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service brake light comes on

GASBP
Explorer
Explorer
2000 diesel Zanzibar has service brake light and buzzer that comes on when brakes are applied traveling down road.
This is normal when MH is sitting with key off or with key on with no motor running but just started doing this. Anyone have this experience. It is a Hydra max system
11 REPLIES 11

wolfe10
Explorer
Explorer
Clicky: http://www.powerbrake-drivetrain.com/medium-duty-truck-1/
Brett Wolfe
Ex: 2003 Alpine 38'FDDS
Ex: 1997 Safari 35'
Ex: 1993 Foretravel U240

Diesel RV Club:http://www.dieselrvclub.org/

johnhicks
Explorer
Explorer
http://www.powerbrake-drivetrain.com/medium-duty-truck-1/
-jbh-

Jim
Explorer
Explorer
I had the same symptom on my rig years ago. Just topping the fluid helped initially but where was that fluid going? Couldn't tell in the beginning as it didn't leave a very good telltale.

Eventually, the brake pedal went almost all the way to the floor and left me with manual brakes only. Kind of pointed to a bad master cylinder. And that's what it turned out to be. Replaced it myself after Freightliner quoted $2800 for the job.

It was on a '94 Bounder Diesel, on a 35' Freightliner chassis and had the Hydroboost system. Most everything in it was made by Bendix. All the parts had numbers embossed on the metal cases.

Fairly easy job once I figured out how to do it...



The hydroboost is that assembly just to the left of the master cylinder (the assembly with the white plastic fluid container on the top). They are really simple, have a plastic filter screen, a machined core with 5 large 'O' rings that moves in/out with applied brake, a couple hoses going to/from the pump, and a case it all fits in. And on the bottom is an electric motor that gives an assist if you lose engine power or it's not running. Takes the place of the power fluid pump.

Really not much too it. That device's screen just needed cleaning in my case. Nothing wrong with it...and not much can go wrong with it. All it does is takes some hydraulic pressure from the pump, and when you step on the brakes, it pushes on the master cylinders input shaft giving an assist. Didn't even need to remove it from the chassis as the shaft and filter screen was easily pulled out once the master cylinder was removed.

The master cylinder though...that was obviously leaking once I did a close up inspection. So the leak was brake fluid, not ATF supplying the Hydroboost device. They don't rebuild these big MCs generally so I had to buy a new one for ~$500.

On my chassis the MC was mounted in the drivers wheel well so everything was easy to get to, even with the tire still mounted.

Good luck with yours, hope it's something simple.
Jim@HiTek
Have shop, will travel!
Visit my travel & RV repair blog site. Subscribe for emailed updates.
Winnebago Journey, '02
Cat 330HP Diesel, 36.5', two slides.

tropical36
Explorer
Explorer
DrewE wrote:
tropical36 wrote:
GASBP wrote:
This Safari Zanzibar has juice brakes, and I think your response is in reference to air brakes. Thank you for your response.

Gee, didn't know that for sure, so is the hydraulic system, air assisted or what?


Hydro-max is one of the hydraulically boosted power brake systems. The main source of boost pressure is the power steering pump. (Standard power brakes, of course, are vacuum powered rather than hydraulically powered; but the basic principles are similar.) The Hydro-max system also has a backup electric pump to power the system when the engine isn't running or the belt to the steering pump breaks or some similar calamity strikes.

This is the way my old gas puller worked and for most gas powered, I thought. Just didn't realize that they did this with DP's as well.
Was thinking air and then air over hydraulic, although you did originally say that it was a hydo-max system and must have missed that.
"We are often so caught up in our destination that we forget to appreciate the journey."

07 Revolution LE 40E_Spartan MM_06 400HP C9 CAT_Allison 3000.

Dinghy_2010 Jeep Wrangler JKU ISLANDER.

1998 36ft. National Tropi-Cal Chevy Model 6350 (Sold)

DrewE
Explorer II
Explorer II
tropical36 wrote:
GASBP wrote:
This Safari Zanzibar has juice brakes, and I think your response is in reference to air brakes. Thank you for your response.

Gee, didn't know that for sure, so is the hydraulic system, air assisted or what?


Hydro-max is one of the hydraulically boosted power brake systems. The main source of boost pressure is the power steering pump. (Standard power brakes, of course, are vacuum powered rather than hydraulically powered; but the basic principles are similar.) The Hydro-max system also has a backup electric pump to power the system when the engine isn't running or the belt to the steering pump breaks or some similar calamity strikes.

johnhicks
Explorer
Explorer
It's telling you that you're low on brake fluid. Don't ignore it or your next stop may be your last.
-jbh-

tropical36
Explorer
Explorer
GASBP wrote:
This Safari Zanzibar has juice brakes, and I think your response is in reference to air brakes. Thank you for your response.

Gee, didn't know that for sure, so is the hydraulic system, air assisted or what?
"We are often so caught up in our destination that we forget to appreciate the journey."

07 Revolution LE 40E_Spartan MM_06 400HP C9 CAT_Allison 3000.

Dinghy_2010 Jeep Wrangler JKU ISLANDER.

1998 36ft. National Tropi-Cal Chevy Model 6350 (Sold)

DrewE
Explorer II
Explorer II
Have you checked the brake fluid level? Sometimes if it's just at the edge of where the float switch in the reservoir activates, it will turn on when using the brakes since a bit of the fluid is being pushed to the rest of the system.

GASBP
Explorer
Explorer
This Safari Zanzibar has juice brakes, and I think your response is in reference to air brakes. Thank you for your response.

tropical36
Explorer
Explorer
GASBP wrote:
2000 diesel Zanzibar has service brake light and buzzer that comes on when brakes are applied traveling down road.
This is normal when MH is sitting with key off or with key on with no motor running but just started doing this. Anyone have this experience. It is a Hydra max system

What is the PSI in your air tanks, while this is happening?
"We are often so caught up in our destination that we forget to appreciate the journey."

07 Revolution LE 40E_Spartan MM_06 400HP C9 CAT_Allison 3000.

Dinghy_2010 Jeep Wrangler JKU ISLANDER.

1998 36ft. National Tropi-Cal Chevy Model 6350 (Sold)

1492
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