air in brake pedal

amp1 · Post by **amp1** » 19 Oct 2003, 17:03

Hi everyone,
Got a 94 TD xantia with air entering the brakes overnight. This all started a couple of weeks ago when I tightened a couple of pipe-leaks on top of the pump - about 2 days later I noticed the brakes did not "feel" the same - ie a gentle pressure did nothing making your reaction press harder where upon the brakes worked more than effectively! I suppose what i am trying to describe is that the brakes worked effectively but without the gradual feel that they should have. I've tried bleeding the air out of the suspension system and also out of the braking system at my local garage which cured the problem fine until the next day when the problem re-appeared. I guess there is air entering the hydralics system through a leaky pipe? Should the LMH tank have a foamy bubble appearance when the engine is running or is this the air being returned from the problem? I wonder if the air used to escape through the joints that i've tightened?
Thanks in advance for any help
Andrew

Dave Burns · Post by **Dave Burns** » 19 Oct 2003, 17:54

Only two ways for air to get in as far as I can see, one is low LHM level in the reservoir, so air gets in at source, and the other is a leak in the pump intake pipe somewhere, not uncommon.
Check the fluid level with suspension on high, float must be at least between the rings on the sight glass, doesn't much matter if its higher so long as it doesn't overflow when the suspension is on low.
There are other possible causes one such is a burst sphere putting nitrogen gas in to the system, when its empty of its gas it will fill with oil, lowering the level in the tank by as much as 0.4L.
Dave

amp1 · Post by **amp1** » 21 Oct 2003, 21:28

Thanks for the advice Dave, but i'm still having problems... I've cleaned the LHM filters which were very dirty and currently just put hydraflush in the tank. I've replaced the accumlator sphere as i was unsure to when it was last changed, but the brakes still feel the same. I cannot see any breaks in the inlet hose on from the tank to the pump. If you "ride" the brakes with your foot then they work fine. Also should i see foamy air bubbles on the top of the LMH tank?
Thanks in advance,
Andy

jeremy · Post by **jeremy** » 21 Oct 2003, 21:54

No the LHM should not appear foamy. If it does it means that there is an air leak in the feed to the pump and this will not show as a leakage as its under suction.
it is in fact quite common for the pipe from the reservoir to the pump to perish, or for its ends to become a bit ragged. Disconnect both ends and have a good look at them for stretching or splits and make sure they are a good fit. If this does not stop any air leak then suspect the pipe itself. Anders suggests as a temporary measure replacing the pipe with a (Clean) section of garden hose to see if this makes any difference.
Foam is of course acceptable when bleeding the system by opening the valve on the regulator but once the initial air has been expelled no more should get in.
jeremy

amp1 · Post by **amp1** » 30 Oct 2003, 04:25

Just an update incase anyone else has this problem (pretty unlikely) - Found where the air is getting in - a hairline fracture on one of the corners of the hydralic pump hub - the hub itself is made of something plastic - could be bakelite - it has 3 boltholes and the mounting surface is triangular in shape - i guess because the pressure is not quite enough from the 3rd bolt as the fracture is just past the hole it's letting the air in. I only discovered this by cleaning the pump thorougly. Apparently you can buy from citroen a new hub/set of seals/ and pulley for some pumps, but not mine [V] I'm going to try a trick (in daylight!)with a packed out washer on one side to see if that holds the hub tighter in place.....
fingers crossed.
Andy