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No abs brake pump - RR Classic help


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Hoping someone can help, or point me in the right direction here.

My 92 RR has lost its brake pressure, so there is no servo assistance from the accumulator pump, so unsafe. The abs light was on for a while, but as I presumed this was an abs sensor I continued to use it without further investigation, clearly I cannot continue this now!!!

I am at a bit of a loss as to how to diagnose the problem. I have checked all of the abs fuses under the passenger seat, and non have burnt out, the relay on the far right clicks when the ignition is turned on and becomes warm to the touch. I have unplugged the smaller plug on the accumulator pump to check the supply and this registered only a few volts, and not 13, like the battery?!

How do I determine the source of the fault, many of the forums mention the accumulator is often the problem, or at least the pressure switch. Any help would be greatly appreciated.


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Hi Richard,

OK, first calm yourself - if the plug only feeds a few volts, its most likely that the failure is from the relays or fuses - not so expensive/"hard to get in good condition" as the pump. The pump/motor is a self contained unit with mechanical pressure switches (three of them!), working independly of the wabco ecu, so you should be able to feed it direct with 12 volts to get it going (just to check if it´s OK). Then go on check all the relays - they shouldn´t get very warm (this is a sign of worn out contact points).

Schematics and repair manual here: http://www.muddyoval.com/articles/manuals/rrm_brakes.pdf - and you can find the complete electric schematics on the muddy oval site too.

The Wabco (or Clayton-Dewandre) abs braking system is from page 70 and forward on the linked pdf-file.



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That sounds relieving! I'll check later, thanks for the advice.


Just glanced at the schematic again (pages 52-53 in the pdf), and it´s not true that the unit is self contained, as the pressure switches uses the relays to switch the pump on/off.

But you can still feed the pump directly with 12 volt, to see if the pump runs OK - just don´t run it too long (overpressure and eventually overload).



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