Community Forums

bdpreece · 08-12-2012, 08:59 PM

I have seen this before and now again tonight where it is stated that you should not depress the air brake while the emergency brake is set. There has to be a reason this is on the CDL test. When I purchased my coach on the walk through I was told to set the emergency brake, turn off the engine, extend my slides then while depressing the air dump switch I should fan the brake peddle until the air gauges were below 40 pounds. Then deploy the leveling jacks. Does anybody else do this and am I damaging anything.

Brian

Dik · 08-12-2012, 09:17 PM

The reason they tell you not to apply your foot brake with the emergency brake applied is you already have a spring brake pushing on your brake linkage @ 60 pounds and to add more would compermise the linkage.

Dik

bdpreece · 08-12-2012, 10:26 PM

So does this mean that the dealer gave me wrong advise as to how to dump the air and level the coach?

sc3283 · 08-12-2012, 10:34 PM

bd, you can press the brake pedal gently and repeatedly to make air release quicker.
You do not have to press HARD on the brake pedal. Use just enough pedal pressure to make the swoosh sound and you will be fine. Just don't be pushing hard on the brake pedal.
Enjoy your new RV!

Mr_D · 08-12-2012, 10:51 PM

The newer air brakes can not be overpressurized! You can have the parking brake and and hold the tredle in for as long as you want, it won't hurt them.

itdave · 08-13-2012, 08:49 AM

I don't think fanning the brakes lightly will cause a problem. I have found that pressing down lightly on the park brake button will help to bleed the are without releasing the park brake.

BFlinn181 · 08-13-2012, 09:26 AM

Quote:

Originally Posted by Mr_D

The newer air brakes can not be overpressurized! You can have the parking brake and and hold the tredle in for as long as you want, it won't hurt them.

I agree, an 'anti-compounding valve' prevents the foot pedal from adding pressure to the spring brake. I don't know when this feature was added, but if you could damage or disable your brakes by applying foot pressure to already applied spring brake, lawyers would have bigger boats.

I imagine any CDL air brake test that refers to this possibility is out of date or for older brake systems.

From "The Air Brake Handbook" by Bendix, 2004, pg 16:

"For vehicle parking, rear brake actuators are designed
with large internal springs that, when engaged, hold a
parked vehicle in position. When the driver prepares
to move away and releases the parking brake, the spring
force is countered by the introduction of air pressure
into a chamber within the spring brake portion of the
actuator. A feature called anti-compounding helps
prevent the application of both the spring and service
brakes together."

bdpreece · 08-13-2012, 10:53 AM

Quote:

Originally Posted by BFlinn181

I agree, an 'anti-compounding valve' prevents the foot pedal from adding pressure to the spring brake. I don't know when this feature was added, but if you could damage or disable your brakes by applying foot pressure to already applied spring brake, lawyers would have bigger boats.

I imagine any CDL air brake test that refers to this possibility is out of date or for older brake systems.

From "The Air Brake Handbook" by Bendix, 2004, pg 16:

"For vehicle parking, rear brake actuators are designed
with large internal springs that, when engaged, hold a
parked vehicle in position. When the driver prepares
to move away and releases the parking brake, the spring
force is countered by the introduction of air pressure
into a chamber within the spring brake portion of the
actuator. A feature called anti-compounding helps
prevent the application of both the spring and service
brakes together."

That's the answer I was looking for. Now that I see it I remember hearing about anti-compounding valves. I will still only fan the brakes lightly but at least I will feel better about it.

Thanks
Brian

Route 66 · 08-13-2012, 11:08 AM

Most states don't require an air brake endorsement and I suspect most MH drivers know very little about air brakes.

If applying the service brakes when the park brake is engaged was a real problem, we would have heard about actual brake problems, and we don't.

Dutch Star Don · 08-13-2012, 05:42 PM

I do the same as "itdave". I push down lightly on the Park Brake knob and it releases air quickly.

Bigd9 · 08-13-2012, 06:03 PM

I'm going to ask a really dumb question. Why are you lowering or bleeding the brake air?

BFlinn181 · 08-13-2012, 08:21 PM

Quote:

Originally Posted by Bigd9

I'm going to ask a really dumb question. Why are you lowering or bleeding the brake air?

To deflate the air bags so you don't have to lift so far to level, also shortens first step.

Bigd9 · 08-14-2012, 06:10 AM

Oh........ I used the air dump switch to lower the coach, but still had full air pressure in the tanks. In fact, I could dump the air and lower the coach even if the engine was running.

bdpreece original post said

Quote:

When I purchased my coach on the walk through I was told to set the emergency brake, turn off the engine, extend my slides then while depressing the air dump switch I should fan the brake peddle until the air gauges were below 40 pounds.

I was wondering why fan the brake peddle until the air gauges were below 40 pounds? If I was to come up with a reason, I would say if the transmission is in neutral, parking brake is set, and someone like my grandchild were to inadvertently push the parking brake switch in and release the parking brake without any air pressure in the tank the brake would never release.

Sounds logical???

sc3283 · 08-14-2012, 07:49 AM

Bigd9, some of the newer air ride RVs dump quick, some of the olders dump the bag air slow...so fanning the pedal makes quicker work of the dump.

Yes....that sounds logical, no air in system insures the parking brake stays applied no matter switch position