Pressure differential warning light 1988 740

I have been running around for a few weeks with the red brake warning light
on.
I did a few checks and found it to be the pressure warning differential
valve.
If as expected the valve is gone will this cause a problem with different
pressure to front and back brakes.

I changed the back brake pads a few months ago and they are now grinding,
could I have warn out the back pads that quick.
I am going to go to a breakers to get a valve, what models fit the 1988
series.




Les.

 

Some Volvos have a fluid level switch in the master cylinder reservoir, if
you do, unplug the connector, just to make sure that the float is ok. To be
100% sure it is the differential pressure switch, unplug the wire that goes
to it, and if the brake light goes out, then probably the unit is defective.
Inside the pressure switch there is a piston that is subject to both brake
circuit pressures, any unbalance will cause the piston to slide and give you
a ground that will cause the light to come on. It should be self resetting,
however, if water is present in your brake fluid, it may seize the piston.
How long ago did you flush your brake fluid and how did it look like?

 

Long time ago.

 

How do I check to see if the piston in ceased.
Can I get away with just flushing the system not have to replace the unit.
The car is a 1988.

 

I replaced mine in an 86 240 long time ago and bought it from an online
store, FCP Groton, here is the link:
http://www.fcpgroton.com/volvo700900brakes.htm#hydraulics there is little
you can do other than taking the thing apart, I did see that they sell the
switch separate for $14

Good Luck