master cylinder

[rvGator]

The master cylinder on my workhorse W24, the pressure switch had been broke off. What does the pressure switch on the master cylinder do? Should the pressure switch been repair or replace? I have over 1,000 miles with the switch off of the master cylinder with no problem.

[DannyB1954]

The pressure switch is usually what turns on the brake lites on the rear of your rig.

Some units put a switch on the brake pedal, Some had a pressure switch on the master cylinder.

Start your rig, step on the brake, and have someone tell you if your brake lites come on.

The switch is not repairable, but they are not expensive to replace.

[DriVer]

Quote:

Originally Posted by rvGator The master cylinder on my workhorse W24, the pressure switch had been broke off. What does the pressure switch on the master cylinder do? Should the pressure switch been repair or replace? I have over 1,000 miles with the switch off of the master cylinder with no problem.

Please refer to this publication. Bosch Hydro-Max Manual (BH-M)

There are 2 pressure switches on the BH-M, Differential and Flow. Both of these switches will trigger a DTC if compromised and will affect the ABS system. The differential switch if disconnected will take itself out of the ABS circuit and restore operation to the ABS. If the switch is broken and hanging off the BH-M, an ABS light will not set. In newer model WCC chassis this switch is no longer used.

There isn't a switch on the Hydro-Max that will send current to your tail lights. This event is completely the jurisdiction of the brake light switch inside the coach and located just behind the brake pedal.

[rvGator]

my look like this.

[DriVer]

Quote:

Originally Posted by rvGator mine look like this.

Pressure Diffenrential Sensor. The pressure differential sensor can sense if one circuit is over powering the other. If there was a leak in either the primary or secondary circuit a rod would shift from left to right or VV. This action would cause the sensor to close and the DTC would be set. The switch is redundant and is not longer used.

You can install a new one if you want to, I did but the slider inside the BH-M on my rig is seized and the sensor when connected will only indicate a DTC and disable my ABS. So .... I left the modular connector ty-wrapped on the brake line and it's not connected. ABS is fine at the moment.

[oemtech]

Mills Supply has the replacement part for about $10

[DriVer]

Quote:

Originally Posted by oemtech Mills Supply has the replacement part for about $10

Thanks Dale. The sensor cost me about $15.00 at the WASC - no shipping. It's just a very inexpensive looking piece of plastic with a plunger and a spring.

[rvGator]

Thanks DriVer, oemtech and others. Will order one today.
Thanks again
Harry

[Shadow520]

Quote:

Originally Posted by DriVer Pressure Diffenrential Sensor. The pressure differential sensor can sense if one circuit is over powering the other. If there was a leak in either the primary or secondary circuit a rod would shift from left to right or VV. This action would cause the sensor to close and the DTC would be set. The switch is redundant and is not longer used. You can install a new one if you want to, I did but the slider inside the BH-M on my rig is seized and the sensor when connected will only indicate a DTC and disable my ABS. So .... I left the modular connector ty-wrapped on the brake line and it's not connected. ABS is fine at the moment.

Sorry to bump an old thread, but this is exactly the problem I am having on my new-to-me RV. I have a Workhorse W20 chassis and the pressure diff sensor was broke. If I would have read this first, I wouldn't have had it fixed. But I digress.

I had the switch fixed while having the brake recall completed (I did find out that it hadn't been done and got it in immediately after picking it up!). After the switch was fixed, the ABS and Brake warning lights came on. The dealer diagnosed it as the slider valve inside the master cylinder as being seized up and the MC would need to be replaced. It somewhat sounded like a line of crap, since the brakes seemed nice and strong on the 250 mile drive home, so I opted not to have the work done. In researching the issue, I came across this thread.

So my question is, is there any adverse affects to this seized slider valve, all other things seemingly fine? I was looking into replacing the MC, but after reading this, I'm not so sure I should bother. Plenty of other things to do.

Thanks!

[wa8yxm]

Driver... You know some days you answer questions before I even have a reason to go looking for an answer.. Thanks. Both the manual and the JPG have been saved for the day when I do need the answer..

[DriVer]

Quote:

Originally Posted by wa8yxm Driver... You know some days you answer questions before I even have a reason to go looking for an answer.. Thanks. .

Roger, That!