I found the following air brake system check on a FMCA forum and thought I would post it here for our members. Those with more knowledge may want to comment on the accuracy of this test.

• 1. Be on reasonably level ground. Block wheels so the coach can not move even with the parking brake off.
  
• 2. Start engine and run until full air pressure is reached. Listen for the dryer to purge (about 120 PSI).
  
• 3. Shut off the engine.
  
• 4. Release the parking brake by pushing in the yellow button (make sure you don't roll, and do NOT apply the brake pedal).
  
• 5. After the initial pressure drop, the system should not lose more than 2 PSI per minute.
  
• 6. Apply the brake pedal firmly (still with the parking brake OFF).
  
• 7. After the initial pressure drop, the system should not lose any more than 3 PSI per minute.
  
• 8. With the engine off and parking brake off, rapidly pump the brake pedal to bleed down the air supply. During this stage you should watch for the warning light and buzzer at about 60 PSI and then the yellow button (parking brake) should pop out at about 30 PSI.
  
• 9. Restart the engine and build up air pressure. While building up pressure, check how long it takes for pressure to go from 85 to 100 PSI at cruising RPM. It should be less than 45 seconds.

I hope this is helpful information and one more thing to add to the safe operation of our beloved Barths,atleast the ones with air brakes.

Nick

Good advice, Nick. Below is an addendum to your checklist.

A few days ago a new "full-timer" in his S.O.B was parked next to us dealing with the air system on his cummins 8.3L. While driving, his air system kept dropping to 90 PSI triggering his "SHUTDOWN" alarm so he pulled in here to fix it. After a few phone calls on what to check he removed the air dryer filter (looked like a HUGE FAT oil filter) and another filter (looked like skinney air filter guts - no housing). They were both plugged solid ... so much so that the air had no place to go so it just dumped. Since there are no parts places within 120 miles of Hawthorne, he simply bought a coupling from the local hardware store and connected the in and out lines to his air dryer (bypassing the filters) and headed for Las Vegas where he was going to pick up new filters.

Hope this additional tidbit helps anyone who gets on the road and has a problem.

Carl Feren

bypassing air dryer isnot the best idea, but sometimes got to do what ya got to! the dryer is to keep water and most importantly oil that can gum up and ruin air valves...read$$$$$$ and safty! Ifit has to be done repace or overhaul air dryerput back in service asap a littel air brake conditioner in out put air line 1 2 oz helps get krud out also drain air tanks a few times to flus out.. also look in supply line to air dryer for oil can tell u a lot about condition of compressor
trump

Change the air dryer filter once a year. We just did it on the big truck with a 600 Cummins. Kenworth got a special on air dryer filters this month for $18.99. Usually they run about $50. Best time to change is fall (so the water don't get into your brake lines in cold weather and freezes).

This check-out procedure is extremely similar to the one in the Florida CDL manual. I highly recommend everyone who drives a large RV to get their state's CDL manual then read and heed it. They are full of very essential information concerning safety and operation of a large rig.

I HAVE A FRIEND can't figure that one out.He drives a big truck for a living told before winter to put alcohol in the primary air tank.Is the air brake conditioner alcohol based? .He said that condensation in the air lines could a block and allow a freeze in the brake line and cause the brake to apply .is this possible? He drives in the north all year around.
thanks lenny

Hi Lenny
Tractor trailers don't have an air dryer and purge system to automatically remove moisture from the system, hence the need to manually dump the air tanks before a run and why they add air brake conditioner, especially in winter. On our Barth's it shouldn't be necessary. It's also not a good idea to be messing with the air system if you don't know what your doing. Some dangerous stuff under there if the pressure is up.
Even so, it is a good idea to dump the tanks periodically and check each for moisture and oil in the air because you'll know then if your system is contaminated and since this is what runs your brakes that's bad. Always dump and check the wet tank first, then the primary and secondary tanks next, so nothing but clean air get into your braking system. This also will excercise the drain valve and keep them from seizing up.
To be licensed to drive any type of air brake equipped vehicle here in Ontario (even the Regency) we must have an air brake endorsement on our drivers license. It's a 2 day 16 hour course with a written and a practical test.
Don

thanks Don but do they put anything into air tanks of the big rigs?
just wonder if he was pulling my leg?
lenny

We do have a big rig WITH air dryer and all. Yes you can pour a special antifreeze in your airlines, but if you got a good working dryer, good filter and bleed your tanks regularly you do not need it. Only time we froze up was when we run in wet weather, stopped for the night and the brakes froze overnight. So some big rigs do not set the trailer brakes or move 30min after stopping to loosen it up.

quote:

Originally posted by Don in Niagara:
Tractor trailers don't have an air dryer and purge system to automatically remove moisture from the system...

99% of the tractor trailer trucks that I've worked on do have air dryers. Adding alcohol to the air compressor discharge line and allowing it to blow out frees up the dryer when the desiccant gets saturated. The filter is nothing more than a desiccant type cartridge that removes the moisture and purges it on the unload/blow off cycle of the air compressor.

The difference between build and cutoff is 20psi. The air compressor, without any air, will build up pressure. The lack of air is what forces the air compressor to go into a build cycle. At around 120psi the gov opens up and forces air into the unloader port of the compressor to get it to stop building... The same air signal that just caused the compressor to stop building is what opens up the purge port of the dryer and purges the moisture out of the dryer.. At 20psi less... or around 100psi the governor allows the compressor to start building at repeats this cycle all over again.

In regards to the alcohol in the tank... I add it too to keep any moisture from freezing up. Eventually the alcohol will evaporate. Alcohol is not recommended because it does dry out the seals in valve... But, in the real word we all use it to hedge bets and to unfreeze a frozen valve.

thanks guys
lenny