Symptons of a failed rear anti-sink/accumulator sphere?

bigblackfalco · Post by **bigblackfalco** » 15 Jun 2011, 20:12

When I start my Xantia it drops at the back. I'm guessing this is a sign of a failed rear anti sink/accumulator sphere?

If the front main accumulator is failed (my tick rate is about 10 secs!) in theory should the front drop down like the back does on start up?

Xaccers · Post by **Xaccers** » 15 Jun 2011, 20:22

The only sure way to test the A/S sphere is to use a sphere pressure tester.
If the accumulator sphere needs changing then chances are the A/S does too.

rory_perrett · Post by **rory_perrett** » 16 Jun 2011, 08:57

A poor accumulator sphere can give the symptoms you describe, if it has a tick rate of 10 secs it sounds like it needs doing anyway so you might as well start there.

Clogzz · Post by **Clogzz** » 16 Jun 2011, 16:29

Sign of my flat anti-sink was the rear brakes not working when setting off in reverse after sitting overnight.

Post by **CitroJim** » 16 Jun 2011, 18:43

Clogzz wrote:Sign of my flat anti-sink was the rear brakes not working when setting off in reverse after sitting overnight.

Indeed, that's the purpose of the sphere. To provide a reserve of pressure for the rear brakes before the rear anti-sink valve opens.

One way of assessing the condition of the sphere is an ability or otherwise to be able to bleed the brakes when the engine has been off for a good few minutes. Or even operate them. This can be achieved by sopping the car with he suspension on high and then jacking one rear wheel clear of the ground. If the rear brakes still operate after you've done that the anti-sink is not bad.

The sphere is so called as it was a requirement to fit it when anti-sink was introduced. It's correct name is SC/MAC Accumulator.

bigblackfalco · Post by **bigblackfalco** » 18 Jun 2011, 06:14

My rear brakes aren't working 100%, I can see from looking at the discs.
There's no reason why there should be any air in the circuit.
I'll renew that sphere too.

Xaccers · Post by **Xaccers** » 18 Jun 2011, 08:41

bigblackfalco wrote:My rear brakes aren't working 100%, I can see from looking at the discs.
There's no reason why there should be any air in the circuit.
I'll renew that sphere too.

Nitrogen leaks from the spheres, if it gets into the brake lines it will be there until you bleed.
Also limescale like stuff builds up between the arm and the caliper making the brakes wear at an angle, and eventually stressing the caliper bolts so much they sheer when you try to remove them to clear it up.
Eventually the rear brakes stop being able to apply pressure to the disc and you fail your mot.

bigblackfalco · Post by **bigblackfalco** » 18 Jun 2011, 13:17

Xac wrote:
bigblackfalco wrote:My rear brakes aren't working 100%, I can see from looking at the discs.
There's no reason why there should be any air in the circuit.
I'll renew that sphere too.
Nitrogen leaks from the spheres, if it gets into the brake lines it will be there until you bleed.
Also limescale like stuff builds up between the arm and the caliper making the brakes wear at an angle, and eventually stressing the caliper bolts so much they sheer when you try to remove them to clear it up.
Eventually the rear brakes stop being able to apply pressure to the disc and you fail your mot.

Didn't realise they were on the same circuit like that.
Well my rear spheres are deffo knackered, so I'll have to bleed brakes after putting new spheres on