checking an ABS accumulator

[Richard123]

I've removed the ABS accumulator as my brakes on my new (to me) 1994 S4 seem completely unassisted and the pump runs every time I press the brakes.

Is there any way to test the accumulator now that it is off? The entrance to the accumulator seems to have a metal check valve in it that gets pushed back when you screw it onto the brake system, so I can't see how i can test to see if the diaphragm is punctured.

Any ideas before I commit to a new one?

Thanks,

Richard

[ramjet]

Richard

There are heaps of threads on this on here. Try a search and see what you come up with. If pump runs on every brake press, it definitely sounds like the accumulator. A pressure test rig is cheap and makes testing the system real easy. If you completely depressurise the system (key off and keep pressing brake pedal until it goes real hard - about 40~50 brake presses normally) and the turn the key on and time the period it takes from the pump starting to pressurise the system until it stops. It should only take about 40 seconds according to the manual to reach pressure and turn off. Quicker than this would make you suspect your pressure switch, longer, the accumulator.

Michael.

Big thread on this

[RV_ABZ]

You can always buy a new accumulator, they don't last for life any way (I'm told life expectancy is about 10 years). You'll be in much deeper sh*t if the problem is not fixed after you replace the accumulator. This is what's happened to me: it ain't the accumulator, it's that damned pressure switch.

My S4s is therefore off the road until I can source a replacement switch or manage to fix it with a good clean.

Bugger, bugger, bugger!!!

[ramjet]

Herve,

I believe Bibs has some info on the factory working on a replacement switch option for us all. Also, Steve Taylor (Lotus mechanic) in Melbourne, Austrlia has developed a 2 switch system that has all the necessary engineering certs etc required. I am pretty sure the details for this are in the thread I attached the link to previously.

Michael.

[Richard123]

Thanks guys, I will slip the accumulator back on and see how long it takes to charge up. I don't think it takes more than 40 seconds though.

So there is no accepted way to test the accumulators when they are off the car? I thought I had read that someone was able to push a thin screwdriver in and move the diaphragm back and forth......I definitely cannot do that. Whatever covers the opening to the accumulator is rock solid.

The car has 'V8 brakes installed' which I presume is rotors and calipers. So I was thinking that they might not have been properly bled. Would a lot of air in the system possibly cause the quick cycle of the pump and the hard unassisted pedal?

[Rich H]

Accumulator runs at several thousand PSI - stop poking the diaphragm...

Hydraulics place should be able to test it, but if it charges up and the pump stops then it's working.

Poorly bled brakes make them utterly rubbish, bleeding them is a pain too...

Read the existing threads, they will help.

[Richard123]

It was 50 seconds to charge up. Definitely a change in tone from the pump about half way through. One pump of the brakes brought the pump back on though.

I'm going to try bleeding the master cylinder and the rear brakes to see if that does anything.

After that I might tee a gauge to the pressure switch and see what is really happening there.

[ramjet]

Richard,

Your car is showing the same symptoms that mine did have. I had to replace my accumulator. However, what I also found using a test gauge plumbed into the brake system was that the high pressure side of my switch has gone 'soft'. While my pump run time was in spec, which made me think my accumulator was ok, with the switch shutting the pump down, it only appeared ok. I also got the pump running on every brake press. With the new accumulator, it is now only every third press. Still does not get up to the max pressure as shown in the manual, but I am not getting a flashing ABS telltale anymore.

I am waiting to see what comes from Bibs re the new switch being developed by the factory (though development money for that may have gone on naked models for the silly photo shoot) or failing that, I have tried to drum up some interest in a group buy from Steve Taylor at the Elan Factory in Melbourne, Australia. Details of that are in here. Click here

Michael

[Richard123]

Well, i bled both sides of the master cylinder and then the rear brakes which seemed to have lots of air.

Now the pump turns on every second press....better, but not good enough. Not sure if this means the accumulator is good or not. But I'll assume it isn't punctured through.

I'm going to see if I can take it for a run tomorrow to see if the brakes feel more assisted now.

OK to drive these cars in freezing weather if the roads are ok? I'll just warm it up a bit in the garage?

[RV_ABZ]

My favourite local garage may have found an alternative source to replace my pressure switch. My switch is Ok on the high pressure side but not responding on the low pressure;hence my loss of braking assistance.

Meanwhile, he's worked out a temporary solution with a relay to bypass the low pressure issue. I still have the ABS warning light flashing on the dash, but assistance is back and I can brake!

For info, pressure switches we've looked at:

- Renault 21 2.0l Turbo

- Peugeot 505

Saab 900/9000 look similar but have a 6point connector instead of 3.We did not find technical specs of that kind of switch either.

'will just have to wait for Lotus to come up with that new switch...

Edited November 14, 2010 by RV_ABZ

[Rich H]

I can't see it being that hard to fit an adapter with 2 switches and a bit of relay logic...