Activa brake feel

Sl4yer · Unread post by **Sl4yer** » 14 Nov 2008, 22:30

Just been out for a fairly spirited drive, and I'm getting more and more curious about the Xantia brakes. There doesn't seem to be any constant braking effort for the pressure applied to the pedal. It can be hard to come to a smooth, gentle stop.

I've got an idea that this is related to the road surface, i.e. undulations or rough surfaces increasing the braking effort. Is this possible with the hydraulic system, either by design or fault? Or is it more likely that I'm struggling to maintain an even pedal pressure under such circumstances?

I've read the threads about the pedal spring mod, and the experiences of others seem to match mine (e.g. brakes feel like the discs are badly warped at times). Has anybody done the mod recently? And does anybody have any pictures of the parts in question? Aussiefrogs seems to be password protected at the moment.

Thanks,

James

XantiaMan · Unread post by **XantiaMan** » 14 Nov 2008, 22:37

Mine is exactly the same. It was better after a new anti-sink and bleed but they are still what i would describe as 'pulsy', i have got used to it though and they definatly work very well when needed. Jim tried the brake pedal mod and TBH, the lack of progression made it even worse so i refitted the spring.

My TD in contrast has alot more feel to the brakes, free of ABS they can lock up if you want and give you a solid stop too.

Rest assured i dont think there is a problem, your car is virtually identical to mine so its good to hear another has similar brakes...

Sl4yer · Unread post by **Sl4yer** » 14 Nov 2008, 22:40

Thanks for the reply.

All the spheres are (should be!) good, as they were only done a few months ago. It's probably worth me bleeding the brakes though. Nothing lost if there's no change!

James

handyman · Unread post by **handyman** » 14 Nov 2008, 23:18

It took me ages to track this phenomena down and resolve the issue, as it is very simple but seems to affect the Activa more so than other cars.

Air in the front brake calipers.

The only effective way I found to cure it was to vacuum bleed the brake calipers at the front.

My very early Mk1 suffered it, even after new discs and calipers, hubs, flanges checked for run out, wheels rebalanced, tyres check for mis-alignment.

It was only after vacuum bleeding the brakes that cured it. None of my other Activas, both Mk1 and Mk2 suffered it.

Downside, I do not know where you can buy a brake vacuum bleeder nowadays. I've had mine for years and it has been invaluable for all sorts of hydraulic problems.

Handyman

Unread post by **xantia_v6** » 15 Nov 2008, 07:16

XantiaMan583 wrote: tried the brake pedal mod and TBH, the lack of progression made it even worse so i refitted the spring.

On my Mk1 V6, due to this, I kept the spring but put a 6mm spacer in the spring casing to give the spring some pre-tension, and I am happy with the result.

citronut · Unread post by **citronut** » 15 Nov 2008, 09:33

99.99999999% it is air in the system, although i have never had the need to vaccum bleed a hydraulic citroen???, but if that worked for Richard (HANDYMAN ) it cant hurt giving it go, even tough i would have said they are quite capable of shuving enough citro blood through on there own,

as the bleed KNIPLE is at the top of the calliper i cant see why it should be a problem

regards malcolm

Unread post by **CitroJim** » 15 Nov 2008, 10:16

One thing Gareth and I intend to try on his Activa is new brake flexi hoses. If these are not poerfect, they could be swelling under braking.

Not got round to it yet but when we do, We'll report back.

Gareth and I have bled his brake lines very effectively. Where do you reckon the air is stuck Handyman? Any why will a vacuum bleed do the trick when conventional techniques won't?

handyman · Unread post by **handyman** » 15 Nov 2008, 10:17

Hello Malcolm, although the bleed nipple looks to be at the top of the caliper, it isn't.

When I vacuum bled my front calipers, I got a couple of cc.'s of air in the bleed line and as everything is under a vacuum it could only come from the calipers.

Brakes worked fine after that, with a positive feel, no undue pressure required to make them work and no split second lag, when you wondered if the brakes were REALLY GOING TO STOP the car.

My wife noticed it more than me, as her feet are more delicate.

Handyman

Unread post by **CitroJim** » 15 Nov 2008, 10:24

handyman wrote:When I vacuum bled my front calipers, I got a couple of cc.'s of air in the bleed line and as everything is under a vacuum it could only come from the calipers.

That makes sense Handyman

Now, if one bled with very worn pads, so the piston was well extended, and then retracted for new pads, that might help dislodge air trapped in the caliper itself.

The nipple being at the top of the caliper is not best placed for effective air extraction.

handyman · Unread post by **handyman** » 15 Nov 2008, 10:25

I think that the flexible hoses could be another faulty component, but they would not give a pulsating effect. Its always worth checking them for any splits or cracks, but I have never had a car in recent years fail an MOT due to worn flex hoses.

It used to be quite common in the sixties and seventies with the advent of servo assisted brakes, as the hydraulics were running at higher pressures and I am sure materials technology was lagging slightly.

Handyman, IKBA.

Sl4yer · Unread post by **Sl4yer** » 15 Nov 2008, 12:29

Definitely sounds like air, and I suppose it feels like it too when I think about it.

It's going to meet my regular garage for the first time on Tuesday, so they can get to know each other. I'll ask them to bleed the brakes when it's in.

James

deian · Unread post by **deian** » 15 Nov 2008, 16:13

I see the theory behind you vacuum pump but I don't think combining two techniques would work well. I doubt there would be any nooks and crannies in the caliper where air could get trapped. That would be a poor an dangerous design by Citroen.

I think if you suck more than the car can pump then you may suck pockets of air out of the circulating system (steering/suspension) and then you may have created a problem.

You would be better off sticking to one way of doing it... pushing with the brake pedal with the engine running.

Also do some citrobeotics before bleeding in case you somehow push some air down that you won't push out. That shouldn't happen but it may do somehow.

Also I like to open the bleed valve on the hydractive block to relieve the pressure there too, there is some theory in the back of my mind which I cannot explain which tells me this technique works.

Maybe do it like this... citrobeotics, bleed, citrobeotics, bleed, citrobeotics, bleed, and finally citrobeotics.

The caliper may not be screwing out properly (smoothly) either, depressurise the system, jack up a wheel, take it off, and try to manually feel any weirness as you screw it in and out yourself.

Finally, air in the brakes would almost certainly show up as a slight sometimes scary delay between pushing the brake pedal and the car actually doing something.

As for the spring in the pedal, I took it out of my xantia 2.1, and put a load washers in place of the spring, it wasn't THAT much of a difference to be honest.

Going from the 2.1td to the V6, I couldn't feel any difference (unless the V6 had the mod done, I was not aware of this). The reason the spring is there is to make the pedal feel more conventional for people coming from conventionally braked cars in case they slam on the brakes.

Hope that helps.

citronut · Unread post by **citronut** » 15 Nov 2008, 17:14

it was always said in the garage trade callipers with kniples lower that the highest point are a bbbbbbbb to get all the air out, similar on the cooling system, as the air will go to the highest point,

the old wedgy princess had two kniples on one side of each calliper, they were orible to bleed

regards malcolm

handyman · Unread post by **handyman** » 15 Nov 2008, 18:10

Ah, Malcolm, the old wedgy Princess, did the British car industry get any better! Like driving on a pile of mattresses

Deian, if you are vacuum bleeding a brake system, you do not need to operate the brake pedal, you only need the engine running. No need to phaff around doing Citroebics. I am intrigued to know where the air leaks in, in your hypothesis, as surely fluid will leak out once the system is pressurised.

I know that vacuum bleeding worked well on resolving the issue on one of our Activas, and the brakes now feel as they should do.

Also, I think you will find in commercial garages, vacuum bleeding is the norm, at least it was in the garages I ran and owned.

It is well known that the front calipers on the Xantia have air pockets. Look at the location of the nipple in relation to the chamber.

Handyman

deian · Unread post by **deian** » 15 Nov 2008, 20:04

I'm not saying you're wrong handyman, but in my opinion there is no need to use the vacuum system to bleed the xantia, as you may well know, the brakes are operated directly by pressing an on/off switch under a brake pedal, it will push itself out under the pressure of the pump when you press the pedal. Where as on a conventional car, sucking the fluid (then air) out is the easiest way to do it.

The two techniques achieve the same goal. But I think pushing the fluid out at full pressure may have more force than sucking it out, hence getting rid of air better.
I think the pressure of the fluid being pushed out would overcome any nooks and cranies in the caliper better than sucking it out.

My ideas are just theories based on what i've done in the past and my intelligence (or maybe lack of in this area). I'm just throwing in some ideas that I would think would work and ones I would try myself.

As for you questioning my theory of where the air gets in by combining both techniques... Say you have air in your "system", but not in your brakes... say this bubble lies over the entrance to the pipes that go to the calipers... and you start sucking... you may suck it down, and stop sucking before it comes out. If you do citrobeotics first, this air bubble would be expelled before you suck it down.

Obviously that is a glorified theory and the reality is you may well suck that bubble of air out the brake lines, but I think the theory is true. Citrobeotics needs to be done first.

I think a clean system would help brake pressure too, maybe small pockets of air get 'stuck' behind dirt in the system.