Brake booster

[Rick78EFI460]

I am wondering if anyone has a bus ( not including van type ) that does not have an electric brake booster back up. It will make an electric motor whirring noise when you step on the brake pedal without the motor running....key on or off. Battery must be connected to test of course.

 

[the_experience03]

I'm not sure that I've ever seen a vehicle with air brakes having an electric backup motor since they're kind of...well...fail safe. If you lose air, you better believe those brakes are coming on. Same goes for buses with Lewis-Ghirling (sp?) brakes (primarily Fords) because if the poewr steering pump takes a dive, the brakes will go into a fail safe. I have seen them both with and without the assist. I would imagine it is to give a chance to get the bus pulled over safely before the rear end locks up. I can't imagine the intent was that a bus driver would get out, cage the rear brakes, and then drive around using the electric back up system....

 

[phillbus914]

If my key is on and the engine is off - it will run that electric motor, but when I turn off the key it shuts that motor off. Is that normal?

I've had problems with this system due to a faulty brake switch.

You can read about that adventure here.

 

[the_experience03]

I've seen them work both ways. I guess in a perfect world they would work no matter what, just like your brakelights. Of course if you have children running around you might find your batteries. Lord knows they love stuff that makes noise. I can't tell you how many times I've walked away for 10 minutes only to find my air pressure at 0...and that's with the 21 year old variety of kids around.....

I guess the one question is are your brajkes capable of stopping the bus with the parking brake off? Obviously with air brakes that's not an issue, but without the backup motor, can you or whomever accidently releases the parking brake cock your leg hard enough to stop that thing? If not you might want to consider a set of wheel chocks. Heck...they might be a good idea anyway.

 

[GoneCamping-SKO]

To me it sounds like hydraulic brakes with a Hydra boost system.... I had a Ford F800 wrecker that had that...would get the buzzing & whirring sound mostly when the control relay was faulty...

 

[Rick78EFI460]

To me it sounds like hydraulic brakes with a Hydra boost system.... I had a Ford F800 wrecker that had that...would get the buzzing & whirring sound mostly when the control relay was faulty...

It is a hydraboost system, the poll is to find out which busses do have it ,and more importantly to me, which ones do not. A friend of mine told me that he had not seen one on any bus in his part of the world ( Montana) . I work on buses for our local school division for a living and have yet to see a hyd/diesel without it , but there seems to be an exception to every rule. The booster backup should kick in whenever there is inadequate pressure from the power steering pump... to ensure that you can always stop safely.


p.s. you forgot to enter your poll answer I can assume you have the air/diesel / no whir, but I can't enter it for you

 

[the_experience03]

It looks like the buses without a backup motor on their hydaulics are winning out. Scary

 

[Rick78EFI460]

Gas powered busses don't ususually require the electric backup as they use a vacuum booster, which holds a reserve if the motor stalls. A diesel itself does not produce vacuum so they use a different booster (some have an external vac pump) so the electric pump is necessary.

 

[the_experience03]

I have never seen a medium duty truck chassis with vacuum assist, only hydraboost though they exist no doubt.

 

[Jarlaxle]

I have one--mine has a gas engine & vacuum-assist brakes. A mid-80's International/Carpenter (2bbl 345/AT545) had the same setup...the DT466-powered S1700 wrecker at work I seem to recall uses hydroboost. Also, some newer Internationals & Freightliners have air-assist.

 

[EldoMike]

I just bought a Ford off ebay with Vacuum assist....you can see the link below...I'll be looking for a vacuum booster....

http://cgi.ebay.com/ebaymotors/ws/eBayI ... 707&rd=1,1