Wabco ABS runs (too) much

[Roverbo]

Hi,

I´ve got a 1990 RRC with the Wabco ABS system. For about a year ago, the abs pump started running at shorter and shorter intervals, down to every 1 minute, and I changed the Nitrogen-charged Accumolator to a new one (bought from Britishparts). Everything then worked fine, I could accept the pump now running every 5-7 minutes.

But now everythings seems to be "as before". Yesterday I tracked a interval at 1 min. 40 sec. (without applying the brake pedal at all).

Could it be the "new" accu allready has leaked the pressure out, or did I buy a piece with 10 years on the shelf, "almost done" at the day I got it?

The pump and relays etc. seems to be OK, from start the pump runs 40 secs to charge up, as stated in the RAVE manual.

BR

Bo Helsted

[geoffbeaumont]

You might have a leaking brake line?

[Roverbo]

Hmmm...Wouldn´t I see some brake fluid dripping somewhere ? And the level in the reservoir drop?

/Bo

[geoffbeaumont]

Possibly - but I suspect a corroded line could let air in before it's bad enough to let brake fluid out. What do others think? Am I talking rubbish?

[Roverbo]

Hi Geoff,

this is a drawing of the high/low pressure system.

The thick, black lines shows the high pressure parts (Valve block, pump, accumolator, mastercylinder, lines, calibers).

I could understand if the pump would run often if a brake line was corroded/leaking - IF i pushed the pedal. But its like the high pressure system looses pressure even though i´m just idling without using the brakes. No pressure is reliefed from the pump/accu parts. Lack of Nitrogen ("biased" pressure) in the accu would make the pump run more in case if deep brakings, I understand this (less energy would be accumolated). This has always been a small mystery to me (well, many parts of my rangie is...), even when the pump only had the pleasant 5-7 minute intervals. Anyone who can explain ?

Cheers

Bo

[geoffbeaumont]

That probably shoots my theory down then.