Community Forums

awol50 · 04-10-2018, 10:48 PM

But, per mile driven are big rvs at fault more than other vehicles?
I tend to think not.
I drive a 2 year old, $200k RV and pay half of what I pay to insure my $12k, 6 year old kia.
The insurance market has spoken. And they are the ultimate arbiters of pricing risk.
Keep the government out of more regulation to fix a problem that don't exist.

guardrail53 · 04-10-2018, 10:53 PM

Back to the subject of the OP? After all it is his thread!

Dumping the air?= depleting the air pressure in the air ride system, (Air Bags)
Has nothing to do with setting the brakes! Totally different system!

Pulling the Air Brake Knob/Button= setting/applying the brakes!

If you want to deplete all of the air in the system, to work on the brakes/anything air related, apply the air brake, chock the wheels, dump your air, then with the engine off, you can pump the brake pedal repeatedly and watch your dual air pressure gauges till they both reach 0! There may still be air pressure in some of the lines, so unscrew the fittings slowly to let the remaining air escape.

If you want to test the air brake system, chock the wheels on flat ground, and leave the air brake knob/button in, (brakes released), engine off, and pump the pedal till the pressure gets down to around 60lbs., give or take, the air brake knob/button should pop out, and the brakes apply! This is a safety feature, that all air brake systems have!

Hope this answers your question?

Nice ramps, by the way! Rail!

jelag · 04-11-2018, 01:51 PM

when you set the parking brakes you release air from the rear spring brakes... one chamber holds a large spring... that applies the rear brakes when that chamber is out of air.... when you want to move, you release the parking brake, air flows to the parking brake chamber on the spring brake and air pressure compresses the spring,,,,,,

Each air system has a alarm which tells you when the air tanks in the brake system goes below 60 psi.... this is a warning signal that you will not longer have enough air to use the brakes....

The second chamber in the rear spring brake, and if your front axle has a brake can, is the service brakes... applying pressure to the foot brake applies air to these chambers and stops the coach... if you have spring brakes on both, or all 3 axles... there is what is called a crack valve on each axle... this valve sets the crack pressure (the pressure at which the chamber will start to accept air)... the crack pressure is lowest on the rear axles... so that when you apply the brakes the rear start to apply, thus hopefully pulling the coach in a straight line... and a couple of pounds later the fronts apply... If you are pulling a trailer you would want the brakes on the trailer to start to apply before the rear axle and than the front axle... again to keep the truck in a straight line...

Pumping the brake pedal will drop the pressure to less than 60 psi.... thus your brakes will not longer apply correctly... and when the air system drops below about 45 psi, the rear parking brake chambers no longer have enough air pressure to prevent the parking brake from starting to apply so they will come on...

Its extremely important to absolutely know that your slack adjusters are working... the spring brake has only a limited amount of travel... if the slacks are out of adjustment than you won't get proper braking force... Have you seen RVs roll with the parking brake set.... that is usually a sign the slack adjuster is out of adjustment.... OR

when the brake shoes hit the drum... the angle at the slack adjuster and the brake can rod must be 90*.... this applies proper torque to the slack adjuster and thus to the brake cam on the wheels, and than brake application occurs... more or less than 90* means you don't have proper mechanical advantage and proper braking will not occur...

LAST.... always, always know that you have checked for water in your air tanks... all have a mechanical drain... water not only rusts the tank but also takes up space for proper brake application... on a commercial truck the draining of the air tanks is a mandatory daily routine....

LAST ... the air compressor on your engine has about a 15-20% duty cycle... it will overheat and fail if it runs all the time ... if you hear the air drier cycling too often its a sign of a leak... if you hear the compressor run all the time its a sign of a leak... excessive running of the air compressor will cause the air compressor to use engine oil... and it will cake/coke on the exhaust of the air compressor line to the air drier.... and this will limit the time the air compressor can charge the air tanks... and limit the life of the compressor...

BigBillSD · 04-11-2018, 07:27 PM

Quote:

Originally Posted by Zigzag03

Bill, give us the short how-come on not pumping air brakes please.

Its on the DMV air brake test back when I had to get licensed to drive trucks in a prior life... ?
Seriously, each time you pump the air brakes you lose some air pressure, if you do that enough and your compressor cannot keep up you may lose braking power to the point it may not stop you.

Plus Mikey C went over it in the Camp Freightliner class last month.

BTW, he also mentioned you might want to test pulling the parking brake as a test so you know what to expect if you lose air on the highway some day. He mentioned you should be at a good speed like 45 mph. He said it might be too abrupt if you do it at lower speed, like 15 or 20mph. I have never tried it. Might be fun in a big parking lot with everything fully stowed and being fully strapped in.

-Bill