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April 3, 2012

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A set of visual brake stroke indicators costs no more than a few bucks per wheel-end, and can save hundreds by preventing just one out-of-service situation. So why aren't more fleets and owner-operators using them?
Brake stroke indicators are your best hedge against drivers who won't do mark-and-measure brake inspections.
Brake stroke indicators are your best hedge against drivers who won't do mark-and-measure brake inspections.

Recollections abound of lying under a trailer with a 9/16ths wrench and a hammer adjusting my brakes. I went through the procedure each time I picked up a different wagon, and I set up my tractor brakes at least once a week in the days before automatic brake adjusters. Today it seems we've come to think of automatic brake adjusters and infallible brake adjusters, and nothing could be further from the truth.

I mean no disrespect to the producers of automatic brake adjusters -- they have dramatically improved brake performance and reduced the out-of-service rate due to bad brake adjustment by nearly half -- but since the OOS rate for brake adjustment still hovers around the 20-22 percent range, clearly something still needs to be addressed.

Automatic brake adjusters, or autoslacks as they are often called, are designed to maintain a pretty close line between under and over-stroking. If a brake has a 2-in. stroke limit, an autoslack will probably maintain a stroke length of about 1-5/8 to 1-3/4 of an inch. There's not a lot of margin there.

And chances are, when a wheel equipped with an automatic adjuster is over-stroking it's not the fault of the adjuster, but of something else at the wheel-end, such as worn cam bushings, a seized clevis pin or something. The warranty rate on autoslacks is very low, I'm told, which buttresses my previous statement. Over-stroking with autoslacks is very often an indicator of some other problem with the foundation brake.

Amazingly, overstroking autoslacks are often readjusted and set to the proper length -- even by so-called qualified mechanics. Autoslacks should never be "adjusted" to cure excess pushrod travel. If there's any misunderstandings about adjusting automatic brake adjusters, please read the NTSB report on the truck crash at Glenn Rock, Penn. that claimed one life in 2003. NTSB attributed that incident to slack adjusters that were so badly worn due to constant readjustment that were unable to maintain their stroke, and just backed off each time the brakes were applied.

That's another story for another day. Getting back to brake stroke indicators, we have a situation where problems can occur with a mission critical component and there's no practical roadside fix, short of inspection the brake to reveal the source of the over-stroke condition.

Given the CSA emphasis on brake stroke -- violations carry four points -- and the semi-annual reminders we get from CVSA on our brake adjustment shortcomings, why is more emphasis not placed on checking brake stroke?

Let's face it; drivers are not going to do a mark-and-measure brake inspection every day. If they tell you they are or if you think they are, you're deluding yourself. It just doesn't happen.

So what's the answer to a 22-percent out of service rate due to improper brake adjustment? Visual brake stroke indicators. When installed properly, and when drivers check them periodically, they are near-guaranteed prevention of brakes out of adjustment citations.

I've noticed over the years that almost every Canadian truck or trailer you see has visual brake stroke indicators installed, but a very small percentage of American trucks have them. No commentary here, just an observation, but I've always wondered why something so inexpensive and so reliable that can prevent such a costly problem isn't on every wheel on every truck in the land.

Once the driver understands what the brake stroke indicator is telling him, and assuming he does the inspection properly, there should never be a brake stroke problem because the situation went undetected.

There are also electronic versions of the visual stroke indicators, for those who like blinking lights and messing around with wiring. But I honestly can't see going to those lengths and expense. The plastic ones work fine if they are set up properly and checked for accuracy once in a while.

To me, these are one of the highest ROI items you can hang on a truck. And I'm not just talking about the OOS citations. That would be the least of your worries. If the truck is involved in a fatal collision, you can count on the plaintiff attorneys doing a forensic inspection of the truck -- including brake adjustment. God help you if you have one or more brakes out of adjustment. You'll be handed a hefty portion of the blame for the crash, even if your driver did nothing wrong.

Brake adjustment is a serious concern for trucking, or at least it should be. With one in five trucks sidelined for bad brake adjustment during highly publicized brake blitzes -- the number is often much higher during surprise brake inspection blitzes -- as a fleet owner or an owner-operator, I'd be looking for a tool to help solve that problem.

Below are a few links to brake stroke indicator manufacturers. Check them out.







... or just google "brake stroke indicator"


  1. 1. Kurt Keilhofer [ April 04, 2012 @ 10:50AM ]

    I have wondered ever since auto adjusters were mandated, and the out of service rate did not change, why more has not been done to improve the auto adjusters. If NASA, the airline industry, or even the auto industry had a part that had a 20% failure rate there would be investigations and/or recalls. But in the trucking industry, the driver and company are the ones getting penalized. Has any kind of research been done to better analyze this situation as far as specific problem, manufacturer, age of equipment, etc. ?

  2. 2. Deborah Lockridge [ April 04, 2012 @ 12:51PM ]

    Kurt, as Jim writes, the problem typically isn't in the automatic brake adjusters themselves, but a sign of other problems at the wheel-end -- and problems with people trying to manually "adjust" the ABAs, which you're NOT supposed to do. Jim wrote more on this topic last year: <a href="http://www.truckinginfo.com/news/news-detail.asp?news_id=74681" target="_blank">http://www.truckinginfo.com/news/news-detail.asp?...</a>

  3. 3. Doug Fulgham [ April 06, 2012 @ 05:24AM ]


    I hear an echo. I have been preaching from the same pulpit for years. But who listens to a lone voice when the high and mighty have already solved the problem? Do you recall the CVSA survey in 2003 that found only 15 in 4,055 drivers could give the proper response to "How do you check your brake adjustment and what do you do if they are not in adjustment?"

    The sad fact is nothing has changed. Drivers and mechanics alike still don't understand or trust auto-slacks and still adjust and consequently adjust and break them. Schedule 1 says a vehicle cannot be operated with a single brake beyond the adjustment limit. Most drivers or mechanics cannot tell you what the adjustment limit is. I have worked with a company that makes every truck sit in front of the dispatch office and give it a "6 pack" before they leave the yard. What a waste of time and false sense of security. If they are working it is a waste of time. If they aren't working it is a false sense of security.

  4. 4. Jim Park [ April 10, 2012 @ 04:53AM ]

    Thanks for posting that comment Doug. I hope it's well read. And you're absolutely right on all counts: drivers and many mechanics don't know how to tell if brakes are properly adjusted, it's practically impossible to check brake adjustment at the proper application pressure, and too many of us believe that automatic brake adjusters solve all the problems. Not, not, and not. The message I get is that 20 percent out-of-service is a number we can live with. I hope that's not the case, but sadly it seems to be.


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Author Bio

Jim Park

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Equipment Editor

Truck journalist 13 years, commercial driver 20 years. Joined us in 2007. Specializes in technical/equipment material (including Tire Report), brings real-world perspective to test drives.


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