QCDriver Posted September 21, 2006 Share Posted September 21, 2006 I read the forums from time to time, and love looking at all the old Mack pics.. Now I need some advice on modern Macks.I have a 2001 CH613 281k,mi. day cab with the Meritor brakes and ABS. I pulled a load Monday and after I was empty and driving home I had a hard time stopping.( trailer brakes locking up)I took my time back to yard and unhooked drove out from trailer, only brakes that worked, fronts.. Stopped tractor and inspected rear brakes, within adjustment but adjusted agian.. I drove off felt good for 2-3 stops, THEN ONLY fronts./?? I live 6 miles away at this point and limped home..When I got home and asked wife to apply brakes and the seemed to apply full 2-3 times @130psi then nothing till under 100 psi and the appiled harder and harder as pressure dropped.I broke off all service air lines to hear flow, fronts full output all the time. While the rears full at first, then nothing till 100psi or lower.I have installed a new foot valve and did the same thing..??Pulled fuse for ABS ign. brakes worked fine. I thought that when ABS fails you still should be able to stop..?Anyone run into this problem??Thanks in advance for the feed back,Doug Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/ Share on other sites More sharing options...
ThaddeusW Posted September 21, 2006 Share Posted September 21, 2006 ABS when it fails it seems to fail in a most unpleasent way. I almost crashed into another car in my Chevy Tahoe after the ABS module went bad. It decided that normal braking was a skid and just let the brake pressure drop, had to apply the emergency brake to get it to stop. Pulled the fuse and never cared to fix it. There might be some type of pressure sensor within the ABS modulator that went bad. That or the modulator computer itself is bad. Eh I like electronics and computers but when it breaks you better have some asprin handy. Quote -Thad What America needs is less bull and more Bulldog! Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7653 Share on other sites More sharing options...
greg Posted September 22, 2006 Share Posted September 22, 2006 I can't remember the actual name for it but I call it the bobtail valve. Some trucks don't have it, some do. When your trailer is hooked up full pressure is applied to the brakes on the tractor, when trailer is unhooked your only given about 30 to 40 percent of full air until your brake application pressure reaches 100 psi or so and then your given full air all at once. Maybe this valve is gone . I know alot of people that have turned a road tractor into a dump truck and forget to take this valve out. Real scary when loaded for the first time and you have to stop real quick!Hope this helps you try to locate the problem.greg Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7661 Share on other sites More sharing options...
theakerstwo Posted September 22, 2006 Share Posted September 22, 2006 I can't remember the actual name for it but I call it the bobtail valve. Some trucks don't have it, some do. When your trailer is hooked up full pressure is applied to the brakes on the tractor, when trailer is unhooked your only given about 30 to 40 percent of full air until your brake application pressure reaches 100 psi or so and then your given full air all at once. Maybe this valve is gone . I know alot of people that have turned a road tractor into a dump truck and forget to take this valve out. Real scary when loaded for the first time and you have to stop real quick!Hope this helps you try to locate the problem.gregI dont think it will have a bobtail vavle if it has abs. Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7667 Share on other sites More sharing options...
Mack 3P Posted September 25, 2006 Share Posted September 25, 2006 Are you still have problems? I talked to our Wabco rep. Two things pop out. 1. Your auto slack adjuster is out of adjustment.2. Your air compress is shot and you have sludge in the tank and valves.Unfortunately we feel your best bet is to take it to a dealer, you could be chasing a ghost. Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7718 Share on other sites More sharing options...
storkmack Posted September 25, 2006 Share Posted September 25, 2006 had this same problem with an 05 CHN . It was a sensor on a wheel for the abs. same symptoms as your truck toa "T". We let the dealer handle it. Brad Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7721 Share on other sites More sharing options...
Mack 3P Posted September 26, 2006 Share Posted September 26, 2006 had this same problem with an 05 CHN . It was a sensor on a wheel for the abs. same symptoms as your truck toa "T". We let the dealer handle it. BradThe ABS warning light would be on if it was the sensor, he didn't mention anything about the light. Is that on too? Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7724 Share on other sites More sharing options...
David Posted September 26, 2006 Share Posted September 26, 2006 Are you still have problems? I talked to our Wabco rep. Two things pop out. 1. Your auto slack adjuster is out of adjustment.2. Your air compress is shot and you have sludge in the tank and valves.Unfortunately we feel your best bet is to take it to a dealer, you could be chasing a ghost.You could take it to a dealer, let them chase the ghost. Just give them a blank check, let them change parts (at list price), test drive on your fuel and time. Then go change some more parts until they get the right one. Let us know what it cost! Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7728 Share on other sites More sharing options...
b61fred Posted September 26, 2006 Share Posted September 26, 2006 Hey now, Lets not bash on the dealership Tech, I just happen to be one. It can be a hard way to make a living!Fred Quote 15 gears...no waiting! Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7734 Share on other sites More sharing options...
Rob Posted September 26, 2006 Share Posted September 26, 2006 Hey now, Lets not bash on the dealership Tech, I just happen to be one. It can be a hard way to make a living!FredAmen to that Fred. Think how the body shop guys feel chasing water leaks, squeaks, rattles, and inoperable electronics and wiring too!! It can be a very difficult way to earn a living!!Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7735 Share on other sites More sharing options...
David Posted September 27, 2006 Share Posted September 27, 2006 No offence to the guys doing the work. I'm just tired of getting screwed by the local dealer. That's why we do our own work and buy parts from other dealers (the ones who post on here). Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7743 Share on other sites More sharing options...
QCDriver Posted October 2, 2006 Author Share Posted October 2, 2006 Are you still have problems? I talked to our Wabco rep. Two things pop out. 1. Your auto slack adjuster is out of adjustment.2. Your air compress is shot and you have sludge in the tank and valves.Unfortunately we feel your best bet is to take it to a dealer, you could be chasing a ghost.1. Auto slacks work fine and that was the first thing I went to.2. Air compressor is a 4cyl. 31 cfm and works great I air up tankers to off load. I perge my air tanks daily, no sludge.After replacing foot valve, and riding aroud with ABS fuse out for a few hours, I reinstalled fuse after I got loaded, I've not had a problem soo far.When reinstalling foot vavle we noticed that the front brakes had a larger air line then the rears. We decided to switch this around. Everything seems fine. On the topic of dealer, mine could not look at truck for 3-4 days. So I decided to chase the ghost. At this point it cost $262, I have not ever left the dealer for under $1000, even for an ABS sensor that shut down a truck, not this one a Vision..Thanks for all the input,DougBTW, I've had good dealing with the dealer just cost alot. Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7798 Share on other sites More sharing options...
QCDriver Posted October 4, 2006 Author Share Posted October 4, 2006 It's back,, no brakes or lights(on dash or codes).. But fine under 100psi Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7835 Share on other sites More sharing options...
storkmack Posted October 5, 2006 Share Posted October 5, 2006 who do you like those wide tires? How much wieght did ya lose with them? I have heard that your fuel milage goes up too.... is that true? Thanks, Brad Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7841 Share on other sites More sharing options...
ThaddeusW Posted October 5, 2006 Share Posted October 5, 2006 When reinstalling foot vavle we noticed that the front brakes had a larger air line then the rears. We decided to switch this around. Bad idea!The reason the front air line is thick is because the line runs right from the pedal to the brake chambers so you need allot of air flow(also helps supply the trailer and trolly brake). The rears have a relay valve that doesent need the flow of a larger line. A larger air line from the primary tank runs to the relay valves supply port then the thin line from the pedal runs to the control port. Then you have 4 delivery ports to each of the four brake chambers on the rear wheels. Your restricting air to the front brakes. So when you pull the ABS fuse it doesent have that problem? Try driving around for a day with the fuse out or even longer. if there is no problem then its a bad ABS component. Maybe a bad ABS ECU or bad sensor. Brad those super single tires can save something like 1000-1200 pounds on a tractor trailer if both drives and trailer wheels are super singles. Quote -Thad What America needs is less bull and more Bulldog! Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7845 Share on other sites More sharing options...
QCDriver Posted October 5, 2006 Author Share Posted October 5, 2006 who do you like those wide tires? How much wieght did ya lose with them? I have heard that your fuel milage goes up too.... is that true? Thanks, BradI already had aluminum rims on it only cut my weight down about 150-200 lbs.Fuel mileage increased .5-.75 mpg, depending on load.Bad idea!The reason the front air line is thick is because the line runs right from the pedal to the brake chambers so you need allot of air flow(also helps supply the trailer and trolly brake). The rears have a relay valve that doesent need the flow of a larger line. A larger air line from the primary tank runs to the relay valves supply port then the thin line from the pedal runs to the control port. Then you have 4 delivery ports to each of the four brake chambers on the rear wheels. Your restricting air to the front brakes. So when you pull the ABS fuse it doesent have that problem? Try driving around for a day with the fuse out or even longer. if there is no problem then its a bad ABS component. Maybe a bad ABS ECU or bad sensor. Brad those super single tires can save something like 1000-1200 pounds on a tractor trailer if both drives and trailer wheels are super singles.Guess I know what I'm switching tommorrow.. Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7860 Share on other sites More sharing options...
QCDriver Posted October 21, 2006 Author Share Posted October 21, 2006 Well the problem came back in a BAD way. Make a routine stopp for a traffic light in the rain only fronts worked. I did a 180deg stop, and almost flipped as the truck hooked hard. I was bobtailing.Off to the dealer I went. They got it in within 8hrs and said all 4 rear slacks where bad, not racheting properly. That's the first thing I checked and my mechanic checked. I strongly disagreed and told them to check further in the air system.. Well low and behold after many hours of checking then put on the Vis machine, BAD RELAY VALVE leacking internaly. Now that they found the problem I told them to replace slacks just in case. I don't want another round about ride.So hopefully this thread will be closed. Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7995 Share on other sites More sharing options...
David Posted October 22, 2006 Share Posted October 22, 2006 How much did their education cost you? Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7996 Share on other sites More sharing options...
QCDriver Posted October 22, 2006 Author Share Posted October 22, 2006 Hummmm, Good question.Someone to just start replacing parts? AlotSomeone to hook up to a machine and read what's really wrong? Priceless Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-7999 Share on other sites More sharing options...
Elexus Posted September 22, 2022 Share Posted September 22, 2022 On 10/22/2006 at 4:48 PM, QCDriver said: Hummmm, Good question. Someone to just start replacing parts? Alot Someone to hook up to a machine and read what's really wrong? Priceless Was your problem fixed? I’m currently having this exact issue. My brakes are locking up while I break! Mechanic has adjusted the slacks, however I do have a valve leak. Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-510085 Share on other sites More sharing options...
h67st Posted September 22, 2022 Share Posted September 22, 2022 Sounds like his problem was a relay valve, that would be my thought if a truck was acting like this. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-510087 Share on other sites More sharing options...
Joey Mack Posted September 22, 2022 Share Posted September 22, 2022 what model and year,,,, 'R/RD' have sticky pedals and treadle valves... Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-510089 Share on other sites More sharing options...
mrsmackpaul Posted September 24, 2022 Share Posted September 24, 2022 On 9/22/2022 at 11:53 PM, h67st said: Sounds like his problem was a relay valve, that would be my thought if a truck was acting like this. My experience would tell me the same thing I have had sticking brake pedals before that took me a while to find Kind of embarrassing really but we live and learn Paul Quote Link to comment https://www.bigmacktrucks.com/topic/1555-air-brake-problem-no-ones-ever-seen/#findComment-510238 Share on other sites More sharing options...
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