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TedG · 11-05-2009, 05:57 PM

I have a 2001. My ABS light has come on and while troubleshooting that I found a broken sensor on the Hydro Max brake booster. There is an old posting on this ....did anyone know what this sensor is for, where to get a replacement? The Bosch technical data shows only a flow sensor. This broken sensor is on the inboard side of the booster. Other than the ABS light I haven't has any problems with the brakes.

Algoma · 11-05-2009, 06:44 PM

That sensor is the differential pressure switch. It will activate the brake light if there is a difference in the hydraulic pressure between the front and rear brakes, i.e. there is a leak somewhere. Mine was also broken and I had to replace the hydromax master cylinder. Not cheap!

TedG · 11-06-2009, 01:44 PM

Thanks, It took awhile but I found a P/N for the switch and have one on order. I spoke to Bosch and they said the switch is replaceable. Getting the broken part out should not be a major problem.

EngineerMike · 11-08-2009, 04:50 PM

TedG- could you post the part # and your source for ordering? Thanks.

TedG · 11-08-2009, 06:50 PM

I was going to wait until the switch came in on Tuesday to be sure it's the correct part, but here's what I have. If I get the wrong part I'll update Tuesday. I ordered it through Hoover Truck Center here in NJ.

There's only one differential pressure switch for this master cylinder, chassis mfg use their own P/N. Hoover was able to cross reference the Ford number to the Freightliner number.

Bosch P/N 2232548
Ford P/N E1EC-2B264-AB
Freightliner P/N E2FZ-2B264B

I got the info from Dave Smith at Bosch, 574-237-2038. Very knowledgeable and helpful. He gave me the Bossch and Ford numbers.

TedG · 11-10-2009, 02:49 PM

I received the correct switch. It's a Ford part, P/N 6U9Z-2B264-A. Not cheap...$70.00 with tax.

Lindenberg · 11-12-2009, 12:55 PM

Ted,

Mine is also broken right where it enters the brake booster. Must be a poorly designed part.

The one on my 2000 is a green plastic part with a single electrical connection. Does this sound like the replacement Ford part you received? Does it screw into the brake booster? If yours is broken at the same place, how did you get the broken piece out of the brake booster? Do you need to re-bleed the brake lines after replacing the part?

TedG · 11-12-2009, 03:59 PM

The diffrerential pressure switch is on the master cylinder, inboard side. There is a switch mounted on the top side of the brake booster. It's a flow switch, and if it's not working your backup pump won't work.

These switches electrical connectors look the same. I don't know about the flow switch but the differential pressure switch is a mechanical switch, has a metal plunger tha activates when either front or rear brake pressure changes....a leak in front or rear brakes.

The weather is bad so I haven't got the broken part out. My plan is to use a small easyout. The threads are plastic so it should come out without much effort. Not sure if I can get it without removing the master cylinder, but if I can no bleeding of brakes is required.

TedG · 11-20-2009, 12:19 PM

Removing the broken plastic part of the differential pressure switch from the master cylinder with an easyout didn't work out. I removed the master cylinder (4 bolts to remove it from the brake booster) , used a heat gun to soften the plastic , and removed it with an awl. Cleaned up the threads and installed the new switch. Reinstalled the master cylinder and good to go.

I refilled the master cylinder reservoir and let it gravity feed through the master cylinder before connecting the output lines. The brakes are fine, pedal does not pump up so no need to bleed them. However I may go ahead and bleed them just to get some new fluid into the system.