Hydro-Max power steering/brakes

PDBreske · 02-07-2019, 03:01 PM

I finally started the engine on my bus project after letting it sit for a long time. It started right up on the very first crank. Amazing. It had not been started in over six years. (I did change the oil and filter before I cranked the engine.)

But ... now, when the engine is running, the "BRAKE PRESS" light and buzzer are on. The owner manual says this stays on when there is a fault in the Hydro-Max brake boost system and that it should NOT be driven when this system isn't functioning properly. The same pump supplies the power steering and that is working fine. I put it in gear and rocked it back and forth a bit and the brakes seem to be functioning as normal.

The bus is a 1995 International 3800 with a DT466 engine, MT643 transmission, and hydraulic disk brakes.

Anyone have any knowledge of the Hydro-Max system and how I might begin to troubleshoot it?

Johnny Mullet · 02-07-2019, 07:41 PM

When the ignition is "ON" do you hear the electric pump motor running? You will find this electric motor near the hydroboost on the firewall where the foot pedal attaches.

BlackJohn · 02-07-2019, 08:39 PM

Quote:

Originally Posted by Johnny Mullet

When the ignition is "ON" do you hear the electric pump motor running? You will find this electric motor near the hydroboost on the firewall where the foot pedal attaches.

Hmmm....I hear my brake booster pump anytime I touch the brake pedal as long as the batteries are connected, not just when the ignition is on. In my mind this is the better way to let you know you have brake boost at all times.

What do you think of that setup Johnny? I assume it was built that way for safety, kind of glad it is rather than only when ignition is on.

John

Johnny Mullet · 02-08-2019, 06:24 AM

The hydroboost should operate the brakes when the engine is running. The electric part is there in case it's not working for safety.

BlackJohn · 02-08-2019, 08:05 AM

Quote:

Originally Posted by Johnny Mullet

The hydroboost should operate the brakes when the engine is running. The electric part is there in case it's not working for safety.

Ok ty Johnny, that explanation works for me. I don't hear the electric when driving so I guess that is a good thing then.

So nice to have a real mechanic on board to bounce things off, thanks again man!

John

PDBreske · 02-08-2019, 08:24 AM

Quote:

Originally Posted by Johnny Mullet

When the ignition is "ON" do you hear the electric pump motor running? You will find this electric motor near the hydroboost on the firewall where the foot pedal attaches.

No, the pump motor doesn’t run with the ignition key turned on while the engine is not running nor when it is running.

And now that you mention it, I remember I used to be able to press the brake pedal with the engine off and I could hear ... something. I never knew what it was, but I suppose now that it was the electric pump assisting the brake accusation with the engine off. Is that correct?

Johnny Mullet · 02-08-2019, 08:37 AM

Quote:

Originally Posted by PDBreske

No, the pump motor doesn’t run with the ignition key turned on while the engine is not running nor when it is running.

And now that you mention it, I remember I used to be able to press the brake pedal with the engine off and I could hear ... something. I never knew what it was, but I suppose now that it was the electric pump assisting the brake accusation with the engine off. Is that correct?

Correct. That is how it works.

PDBreske · 02-08-2019, 08:43 AM

So I guess the reason for the alarm is because this electric pump motor is not operating. I'll start there. Hopefully it's something simple.

Doe69936 · 02-09-2019, 10:29 AM

This should help

PDBreske · 02-09-2019, 11:18 AM

Quote:

Originally Posted by Doe69936

This should help

Thanks for that! I've got some reading to do.

salty stash · 06-19-2021, 12:29 AM

I have a similar problem. I have a 97 3800 dt466 with a manual 5 speed. The brake press light is intermittent while I drive. Turns off once I'm cruising on the highway. But when I pull into town it turns on again sometimes or when I stop and idle. When I turn the bus off the electric motor that I assume is a brake booster pump. Idk. It's right behind the fire wall under the dot reservoir basically... it won't turn off at all along with the brake press light. I can't sit at night with the bus interior lights on without that motor going constantly. If I turn the ignition to off it still runs until I lift up on the break pedal, when it turns off so does the brake press light.

magnakansas · 06-19-2021, 12:57 AM

three things for you to do.

1) go find the online manual about how the hydromax system is supposed to work. and read it at least twice, cover to cover.

2) have someone else pull up on that pedal with the key on while you watch the brake lights. I wonder if the brake lights are on all the time. because the brake light switch is out of adjustment or broken.

3) adjust the switch and or the return spring on the brake pedal so that the switch "thinks" you are pulling up on the pedal.

william

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