Dyane Brake Problem

[jwalshe]

Hi all!

Had a recurring problem with the front brakes failing. It's fine for a while but then the brake pedal disappears into the floor and only the rear drums kick in.

Had the master cylinder replaced and it was fine for a while but it's started doing it again.

Any ideas?

Thanks in advance!

James

[citronut]

do you have the heat exchanger dump tubes fitted, if not you could be suffering brake fade, otherwise there might be air in the system

[jwalshe]

I guess air in the system would be the most logical explanation Malcolm. It's strange as everything was fine for days until I went up a really long steep hill today (around 2 miles) so could it be the air in the system rose to the front of the car at that point? Thus causing the front brakes to fail?

[Richard_C]

A few thoughts, going back about 30 years in my head to when I had Dyanes.

Air seems most likely as others have said.
Is the brake fluid old? maybe it has absorbed moisture and that lowers its boiling point.
I can't recall if the disc braked Dyanes used LHM fluid or ordinary dot fluid. I think there was a difference between all drum and drum/disc models. Does your have the right fluid after its cylinder swap? Wrong fluid may have softened seals.
Finally, is there a front/rear brake balance valve, usually under the car and linked to a suspension arm. Could that be seized or just faulty? Not sure if Dyanes had them, the main function is to reduce pressure to the rear when there is less loading on the rear tyres, primeval abs!

[jwalshe]

Thanks Richard - the Dyane does use LHM so I think it's a case of renewing the fluid for starters! The Dyane system is new to me but I'm sure it'll be a simple fix. Hopefully! Good to cover all bases with some good advice though. Cheers, James

[citronut]

Finally, is there a front/rear brake balance valve, usually under the car and linked to a suspension arm. Could that be seized or just faulty? Not sure if Dyanes had them, the main function is to reduce pressure to the rear when there is less loading on the rear tyres, primeval abs!

no Richard
no compensator valve on Dyanes,
and when cars do have them it is to allow more fluid pressure to the rear brakes when you have more weight in the rear of the car,

[Northern_Mike]

I had this on a disk braked 2CV. Fair scared the scheight out of me when the pedal went to the floor approaching a queue of traffic.

Anyway, it was the OS caliper seizing half on, not really enough to affect the "performance", but it was getting very hot and boiling the LHM. A secondhand caliper solved the problem.

[Richard_C]

Useful to confirm that Dyane has no compensator, I couldn't remember.

Your rather aggressive "no Richard" taken with the bit about increasing pressure seems to be misguided. The compensator cannot add to the pressure generated from the master cylinder, it has no energy source of its own. It can only reduce the pressure when less is required, which may be the normal state of affairs for most drivers. Imagine a fully loaded car, full pressure is delivered. Take stuff out, less pressure is delivered.

I wouldn't normally make a point like this, but the way you chose to phrase it seems to suggest I am some kind of imbecile child. "No Richard, not in the mince pie tin, how many times have I told you......"

Hope the OP sorts it out. Dyanes with working brakes have a better chance of survival.

[Citroening]

Downsized from CX Prestige to Dyane then James...

[jwalshe]

"NO, FRANKLIN!" Hehe I don't think Citroenut meant to come across like that Richard C - a misinterpretation there, one suspects. I've met Malcolm and he's a nice chap

But yes, Franklin... sort of. The Prestige has been off the road since September but is - I believe - fixed and will be ready for the road on Saturday. The Dyane is actually my parent's new car. I've been occupying my time by fixing her up and enjoying Citroen motoring from the slow lane. A two-cylinder distraction from the devastation of temporarily losing my CX!

Interesting advice re caliper. Thanks Mike! Will report back when it's fixed and let you know what the issue was.

James

[citronut]

Useful to confirm that Dyane has no compensator, I couldn't remember.

Your rather aggressive "no Richard" taken with the bit about increasing pressure seems to be misguided. The compensator cannot add to the pressure generated from the master cylinder, it has no energy source of its own. It can only reduce the pressure when less is required, which may be the normal state of affairs for most drivers. Imagine a fully loaded car, full pressure is delivered. Take stuff out, less pressure is delivered.

I wouldn't normally make a point like this, but the way you chose to phrase it seems to suggest I am some kind of imbecile child. "No Richard, not in the mince pie tin, how many times have I told you......"

Hope the OP sorts it out. Dyanes with working brakes have a better chance of survival.

VERY SORRY if you read my reply that way it certainly was not meant like you read it ( ABSOLUTELY NOT ) ,

besides that when we shout on this forum we use upper case

and please re/read what i said regarding the comp valve,
as i did not say it creates more pressure but "allows more to the rear brakes" with more weight in the rear of the car

HAPPY XMASS to you as well

[citronut]

I had this on a disk braked 2CV. Fair scared the scheight out of me when the pedal went to the floor approaching a queue of traffic.

Anyway, it was the OS caliper seizing half on, not really enough to affect the "performance", but it was getting very hot and boiling the LHM. A secondhand caliper solved the problem.

yes i had forgoten about that one,
very surprised as only a couple of months back we towed a dersh back to my workshop ( about 2 miles ) with the pwners newly acquired VW LT, the ders had been off the road about three years, on unhitching the dersh i noticed a very strong clutch smell and saud the owner i think the clutch on your van is slipping,

then once we had un/hitched the dersh and attempted to push it into my workshop we discovered the O/S calliper was stuck solid and the disc was very hot

[TooMany2cvs]

Unlikely to be overheating, in December, in Brum...

I can only think it's some kind of mechanical failure of a caliper, maybe a bit of carp in a caliper half blocking an outlet intermittently.

I think I'd start by taking the pads out and looking at their thicknesses, seeing if one's been wearing less. If not, then take 'em out one by one and for each one get somebody to press the pedal, then retract the piston, repeat repeat repeat. It might be one's sticking intermittently. If that all looks OK, then take the calipers off, take the pistons out, and give 'em a really good clean and treat them to new seals (including the little one between the halves). Make sure you don't lose any shims between the inner half and gearbox casing. If you've got a spare set of CX caliper seals about, you're laughing - they're the same. Except CX front calipers are dual-piston...

Also worth checking that nobody's done something silly and replaced the pipes to the master cylinder wrong way round. I haven't got an A-series handy to check, but IIRC the front brakes use the port nearer the bulkhead. <checks ECAS> Yep, front port to back brakes, back port to front brakes.

[Citroening]

Excellent, great news on the Prestige James. Hope it's back on the road soon...