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Old 07-27-2006, 11:46 PM   #1
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Your hydraulic brakes use a vacuum canister much like a car to provide the power assist most likely. The low vacuum light and warning buzzer are telling you something ain't right My guess is the reason you're hearing the electric brake motor working is because it IS working because there is no vacuum. If your brakes are working just fine atleast you know the backup system is working correctly I would check for a vacuum leak somewhere if I were you. While most buses with hydraulic brakes use the power steering pump to provide the power boost, I have seen a few medium duty trucks that still used vacuum with big tanks underneath. If you have a low vacuum light, chances are that's why.
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Old 07-29-2006, 12:23 AM   #2
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If the brakes are tied into the power steering pump then chances are the vacuum isn't associated with that. Do you have the owner's manual? Travelling across country I did note that many truckers at truckstops leave their parking lights on while sleep;ing so don't worry about not fitting in. That really is an odd problem though....can you trace the wires back to the vacuum sending unit at all? How does the bus idle? All engines will pull vacuum (assuming forced induction isn't involved obviously). Maybe it has something to do with emissions control systems? I really have no clue. My guess is that it's just an electrical gremlin rearing its ugly head. Make sure all your wire connections are tight I guess.
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Old 07-31-2006, 11:23 AM   #3
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Quote:
Originally Posted by the_experience03
All engines will pull vacuum (assuming forced induction isn't involved obviously). .

is that true of a diesel engine?
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Old 07-31-2006, 11:48 PM   #4
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A diesel will pull a very small amount of vacuum due to the resistance of the air ducting, but ideally it wouldn't pull any. I should have paid attention to the fact that it is an 8.2. Nice catch, Jason. Diesels that reguire vacuum for whatever reason usually have an auxilary vacuum pump. Does your 8.2 have this and if so, is it working?

I feel your pain on the Toyota. As I'm rebuilding mine I'm fiind more lines than I knew existed. The service manual lists 7 main ones. HA! Maybe the other ones I've found aren't "main vacuum lines" but they sure as heck are there. As simple as that motor is, it sure is complex. I'm going to strangle the engineer that thought it was a good idea to run half the wiring harness between the intake runners.....
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Old 08-06-2006, 10:53 PM   #5
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I have an 8.2 as well. The powersteering pump powers the hyd brakes. What body do you have on your bus? Since this mess started when you put in the insulation I would say something got messed under the dash. Check all the wiring under there for loose connections.

There is also a little PCB in the control panel on BlueBird buses. When I bought the bus Greg told me these go bad often and cause all sorts of problems. My bus is a 1990 and the board has a date stamp of 1996.
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Old 08-08-2006, 03:24 AM   #6
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PCB=printed circuit board
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Old 08-09-2006, 12:03 AM   #7
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On my Bluebird/GMC I have the fuses for the body (school bus stuff) behind the switch panel. The fuses for the chassis are way up under the dash on the driver side. They are a pain to get to. I will take a picture of that circuit board that is problematic tomorrow.
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Old 08-14-2006, 09:41 PM   #8
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I probably won't be much help but thought I would let you know you are not alone I have a similar problem but my 466 international with a blue bird body, it is is fine until I turn the lights on.
I just picked the bus up last week and it did it in the parking lot of the bus depot....I asked the mechanic about it and he said there are 2 switches on the brake pedal one for the brake lights and one for a motor (somthing to do with the brake booster) any how all he did was shut the bus off and push the pedal down a coulpe times then he restarted the bus with the brakes pushed in . mabey you bumped the switch while you were under there?
I will be following this post.
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