a mind of their own !

Post by Stewart(oily) »

ISTR the clutch only shares the reservoir with the brakes, I like the idea of lubricating the pivots on the brake linkages but that did not do anything for mine. can you bleed the clutch from the bottom using a syringe ?
BXs since 1993 built 1.9 TZD turbo, got a S2 Xantia estate, brilliant car! 2013, Xantia HDI LX 110 2000 new car with 122,000, l C2 HDI Rusty rocket, C3 Picasso HDI new to me.
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Re: Brakes have a mind of their own !

Post by rookie »

Hi Stewart

I have now actually removed the Clutch master cylinder from the pedal and am awaiting replacement.
When I tried to bleed the clutch I was getting nothing at all from conventional means.
Tried a pressure bleed - Nothing.
Tried a pumped oil can full of fluid back up through the slave cylinder bleed - Nothing.
Even when I removed and stripped the clutch master cylinder I saw no problem with the seals etc and the cylinder inside looked fine but will change for a new one just to be on the safe side. (when it arrives).
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Re: Brakes have a mind of their own !

Post by rookie »

The saga continues.......

Have now fitted the new Clutch Master Cylinder and the clutch is working correctly.
Took the car for a drive and no sign of the brakes locking on (though it was only a drive of 2 miles or so.

Next problem....

I have a light blue smoke coming from the exhaust. When I drive the car it lacks power as if the turbo is not kicking in.
It drives something similar to being in "Limp" mode but there are no management lights on the dash whilst driving.

Any ideas ?

Thanks chaps
rookie
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Re: Brakes have a mind of their own !

Post by rookie »

Just to put this post to bed.

I have finally finished getting this car back on the road.
The problem with the brakes ?.....................

When I collected the car, the clutch master cylinder was almost knackered but not quite.
The clutch pedal had about 2 inches of movement from the floor.
The clutch pedal is fitted with an "Over centre spring" which, when the pedal is in the up position, holds the pedal firmly up and when the clutch pedal passes the mid way point on the way down, the spring helps to floor the pedal.

I concluded that as the pedal was sitting below the mid way point when I picked the car up, the towing of the car was causing the clutch pedal to bounce up and down. The seals in the master cylinder were leaking and this was causing pressurised fluid to travel up into the shared brake/clutch reservoir.
Somehow, that pressurised fluid was transferring into the brake system and applying the brakes.

I have changed the clutch master and slave cylinders and have driven the car numerous miles with no hint of any brake problems.

So if anyone comes across the same problem with brakes locking on whilst travelling along (with or without the engine running), then it would be prudent to check the Clutch Master Cylinder.

Thanks for all the help chaps.

cheers
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