Air Brakes...and what maintenance.

[Jim_HiTek]

My family was never involved with big trucks so I know next to nothing about air brakes. But recently, my RV'ing friend drove my '02 Journey and mentioned that the brakes were stiff. Needed work. I've owned it since 2016, the 2nd owner and the first owners didn't leave any evidence via invoices that they had the brakes worked on.

So I'm planning on stopping at a shop in Winnemucca on my way north (in Tucson now) and having them either service or replace the air brake canister thingy. I've never replaced the filter in there (didn't know I was supposed to), so I'll have them check the canister first, and if it's in bad condition (rust damaged) just install a new one. Or just replace the filter if they say so.

I use the Jake brake (exhaust brake) almost exclusively when traveling but now that my friend mentioned it, yeah, the brakes do seem a bit stiff...taking quite a bit of pressure to stop the RV even after slowing with the exhaust brake.

Given that history, mileage at 98,700, what else should I ask them to check on regarding the brakes on a Frieghtliner XC chassis 36 footer?

Thanks.

[wolfe10]

A good option on the AIR DRYER, is a factory (i.e. the factory that made it) REMAN dryer. That will come with not only new filters, but new valves and new heater.


Particularly if paying labor, likely no more expensive than paying a tech to replace filters and check valves, heater, etc.


I would not go with a "replaces" air dryer-- likely made overseas and of unknown quality.

[DRM901]

You normally need to have the air dryer desiccant cartridge replaced every 3 years. That "thingy" keeps the moisture from getting into your system downstream. (All air compressors create moisture as part of the air compression prices. ) That is critical if you want your brakes & suspension to work.

I would have them check for rust, moisture, and potentially, the desiccant material (some call it kitty litter) from the old cartridge inside your system downstream from the air dryer.

You need to read up on checking your system every time you get ready to head out. Here is one checklist I got from this forum. And a simple overview of the air system.Attachment 388293Attachment 388294

[Jim_HiTek]

Thanks, Brett and DRM901.

Added 'Factory re-manufactured' air dryer to my list.

Will have them check for downstream kitty litter.

One question, DRM901, if the air dryer canister is removed, can they open that and find if the kitty litter might have migrated?

[twinboat]

If you don't do any hard stopping, the brakes can get glazed.

Burnish them every so often by doing hard stops from 60 to 30 ish on empty freeways without the Jake brake.

At your mileage, it wouldn't hurt to have them looked at. Don't tell them " I think I need new brakes " because they will sell you new brakes. You want a brake inspection.

[RV735]

Below are listed MH brake system tests that should be done periodically to ensure safe air brake operation.

Motorhome air brake system testing
| |
by Jerry Fitzgerald

AIR GOVERNOR TEST
This test identifies the upper and lower limits of the air pressures. Start the engine and allow the air pressure to build up until it reaches its maximum and the compressor turns off (this should be no more than 130 pounds of pressure). You may hear the spitter valve pop when the maximum pressure is reached. Then depress the service (foot) brake several times. Each time you depress the service brake pedal the air pressure will go down and you can see the pressure go down on the air gauge. Wait about 2 seconds between each time you depress the brake pedal in order to see if the compressor restarts and the air gauge needles start going up again. Watch the air gauge and keep doing this until the compressor restarts. The compressor should restart at or above 85 pounds of air pressure. Now you know the maximum air pressure in your system and the air pressure where the compressor restarts. NOTE: There are two needles in the air gauge. One is for the front air tank and one is for the rear air tank. They should be close together, no more than 2-4 pounds apart. If they diverge too much it may indicate a problem with one of the air tanks.

STATIC BRAKE TEST
This test checks for leaks in the air tanks. Continuing from the AIR GOVERNOR TEST above, the air pressure should be at its maximum for this test. You should be stopped in a level position (block the wheels if it is not perfectly level). Place the automatic transmission in neutral (manual transmissions can be put in reverse gear), turn the engine off, keep your foot off the service brake, and release the parking brake. NOTE: Be sure the vehicle does not roll. Looking at the air pressure gauge, the air loss should not exceed 2 pounds in one minute.

APPLIED BRAKE TEST
This test checks for leaks in the air lines. Continuing from the STATIC BRAKE TEST above, depress the service brake pedal and keep it fully depressed for one minute. Watch the air gauge needles. After the air pressure has stabilized (the needles stop moving), the air loss should not exceed 3 pounds in one minute (tap the gauge occasionally). One caution, do not apply too much pressure on the service brake pedal.

LOW AIR WARNING DEVICE TEST
This test checks to see that the low air warning system is working. Continuing from the APPLIED BRAKE TEST above, turn ignition switch fully on but do NOT start the engine. Look at the air pressure gauge and continuously pump the service brake until you can see the warning light come on and/or hear the warning buzzer. If your buzzer sounds because of the low oil pressure switch, just look for the low air warning light to come on. The low air light should come on at pressures below 60 pounds. NOTE: If the low air warning light or buzzer comes on while you are driving, immediately move off the highway because soon after the low air warning comes on the emergency brake will be applied automatically and you will stop where ever you are at that time.

EMERGENCY BRAKE SYSTEM TEST
This test checks to see whether the parking brake applies automatically if the air pressure gets too low. Continuing from the LOW AIR WARNING DEVICE TEST above, turn off the ignition and continue to pump the service brake pedal until the parking brake handle pops up of its own accord. This should happen at pressures below 45 pounds. After it pops up, start the engine but do NOT touch the parking brake (it is on at this point). Try to SLOWLY drive the vehicle with the low air pressure warning on. The emergency brake is still on so it should hold you back.

EMERGENCY BRAKE TEST
This test checks whether the emergency brake works manually. Continuing from the EMERGENCY BRAKE SYSTEM TEST, keep the engine running and allow the air pressure to build up until it is at full pressure (the spitter valve will pop). Put the coach in Drive and release the parking brake. Drive the coach at about 5 miles per hour and apply the parking brake (not the service brake pedal). It should stop you fairly quickly.

CHECK SERVICE BRAKES
This test checks whether the service brakes are working and also whether they may need adjusting. Continuing from the EMERGENCY BRAKE TEST, drive the coach at about 5 miles per hour, loosely hold the steering wheel and apply the service brake pedal firmly to see whether the steering wheel pulls to the left or the right. If it pulls in either direction you may need to have your brakes adjusted. Furthermore, if you apply the service brake and the two needles on the air gauge move farther apart than their normal (small) divergence, this is an indicator that the brakes may need adjusting.

Safe travels and THE JOY IS IN THE RIDE

[Ray,IN]

You are new to air brakes and the compressed air system. This is excellent for self-educating: https://www.suspensionspecialists.co...dbook_2009.pdf

[Dutch Star Don]

What year was your friend's coach? My Monaco Diplomat (2005) took a lot more pressure to apply the brakes then my newer Freightliner chassis. They still worked and surprised me one day when I really needed them, they about put me through the windshield.

I spoke to someone at a rally, and he never knew his coach had an air dryer. He had gone 10 years without replacing it. I used to change mine at 2-3 years, but now go to 5 years as it's a nightmare on some of the Freightliner chassis.

Your coach has drum brakes front and rear and the back of the drums are open. You can typically crawl under and look at the thickness of the shoes. If you haven't had the front bearings done in a while, if they're not oil filled, you might want them to pull the fronts, grease the bearings and see what they say about the brakes.

As mentioned, many use their exhaust brake excessively. As you slow down and the exhaust brake kicks out at 15 mph, many then just feather their brakes to a stop. That will glaze the brakes. In traffic, use the brakes and leave the exhaust brake off.

Because of the age of the coach, I think Brett makes a good point about installing a whole new air dryer assembly. Even if it doesn't change your pedal pressure, the piece of mind will be worth it.

[DRM901]

Originally Posted by Jim_HiTek

Thanks, Brett and DRM901.

Added 'Factory re-manufactured' air dryer to my list.

Will have them check for downstream kitty litter.

One question, DRM901, if the air dryer canister is removed, can they open that and find if the kitty litter might have migrated?

Once they open the air dryer, they can see if the cartridge is in good shape. If any question, they can pull the check valve just after it. That would catch the crap.

[Ludo]

I was new to this kind of ride too, my brakes were really bad ... for my feelings.


Until I noticed the idle speed of the Cummins was too high, the tranny kept pushing ��

[wolfe10]

Originally Posted by DRM901

Once they open the air dryer, they can see if the cartridge is in good shape. If any question, they can pull the check valve just after it. That would catch the crap.

Not sure I understand.


A broken desiccant WILL allow white powder to migrate into most of the air system and cause a number of valves to fail.


Have seen that on several coaches I have inspected.

[twinboat]

Originally Posted by DRM901

Once they open the air dryer, they can see if the cartridge is in good shape. If any question, they can pull the check valve just after it. That would catch the crap.

Check valves are not filters, any powder will blow right thru them.

[NCC-1701A]

Have them check the automatic slack adjusters as well. Have those been lubed as part of your annual maintenance program?

[DRM901]

Originally Posted by twinboat

Check valves are not filters, any powder will blow right thru them.

They should see residue.