| Author | Message | ||
| james dean boggs (Jd_boggs)
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Just installed a new set of rear brake chambers 30/30 type and need advise on any manual adjustments needed to the Rockwell brand 'automatic' slack adjusters. When I removed the old chambers, the slack adjuster sprung in the upward direction so this annoyed me because I wanted to place them exactly how I found them. I had to push the slack lever back until it lines up with the clevis and pin. Question: Did I ratch up the adjuster so now the brake linings are too tight/loose? The retraction bolt is still in and will remove it when I get more information from this board. I know there is a worm gear and sprocket inside. Is this the adjust bolt? (I have the maint. manuals but doesn't cover this) Thanks fellas. PS The Rockwell adjuster has two sets of levers one for braking one for adjusting. | ||
| Len Silva (Lsilva)
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http://www.bendix.com/downloads/air_brake_handbook/BW5057_online.pdf Page 18 Len Silva | ||
| james dean boggs (Jd_boggs)
Rating: N/A |
Len, Thanks for the Bendix link. I have this document. My slack adjusters are Rockwell brand and look significantly different. This procedure is for the Bendix 'Ideal ASA-5' slack adjuster. thanks. too bad I'm able to post a pic on this forum. | ||
| Jim Shepherd (Rv_safetyman)
Rating: N/A |
First of all, it sounds like you might be working on an Eagle. If you are and if it is a 10, you might have the wrong chambers. The 10 uses a 30/36 can. Next, the Rockwell is pretty easy to adjust. You will find a square headed adjustment screw (3/8) and you simply turn it down till the shoes are pressing against the drum. Now you need to back the adjustment off. On the side of the slack adjuster is a ¾ inch lock nut and removing it will let you pull the pawl the keeps the adjuster from backing off. Once that is removed, you simply back off the adjustment screw. Let me digress for a minute. I attended the Bendix Air Brake School in Denver last week. It is a great class and I discussed it on the other board. In this class they showed a video that talked about adjusting brakes. It showed a slick method. As mentioned above you adjust the brakes down to where they are seated pretty good on the drum. You then start backing off. As you back off (very slowly), you should tap the drum with a hammer or big wrench. The brakes will be adjusted properly when the drum goes from a thud type response to a “ring” type response (the shoes are no longer contacting the drum). If you want to go just a hair more, that would probably be OK, but not much. Also, do not rely on the slack adjusters to do their job. Check brake adjustment periodically. I had one go bad and the adjustment got so bad that the “S” cams started to “cam over”. Easily could have cause a fire. The Bendix handbook tells you the MAX acceptable pushrod travel for each size chamber. However, I always make sure my travel is about half of that. Hope that helps. Jim Shepherd Evergreen, CO ’85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission Bus Project details: http://www.rvsafetysystems.com/busproject.htm (updated 2/9/06) | ||
| William J Kluge, Jr. (Flx_a_bill)
Rating: N/A |
Note that Jim provided good advise and the Bendix class is great. A 30/36 spring-brake chamber provides a greater brake pressure when the parking brake is engaged, when compared to a 30/30 type used on most tractor-trailer rigs. Often, the 30/30 type spring-brake chambers are only on one of the two drive axles of the tractor that has a GVWR of 40,000 to 52,000 lbs, and on both trailer axles, with a combined GVWR of 80,000 lbs. I believe the regs indicate that the parking brake must hold on a 15% grade and/or stop the rig from 20 mph in 85' to 90', depending on if it is a single unit or combination, such as vehicle and trailer. The regs are intended for the vehicle(s) at the fully loaded state, or GVWR. (Note, there are not too many paved slopes with a 15% grade to test your brakes on.) As for the adjuster spring back when the clevis pin was removed, that is common and assocaited with the design of the S cam and the return springs on the shows. Therefore, it does not mean something is wrong. When reassembling, not only check adjustment by measuring pushrod stroke (brakes released and applied at 80-90 psi application pressure with the Wheels Chalked), but also... check the shoe shoe lining thickness and wear lip formed at the edge of the drum. An excessively worn drum will cause a cam-over, as described by Jim, even if you are on top of adjustment. That my small bit for the day, and hope it helps. | ||
| Buswarrior (Buswarrior)
Rating: |
Hello all. Raising this topic gets me thinking of related info. The first decade of regulated auto slack installation has given us quite a lot of misinformation and downright wrong practices. Let me try to help. In short, auto slacks are a good thing, measure push rod stroke regularly, lube the autos, use 'em with long stroke chambers, and leave them alone to do their job. For the fleets that have figured out how to use auto slacks properly, they have no more problems, and they would never go back to manuals, even if it were allowed. Auto slacks must be lubricated religiously according to manufacturer's spec's. Otherwise, they don't work properly. Lube in slacks has been a notorious problem since the beginning of time. The grease monkey doesn't do them! DO NOT PUT A WRENCH ON AN AUTO SLACK TO SNUG IT UP!! Let it do the job. Re-adjusting the auto has been found to reduce the reliability of the automatic mechanism to doing its job properly. Auto slacks, once installed religiously according to the manufacturer's directions, should not require re-adjusting manually. If one is found to be not keeping the brake within the regulated pushrod stroke limits, either the auto slack or some other brake component is defective and must be corrected. Re-adjusting an auto slack DOES NOT FIX WHAT IS WRONG. It may be over-stroked again within a few brake applications. Best practices in the industry see the mechanic measuring and recording the pushrod stroke for each wheel position. Any found beyond typical strokes are flagged for a sooner return to be checked again, and those found non-compliant are sent for diagnosis and repair. So in the file, there is a history of push rod measurements, establishing the reliability of the part. Past practice was to just throw the wrench on and snug them up. This is how it worked in the manual slack days, it does not promote reliability for auto slacks. The window for legal brake stroke and the stroke travel that an auto slack needs to function correctly are fairly close. This caused a lot of trouble, since an auto slack might take you just a little over the limit before it shortened up the stroke. Industry has found that the combination of auto slacks and long stroke brake chambers gives you a fairly bullet proof combination, since the long stroke chamber has a longer stroke, accomodating the auto slack's need for some stroke travel to function. A recent NTSB investigation into a fatal truck accident was scathing in its observations about the dismal knowledge about the proper care of auto slacks in the industry. Best thing to do is stick closely to the recommendations of the manufacturer. Anything that a fleet person tells you about their auto slack experience needs to be regarded with a fair degree of suspicion. They might not be doing it properly. Perhaps it might be best to assume that every litigation lawyer out there knows about that NTSB report. What notes are you keeping about your coach? Besides being a defence against that creeping senility, it might save your skin and maybe the farm, if you run a diary for the coach. happy coaching! buswarrior | ||
| james dean boggs (Jd_boggs)
Rating: N/A |
OK, things are getting a little more clear. And thank you for your input and advise. Based on what I have read here and in the brake chamber mgf adjustment guide, it says that the push rod travel should be 1-3/4" when the brake is applied or spring/park brake engaged. This is what was not making sense to me. This means that this procedure is done with the bus wheels chalked and NEITHER brake applied, then applied and measured. The auto slacks must be re adjusted because the new brake chambers never have the same rod length and must be cut to size. You all have confirmed for me what I had assumed but I had to be sure. I will report back how things went as soon as I confirm that the new chambers are 'Long or standard' stroke. | ||
| james dean boggs (Jd_boggs)
Rating: N/A |
OK, I'm getting close. I removed the caging bolts and filled the air tanks. Disengaged the park brake and did the hammer test (with a cresent). The curbside drum is tight makes a thud noise. The curbside travel is only 5/8" spec is 2.00" MAX The roadside is fine, it makes the nice ping noise. The roadside travel is 1-1/2" within spec. So, I'm going to loosen the curbside drum and tighten the roadside rod travel. How does this sound? Any comments? | ||
| Jim Shepherd (Rv_safetyman)
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One item we forgot to discuss is the geometry that you should check when you install new chambers. In additon to the stroke, you need to check to make sure that the angle between the slack aduster and the push rod is 90 degrees at close to the max travel. This geometry is affected by the initial pushrod length. | ||
| james dean boggs (Jd_boggs)
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Slack adjuster adjustment complete. Thank you all who game me your knowledge by way of this forum. Final push rod travel measurements for the rear: The curbside travel is 1-1/4" spec is 2.00" MAX. The roadside travel is 1-1/2" spec is 2.00" MAX. | ||
| Buswarrior (Buswarrior)
Rating: N/A |
Thanks for reporting back to the thread! Next thing is run it a whole bunch of miles and report back on measurements. happy coaching! buswarrior |
