Releasing The Parking Brake

[Chunkybeastracin@aol.com]

Once in a while I find it difficult to release the parking brake. It's alway easy to apply the brake, but sometimes when I push in the yellow brake button I have to manually hold it for some time in order to get the brakes to release. Most times it's fine just by pushing it in, but once in a while it will pop back out if I don't hold it in. Any thoughts or advice? This is on a Caterpillar diesel pusher 300 turbo.

[tbutler]

When you press the button you are opening a valve that pressurizes the parking brake system so that the brakes are held open against the spring pressure that closes them if air pressure is lost. When you pull up on the button, you are locking out the air pressure system from the parking brake system and venting the pressure in the parking brake thus engaging the system by letting the springs set the brakes.

If your pressure isn't up to minimum working pressure (90 pounds in our rig) when you lift the button then the parking brake won't be released and the valve will vent again. Once minimum working pressure is reached you should have no problem. Now, here is the important part... If you don't have minimum working pressure and you were able to release the parking brake, your service brakes likely don't have enough pressure to work effectively. That would be a bad place to be with no parking brake and no service brakes. So this is a safety feature.

If you are sure the pressure level is at a working level and you still find the parking brake won't release when the button is depressed then you should have the valve checked. Valves do sometimes fail and if so this one should be replaced ASAP.

[Chunkybeastracin@aol.com]

When you press the button you are opening a valve that pressurizes the parking brake system so that the brakes are held open against the spring pressure that closes them if air pressure is lost. When you pull up on the button, you are locking out the air pressure system from the parking brake system and venting the pressure in the parking brake thus engaging the system by letting the springs set the brakes.

If your pressure isn't up to minimum working pressure (90 pounds in our rig) when you lift the button then the parking brake won't be released and the valve will vent again. Once minimum working pressure is reached you should have no problem. Now, here is the important part... If you don't have minimum working pressure and you were able to release the parking brake, your service brakes likely don't have enough pressure to work effectively. That would be a bad place to be with no parking brake and no service brakes. So this is a safety feature.

If you are sure the pressure level is at a working level and you still find the parking brake won't release when the button is depressed then you should have the valve checked. Valves do sometimes fail and if so this one should be replaced ASAP.

Thank you, I guess now I know the purpose behind having the air pressure gauge on the dash. I will definatley start paying more attention as to what the air pressure build up is before I attempt to release the parking brake

[hermanmullins]

Thank you, I guess now I know the purpose behind having the air pressure gauge on the dash. I will definatley start paying more attention as to what the air pressure build up is before I attempt to release the parking brake

Just to add to what Tom said. As long as you hear the warning sound you do not have enough air pressure to do anything other then wait. In this case waiting is "Good".

Good luck.

[Guest Wayne77590]

Also, the next time you pull the brake knob, listen. You will hear a Whooosh as the air is expelled from the brake air chambers. If you do not have enough air built up, you cannot release the brakes. So, if you are ever running down the highway and you notice air leaking by monitoring the guages, pull over, because the next thing you may feel is a very fast stop as the air is depleted. It is the lack of air that puts on the parking brakes. I never move my MH until the air pressure is up to 125 PSI and holding.

Happy trails.

[Chunkybeastracin@aol.com]

Well, sure enough as usual I got good advice. Now, not only do I know the purpose of the air pressure gauge but I also don't have the problem at all as far as the brakes not releasing. I just watch the guage and when around 100-125 I can release the brakes every time without any problem. What I was doing before was assuming that I could just go as soon as I turned the key on (old gas coach habbit). I was letting the engine warm up but not paying attention to the air pressure and every time I pushed in the air brake it just popped back out.

Amazing when you learn that the guages on your dash actually serve a purpose and you learn to use them correctly how many headaches you can save yourself.

Thanks, again.

[Guest Wayne77590]

Also, remember to let the "glow plug light" go out before you crank the engine. Just in case you were not aware of it, diesel engines need a hot plug to fire - most of the time. Newer engines may fire before the plugs are heated, but it will ruin them. It also takes a lot of cranking power to turn the engine over to start. I typically will hit the booster battery switch and then crank the engine. It's worked every time.

Happy trails.

[Chunkybeastracin@aol.com]

Thanks Wayne, maybe you can clarify what a glow plug is, does it take the place of what a spark plug does on a gas engine. I was told that the catipillar engine I have did not have glow plugs? I did however notice that when I turn the key on there is a light on the dash that says "engine preheat"

[wolfe10]

Thanks Wayne, maybe you can clarify what a glow plug is, does it take the place of what a spark plug does on a gas engine. I was told that the Caterpillar engine I have did not have glow plugs? I did however notice that when I turn the key on there is a light on the dash that says "engine preheat"

You are correct, your Caterpillar engine does not have glow plugs. Like most modern diesels, it uses an intake manifold heater not glow plugs on cold starts. That is why using ether (which is explosive) to start a modern diesel is so dangerous. Spraying an explosive on a red hot heating element is just not smart.

Some diesel engines do use glow plugs. Don't think of them as replacements for spark plugs, but as "individual cylinder heaters". Because it requires one for each cylinder and they live in a much harsher environment, they are not as long-lived as intake manifold heaters.

Brett Wolfe

[Guest Wayne77590]

I'm not familiar with the Cat engine, but if there is a pre-heater light on the instrument panel, I'd wait for it to go out before cranking the engine. You also may have a block heater. It typically requires plug in to 110 volts. In colder areas it may be advisable to plug it in to keep the block warm. I'm not sure just how much time is needed to heat the block with the block heater. Fortunately I live in a temperate climate. Brett will jump in and give us the good info.

[wolfe10]

I'm not familiar with the Cat engine, but if there is a pre-heater light on the instrument panel, I'd wait for it to go out before cranking the engine. You also may have a block heater. It typically requires plug in to 110 volts. In colder areas it may be advisable to plug it in to keep the block warm. I'm not sure just how much time is needed to heat the block with the block heater. Fortunately I live in a temperate climate. Brett will jump in and give us the good info.

Wayne,

My "good info" is START ENGINE, HEAD SOUTH. When an orange tree is happy, I'm happy.

Yes, block heaters are all 120 VAC. Some coaches have a separate switch, some you have to plug in/unplug.

A good idea to use it in temperatures below 40 degrees F. If temps are in the 40's, an hour is all that is needed. If temps are below zero F, 3 hours is adequate.

Most are 1200 to 1500 watt heaters. Most are screwed into the engine coolant jacket in the side of the block.

And read YOUR engine owners manual for proper starting techniques. Some manufacturers suggest cycling the key twice in very cold temperatures to fully heat the engine INTAKE MANIFOLD HEATER.

Brett Wolfe

[Guest Wayne77590]

As always, good info.

However, the orange tree is suffering tonight!!!

At present time in this nice warm clime, it is 31 degrees at 7 p.m. and expected to go lower. Only one more night though and it will be heading back into the 60's.

[jonrjen]

Thank you, I guess now I know the purpose behind having the air pressure gauge on the dash. I will definatley start paying more attention as to what the air pressure build up is before I attempt to release the parking brake

This is my first post here, and I don't want to talk (or write as it may be) out of turn, but I hope you have an understanding of your air brake system.

And of the needed air pressure for braking purposes. There is a point where. if your air pressure drops below. the brakes on your coach will lock up...even if underway on the road. If driving and the warning buzzer and brake light on the dash go off you need to as quick as possible move out of the flow of traffic.

Also you should bleed the mositure out of your air tanks every few months or more often depending on your use and location.

[Chunkybeastracin@aol.com]

This is my first post here, and I don't want to talk (or write as it may be) out of turn, but I hope you have an understanding of your air brake system.

And of the needed air pressure for braking purposes. There is a point where. if your air pressure drops below. the brakes on your coach will lock up...even if underway on the road. If driving and the warning buzzer and brake light on the dash go off you need to as quick as possible move out of the flow of traffic.

Also you should bleed the mositure out of your air tanks every few months or more often depending on your use and location.

Definatey good advice, I am just learning about diesel coaches and need to figure out how to locate/drain the air tanks.

[Chunkybeastracin@aol.com]

As always, good info.

However, the orange tree is suffering tonight!!!

At present time in this nice warm clime, it is 31 degrees at 7 p.m. and expected to go lower. Only one more night though and it will be heading back into the 60's.

Wayne/Brett, you guys are making me jealous with all your talk of orange trees and warm climates. We woke up to a low of -18 degrees here and a high of 1 today.

[tbutler]

You can see the evidence on the highway of what happens when the air pressure is lost and your parking brake engages while driving. Every once in a while, a tractor trailer rig will blow an air pressure hose to the trailer. When it happens the trailer wheels lock up and you'll see the black skid marks trailing off the driving lane onto the shoulder! If it were to happen in your coach you'd likely have everything that isn't tied down piled around the drivers seat or in your lap! In our case, it would be all drive axle wheels that would lock up. That's more excitement than I need!

[vagabond8400]

Doesn't everyone who drives a vehicle with air brakes have an air brake certificate or equivalent? As I am from British Columbia I need an endorsement on my drivers license which shows that I have taken the required air brake course, driving an air-brake equipped vehicle without this endorsement will void the vehicle insurance if you are in an accident. Whether or not it is mandatory, a course on air brakes and how they function is a good idea for anyone driving a vehicle with air brakes.

[wolfe10]

Doesn't everyone who drives a vehicle with air brakes have an air brake certificate or equivalent? As I am from British Columbia I need an endorsement on my drivers license which shows that I have taken the required air brake course, driving an air-brake equipped vehicle without this endorsement will void the vehicle insurance if you are in an accident. Whether or not it is mandatory, a course on air brakes and how they function is a good idea for anyone driving a vehicle with air brakes.

Welcome to the FMCA Forum.

Simple answer is NO. Not all states require Air Brake Endorsements, even for vehicles with air brakes.

As you point out, it IS a very good idea for anyone with air brakes to understand how they function.

[tbutler]

I am an example of that. South Dakota requires only a regular driver's license to drive a motor home. When I got my license I picked up the booklet for a commercial truck driving license and read it over carefully to help me understand how the air brake system works. I have also taken a safe driving course at an FMCA Convention. I highly recommend both. I am a pilot and one of the first things you learn when you are flying a different airplane is how all the various systems work. No one wants to be having a problem while traveling 120 miles per hour and having to read the book to figure out how something works! If people treated driving like flying, there would be far fewer accidents. There is another discussion on the forum related to drivers license requirements in various states for driving motor homes of various weight classes. You can read about that in this discussion.

[Guest Wayne77590]

Air brake restrictions typically apply to Commercial Drivers License (CDL), and require a different section on testing.

It really would benefit anyone who has air brakes to read their manual, and even the drivers license handbook for your state, on air brake systems. There is so much involved. I good understanding may save you some time, money, or even an accident from happening.

I recently had an air leak from the back of the gauges. My hearing did not pick it up, but my wife's hearing did. With the assistance of Brett, we found it was coming from the gauges. Fortunately, my compressor was able to keep up with the leak, but you can bet your bottom dollar I was watching the gauges when I took it to Freighliner for repair.

The overall safety of everyone in the motorhome is at stake if the air brake system is faulty. Inspections should be done on a regular basis by a qualified mechanic. Adjusting the slack adjusters manually on our automatic slack adjuster systems is only a temporary fix and requires professional attention.

Good luck.

Happy and safe trails.

[baldeagle1356]

I am like Tbutler a pilot who had 3 different Piper Lances and am safety conscious. I am new to this RV world ( in America at least as I have owned and driven one all over Europe for the last 4 years ) and will, hit the road soon this side of the pond. I have been reading many of these forums and the familiar names keep coming back : Wayne and especially , Wolfe10 etc... Thank you guys for spending all that time to advise us newbies. I hail from Ontario Canada and here a Z endorsement is needed for air brakes vehicles. It comprises a written and a practical road test. Even if it is not needed in your jurisdictions, it would be sensible to familiarize yourself with the theory and practice of air brakes. Once understood , it is a lot easier to not get in trouble. I also have a lot of experience gained from owning a 42 Ft. trawler with twin diesel that I sailed all over America and the Carribeans for the 4 years prior to Europe. I will miss my dream electrical system with it's 1200 Amp hr battery bank I had on that boat. My deficiencies are mainly with weight and balance, tires steering aids etc...Hoping that a lot of my experience can be transferred to my new 42 DP. Keep up the good work.

[Digitalsteve]

Definatey good advice, I am just learning about diesel coaches and need to figure out how to locate/drain the air tanks.

It's a good idea to to drain them when ever you shut off the engine. There probably is a switch near the pilot's seat, that actuates the drain valve, hood it on for 20-30 seconds.

Leaving water in the tanks, leads quickly to rust, which can get into the system, clogging filters. Depending on the weather/humidity and the type of driving (hills, traffic, etc) the water can build up fairly quickly.

[freya-007@hotmail.com]

One of posts above mentioned letting the engine warm up. Modern diesels do not need to be run for any appreciable time to either warm up or cool down. By the time you are to the highway the engine is warm enough, and if you pull off the freeway into a rest area, by the time you are are the parking spot the engine will have cooled sufficiently to be shut down. The only reason truckers sit with the engine idling is to keep the electricity running for the air conditioner, etc. (since they don't have a generator).

Also, associated with the air brakes is a governor, which can rust and stick. This will prevent air pressure from building.

[t0005pb]

On mine the parking brake is on the drive shaft it would not engaged.It turns out that the lever was rusted at the pivot point. I took it apart and clean and grease it up. Works great now.

[wolfe10]

On mine the parking brake is on the drive shaft it would not engaged.It turns out that the lever was rusted at the pivot point. I took it apart and clean and grease it up. Works great now.

With air brakes, as the original poster has, the emergency/parking brake is the rear brakes, very rarely a drive shaft brake. Drive shaft brakes are common on gasoline chassis and perhaps some FRED chassis.

Brett