ABS accumulator empty every 3 months

[nicknick68]

Hi guys,

need heklp for my Delco Moraine IIIA ABS system: the accumulator gets empty after 3 moths, I have repleced it already 3 times!

In the beginning it works correctly, replacement is done following all instructions (also here in LEW is wrtitten how to do it), pump activate normally after 10 brakings.

Slowly it activate more often, after 7, after 5, after 3 ... till it activate avery time I do brake and then allarm tail goes ON flashing... then fixed.

Repacing the accumulator problem is solved for 3 months. Accumulator are original spare parts from GM (part number GM 25528382) from USA, not Europen recharged or old stocks!

I believe I have a pressure loss... but where? And how can I find it?

NOTE: I have changed FRONT calipers with Monter calipers 10 pistons from TAROX (see my previous post with pics).... I do not believe could be a reason! Or could it be?????

Please help me because I am tired to waste money in accumulators.

Nicola

[RV_ABZ]

ZE infamous pressure switch?

[ramjet]

Hi Nicola,

I've been thinking about this a bit.

First, the chances of three accumulators failing one after the other with the same symptoms would be 1 in a really big number, so as to be so close to zero, it may as well be zero. The accumulator is essentially a high pressure nitrogen balloon. Nothing else.

Having said that, you have another problem which is not the accumulator. Since the pump is running every pedal press, that would indicate air in your system.

I would do the following:

1. Depressurise the system and then time the length of time the pump runs when you turn the key on. I would do this when you believe the system is correctly set up and when you are down to the pump running every pedal press.

2. Once the system has gone 'bad', depressurise the system and bleed it completely with the same accumulator on it and record the pump run time again.

3. Reinstall one of the old accumulators, bleed the system completely and see what result you get for the pump to reach pressure. I presume you have bled the brake system each time you have changed the accumulator? That is a total of six bleed valves on a standard S4. One at each wheel and two on the master cylinder body.

I am also surprised at your statement of getting the pump running after 10 brake presses with a new accumulator!!! Even the manual states 5 to 7 if I recall correctly.

I think you will find that your master cylinder is drawing air in slowly during operation (and possibly while sitting) which is giving you the impression that you are slowly running out of pressure. I don't think your pressure switch is the issue as you would not return back to 10? presses with a new accumulator if the switch had gone soft on the high pressure side. It may be a good idea to follow the switch cleaning thread that is in the tech section somewhere. I did try this, but it made no difference to mine.

When you have depressurised the system prior to changing the accumulator, how many pedal presses have you had to apply before you got a hard pedal? i.e. system depressurised.

Is there any evidence of brake fluid leaking anywhere near the master cylinder or inside the cabin on the firewall? Have you noticed any weeping along any of the brake lines to the calipers?

Are you losing fluid over the same period of the time as your system 'loses pressure' as you put it?

Unless you can recreate the conditions of the system losing pressure, it may take a while to get the results, but without a pressure test rig, you are flying a bit blind and will have to use a bit of trial and error.

Michael.

Edited November 29, 2010 by ramjet

[nicknick68]

Thanks Michael,

I will try what you said next week end.

About the 10 times of pedal pressing: I just said 10 meaning the nurmel number, actually I meant 5 to 7 .

I will also try to use Espritmon software, downloaded before yesterday, hope it works with me.

Nicola