My bus is a 1995 and has ABS only on the tag axle. The ABS has never worked since I got the vehicle so far as I know. The ABS light used to stay on constant, but now it doesn't come on at all. My guess is the bulb has burned out. ABS was not mandated on buses and other large vehicles until 1997. Would I face potential liability if I was in an accident and someone found out the non-mandated ABS was not working? If I was subject to commercial rules there is some question if ABS issues would be considered out of service on a 1995 vehicle. I would prefer not to spend $500 to $600 on a new ABS module if mine is bad. If I had full ABS on all wheels I would think differently.
I determined I have a Bendix MC-11 single axle ABS controller. I called Bendix to see about troubleshooting and parts and they said the MC-11 is totally obsolete with no parts available. The technician said the solenoids often go out and cannot be replaced. The recommendation is to go to a TABS-6 trailer ABS module if I need a replacement. I'm going to look at the unit this weekend hopefully and see if it is even powering up. It may be something as simple as wheel sensor issues.
The ABS module I have is really stupid. It cuts air to both wheels if there is a wheel locking up. I guess it works if all you care about is skidding the tag wheels when braking.
My guess would be that the intent of the system on your bus is to help maintain lateral control if the drive locks up.
If both drive & tag axles lock up, there is nothing to keep the rear from sliding sideways.
I would think lateral stability would be of significant benefit in maintaining control under heave braking when you need to drive around something that you can't stop for.
Doesn't sound so stupid to me. . . .
However, the question remains, how did all the coaches without tag axles manage without it?
The ABS is only on the tag axle so I don't see how it can do anything about the drive axle locking up. My understanding is the tag axle brakes can lock up before the drive axle because of differences in weight on the axles and this is what they are trying to prevent. I did figure out that the ABS light bulb was burned out. My guess is the ABS module is at least powering on if the ABS warning light is coming on based on the wiring diagrams for my bus. Next step is to crawl underneath and look at the LEDs on the module itself. If anything besides the wheel sensors are bad the entire system has to be replaced due to lack of parts.
This doesn't answer my original question about liability if I choose not to repair the ABS. In the commercial world an owner can be found at fault if anything is wrong with the truck even if they got hit while stopped legally at an intersection and it wouldn't normally be their fault.
Quote from: belfert on June 09, 2012, 11:57:37 AM
The ABS is only on the tag axle so I don't see how it can do anything about the drive axle locking up.
It won't, but if working properly, it will do something about the back end sliding around.
Quote from: belfert on June 09, 2012, 11:57:37 AM
This doesn't answer my original question about liability
U need to ask a laywer that question.
I was up under the bus for about an hour this evening looking at the ABS module. The module shows power, but it also shows at least one wheel sensor bad. I checked the wheel sensors and they both ohm out within specs, but at the upper end of acceptable. I didn't have a wrench to pull the harness connector off, or a magnet to reset the ABS module to do further testing. I'll try again tomorrow, but I suspect I'll be calling Bendix again during the week to talk to the technical support folks again.
A lawyer would probably say yes it could be a liability issue, even if incident had nothing to do with braking. The instructor at my Bendix class basically said a lot of things mechanics used to do to save a buck are big no-nos in today's world of liability.
If you know what ABS does and doesn't do...
You'll be able to spend the ca$h on something else.
If that obsolete device is faulty, render it inoperative and carry on.
happy coaching!
buswarrior
All ABS does is prevent wheel lockup. I'm not going to give up yet on getting my ABS working as I've only spent an hour or two on it. I suspect another hour or two of work will tell me if it is fixable or not. At this point I don't intend to replace the unit if I can't get it working.
Brian,
The ABS module went out on our '97 Dina and as per the "law" ANY commercial truck our bus " '97 or new must have working ABS if it was equipped with it from the factory!"
BTW the only place we were able to source the module was MCI for $1300!
Now on yours as per the "law" it's not required to be working for 2 reasons.
1) your not a commercial operator.
2) you bus is older than a '97.
FWIW I had a '95 Setra S217 that had ABS on it that never worked from the day we bought it. (as a matter of fact the previous owners had stripped some parts and wiring off it.)
But after we checked with DOT and verified that it was not required we left it alone!
Had it been '97 or newer we'd fixed it as per the law requirement.
If I were you I'd leave it alone. You've had you bus how long, and driven it how many miles without issues so far?
;D BK ;D
I can't even get the ABS module for my bus from MCI anymore. Mine is only a single axle unit and I'm sure yours is different.
For all I know the ABS might be working fine with just an issue with one wheel sensor. The module modulates the two wheels at the same time so it could still possibly work with only one sensor. I'll probably spend another hour or two on it and then just give up. I can always put the burned out bulb back in so the light doesn't bother anyone.
BK, what is the reference for the ABS requirement?
This will become a point of confusion for busnuts as those model years are going to start showing up in the hobby.
happy coaching!
buswarrior
ABS was mandated March 1, 1997 for tractors. The date was March 1, 1998 for semi-trailers and single-unit trucks. I suspect buses fall under single-unit trucks.
For commercial operators my understanding is if the ABS light does not illuminate at all that the unit will generally be put out of service. If the ABS light illuminates and does not go out then a fix it ticket is generally issued. Some ABS lights do not go out until the unit is driven at 10 to 15 miles per hour and the inspector needs to be made aware of that.
Under current RV rules it generally doesn't matter if ABS is working or not since there are no inspections. The brakes should still work if ABS is not working. Some really early ABS modulators had the delivery lines normally closed which meant no braking if ABS was not working. I doubt anybody will see those on a bus that has ABS. Personally, if I had a bus with all wheel ABS I would really want it working if at all feasible.
BW,
It's been a while since I read it, but it was in one of the bus industry news rags.
Motorcoach News (I think) did an article on it several yrs ago after it was discovered many of the buses with early ABS systems inspected were found to have been removed, altered or simply did not work.
I don't recall the exact date I received it, but dad an I were worried somewhat by it as our '95 Setra fell into that exact description.
We asked a local DOT officer about it an he told us "AS LONG AS IT IS OLDER THAN 1997 YOU ARE OK! If it's a '97 or newer it'd better have it and be working or it's an out of service violation!"
;D BK ;D
The applicable regulation is FMCSA 393.55:
http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.aspx?reg=393.55 (http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.aspx?reg=393.55)
Reading it shows that Brian is correct. Tractors were mandated Mar 1, 1997 and buses, March 1, 1998.
BK, I think your DOT officer needs to go back and reread the regs.
Bob
I'm pretty sure that the FMCA regs apply ONLY to commercially licensed and operated busses...NOT to the ones that are used by most here on this board.
Remember that many many years of busses were manufactured without ABS and we got by just fine. I read somewhere that with the advent of ABS in passenger vehicles, the number of rear end accidents actually increased because drivers thought that ABS brakes would stop them in shorter distances. ABS is not needed but it is nice to have sometimes.