Brake pedal pulsing?

[sparksie]

Hi all

Just a quick question, for once!
Arriving home after a long-ish run the other day, I was creeping down the hill outside, waiting for son and dog to get out of the way. I was using gentle pressure on the foot brake to control my descent, as I was going way slower than tickover in 1st would allow.
After maybe 15 feet of this, the brake pedal throbbed strongly, like a conventional car with ABS active. I stopped the car and applied the handbrake, in case the brakes were about to pack up, but it seemed ok when I tried again after sending the family indoors out of harm's way.
It hasn't done it again, nor put on any lights on the dash.
Anybody know what it was?
Thanks guys

[Old-Guy]

I've had this on at least one occasion in much the same circumstances (following a neighbour with small children on their way to school down our sunken lane). I suspect the ABS software gets confused by 'trickling' at very low speed, particularly if any of the wheels go over anything loose (leaves, bits of twig, stones) that causes an abrupt but momentary change in wheel rotation speed

[sparksie]

Well, you may be right, but most manufacturers have a speed setting, below which the ABS is not operational.
I know we're talking about Citroen, so general rules can never be assumed to apply, but still ABS working at a fraction of a mph seems a bit silly, even for a French car!
I was wondering could it be something like a failed/failing accumulator, allowing the pressure pulses from the pump to be felt through the pedal.
But then, as I understand it, the pedal is operating a valve, not a piston & seal, so would I feel variations in hydraulic pressure, even if they were present?
Just Cit's way of asserting her authority and warning me not to become too complacent, I guess, but I wish it wasn't with the anchor all the same!

[RichardW]

Poor accumulator normally presents as varying strength of brakes on constant steady braking. If the pedal kicked back at you, then it was the ABS, and if this happened at low speed just before it came to a stop, then odds on one of the front reluctor rings is snapped - the CV joint rusts and expands and splits the ring. The 'extra' tooth in the ring confuses the ABS computer. Note that it can prevent the car stopping if it gets really bad (I had to take the ABS fuse out of mine one day!) so it's worth changing the ring - it's not hard (or expensive for a change!).

[Hell Razor5543]

One possibility is the accumulator sphere. Although its' man purpose is to act as a backup pressure reserve should the LHM pump fail, it also dampens out the pressure waves generated by said pump. What is the interval between clicks from the regulator? Ideally it should be over 30 seconds. Less than that indicates the accumulator sphere is on its' way out, and should be replaced (as well as the anti-sink sphere at the back).

[sparksie]

Poor accumulator normally presents as varying strength of brakes on constant steady braking. If the pedal kicked back at you, then it was the ABS, and if this happened at low speed just before it came to a stop, then odds on one of the front reluctor rings is snapped - the CV joint rusts and expands and splits the ring. The 'extra' tooth in the ring confuses the ABS computer. Note that it can prevent the car stopping if it gets really bad (I had to take the ABS fuse out of mine one day!) so it's worth changing the ring - it's not hard (or expensive for a change!).

Yes, I'm familiar with ABS reluctor rings. Any I've replaced have been part of the CV joint. Are you saying in this case they're not?
Yes, again, failure to stop was my main concern, with the handbrake effectively out of reach due to me being engaged in all the activities associated with "abandoning ship" at the end of my journey. I had arrived, stopped, alerted the boy and dog to my presence and was simply rolling the last 20' to where I park, so was removing seatbelt, picking up keys, wallet, diary etc.
If I had to dive for the handbrake, all the stuff would fall on top of it and make it unreachable in the time it would take for a disaster to happen.
Time for a change in routine, I think.
However, it's not long since I was poking around down there, checking discs and pads, and there's practically no corrosion on anything. I'd be somewhat surprised if there turns out to be enough on a drive to break a ring!
I'll have a look at it tomorrow, provided we're not required in the hospital.

[Hell Razor5543]

The front reluctor rings fit over the CV joint body, they are not part of it (unlike the rear reluctor rings, which are part of the wheel hub). I had to replace both of Gracies' rings, and (with the gratefully received assistance of CitroJim) we replaced both of them within a couple of hours. The ABS has not had anything to complain about since.

If you do need to get reluctor rings I got mine from here;

http://www.ebay.co.uk/itm/CITROEN-XANTI ... 27c0132920" onclick="window.open(this.href);return false;

The following post covers reluctor ring replacement in the usual forum manner!;

http://www.frenchcarforum.co.uk/forum/v ... t=reluctor" onclick="window.open(this.href);return false;

[sparksie]

Ok, thanks guys.
After reading the post Hell Razor referred to, I don't think this is my problem at the moment.
There's no ABS light, at any speed, so the symptoms don't match.
I have to go hospital visiting, so I won't be getting dirty checking it today.
Let's see what todays 200 miles bring...

[Hell Razor5543]

How is the accumulator sphere?

[sparksie]

Well, not being sure which sphere does what, that's a question I can't really answer.
However, having listened out for clicks, they're almost a minute apart, though not regular.
I timed them a few times and got 48s as the shortest but 61s as the longest interval.
I believe that's good...?
As an aside, Cit's a non-sinker, but for a while now has been sinking to the floor at the back after a cold start, then settling to the correct height.
It runs for about 20 seconds before putting out the stop light, then the back drops, the front rises a little (sometimes a lot!), then she sorts herself out. The whole process taking about a minute, maybe a little more, after starting before I can drive off.
Is it possible there's any connection?

[Xaccers]

The accumulator spheres (one at the front of the engine, one at the back of the car up in front of the spare wheel (known as the anti-sink sphere) are pressure reservoirs giving you brakes in the event of a pump failure and also keep the pressure up when you brake.
The corner spheres on a LX/SX provide ride comfort. On a VSX/Exclusive the corner spheres are harder and the comfort comes from the hydractive sphere (one at each end of the car) which is isolated when throwing the car about to stiffen the ride.
Height is controlled by the height controllers (one at each end of the car) which connect to the anti-roll bars via swivelling linkages that often seize up and need regular lubing.

[Hell Razor5543]

That interval is good, and it means the accumulator sphere is holding pressure. It would be reasonable to eliminate it as a cause for your brakes pulsing.

[sparksie]

Ok, thanks James and xac.
Whenever I get another opportunity to lift her, I'll have to go under and have a proper look at the hydraulics.
Cit has no trim level badge, she's just a "TurboD", so all the LX/SX/VSX etc not really helping me, at the moment.
Is there a way of figuring out which she is, just by looking?
In the '80s and 90's trim levels were very different on UK spec cars. I don't know whether that continued into the "noughties", though.
In the early days luxuries like am radios and front seat headrests were to be found on UK cars but not on Irish ones.
Later, electric screen wash as opposed to rubber bulb, or factory fitted rear demisters, then electric windows were all associated with UK spec cars and made "British imports" highly prized, while similarly specced "Jap imports" were stigmatised.
It's possible Cit is an "Irish spec" car with a different system of trim badging, having no heated seats, leather, AC, cruise control etc. She does have electric windows all round, including the roof, and radio controls (that still work!) on the wheel. She has airbags everywhere, which came as a bit of a surprise!
Thanks again, guys

[Hell Razor5543]

If you post up the last 8 digits of her VIN, somebody with access to the relevant database will be able to let you know what she left the factory wearing.

[Xaccers]

Ok, thanks James and xac.
Whenever I get another opportunity to lift her, I'll have to go under and have a proper look at the hydraulics.
Cit has no trim level badge, she's just a "TurboD", so all the LX/SX/VSX etc not really helping me, at the moment.
Is there a way of figuring out which she is, just by looking?
In the '80s and 90's trim levels were very different on UK spec cars. I don't know whether that continued into the "noughties", though.
In the early days luxuries like am radios and front seat headrests were to be found on UK cars but not on Irish ones.
Later, electric screen wash as opposed to rubber bulb, or factory fitted rear demisters, then electric windows were all associated with UK spec cars and made "British imports" highly prized, while similarly specced "Jap imports" were stigmatised.
It's possible Cit is an "Irish spec" car with a different system of trim badging, having no heated seats, leather, AC, cruise control etc. She does have electric windows all round, including the roof, and radio controls (that still work!) on the wheel. She has airbags everywhere, which came as a bit of a surprise!
Thanks again, guys

Pop the bonnet and look at the pipes going into the strut spheres. If they're thin (a few mm across) then it's a LX/SX non-hydractive. If they're thick (6mm I think) then it's hydractive so you have the extra spheres and electrovalves to isolate them.