HOW QUICKLY CAN AIR BRAKES GO OUT OF ADJUSTMENT
 

HI FOLKS, I WAS WONDERING HOW FAST AIR BRAKES WITH SLACK ADJUSTERS COULD GO OUT OF ADJUSTMENT? I DRIVE A FIRE ENGINE IN A BUSY CITY AND HAD A BUNCH OF HARD STOPS. I HAD MEASURED MY BRAKES IN THE MORNING AND 24 HOURS LATER AFTER A BUNCH OF RUNS ONE OF MY BRAKES WAS OUT OF THE SAFE RANGE IS THIS POSSIBLE OR DID I JUST SCREW UP AND MEASURE WRONG? THANKS FOR THE TIME AND BE SAFE OUT THERE! 8)

It is possbile for brakes to need adjusting everyday, however with automatic slack adjusters they should not need touched very often assuming th adjuster is working properly.

If you have one axle that is needing adjustment more than the others this might indicate a problem with the adjuster, the pads, or somewhere else in the braking system and you should have it checked out by a mechanic.

Keeo an eye on this and if it continues have it checked out.

UTurns right

If you have auto slack ..which you should in your truck...then it shouldnt go out of adjustment so quickly but it might have ...Ive see it

The auto slack will have have a nut on top which is the actual adjuster...then on the front of the slack will be a another nut with a button on the top thats called the dawg Paw

The top nut usually 5/16 and if you can back off the brakes with out messing with the dawg paw then you have a bad slack

guess I'm old school but i hated automatic slack adjusters when they came out and when they had to be adjusted they were a pain in the Butt.

yeah they still are a pain in the but but Matco tools have a slack adjuster tool and it comes with a little lever type thing to hold the dog paw out while doing so ...but you do need the air on

I check and adjust my brakes every time I do a pm. It depends on the type of driving you do as to the length of time brakes should be adjusted. The more you use them the more likely they should need to be adjusted. The newer trucks have self adjusting brakes but may still need to be manually adjusted. Trucks pulling trailers with small brakes and wheels may need more frequent adjustments.

Most of the time, I run very short runs (35 or so miles each direction). When I run from one certain location to my usual terminal, I have to adjust my brakes every few days, due to the stop lights I have to go through being out-of-sync for trucks. If I run from any other location, to the same destination, I can go2 or 3 weeks before they really need adjusting. One of these days, I'm gonna get fed up with those **** lights, and just run down the shoulder, and take all of them out!!!!! :P

GMAN - I prefer to check my brakes, too, "auto-adjust' or not....
I have been 'instructed' that in order to adjust "Self-adjusting" brakes, you back up (straightline) to about 5MPH and hit the brake pedal firmly - and hold 'til it stops. Also - need to repeat that procedure about five times. Applies to both tractors and trailers.

If that's the case, just how many times or how many places will you find yourself able to perform that procedure? :wink:
In my case, I pick up and drop at least one flatbed trailer per day - usually the pickup trailer is pre-loaded... (not possible to 'do the procedure')
Add to that, I simply don't trust Anything touted as "Self-Adjusting"... It's a misnomer, especially in real world terms where most drivers aren't instructed specifically on the procedure - and generally don't fool with it at all. :roll:

My company trains and certifies its drivers on manual Slack Adjustment.
Got my training yesterday, 4AM.... followed by further mayhem and chaos of being issued my truck and equipment. And after performing the procedure under my Instructor, in the grease pit, AND after taking notes on it - my memory went away and the notes aren't specific enough for my satisfaction. :sad:
On the tractor differentials, there's a Short Side and a Long Side - and a difference between the 'back-offs' involved... GMAN: I have a need to discuss particular parameters of the operation with you...
If possible, could you contact me - please, sir...
[email protected]

One of the big problems with Auto Slacks, is that some drivers expect them to behave like manuals.

They are fundamentally different.

First of all, Auto Slacks usually require a longer stroke if you are doing the hand pull method. If you are use to 1/2 inch on manuals, then you will find that Auto's will stroke longer than that. Probably on the 3/4 inch side. If you "set them up" to 1/2 then they will back off to 3/4 as you drive them. It has to do with brake drum expansion. If you get the drums expanded due to heat and if the Auto's set up to 1/2, then when they cool, they will drag. You need to find out the right set up for them and that can only be done with a Full Brake Application Test. Block your vehicle on flat ground, turn it off with the truck in gear (take the keys out of the truck), supply your Spring brakes and then measure them with a ruler at rest, and with them at about 90 psi. You should have about 1.5 inches of stroke. Any less, and you may be dragging the brakes, any more and you end up with to much break lag. Using your spring brakes to to the "applied part" of this does not give you a true reading as spring type parking brakes (type 30 or 30 square inches on the diaphram) will only give about 1500 to 2000 lbs of pressure, but 90 psi against a type 30 will closer to 3000 lbs of pressure. This is how they brakes are checked to get a Certificate of Inspection and how it is done by the Commercial Vehicle Inspectors.

Then if they are set properly, check them again and see what the clearance is with a hand pull.

A hand pull method of checking your brakes is the most unreliable way of doing it, yet it is the way most truckers check their brakes. It is NOT what I teach my students. All my students are shown the "Applied Brake Method".

Then, once you know they are set, you should check them daily.

If you have an Auto Slack that goes out of adjustment, then it is broken and it should be replaced. Bottom line, it is broken.

I have had my International Eagle now for two years and NEVER have set up the Auto Slacks. My trailer needs to have one Auto Slack set up about every six months, and the rest have never been touched, except to show the students how to do a "Full Brake Application Test".

You can actually ruin an Auto Slack by over adjusting it. The other main reason Auto's fail is because the wrong grease is used when maintaining them, or they are not greased enough.

Auto Slacks need to be checked just as often as Manuals. Every day, every time you drive the unit, every time you change from one trailer to the other.

This is just a very small component of an Air Brake Course.

Rocky

Rocky I agree with most of your post except...

"If you have an Auto Slack that goes out of adjustment, then it is broken and it should be replaced. Bottom line, it is broken. "

1) If there is never a "full application", the slacks will not adjust

2) The slacks will also not adjust if the actuation of the brake is improper. A broken return spring, shoe rollers that fall out(happened to me once), rusty/seized clevis, rusty/seized shoe rollers will all cause your slack to not adjust properly. Yet it could be 100% fine.

Ya, I agree, but my post would assume that you are doing what is necessary to set the brakes properly. And putting enough brake pressure on the peddle is part of that.

There are other reasons for your slacks to not adjust properly, but most of the time it is because the slacks are bust.

I think the key is that you need to do proper pre-trips to insure that the equipment you are driving is working properly.

If you spend any time up in BC and sit at the top of the hills where there are brake checks you would be astounded at the amount of "Professional" drivers that don't even get out of the trucks when they pull over, even if they pull over at all.

I was teaching an Air Brakes course this weekend and we where talking about brake checks and I always ask the same question.

"How many people in this classroom make a brake application at the top of the hill in their cars before they start to go down the big hills?"

The only person in the room that raised their hand was me.

I asked the same question at the end of the lesson after we talked about what causes brake failure and what the result can be.

Then I asked the same question again and all of them raised their hands.

I am a firm believer that brakes are for stopping, not slowing or controlling your speed. That is what your engine is for. And with good planning and road managment, you will hardly ever use your brakes, even in a city.

Dangit rocky I agreed with all of your post except I do kinda like them brakes for slowing down, as well as stopping! I must be spoiled or sumthin....

Don't tell me you use the jake down at 25mph in 6th gear!

He does.

If your running in snow, you must use your brakes! If you don't use them, you willlose them! Ice will coat your drums,even a 90 p.s.i. application will take awhile to melt that ice! I know this firsthand, it's alitle unnerving. You should be using your brakes on ice to slow your unit down as a whole, every Axel, not just the Jake slowing 1 corner of your drive tires. When it's icy, use your power divider. Touch the brakes once in awhile!

I'm kinda confused on the automatic 'auto slack' adjustment. I've heard of several methods.
1) hard stop when reversing
2) several full pedal applications when stopped
3) five hard stops at slow forward speed


Just want to make sure all is good before I do the mark and measure. I sometimes need to pass the lot where the inspectors pull trucks in for a closer look.

The correct awnser is #2

#2 SHOULD (and make sure you read should, and not always) do the adjustments. But you have to make sure that you have 80 psi or more in the tanks.

You cannot assume that this will do it, you still need to get underneath and check for the 1/2 to 3/4 inch hand pull, or best yet, do a full brake application and you should be about the 1 1/2 inch of stroke from rest to full brake application.

Yes I do, and at a lot slower speed than that when I am heavy and running steep grades.

This was what you did when you had "self-adjusting brakes" on a 4-wheeler. There was a cable from the top of the rear shoe to the adjuster at the bottom. If the top spread apart too far, the little lever at the bottom would turn the adjuster another notch.

Air brakes are a bit different. #2 is right. Not that it works all the time.

With regard to automatic slack adjjusters, I guess it's a matter of who made the thing. Some adjust properly; some don't.

If you have auto-slack-adjust which don't, driver braking techinque has a lot to do with it. If your slack adjusters aren't adjusting, do a bit a stab (read hard) braking for three or for braking incidents. Force them to adjust.

I've had many instances of drop-and-hook in which I had poor braking in the trailer. Hard braking a few time forced the auto-slak-adjust to adjust properly. Otherwise, I also carry a small throw rug, breaker bar and socket, so that I can manually adjust if all else fails.

Autoslacks have been required by law here since 1997 on OTR trucks and 1998 on trailers. Most auto slacks do not require any manual adjustment beyond full service brake applications, with the exception of ; a new installation (initial adjustment), or during brake reline/disassembly. In fact, many auto slacks can be damaged by regular manual adjusts if they use a one-way clutch mechanism. If an auto slack is found to be "out of adjustment" with no obvious damage, it should be re-adjusted and tested for proper operation before replacement, as the slack may have been previously misadjusted.

out of adjustment..
 

"They are self adjusting", once stated that to a DOT inspector, I was a nubee. :oops:

And...Do your brake system pressure check, brake pedal mashed to the floor while you watch the gages and listen for air leaks. Being easy on the brakes I did not do the check 8) . When a car cut me off and stopped short I realized :shock: SOMETHING WAS WRONG...a blown diaphragm. It very well would have shown up in the system pressure check, had I done it.