Emergency Stops with air?

Audiomaker · June 09, 2014, 05:19:08 PM

Hey all,

Since my truck is about the same size and configuration as a bus, I was wondering...

Has anyone had to pull the air brake knob while underway?

If so, what happens? Do any of the wheels lock up? Do you think they might in the wet..on a grade...etc?
How long to come to a stop? ..etc ..etc.

I am curious to the experiences of those who have engaged the parking brake while still moving.

Thanks!
Sean

Ralph7 · June 09, 2014, 06:38:52 PM

Talk to Luke on that one!!!!!!!!!!!!
IF it does NOT lock the wheels you NEED a brake adjustment NOW!!!!!!!!!!!!!!!!
to pass some states inspection you must do 15 or 20mph and pull the e brake and it must stop within spec.

digesterman · June 09, 2014, 06:45:06 PM

Not sure I would want to do that, slamming on the brakes can't be good on things if you are going at any speed. I am not sure but when hitting the parking brake aren't you allowing the spring brakes to engage? I have tested mine by just engaging them on a steep hill when fully stopped and they held when coach was in neutral. Mine adjust automatically so I have concluded that everything is in working order.

I know on a fully loaded Pete when you blow a main air line you will leave enough of your tires on the pavement to see them in the form of some very long black marks for a few months,,,,,,happened to me once years back in Sacramento, during traffic of course, not fun.

Audiomaker · June 09, 2014, 06:55:47 PM

Quote from: digesterman on June 09, 2014, 06:45:06 PM
Not sure I would want to do that, slamming on the brakes can't be good on things if you are going at any speed. I am not sure but when hitting the parking brake aren't you allowing the spring brakes to engage? I have tested mine by just engaging them on a steep hill when fully stopped and they held when coach was in neutral. Mine adjust automatically so I have concluded that everything is in working order.

I know on a fully loaded Pete when you blow a main air line you will leave enough of your tires on the pavement to see them in the form of some very long black marks for a few months,,,,,,happened to me once years back in Sacramento, during traffic of course, not fun.

Yes, it would engage the spring brakes.
I'll have to go back and look, but the CDL manual makes mention of it "slowing" the vehicle. Because all vehicles are different, I wanted to see if anyone knew what a 40-45' 30-40,000lb tandem did under those circumstances.
I figured someone here might have been through it.

eagle19952 · June 09, 2014, 07:26:46 PM

tires are 6-800$ apiece...you test that at 4-6 mph max. if it works it might be useful in an emergency....but they are not called emergency brakes, they are parking brakes...

eagle19952 · June 09, 2014, 07:31:51 PM

PS the emergency brake is between your ears, the foot brake, and the transmission shift lever...then the yellow button...

Audiomaker · June 09, 2014, 08:02:34 PM

Quote from: eagle19952 on June 09, 2014, 07:31:51 PM
PS the emergency brake is between your ears, the foot brake, and the transmission shift lever...then the yellow button...

Yes, of course, but the Oregon CDL manual does go into pulling that yellow button while underway. I don't have a CDL, but I am studying to get one, so I came across that. The manual describes spring brakes as slowing the vehicle. I would imagine in an empty or lightly loaded dry van, that this would lock up the wheels...at least on the trailer, but the weight distribution and whatnot is a little different on these buses and I kind of wanted to know if anyone had done it and knew the result (and the resulting behavior).

Here's one... is the parking brake only on the rears, or does it apply the steers too? It seems like it would be better only to apply the rears and the steering tires would apply as the truck lost it's air pressure while parked.

Thoughts?

lostagain · June 09, 2014, 08:43:04 PM

Pulling the knob to apply the parking brakes, be it Maxis or DD3s, will not lock up the wheels on dry pavement. Everyone should practice this because if you have a catastrophic loss of air pressure one day, this is what will happen when you loose enough air: the emergency/parking brake will come on. On a bus or a truck, they are on the drive axle, not on the front steer. Of course on wet pavement or snow/ice, it could easily lock up the wheels.

JC

digesterman · June 09, 2014, 08:52:28 PM

On a semi it locked up my tires as I previously said, there was no slowly slowing down, it was a very rude stop, slid over to the side.

niles500 · June 09, 2014, 09:39:24 PM

Successful emergency brake engagement is a function of air pressure/volume, brake type/condition, square inches of braking surface of and condition of braking surface, brake diaphragm size/volume, and condition of brake shoes, calipers, etc... No individual past history of an emergency brake engagement is determinate of any future outcome. You just have to maintain your brake system as diligently as possible and hope you have done enough to survive a catastrophic failure - HTH and FWIW

RJ · June 09, 2014, 09:46:23 PM

Sean -

Looks like it's time to resurrect this thread I started awhile back:

http://www.busconversions.com/bbs/index.php?topic=1489.0

Be sure to read the whole thing, it's quite entertaining!

FWIW & HTH. . .

PS: Brian's video link in the above thread is now dead, I believe he moved it to a private YT account. I'll contact him and see if I can bring it back.

Audiomaker · June 09, 2014, 09:53:28 PM

Quote from: lostagain on June 09, 2014, 08:43:04 PM
Pulling the knob to apply the parking brakes, be it Maxis or DD3s, will not lock up the wheels on dry pavement. Everyone should practice this because if you have a catastrophic loss of air pressure one day, this is what will happen when you loose enough air: the emergency/parking brake will come on. On a bus or a truck, they are on the drive axle, not on the front steer. Of course on wet pavement or snow/ice, it could easily lock up the wheels.

JC

Lost again: do you happen to know if the steers simply don't have spring brakes, or is it that they just don't dump with the parking knob, but would apply once the air pressure dropped off over time (ie...when parked)?
I didn't (and still do not) know if the fronts are air against spring... I mean "something" must be handling the brake return pressure or?

niles500 · June 09, 2014, 09:54:52 PM

Darn, left out the most important thing - BRAKE ADJUSTMENT - sorry = HTH

RJ · June 09, 2014, 10:06:17 PM

Quote from: Audiomaker on June 09, 2014, 09:53:28 PM
. . .do you happen to know if the steers simply don't have spring brakes. . .

Sean -

The emergency/parking brake, be it DD3 or Spring, is only installed on the drive axle. In the case of your tandem rears, most likely the emergency cans are on the front, or engine side, axle.

Most commonly, the third axle and the steering axle have simple brake cans with no parking/emergency feature, altho your beast may have them on the third axle.

You'll never find parking/emergency brake cans on the steering axle.

FWIW & HTH. . .

Audiomaker · June 09, 2014, 10:24:42 PM

RJ, thanks... and that was a fantastic read. Thanks for the link.

Still, there are some conflicting views on whether the wheels will lock at speed (dry pavement).

I suspected that they would not...as the parking brake has plenty of force to keep the vehicle from rolling, but not enough to stop the wheels at speed.

I would also imagine that the higher the speed, the less traumatic it would be... as the kinetic energy dissipates to the point where it will create an abrupt stop (at the end).

The test I might try at some point...in a safe place... might be to roll about 40 and pull the plug.... then try to push it back in before the microwave oven launch... if that makes sense?