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Just part of a article I read about automatic slack adjusters. Found it interesting for those of us who are not hard on the brakes.

Automatic slack adjusters are supposed to adjust themselves automatically, just as the name implies. And all things being equal, that’s what happens – most of the time. When an auto-slack comes up out-of-adjustment, there’s a reason – usually one of two reasons actually.

One, the slack adjuster is defective; or two, the adjustment mechanism is not being given the opportunity to perform.

A defective slack may not appear broken, but if it’s slipping and not maintaining the proper pushrod stroke – it’s broken. When you write up a defective auto-slack, don’t be satisfied with having a mechanic “readjust” it for you. It’ll likely go out of adjustment again by the third or forth brake application. In fact, a manual readjustment of a defective auto-slack is about the last thing you want to do. The National Transportation Safety Board (NTSB) condemns Auto-slack Adjustment Process.

Let’s clear up a few issues on auto slacks and how they work. The adjustment mechanism works by sensing the length of the stroke – either the application stroke or the return stroke. There’s a ratchet device inside the slack that clicks over if the stroke is longer than it should be, but it takes considerable force to click the ratchet over. The more force you apply to the brake pedal, the more opportunity the brakes have to adjust themselves.

Ironically, it’s often our better drivers who get caught with over-stroking brakes. Drivers today are taught defensive driving skills, which include leaving enough space for stopping, reducing following distances, etc. So more and more, we see drivers who require only light brake applications while stopping. The problem with this scenario is that the slack adjusters are not receiving enough air pressure to force an auto-adjustment. In other words a good defensive driver who anticipates problems before they happen and doesn’t make hard brake applications may actually be a detriment to self-adjusting slacks.

The Solution is Under Your Foot.

So what can you do to combat this problem? The answer is very simple! A twelve-pack! And I don’t mean your favorite wobbly-pop. What I mean is 12 solid brake applications at the beginning of your day.

With your brakes released and the system charged with air, make sure your wheels are chocked, or the truck is in gear, if you are running a multi axle trailer make sure all axles are in the down position, otherwise they will not adjust. You should start with full air tanks -- about 125 psi. Make 12 full-pressure brake applications. You will probably run out of air pressure after the first four or five, so be prepared to start up and refill the tanks. This procedure will ensure you have applied enough force to the adjuster to click the ratchet over. You should do this procedure every day to ensure that your slack adjusters are doing their job.

But what if they still go out of adjustment? Better question, first things first: how will you know if they’re maintaining their adjustment?

The only way to check proper adjustment and pushrod travel is by visually checking them regularly.
 

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Correct me if I'm wrong because I have not been able to find any information proving one or the other. Do the auto adjust slack adjusters not adjust when the button is pulled and brakes are applied? To me that is a hard brake application.
 

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Actually, that procedure your describing is nonsense. Every time you use the spring brakes you are getting full application, also twelve full applications should adjust the slack adjuster around a quarter turn so ten of those applications is just wasting air and time.

I have run into this issue with officers before and challenged it, here's the problem http://www.th.gov.bc.ca/cvse/references_publications/booklets1-6/pdf/PI221.pdf http://www.wsp.wa.gov/traveler/docs/cvd/396_form10.pdf . Most officers didn't realize automatic slack adjusters were still in adjustment with longer travel. Here some info on Meritor slack adjusters (the best in my opinion) http://www.axletech.com/resources/service_manuals/pdf/MM_4B.pdf

I've seen people screw around with slack adjusters for days only to have them go right back to 1 1/2" travel. I've also seen some tighten right up after the driver over heated the brakes.

It's interesting over ten years after I've been through this officers still don't have it figured out.
 

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Correct me if I'm wrong because I have not been able to find any information proving one or the other. Do the auto adjust slack adjusters not adjust when the button is pulled and brakes are applied? To me that is a hard brake application.
I don't think so, but I could be wrong. When you pull your red button you are just exhausting the air from the pots basically and it's spring pressure inside taking over and applying the brakes. So if your push rod is fully extending and not applying your brakes, it would not have enough back pressure to ratchet the slack adjuster to tighten it up.
 

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Good post, have seen a lot of times where slack adjuster was a issue, never greased, Scott.
Actually Scott, I don't think greasing the slack adjust is the issue, most are over serviced according to some manuals. Recommended lube intervals seem to be four times the service life of the shoes or every six months. I try not to over lube them and push the seals out.
The biggest issue is greasing the cam bushings, the ones in the wheel ends are the worse, they seize up and don't allow the adjuster to travel far enough to set itself into the next notch. Personally I try to give the bushings a couple pumps every few days, it's quick and keeps them full of fresh grease and keeps the dirt out.
 

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Correct me if I'm wrong because I have not been able to find any information proving one or the other. Do the auto adjust slack adjusters not adjust when the button is pulled and brakes are applied? To me that is a hard brake application.
That's exactly how it works. Every time you set the brakes if there is enough travel the slack adjust will set into the next notch thereby adjusting itself.
 

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The worst enemy of auto slacks is improperly backing them off, this damages the ratcheting mechanism inside. Most of the newer style ones have a means of releasing the pawl so this doesn't occur, however few of the early ones had such possible. It was for this reason that rotation gauges should be installed, as most commonly in the past, it was during roadside inspections, if no rotations gauge is in place, the only way possible to check for an overcamming brake from out of spec brake drum wear, was to back them off. Here in Alberta, DOT ended up being billed by many companies for damaging auto slacks. I signed a few of those bills myself when I was still pulling wrenches in the patch. It was then accepted that if a unit had the gauges, they would not back them off, mostly in result of how many companies were *****ing about damaged slack adjusters during inspections. However, if during the roadside they had reason to believe something was out of wack, they would still back them off anyway. This was due to some guys "readjusting" the rotation gauge one spline to make it look proper...unbelievable what some will do to put off doing a brake job.

Applying the maxis is not really considered a heavy application, guess it depends on what book you read or opinion, but in my world that would be anything over a 90PSI application with the treadle, quickly applied, in other words, slam the treadle hard. And even with auto slacks, though many don't...onus is still on the driver to ensure they are within operating spec.
 

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Also don't jump on the brakes during a roadside inspection, all you need is around fifty psi. If you have warm drums a full application is going to exaggerate stroke.

Albertabuck is correct about ratcheting autoslacks only they are still very common. I do everything possible to avoid turning those back, during brake jobs after I pull the drums I'll turn them forward until the shoes are bottomed then replace the shoes, install the drums and wheels and then carefully adjust them until the stroke is a little tight, then let the adjuster do it's thing. I've never seen an inspector touch a slack adjuster, must be a "Northern" thing :D.

The most common problems I see with slack adjusters is incorrect rod length out of the brake pot, it seems most people don't realize at mid stroke the rod to center of pin to center of cam should be just over ninety degrees at mid stroke of the brake pot. Travel should be from around one hundred degrees to around eighty degrees full stroke (this varies depending slack adjuster length and brake pot stroke. During my walk around before I release any brakes I check all push rod to slack angles, I'm looking for the push rod slack, adjuster angle to be around 95-100 degrees and all angles to be very close to the same on all wheels, anything off is cause for further investigation.
 

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I was reading through some of the two instruction pdf's that offroadnt posted and just to clarify, under the assumption that the auto slack is working properly which definitely seems to leave a pretty long free stroke measurement compared to what I have been used to in the past with older units that still have manual slacks, is it deemed ok to manually adjust up a fully functional auto slack to a somewhat closer shoe to drum clearance, when the drums are stone cold that is. Or put another way, reduce the free stroke by measuring with the hand/pry bar method and by turning the adjuster hex as in that direction it does not ratchet and I "assume" not ruin the ratcheting pawls ?. Now obviously I shouldn't have to touch anything if its working correctly but I can see where it may pass a misinformed DOT person by gaining that extra 1/4 inch or so while still maintaining a good free travel for no brake shoe dragging issues.

Also is that somewhat telling of the auto slacks internal condition by the adjuster screw being able to be adjusted up slightly and then feel instant resistance to turning backwards ( it would ratchet on the pawl if forced enough )

Speaking of grease for the auto slacks, I had read a few years ago in the Truck West magazine about them warning of not using a grease with any moly in it because it could cause the auto slack to not adjust up. I assume those words came from an auto slack manufacturer.
 

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I've never seen an inspector touch a slack adjuster, must be a "Northern" thing :D.
Leduc and Whitecourt scales were the worst:eek: Us guys at Raydan, K&C, and Mullen just to name a few that were operating out of Nisku and Leduc were pulling our hair out over the **** that was going on with those roadsides. More than once we'd get a driver calling in he'd been parked at the scales and one of us would run over and then the ****show would start. Was never a time the truck didn't leave under its own steam, so guess that says who won the arguments:D
But then that's back in the day when auto slacks weren't that common, got to thinking after I posted earlier, I suppose my thoughts are a bit dated, dam has to have been ten years since old Bill English sold out Raydan to Producers, and that was when I packed my stuff, left the patch and went home for good as it was the end of an era:(

I know my brother and I have discussed the rotation gauge thing before, as he now runs his own CVIP shop, forget whether they are really used anymore or not. Took a bit to find a link, but for those who don't know what they are and how they work, here is a page I found. Where they are ideal, is for an owner operator or closed fleet, great for knowing where you're at regarding brake life and really speeds up inspections when you have sufficient records as well.

BWI 2 PV
 

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Some time on a clear backroad take a set of trains at 30 MPH and apply the trailer maxi brakes only. Might surprise you with results. Could be 5 seconds before pup trailer air is exhausted. And that could be a couple hundred feet.
 

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What exactly were the officers doing Albertabuck? That actually makes no sense to me. As a matter of fact it should be against the law for them to touch the slack adjusters. If they are going to piss around with them they may as well set them up. Backing the brakes off isn't going to tell them anything or am I missing something?

I've got a portable gauge like that I bought for doing service rigs, trucks with Dayton wheels and inboard drums, auditor told me it wasn't recognized for checking brake or drum wear for CVIP inspections.
 

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Some time on a clear backroad take a set of trains at 30 MPH and apply the trailer maxi brakes only. Might surprise you with results. Could be 5 seconds before pup trailer air is exhausted. And that could be a couple hundred feet.
You got a relay valve hanging up, kinked or blocked line, we have the same issues with a couple of our trailers. It's something I should address one of these days but it doesn't affect self adjusting slack adjusters.
 

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It takes a long time to dump air. A lot quicker to apply service brakes. Fairly new all in 1 valves, and quick release on gladhands. And a bit of ATF or air tool oil in gladhands. This really helps keep the moisture out of a system. Gladhand seals have a screen in them. A long set of trains just take a long time dump the maxis on. With a load on most people would not believe how long it takes to stop from 30 mph with trailer brakes.
 
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