air brake safety

[mike_belben]

i think we all recognize theres a trend for normal joes going toward medium and heavy duty trucks for their incredible value in service life per dollar, then subsequently towing huge loads with them. many of these trucks run air brakes, and many of us are using motorhome tags to skirt air endorsements without learning what we need to about said brakes before driving.

ive been a mechanic my entire life, and ive even done a little work on heavy equipment, but still knew nothing about the operation of air brakes until today while looking up some info to work on mine. spoiler alert, air brakes are VERY EASY TO GET WRONG and find yourself instantly inside a 20,000+ pound wrecking ball with no means to stop. i had no clue how easily they fail not from ruptures or broken/worn parts but simple lack of adjustment. they REQUIRE constant adjustment to continue working.

we spend all our time thinking about how to go faster until its time to stop. so im asking you, for the sake of all our loved ones, to read this simple primer on air brakes before you get behind the wheel of an air brake rig and change someones life for the worse.

http://flxibleowners.org/flxbk/airbrks.htm

[Urban Wheeler]

You really have to know wtf you are doing when you adjust them. Truck drivers are not allowed to adjust them by law, as too many of them have adjusted the the wrong way. Yes there are self adjusting brakes, but I was always told they they often didn't self adjust. One good point for doing it yourself is being able to check you shoes while you are down there.

I'm going to disagree about checking them daily, depending how much you drive.

[angryblack]

Thanks for posting that. I know very little of mdt hdt air brakes..While im well versed on fixing them on front end loaders they are completely different as most are air over hydro...

Its one of the thing i will have to learn before i step into a bigger truck.

[gavan]

I have been through CDL classes in 3 states and it is always good to go over the basics yet again.

[Machinos]

This is important stuff to know but I sure haven't heard of anyone checking the brake adjusters every single day, much less multiple times in one day.

It mentions necessary compressor speed but doesn't say anything about the leakdown test, either, and I think brake fade is a big issue too.

[gavan]

Yea, they dont go into application pressure, brake lag time from hitting the brake to actual brake action. No mention about using jakes or other methods of slowing yourself down on a hill.

And the parking brake section mentions that they apply the brakes for you if the pressure gets too low, not that they LOCK THE FUCK UP below 40 PSI, skidding the rear axle if you are at speed and you CAN NOT UN LOCK THEM till you get the pressure above 40 PSI or you cage them. Basically if you can not maintain above 80 PSI you need to figure out who before you move, and if you get down to 60, get off the road before your cans pop. And don't cage them until you have pressure or you are hooked up to a tow truck, because you will then have no brakes at all.

They also do not go into the way to check the cans, to feather off your pressure with the brake pedal and the truck off and make sure the cans pop around 40 PSI.

It is all good information, just seemingly not enough.

[ToughBowtieTruck]

Easiest way to check slacks is to "feel" how the truck is slowing down with pedal effort, and to check the hubs with the back of your hand at the end of the day. The brakes all should have a similar warmth to them after stopping.

[Bustin Loose]

Originally Posted by Urban Wheeler

Truck drivers are not allowed to adjust them by law

Would you please show me the law? I've never heard about that before except that some of the companies I worked for(usually union) had it as a policy. I know I was required by law to stop and check my brakes before going down some of the passes out west which would make a law like that impossible to follow unless a company had a mechanic posted at each brake check.

Edit: NVM, I forgot about companies being allowed to have a certification program and could certify drivers to adjust brakes. Yeah I was that anal, I never missed the class.

Originally Posted by Urban Wheeler

Yes there are self adjusting brakes, but I was always told they they often didn't self adjust.

I personally never ran into a truck with self adjusters that actually worked. They may work on one or two wheels but I've never had an entire set that did.

Originally Posted by Urban Wheeler

I'm going to disagree about checking them daily, depending how much you drive.

For the slack adjusters true, for checking the air pressure warning system it should be checked every time you drive before you leave.

Originally Posted by gavan

And the parking brake section mentions that they apply the brakes for you if the pressure gets too low, not that they LOCK THE FUCK UP below 40 PSI, skidding the rear axle if you are at speed and you CAN NOT UN LOCK THEM till you get the pressure above 40 PSI or you cage them.

Ah yes, the 30 second rule. You have 30 seconds of sucking the seat cushion up your ass before all comes to a halt. Add blowing a steer tire to that and being in the fast lane and it makes for an exciting time!! They were nice and brought me some Gatorade to bring me out of shock but I can proudly say I did not shit my drawers. It was more like "WTF just happened?".

I can honestly say that there was not one piece of equipment I drove or pulled that I didn't check the brakes on first before hitting the bricks, even if it just came out of the shop. I was incredibly anal about brake adjustment even to the point of carrying wax pencils, slack adjuster washers, a small ruler and the bolts for caging the cans in a kit bag I made.

If there is one thing I would stress over any other it's brake adjustment no matter what kind of brakes you have. Not being able to go won't kill people, not being able to stop will.

[spreader]

Originally Posted by Bustin Loose

I personally never ran into a truck with self adjusters that actually worked. They may work on one or two wheels but I've never had an entire set that did.

I drove quite a number of class 8's with self-adjusters. Didn't have too many problems with them. Checked for travel and all were within the 1/2" required.

[DRTDEVL]

Driving HETs weighing in at 232,000+ lbs, I make DAMNED sure my brakes are properly adjusted before I start my day, at the end of my day and any time we have an extended halt (meals, breakdowns, etc).

The worst feeling in the world is coming in at 116 tons, pressing the brake and *nothing*... Seen the results of that first-hand (seized slacks went unchecked by another driver, then a student got in the truck). I'll see if I can find the pics of the "Opel Sammich."

[DRTDEVL]

"FAHRSCHULE" means "Driving School", AKA Student Driver.

She could never bring herself to drive a HET again after that fateful night. The 2 German chicks (no pics) made it out alive and were charged with breaking into the convoy (illegal in Germany) and illegal passing. Had they not cut in there, however, the Opel would not have slowed the second truck enough and it would have eaten the back of the first one HARD. Its presence actually svared the troops from serious injury.

This occurred on B299 headed South where the road doglegs to the right at the bottom of a long grade between Tanzfleck (GTA exit) and Amberg outside the town of Gebenbach in the German state of Bayern (Amberger Landkreis).

[mike_belben]

67 page bendix air brake handbook .pdf complete with excellent schematics
http://www.mrsharkey.com/Download?fi...e_Handbook.pdf

4 page bendix slack adjuster .pdf
http://www.mrsharkey.com/Download?fi..._Adjusters.pdf

just type in 'humans only' and save. free downloads, not viruses.

[chimaira989]

Properly set up and maintained automatic slack adjusters should never need human attention. If you are having to adjust them, something is wrong and it needs to come apart IMO.

That is not to say they should not be checked, but if it needs adjustment, it needs attention.

[LOGANSTANFORTH]

I work on airbrakes every day for a living...


Slack adjuster arm and brake can rod should be as close to 90* as possible...

There are two different types of brake cans, long and short stroke. Long stroke has square ports where the hoses go and short stroke has round ports, this applies to the front and rear cans...

Stroke on the brake can rods need to be under 2 inches...

Supply the brakes with air, crank them in tight on the slack adjuster, back them out 1/4 to 1/3 of a turn and that is just about the perfect adjustment...

There are different types of slack adjusters, they need to be matched all the way around or atleast matched for the axle...

Keep EVERYTHING greased and greased liberally...

If your linings are at or under 5/16 inch (1/4 inch by DOT laws) you really need to plan on changing them very soon...

Make sure your hardware, linings, pins, drums, seals, etc. are all matched for what you working on, do not mix and match parts unless the brake manufacturer specifically says you can...

Check your wheel seals for leakage, its easy to do, just look into the back of your hub where it meets the spindle, if its wet then change them. It is very simple to do. If anyone has ever tore down a full floating 1 ton axle then you can do one of these, it is identical, just bigger and HEAVIER parts. I suggest a tire jack for taking the duals, hub, and drum off...

We run a fleet of over 275 trucks just in our yard (couple thousand trucks total in the company) and we measure stroke and adjust brakes every 800 hours and do brake inspections every time the trucks come back from a job site...

[redtruggy]

[[qoute]]Stroke on the brake can rods need to be under 2 inches...
[[qoute]]


just remember this measurment only applys to a type 30 chamber

[[486]]

Originally Posted by chimaira989

Properly set up and maintained automatic slack adjusters should never need human attention. If you are having to adjust them, something is wrong and it needs to come apart IMO.

That is not to say they should not be checked, but if it needs adjustment, it needs attention.

This guy. Get the proper template for your setup and check the angles. If they're right then check the teeth on the pawl and for rust/gunk in there.

[LOGANSTANFORTH]

Originally Posted by redtruggy

[[qoute]]Stroke on the brake can rods need to be under 2 inches...
[[qoute]]


just remember this measurment only applys to a type 30 chamber

Yes, sorry...

[mike_belben]

bump. keep your air brakes in good repair. heres lots of parts and prices, now you got no excuse.

http://www.easternmarine.com/em_stor...ir_brakes.html

[ramv]

Also be careful adjusting and working on frozen brakes. An old friend of mine was killed recently working on his trailer brakes when the tractor jumped in gear. Make sure your tra tor engine is shut down and brakes are engaged before crawling under the trailer. Especially with an automatic tractor.

[hasteranger]

daily scene on I-68 just east of Lavale, md, coming off a 13 mile 6% that levels out a bit at the end, then drops to maybe 8% or so for the last mile or 2 into a congested cloverleaf and a 55mph limit:
Trucks flying to the bottom of the hills with trailer brakes on fire.

Adjusted fine, probably.

[FSJ Man]

Originally Posted by Bustin Loose

Would you please show me the law? I've never heard about that before except that some of the companies I worked for(usually union) had it as a policy. I know I was required by law to stop and check my brakes before going down some of the passes out west which would make a law like that impossible to follow unless a company had a mechanic posted at each brake check.

Edit: NVM, I forgot about companies being allowed to have a certification program and could certify drivers to adjust brakes. Yeah I was that anal, I never missed the class.

49 CFR 396.25 - Qualifications of brake inspectors. - Code of Federal Regulations - Title 49: Transportation - PART 396: INSPECTION, REPAIR, AND MAINTENANCE - Id 19947941 - vLex