Need help w/master brake cylinder

[Bigdaddy]

I have my "brake and ABS" warning light on. Both lights are on. They come on when I first turn the key on and then stay on. I bleed the brakes and have clear fluid at all four wheels. Lights did not go out. I can remove the plug to the pressure diff. switch and both lights go out. Question is, will the diff switch go bad? Or, how do I correct the fault. I let some fluid out of the end plug on the diff. switch, but this did not correct the fault. BTW, I have replaced the brake fluid several time and did not have this problem. Just returned from a 700 mile trip and stopping the RV gave me no problems. The brake peddle is firm and only a small amout of travel (like new). Any help would b e a great help.
Thanks

["007"]

If you do not have a burnt ABS sensor the system should reset itself after a couple of starts.
Brake light should be off if released, maybe something wrong with switch.

[DriVer]

Quote:

Originally Posted by Bigdaddy I have my "brake and ABS" warning light on. Both lights are on. They come on when I first turn the key on and then stay on. I bleed the brakes and have clear fluid at all four wheels. Lights did not go out. I can remove the plug to the pressure diff. switch and both lights go out. Question is, will the diff switch go bad? Or, how do I correct the fault.

Hydro-Max with 3 switches differential, low fluid and pressure (right)

I just went through this process. As you can see my differential switch is disconnected. The purpose for the switch is to alert the ABS system that a differential in pressure exists between the front and rear systems. A fault at this switch will light the ABS lamp and disable the system.

Just a few days ago I opened the hood on a 2009 W24 and took a look at the Hydro-Max (H-M) and what I saw was that the casting was absent hole to accommodate a differential switch. The purple wire was tied off just like you see in the picture.

I called WCC Tech Support and what was told to me is that the switch is redundant and not required. There is a rod that slides back and forth in the H-M that is moved my a pressure differential that would cause the sensor to ground out and set an ABS fault. When I had my recall done an ABS light set and this was the condition that developed when the broken sensor was replaced. Leaving the wire OFF the sensor "enables" the ABS system and it will operate normally as if there were no fault.

The other 2 switches for low fluid in the tank and pressure are more critical, required and essential.

To resolve this condition a new H-M will be required which could run several hundred dollars. It might even be possible that a new H-M might not have the sensor position available like the 2009 H-M that I saw so for the cost of several hundred bucks this position may still be non-functional.

My ABS light is OFF and I expect that the ABS will work when required.

[Bigdaddy]

Thanks DriVer!!!!
I was under the same impression. I will unplug one of the ABS sensor to prove the point. I think that you might be unable to buy just the switch. The slide rod should self center when pressure is off, but my switch is grounded with pressure off.
There is nothing like getting the correct poop from the experts!!!! Thanks

[DriVer]

Quote:

Originally Posted by Bigdaddy Thanks DriVer!!!! I was under the same impression. I will unplug one of the ABS sensor to prove the point. I think that you might be unable to buy just the switch. The slide rod should self center when pressure is off, but my switch is grounded with pressure off.

The sensor (switch) was readily available. Now as to why the broken switch didn't set an ABS light was because the switch was broken. Once we fixed what was broke it broke again so we broke it to fix it.

[tpmcn]

Quote:

Originally Posted by DriVer The sensor (switch) was readily available. Now as to why the broken switch didn't set an ABS light was because the switch was broken. Once we fixed what was broke it broke again so we broke it to fix it.

Driver let me get this correct the Dif. Pressure switch is not needed? But it is replaceable? and the new H-W do not have the switch? I gather from your discussion here that the Dif. Pressure swith is not needed but why did it break is the question that I would want an aswer to if possible. One more thing if the sensor switch is available do you have the correct pt. number? Mine is a Wh2002 chassis in a 2003 Georgie Boy.

[DriVer]

Quote:

Originally Posted by tpmcn Driver let me get this correct the Dif. Pressure switch is not needed? But it is replaceable? and the new H-W do not have the switch?

Yes that's correct.

Quote:

I gather from your discussion here that the Dif. Pressure switch is not needed but why did it break is the question that I would want an answer to if possible.

The switch was broken apparently due to blunt force trauma. It was physically broke in 2 pieces. Did not notice it, until it was pointed out. Once we put a new switch in the port W8000130, an ABS condition was set and lit the lamp disabling the system. Currently unplugged and tied, the ABS system is working fine. No adverse ABS condition is recognized and the lamp is off.

Just for kicks, I plugged the modular connector onto the switch after we came back home and the ABS lamp lit up. So I unplugged it.

Like I said, I checked Ed Gray's 2009 chassis and that switch port is no longer used.

[tpmcn]

Quote:

Originally Posted by DriVer Yes that's correct. The switch was broken apparently due to blunt force trauma. It was physically broke in 2 pieces. Did not notice it, until it was pointed out. Once we put a new switch in the port W8000130, an ABS condition was set and lit the lamp disabling the system. Currently unplugged and tied, the ABS system is working fine. No adverse ABS condition is recognized and the lamp is off. Just for kicks, I plugged the modular connector onto the switch after we came back home and the ABS lamp lit up. So I unplugged it. Like I said, I checked Ed Gray's 2009 chassis and that switch port is no longer used.

Thanks for the quick response. The reason I requested the information is that mine did the same thing as Bigdaddy and I was on the road and have not contacted Tech Service yet but did notice that with the Dif. Pressure Switch disconected both lights (!P) (ABS) went out and the brakes seem to be working fine. When you pulled out the old DPS did it come out all together and no problem setting the new switch? Did
anyone find out why the ABS Light came back on with the new DPS installed?

[DriVer]

Quote:

Originally Posted by tpmcn When you pulled out the old DPS did it come out all together and no problem setting the new switch? Did anyone find out why the ABS Light came back on with the new DPS installed?

The threaded piece of the DPS came out intact. Installing the new switch was not a problem.

There is a pin at the other side of the bore with a detent that is supposed to be self centering. When centered, the DPS sits in a recess and the ground remains "Open" so no light. In my case the rod is stuck to one side or another and the detent is not centering presenting a high side. When the switch is installed a circuit to ground is immediately present and when connected the DPS lights up the ABS lamp and disables the system.

Tech support told me that a couple of things could cause this and in some cases rust might set in from water suspended in the brake fluid. All it takes is a little irregularity on the surface of the rod to seize it. Flushing brake fluid regularly should help prevent these types of issues from happening.

[tpmcn]

Quote:

Originally Posted by DriVer The threaded piece of the DPS came out intact. Installing the new switch was not a problem. There is a pin at the other side of the bore with a detent that is supposed to be self centering. When centered, the DPS sits in a recess and the ground remains "Open" so no light. In my case the rod is stuck to one side or another and the detent is not centering presenting a high side. When the switch is installed a circuit to ground is immediately present and when connected the DPS lights up the ABS lamp and disables the system. Tech support told me that a couple of things could cause this and in some cases rust might set in from water suspended in the brake fluid. All it takes is a little irregularity on the surface of the rod to seize it. Flushing brake fluid regularly should help prevent these types of issues from happening.

Driver, Thanks for the info. I need to make a decision on replacing mine and this give me more info. I think I will remove mine and see if it is ok before buying a new one. I gather by our discussion that the area were the Switch sits is isolated from the Tank? If that is not the case I will have to have something available to plug the hole when I pull it. Let me know and thanks in advance.

[Dirtbuster]

Interesting thread, just a few questions?. If the switch worked for years, why does it suddenly not work. The valve that the switch goes in sounds like a compensation valve. This valve should operate when either the front or rear brakes suddenly have a ruptured brake line. It then cloes to the other side, to give more force to the working axle. When this valve shifts, it causes the sensor to ground out. I don't think disabling this sensor, is the correct fix. Once this valve closes towards the operating brakes, flow is pinched to the side that is not working. That means a loss of flow to half of your brake system. To reset the compensation valve, bleed pressure to the side of the system that is not working properly. Have someone open the bleeder, why you suddenly slam the brake pedal. This should reset the valve, if not the valve may be defective!

Hope this might help!

[DriVer]

Quote:

Originally Posted by tpmcn I gather by our discussion that the area were the Switch sits is isolated from the Tank?

The PDS sits in the casting in between the output port of the master cylinder.

Perhaps this pub will give you some additional information.

Attached Files: HydroMax_Hydraulic_Brake_Booster_Manual.pdf (1.10 MB, 47 views)

Right on the front cover you can see the switch below the tank. It's white in color.

[tpmcn]

Quote:

Originally Posted by DriVer The PDS sits in the casting in between the output port of the master cylinder. Perhaps this pub will give you some additional information. Attached Files: HydroMax_Hydraulic_Brake_Booster_Manual.pdf (1.10 MB, 47 views) Right on the front cover you can see the switch below the tank. It's white in color.

Driver, It appears that the DPS sits between the two supplies lines to the brake circuts. This is identified on Page 8 #4 "Differencial Pressure Switch" and I think it is like you say and indicator but not a pressure change source. It is in place to show that there is a difference in the two pressures but does nothing further. It shows the DPS circuit on Fig.#5 Page 6 It doesn't say if it is in the brake fluid or a dry area. Since you changed the DPS out do you remember if it was dry or not. I can see that the rod could become stuck if water was in the tank and got on the rod and then when it moved it stuck to one side due to rust. If it is in a dry area we should be able to reset it after the switch is removed and at the same time we could check the switch to see if it is shorrted to ground or still ok. If it is in the fluid we would have to drain the tank and then do the check. Thanks for the help

[tpmcn]

Quote:

Originally Posted by Dirtbuster Interesting thread, just a few questions?. If the switch worked for years, why does it suddenly not work. The valve that the switch goes in sounds like a compensation valve. This valve should operate when either the front or rear brakes suddenly have a ruptured brake line. It then cloes to the other side, to give more force to the working axle. When this valve shifts, it causes the sensor to ground out. I don't think disabling this sensor, is the correct fix. Once this valve closes towards the operating brakes, flow is pinched to the side that is not working. That means a loss of flow to half of your brake system. To reset the compensation valve, bleed pressure to the side of the system that is not working properly. Have someone open the bleeder, why you suddenly slam the brake pedal. This should reset the valve, if not the valve may be defective! Hope this might help!

Dirtbuster, Looking at the book that Driver sent I don't think it is to cut flow but to show a difference. Mine failed soon after the Brake recall was completed and it could be that the brake were not bled correctly and some air was left in the system. I have not rebled the system and just took a 2500 mile trip to Durango,Co. with not a problems except that the light came on about half way though the trip. I'm trying to get as much information on the operation of the circuit as possible prior to removing anything. Braking is still good, No leaks in the MasterCyl. or any of the Calipers, just the light showed up on day after driving and like you I'm wondering why if went into this situation. I'm in a place where I can ckeck it now and will do so before going anyplace else.