Does anyone know what year the Gov't started requiring bus manufacturers to equip buses with auto slacks?
393.53
(b) Automatic brake adjusters (air brake systems). Each commercial motor vehicle manufactured on or after October 20, 1994, and equipped with an air brake system, shall meet the automatic brake adjustment system requirements of Federal Motor Vehicle Safety Standard No. 121 (49 CFR 571.121, S5.1.8) applicable to the vehicle at the time it was manufactured.
So what I read here is that if your coach is a 1995 or newer (give or take) it SHOULD have auto slacks, and if it doesn't, you should consider putting them back on.
As noted, 1995 model year started the march to automatic slack adjusters. We need to check FMVSS 121 to be sure there wasn't a phase in period allowed for certain market segments.
However, they have been optionally available for much longer. My 1975 MC8 has auto slacks from the factory. Did I read somewhere that they were sourced from SAAB? Very similar in appearance to the Haldex ones with the separate adjusting lever around the circumference of the camshaft.
happy coaching!
buswarrior
There are about half a dozen manufacturers of auto slacks, some clearance sensing, some stroke sensing. Best to keep them all the same on the same vehicle.
Bendix, Rockwell/Meritor, Crewson Brunner, Gunite, Midland/Haldex come to mind on the short list.
Thanks for chipping in BW.
If you have or are thinking about changing to automatic slacks remember that you have to keep them greased and the seals and boots in good shape or they will stop working correctly. Some places think that they are set and forget and can't figure out why the brakes on the vehicle are lousy.
I have equipment both ways and I find more out of adjustment brakes on the auto slacks than on the manuals.
You still have to check and adjust automatic slacks. Some are sensitive to too much grease and some are sensitive to not enough. Some just quit working on their own time table. Bottom line is they need just about as much attention as manuals if you want to have reliable brakes.
I adjust the auto slacks on my Eagle before every road trip because I don't trust them as much as I would the old manual style. There is more to go wrong because there are more working parts.
In my humble opinion, 1000 miles is the outside limit for a brake inspection and adjustment if you run west coast mountains like I do, no matter what kind of slacks you have.
NJT, sorry to hear about the problems you are having with ASAs. For what it is worth, any ASA that needs to adjusted more than about once is defective. Maybe you are not happy with the stroke that yours are maintaining? Sometimes ASAs can be set up incorrectly, and sometimes that can be changed.
I knew a guy that would adjust his ASAs all the time and when I asked him why he said because they were stroking more than 1-1/2". I suggested that he skip an adjustment interval and see how far out of adjustment they go...you guessed it, they never went beyond the 2" stroke that they were set up for.
Also, we have found that a #1 grease works better in ASAs than a typical #2 chassis grease...pretty minor stuff but something that helps in the long run.
Would be glad to hear more about your specific problem with Auto Slacks, and would be glad to help if I could.
Thanks for the offer Dave, but the bottom line is as the driver, I am responsible for the brakes when I hit the inspection stations and the fines come out of my pocket. The only way I know what I'm running is to look at them and pull them with my J hook to check for slack, so I'm not really looking to change anything. I doubt I am having problems with auto slacks that are anything other than normal, but if you don't look at your stuff and keep it up, weather it is auto or manual it is still mechanical and subject to failure.
Nowdays if you kill someone with a commercial vehicle and you have anything at all wrong, let alone a bad brake, your family will be visiting you for several years in prison.
You are right about the excessive slack issue, its my main issue. I love crisp brakes that you only feel when your in the 1 inch range. Guess thats why I'm still fond of manual slacks. 2 inches takes away my comfort zone, the brakes apply much slower and the vehicle travels more distance before I get a response. Also with a 2.5 inch stroke max, thats only 1/2 inch of action left and I can do alot better than that with a manual slack.
Checking the bus brakes before I leave town with the family just makes me feel better. I know what I have and that it's all working like it should. I don't mind letting the auto slacks ride along and do their thing, its just my job to make sure they haven't taken a vacation.
Putting a wrench on an automatic slack adjuster, ASA, to snug it up is one of the big ways to ensure it won't do its job in the future.
In effect, once you start adjusting it manually, you've made it a manual adjuster.
Measure your applied pushrod stroke, and leave them alone if they are within specs. If they are out of specs, the entire brake assembly should be inspected as to the reason. ASA's work just great if they are installed correctly, (that's a big stretch, mechanics are all over the map) they are lubricated regularly, and they are left alone to do their job.
ASA's that don't do their job will be found to be missing one of the three above conditions, some will have been damaged by adjustment attempts, or there are underlying problems with the brake assembly, worn cam bushings, mix of roller sizes/worn linings/oversize drums, etc.
ASA's don't mean stop looking at the brake adjustment, they just take care of the wrench work for you.
ASA's get a bad rap. Too many big fleets have got it worked out, have no more troubles, and have fired the offending mechanics who wouldn't do the job properly. And dealer mechanics may be the worst at following proper procedures. Local Kenworth dealer wanted to argue with the local community college driving school who had bought 4 trucks over proper method of install...indicating needles were all out of place... needless to say, they went elsewhere next time.
From a spec'ing standpoint, ASA's and long stroke brake chambers give a bigger overlap between the adjustment and the regulated stroke length, with standard chambers, many get close to the limit before they adjust.
As usual, follow the manufacturers procedures and you'll be fine.
happy coaching!
buswarrior
NJT-I hear what you are saying, and it is hard as a driver to not have that crisp brake action you are refering to once you have gotten used to it. Like I said, all ASAs have different set-up procedures upon installation, and some are "adjustable" (meaning the set-up tech has some lee-way in the amount of stroke) and others are not, depending on the brand. BUT, all that said, they are designed to keep stroke at a specific length (or drum clearance) and if the trained and knowledgeable driver is not comfortable with that, then do what you do! The whole ASA/gov't intervention is probably another of those things to protect us from ourselves! If the trained and knowledgeable driver gets under his equipment to check/adjust brake stroke, then he is probably looking at other things too, which is a good thing.
BW-I tend to agree with your comments, however from a mechanics and parts man standpoint, I can't think of anythng you could do in the normal course of manually adjusting an ASA which would stop it from doing it's job, which is adjusting...so what I am saying is that it is okay to manually adjust an ASA, but if you stop manually adjusting it, it will continue to do it's job as designed. That said, some types are more prone to getting messed up if not manually adjusted properly.
Thanks everyone for your comments.
The government requires these things so the steering wheel holders won't kill the motoring public. I'll bet a lot of professional drivers have no clue how to adjust a manual slack adjuster let alone actually do it if they still have manual slacks.
Most busnuts do a really good job checking and adjusting brakes, but how often do you think most diesel pushers would check and adjust their brakes if slack adjusters were still manual? They probably wait until the brakes are broke in some way before they ever get serviced.
At the bus garage I work at we have 1300 buses with Haldex automatic slacks. We have very few problems. We only change them when they don't meet the criteria of 13ft lbs of torque required to adjust them on the ratchet side. The only thing the is very critical is the foundation brake parts. the cam bushings, clevis pin bushings, and sack adjuster bushings MUST be in good shape. If they are not, the adjuster will not adjust.