farting brake pedal

Chrispy · Post by **Chrispy** » 11 Jul 2005, 16:00

Anyone else have this? When you press the brakes, the pedal buzzes for a second or so as it depresses. It almost feels like air escaping from around where the (now modified) piston enters the doseur valve under the dash, which kinda 'farts' and makes the pedal buzz as it goes.
Seems to only do it in warmer weather too and not every time you press the pedal, perhaps 8 times out of 10.
The brakes themselves work well and bite as they should. I have no LHM leaks and my accumulator sphere is brand new with a 2 min ticking interval.
Is this the doseur valve going kaput? Any ideas?
Cheers,
Chris.

AndersDK · Post by **AndersDK** » 11 Jul 2005, 16:04

Get down there and have a very good look for any greasy/wet spots on the carpeting. Chances are the rubber bulb on the brake valve has split. No big deal replacing though.
Any leaking LHM from this problem is coming from the low pressure return side of the brake valve - no panic [;)]

Chrispy · Post by **Chrispy** » 11 Jul 2005, 16:17

So is it possible to replace the rubber bulb on it's own or is it the whole valve that needs to be replaced, assuming that's what is at fault? It made this noise a while ago, before I did the brake mod, and I never noticed any wet carpet down there at the time when I pulled the silly piston out to be de-springed.
Strange how it only seems to do it in warmer weather too.

AndersDK · Post by **AndersDK** » 11 Jul 2005, 16:26

No big deal [:)]
Rubber bulb can be replaced in-situ. No big dismantling. No pipes to worry about unscrewing. [;)]

Chrispy · Post by **Chrispy** » 11 Jul 2005, 17:55

Right, just had a good feel around under there. It's totally bone dry...no fluid or anything. I think I may know what's wrong though. The rubber bulbs edges go all the way out to the entrance of the valve. The piston that enters it (the one you modify with the bit of pipe) must rub against the rubber and make it difficult for the air to exit. In warmer weather I'd imagine the rubber expands and makes a tighter seal between the piston and the rubber bulb thus causing the farting as the air between them escapes when you press the pedal. If I push diagonally down on the pedal from the left, away from the clutch there is no farting/ buzzing. But if I push straight down on it, then it buzzes.
Just a theory mind.... I'm tempted to drill a hole in the middle of the piston the give the air somewhere else to go. We shall see if that fixes it! It's not affecting the brakes or anything, it's just annoying!

Post by **CitroJim** » 11 Jul 2005, 23:15

That's a fine piece of detective work Chrispy!

JohnD · Post by **JohnD** » 11 Jul 2005, 23:28

My Xantia did this from new, but only when the weather was hot. But then about two years ago, I noticed that it had stopped.

pagh · Post by **pagh** » 11 Jul 2005, 23:44

Mine did/does it as well. It hasn`t done it for about a month now. We have between 25-30 celcius atm., so it should be farting.

I came to the same conclusion as crispy, although i didn`t investigate. I just had a theory, and hoped it wasn`t anything serious.

Richard Gallagher · Post by **Richard Gallagher** » 12 Jul 2005, 02:16

Try bleeding the brakes, this can be a sign of air escaped from the sphere's getting into the brake pipes.
A good bleeding, or should I say a bleeding good bleeding sorted this problem on my Dad's Xantia after the rear sphere's gave up the ghost.

citronut · Post by **citronut** » 12 Jul 2005, 03:12

this is usuly air in brake system,the rubber bulb is held in place by an alliminium ring,if this is a xant you cant see this from inside the car as there is an extention block about 2'' long between bulk head and dozer valve which has a metal push rod inside that pushes onto bulb regards malcolm

Chrispy · Post by **Chrispy** » 12 Jul 2005, 13:23

I had a go at this liast night. I doused the rubber behind the piston canister in grease, but to no avail....it still does it. There is enough of a gap around the canister to allow air out so it can't be that sadly. This morning, in the cooler weather, it has hardly done it at all so it's definitely temp related. It does it only on the first bit of travel in the pedal and not if you press really gently.
So it could be air in the brakes? They don't feel spongy at all and are quite effective at all times. If there was air in the rear brakes I doubt this would make the pedal buzz as it does when you prod it. It almost feels like if there is air in the system, it's in the doseur valve itself. If you press the brake quite hard and let go there's also a 'Cha' noise like air being released under pressure. Is this normal?

pete_wood_uk · Post by **pete_wood_uk** » 12 Jul 2005, 13:31

Yes, I also have a sort of rattling/farting as I first lay my foot on the brakes on my 97TD. It's become apparent after I changed the pedal spring for pipe, but that may be a co-incidence. I suppose it could well be air/gas. However, the old dear also has 5 ****ged spheres and intermittent ABS problems (momentary loss of brakes at walking speed). I thought I'd start with the fundamentals and take a run up to P......s in Sawtry (they're 20 minutes up the road, so it's hardly worth DIY) to get some new spheres fitted, then we'll take it from there with whatever problems are left.
Pete

pete_wood_uk · Post by **pete_wood_uk** » 12 Jul 2005, 13:33

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Chrispy

If you press the brake quite hard and let go there's also a 'Cha' noise like air being released under pressure. Is this normal?
<hr height="1" noshade id="quote"></blockquote id="quote">
That's normal. Or I should say, every Citroen I've had has done it. So it's normal for mine. [:)]
Cheers
Pete

Chrispy · Post by **Chrispy** » 12 Jul 2005, 13:49

Hmmm...seems to be a common thing then! At least the "cha" noise is normal (Cheers Pete). Would be interesting to see if the end of summer fixes it. [:)]

nick · Post by **nick** » 12 Jul 2005, 22:40

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Chrispy

So it could be air in the brakes? They don't feel spongy at all and are quite effective at all times. If there was air in the rear brakes I doubt this would make the pedal buzz as it does when you prod it. It almost feels like if there is air in the system, it's in the doseur valve itself.
<hr height="1" noshade id="quote"></blockquote id="quote">
My Xantia does this every summer! On mine its always been caused by air (or maybe nitrogen from the spheres) getting into the osr brake line. Bleading the osr brake (there's never any in the other 3 on my car, no matter what order I bleed them in) seems to stop it - until the following summer when the weather warms up & it starts doing it again.
Don't ask me why its always only the off side rear that collects it......but that could just be peculiar to my car anyway.