Thread: NRC4282 Pressure Differential Warning Actuator

Hi Garry the part number for the one you have should be NRC4880.one bolt hole.

Originally Posted by 85 county

what i was trying to say, is that the piston in the middle of the valve has to move about 10mm to activate the switch, this gives about 6ml of fluid that can go to ether circuit before the switch is activated. unless you have a wobbly disk this will inevitably will be to the rear drums. if your rear drums are good and you have the correct Dia shoes fitted and adjusted correctly then there will be in theory no movement of the piston in the center of this valve.

if you unit has failed or is leaking fluid ver the switch, it is probably because the piston inside this valve has a lot of flow past, thus putting fluid pressure on the switch housing which it was never designed to do.
this flow by may also be masking another problem with your brakes, usually the rear being to slack in there adjustment.

I know YT110 spent a lot of time on this topic, rebuilding the unit vers buying a unit and in the end removing the unit which seems to be working well in an immaculate maintained 110.

but i have it stuck in the back of my mind. what if you were to put it over the pits? or what if you fill your drums full of mud (not a problem in SA)

what if you are crossing the Simpson and use up a bit of your rear pads, do you readjust you drums every other day. although disks are a bigger problem in these sorts of environments. and i am exaggerating for effect.

Well thats interesting what you have posted about this unit, I had not adjusted the rear brakes I have had the 120 on the road for some months now and the fronts had been locking up. when I checked the rear brakes they were quite a lot out of adjustment this was at the time I noticed the leaking fluid from the unit. So this situation may have led to the premature failure of the switch, as it has meant that "the piston inside this valve has a lot of flow past, thus putting fluid pressure on the switch housing which it was never designed to do."

It has worried me too be put over the pits also or be involved in an accident where I have removed our said switch and thus altered the car and its ability to comply with the ADR's of the build. Stuff insurance companies would love because it gives them an instant out of the 3rd party policy I have.

My 101 has one of those valves and it was seized - pulled it apart is basically a piston with some 0 rings on it - I went to a brake place and got a couple of brake fluid O rings - cleaned it all up and put it back together - works fine and the brake failure light also started working.

They are designed to be pulled apart to set them back to the centre position if there has been a fluid loss or major unequal pressures on either side.

Agree they are hellish expensive and on a truely dual system are really not needed as you maintain your dual circuitry but this system does tell you if there is an issue. Not sure if you have a full dual circuit system - as you have two inlets and two outlets I assume so.

Garry

well after 3 phone calls with YT110, a normal state of affairs between isuzu pilots.

As i said before YT110 put a lot of time into looking at rebuilding these. there is one difference. my one had springs ether side of the piston, while YT110s 3 units none have springs. my springs were so weak as i suspect they did Little anyway. YT110 pulled down a unit while we were on the phone, and what he described was a little different to what i remember seeing when i striped my unit.

now i think about it, YT110 said that the switch was hard up inside the piston where my unit this was not the case. so i suspect the the spring on the wedge of the switch in YT110s unit centralizes the piston when there is no pressure and in my unit the springs centralized the piston. which also would change the concept that in YT110s unit only 2 mm of travel in the piston would activate the switch where in my unit 5 mm each way was needed to activate the unit.

so if we were to take the bore at 1/4 or 6mm and stroke to activate at 2mm, that would give us a volume of 3.142 * 3 2 * 2 = 56ml just over 1/2 a CC

my book says there is 123 cc of fluid in the rear system a loss of 56 ml of pressure equates to 86 psi say a given 100psi of applied. IE if the front system has 100psi then the rear system would only have 14psi. both systems should have the same fluid pressure. mechanical pressure or stopping force is governed by the difference in piston dia.

now that is fluid pressure not mechanical pressure.

and if i got my maths right

ummm.....

not to be rude but the loss of 56ml of fluid from the rear brake system would leave you with no brake pressure on the rears.

basically the 2 versions of the valve are a push off center type which has no springs and is prone to false triggers after a bleed of the brakes (during the bleed the piston is pushed over center and because youve then got equal pressure on both sides of the piston it stays off center) and the return to center type (the one with the springs)

the unit with the springs fitted was replaced due to a potential safety issue. drivers became accustomed to the light flicking on with the brakes coming on when the front or rear brakes had excessive clearance so ignored the brake failure light.