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02-07-2019, 04:01 PM
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#1
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Bus Nut
Join Date: Sep 2010
Location: Ocala, FL
Posts: 611
Year: 1995
Coachwork: Bookmobile body by Farber
Chassis: International 3800
Engine: Navistar DT466/Alison MT643
Rated Cap: 1
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Hydro-Max power steering/brakes
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?
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02-07-2019, 08:41 PM
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#2
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Site Team
Join Date: Oct 2017
Location: Ashtabula, Ohio
Posts: 1,487
Year: 1996
Coachwork: Thomas
Chassis: International
Engine: T444E 7.3L
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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.
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02-07-2019, 09:39 PM
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#3
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Bus Crazy
Join Date: Jun 2013
Location: Picton,Ont, Can.
Posts: 1,956
Year: 1997
Coachwork: Bluebird
Chassis: GMC
Engine: Cat 3116
Rated Cap: 72
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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.
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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
__________________
Question everything!
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02-08-2019, 07:24 AM
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#4
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Site Team
Join Date: Oct 2017
Location: Ashtabula, Ohio
Posts: 1,487
Year: 1996
Coachwork: Thomas
Chassis: International
Engine: T444E 7.3L
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The hydroboost should operate the brakes when the engine is running. The electric part is there in case it's not working for safety.
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02-08-2019, 09:05 AM
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#5
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Bus Crazy
Join Date: Jun 2013
Location: Picton,Ont, Can.
Posts: 1,956
Year: 1997
Coachwork: Bluebird
Chassis: GMC
Engine: Cat 3116
Rated Cap: 72
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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.
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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
__________________
Question everything!
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02-08-2019, 09:24 AM
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#6
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Bus Nut
Join Date: Sep 2010
Location: Ocala, FL
Posts: 611
Year: 1995
Coachwork: Bookmobile body by Farber
Chassis: International 3800
Engine: Navistar DT466/Alison MT643
Rated Cap: 1
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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.
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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?
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02-08-2019, 09:37 AM
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#7
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Site Team
Join Date: Oct 2017
Location: Ashtabula, Ohio
Posts: 1,487
Year: 1996
Coachwork: Thomas
Chassis: International
Engine: T444E 7.3L
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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?
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Correct. That is how it works.
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02-08-2019, 09:43 AM
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#8
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Bus Nut
Join Date: Sep 2010
Location: Ocala, FL
Posts: 611
Year: 1995
Coachwork: Bookmobile body by Farber
Chassis: International 3800
Engine: Navistar DT466/Alison MT643
Rated Cap: 1
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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.
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02-09-2019, 11:29 AM
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#9
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Skoolie
Join Date: Dec 2017
Location: Arkansas
Posts: 177
Year: 2005
Chassis: School bus
Engine: Cummins
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This should help
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02-09-2019, 12:18 PM
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#10
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Bus Nut
Join Date: Sep 2010
Location: Ocala, FL
Posts: 611
Year: 1995
Coachwork: Bookmobile body by Farber
Chassis: International 3800
Engine: Navistar DT466/Alison MT643
Rated Cap: 1
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Quote:
Originally Posted by Doe69936
This should help
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Thanks for that! I've got some reading to do.
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